// Copyright (c) 2015-2018 Khronos Group. This work is licensed under a // Creative Commons Attribution 4.0 International License; see // http://creativecommons.org/licenses/by/4.0/ [[fragops]] = Fragment Operations Fragment operations execute on a per-fragment or per-sample basis, affecting whether or how a fragment or sample is written to the framebuffer. Some operations execute <>, and others <>. Fragment operations always adhere to <>. [[fragops-early]] == Early Per-Fragment Tests Once fragments are produced by rasterization, a number of per-fragment operations are performed prior to fragment shader execution. If a fragment is discarded during any of these operations, it will not be processed by any subsequent stage, including fragment shader execution. ifndef::VK_NV_scissor_exclusive[] The <> and endif::VK_NV_scissor_exclusive[] ifdef::VK_NV_scissor_exclusive[] The <>, <>, and endif::VK_NV_scissor_exclusive[] <> are always performed during early fragment tests. Fragment operations are performed in the following order: ifdef::VK_EXT_discard_rectangles[] * the discard rectangles test (see <>) endif::VK_EXT_discard_rectangles[] * the scissor test (see <>) ifdef::VK_NV_scissor_exclusive[] * the exclusive scissor test (see <>) endif::VK_NV_scissor_exclusive[] * multisample fragment operations (see <>) If early per-fragment operations are <>, these operations are also performed: * <> * <> * <> ifdef::VK_NV_representative_fragment_test[] * <> endif::VK_NV_representative_fragment_test[] * <> for <> ifdef::VK_EXT_post_depth_coverage[] If post-depth coverage operation is <>, the <> coverage is determined after the early stencil and depth tests. endif::VK_EXT_post_depth_coverage[] ifdef::VK_EXT_discard_rectangles[] [[fragops-discard-rectangles]] == Discard Rectangles Test [open,refpage='VkPipelineDiscardRectangleStateCreateInfoEXT',desc='Structure specifying discard rectangle',type='structs'] -- The discard rectangles test determines if fragment's framebuffer coordinates [eq]#(x~f~,y~f~)# are inclusive or exclusive to a set of discard-space rectangles. The discard rectangles are set with the sname:VkPipelineDiscardRectangleStateCreateInfoEXT pipeline state, which is defined as: include::../api/structs/VkPipelineDiscardRectangleStateCreateInfoEXT.txt[] * pname:sType is the type of this structure. * pname:pNext is `NULL` or a pointer to an extension-specific structure. * pname:flags is reserved for future use. * pname:discardRectangleMode is the mode used to determine whether fragments that lie within the discard rectangle are discarded or not. * pname:discardRectangleCount is the number of discard rectangles used by the pipeline. * pname:pDiscardRectangles is a pointer to an array of slink:VkRect2D structures, defining the discard rectangles. If the discard rectangle state is dynamic, this member is ignored. .Valid Usage **** * [[VUID-VkPipelineDiscardRectangleStateCreateInfoEXT-discardRectangleCount-00582]] pname:discardRectangleCount must: be between `0` and sname:VkPhysicalDeviceDiscardRectanglePropertiesEXT::pname:maxDiscardRectangles, inclusive **** include::../validity/structs/VkPipelineDiscardRectangleStateCreateInfoEXT.txt[] -- [open,refpage='VkPipelineDiscardRectangleStateCreateFlagsEXT',desc='Reserved for future use',type='enums'] -- include::../api/flags/VkPipelineDiscardRectangleStateCreateFlagsEXT.txt[] sname:VkPipelineDiscardRectangleStateCreateFlagsEXT is a bitmask type for setting a mask, but is currently reserved for future use. -- The sname:VkPipelineDiscardRectangleStateCreateInfoEXT state is set by adding an instance of this structure to the pname:pNext chain of an instance of the sname:VkGraphicsPipelineCreateInfo structure and setting the graphics pipeline state with flink:vkCreateGraphicsPipelines. If the bound pipeline state object was not created with the ename:VK_DYNAMIC_STATE_DISCARD_RECTANGLE_EXT dynamic state enabled, discard rectangles are specified using the pname:pDiscardRectangles member of sname:VkPipelineDiscardRectangleStateCreateInfoEXT linked to the pipeline state object. [open,refpage='vkCmdSetDiscardRectangleEXT',desc='Set discard rectangles dynamically',type='protos'] -- If the pipeline state object was created with the ename:VK_DYNAMIC_STATE_DISCARD_RECTANGLE_EXT dynamic state enabled, the discard rectangles are dynamically set and changed with the command: include::../api/protos/vkCmdSetDiscardRectangleEXT.txt[] * pname:commandBuffer is the command buffer into which the command will be recorded. * pname:firstDiscardRectangle is the index of the first discard rectangle whose state is updated by the command. * pname:discardRectangleCount is the number of discard rectangles whose state are updated by the command. * pname:pDiscardRectangles is a pointer to an array of slink:VkRect2D structures specifying discard rectangles. The discard rectangle taken from element [eq]#i# of pname:pDiscardRectangles replace the current state for the discard rectangle index [eq]#pname:firstDiscardRectangle {plus} i#, for [eq]#i# in [eq]#[0, pname:discardRectangleCount)#. .Valid Usage **** * [[VUID-vkCmdSetDiscardRectangleEXT-None-00583]] The bound graphics pipeline must: have been created with the ename:VK_DYNAMIC_STATE_DISCARD_RECTANGLE_EXT dynamic state enabled * [[VUID-vkCmdSetDiscardRectangleEXT-firstDiscardRectangle-00585]] The sum of pname:firstDiscardRectangle and pname:discardRectangleCount must: be less than or equal to slink:VkPhysicalDeviceDiscardRectanglePropertiesEXT::pname:maxDiscardRectangles * [[VUID-vkCmdSetDiscardRectangleEXT-x-00587]] The pname:x and pname:y member of pname:offset in each slink:VkRect2D element of pname:pDiscardRectangles must: be greater than or equal to `0` * [[VUID-vkCmdSetDiscardRectangleEXT-offset-00588]] Evaluation of [eq]#(pname:offset.x {plus} pname:extent.width)# in each slink:VkRect2D element of pname:pDiscardRectangles must: not cause a signed integer addition overflow * [[VUID-vkCmdSetDiscardRectangleEXT-offset-00589]] Evaluation of [eq]#(pname:offset.y {plus} pname:extent.height)# in each slink:VkRect2D element of pname:pDiscardRectangles must: not cause a signed integer addition overflow **** include::../validity/protos/vkCmdSetDiscardRectangleEXT.txt[] -- The sname:VkOffset2D::pname:x and sname:VkOffset2D::pname:y values of the discard rectangle sname:VkRect2D specify the upper-left origin of the discard rectangle box. The lower-right corner of the discard rectangle box is specified as the sname:VkExtent2D::pname:width and sname:VkExtent2D::pname:height from the upper-left origin. If [eq]#pname:offset.x {leq} x~f~ < pname:offset.x {plus} pname:extent.width# and [eq]#pname:offset.y {leq} y~f~ < pname:offset.y {plus} pname:extent.height# for the selected discard rectangle, then the fragment is within the discard rectangle box. When the discard rectangle mode is ename:VK_DISCARD_RECTANGLE_MODE_INCLUSIVE_EXT a fragment within at least one of the active discard rectangle boxes passes the discard rectangle test; otherwise the fragment fails the discard rectangle test and is discarded. When the discard rectangle mode is ename:VK_DISCARD_RECTANGLE_MODE_EXCLUSIVE_EXT a fragment within at least one of the active discard rectangle boxes fails the discard rectangle test, and the fragment is discarded; otherwise the fragment passes the discard rectangles test. The discard rectangles test only applies to <>, not to other commands like clears or copies. [open,refpage='VkDiscardRectangleModeEXT',desc='Specify the discard rectangle mode',type='enums'] -- Possible values of slink:VkPipelineDiscardRectangleStateCreateInfoEXT::pname:discardRectangleMode, specifying the behavior of the discard rectangle test, are: include::../api/enums/VkDiscardRectangleModeEXT.txt[] * ename:VK_DISCARD_RECTANGLE_MODE_INCLUSIVE_EXT specifies that a fragment within any discard rectangle satisfies the test. * ename:VK_DISCARD_RECTANGLE_MODE_EXCLUSIVE_EXT specifies that a fragment not within any of the discard rectangles satisfies the test. -- ifdef::VK_NV_shading_rate_image[] When the use of a shading rate image results in a fragment covering multiple pixels, the discard rectangle test is performed independently for each pixel in the fragment. If a pixel covered by a fragment fails the discard rectangle test, all samples in the fragment associated with that pixel are treated as not covered. If the discard rectangle test results in a fragment with no samples covered, that fragment is discarded. endif::VK_NV_shading_rate_image[] endif::VK_EXT_discard_rectangles[] [[fragops-scissor]] == Scissor Test [open,refpage='vkCmdSetScissor',desc='Set the dynamic scissor rectangles on a command buffer',type='protos'] -- The scissor test determines if a fragment's framebuffer coordinates [eq]#(x~f~,y~f~)# lie within the scissor rectangle corresponding to the viewport index (see <>) used by the primitive that generated the fragment. If the pipeline state object is created without ename:VK_DYNAMIC_STATE_SCISSOR enabled then the scissor rectangles are set by the slink:VkPipelineViewportStateCreateInfo state of the pipeline state object. Otherwise, to dynamically set the scissor rectangles call: include::../api/protos/vkCmdSetScissor.txt[] * pname:commandBuffer is the command buffer into which the command will be recorded. * pname:firstScissor is the index of the first scissor whose state is updated by the command. * pname:scissorCount is the number of scissors whose rectangles are updated by the command. * pname:pScissors is a pointer to an array of slink:VkRect2D structures defining scissor rectangles. The scissor rectangles taken from element [eq]#i# of pname:pScissors replace the current state for the scissor index [eq]#pname:firstScissor {plus} i#, for [eq]#i# in [eq]#[0, pname:scissorCount)#. Each scissor rectangle is described by a slink:VkRect2D structure, with the pname:offset.x and pname:offset.y values determining the upper left corner of the scissor rectangle, and the pname:extent.width and pname:extent.height values determining the size in pixels. .Valid Usage **** * [[VUID-vkCmdSetScissor-None-00590]] The bound graphics pipeline must: have been created with the ename:VK_DYNAMIC_STATE_SCISSOR dynamic state enabled * [[VUID-vkCmdSetScissor-firstScissor-00591]] pname:firstScissor must: be less than sname:VkPhysicalDeviceLimits::pname:maxViewports * [[VUID-vkCmdSetScissor-firstScissor-00592]] The sum of pname:firstScissor and pname:scissorCount must: be between `1` and sname:VkPhysicalDeviceLimits::pname:maxViewports, inclusive * [[VUID-vkCmdSetScissor-firstScissor-00593]] If the <> feature is not enabled, pname:firstScissor must: be `0` * [[VUID-vkCmdSetScissor-scissorCount-00594]] If the <> feature is not enabled, pname:scissorCount must: be `1` * [[VUID-vkCmdSetScissor-x-00595]] The pname:x and pname:y members of pname:offset must: be greater than or equal to `0` * [[VUID-vkCmdSetScissor-offset-00596]] Evaluation of [eq]#(pname:offset.x {plus} pname:extent.width)# must: not cause a signed integer addition overflow * [[VUID-vkCmdSetScissor-offset-00597]] Evaluation of [eq]#(pname:offset.y {plus} pname:extent.height)# must: not cause a signed integer addition overflow **** include::../validity/protos/vkCmdSetScissor.txt[] -- If [eq]#pname:offset.x {leq} x~f~ < pname:offset.x {plus} pname:extent.width# and [eq]#pname:offset.y {leq} y~f~ < pname:offset.y {plus} pname:extent.height# for the selected scissor rectangle, then the scissor test passes. Otherwise, the test fails and the fragment is discarded. For points, lines, and polygons, the scissor rectangle for a primitive is selected in the same manner as the viewport (see <>). The scissor rectangles test only applies to <>, not to other commands like clears or copies. It is legal for [eq]#pname:offset.x {plus} pname:extent.width# or [eq]#pname:offset.y {plus} pname:extent.height# to exceed the dimensions of the framebuffer - the scissor test still applies as defined above. Rasterization does not produce fragments outside of the framebuffer, so such fragments never have the scissor test performed on them. The scissor test is always performed. Applications can: effectively disable the scissor test by specifying a scissor rectangle that encompasses the entire framebuffer. ifdef::VK_NV_shading_rate_image[] When the use of a shading rate image results in a fragment covering multiple pixels, the scissor test is performed independently for each pixel in the fragment. If a pixel covered by a fragment fails the scissor test, all samples in the fragment associated with that pixel are treated as not covered. If the scissor test results in a fragment with no samples covered, that fragment is discarded. endif::VK_NV_shading_rate_image[] ifdef::VK_NV_scissor_exclusive[] [[fragops-exclusive-scissor]] == Exclusive Scissor Test The exclusive scissor test determines if a pixel's framebuffer coordinates [eq]#(x~f~,y~f~)# lie outside the exclusive scissor rectangle corresponding to the viewport index (see <>) used by the primitive that generated the fragment. The exclusive scissor test behaves identically to the <>, except that it passes only if the pixel is outside the rectangle instead of passing if the pixel is inside the rectangle. [open,refpage='VkPipelineViewportExclusiveScissorStateCreateInfoNV',desc='Structure specifying parameters controlling exclusive scissor testing',type='structs'] -- If the pname:pNext chain of sname:VkPipelineViewportStateCreateInfo includes a sname:VkPipelineViewportExclusiveScissorStateCreateInfoNV structure, then that structure includes parameters that affect the exclusive scissor test. The sname:VkPipelineViewportExclusiveScissorStateCreateInfoNV structure is defined as: include::../api/structs/VkPipelineViewportExclusiveScissorStateCreateInfoNV.txt[] * pname:sType is the type of this structure. * pname:pNext is `NULL` or a pointer to an extension-specific structure. * pname:exclusiveScissorCount is the number of exclusive scissor rectangles used by the pipeline. * pname:pExclusiveScissors is a pointer to an array of slink:VkRect2D structures defining exclusive scissor rectangles. If the exclusive scissor state is dynamic, this member is ignored. If this structure is not present, pname:exclusiveScissorCount is considered to be `0` and the exclusive scissor test is disabled. .Valid Usage **** * [[VUID-VkPipelineViewportExclusiveScissorStateCreateInfoNV-exclusiveScissorCount-02027]] If the <> feature is not enabled, pname:exclusiveScissorCount must: be `0` or `1` * [[VUID-VkPipelineViewportExclusiveScissorStateCreateInfoNV-exclusiveScissorCount-02028]] pname:exclusiveScissorCount must: be less than or equal to sname:VkPhysicalDeviceLimits::pname:maxViewports * [[VUID-VkPipelineViewportExclusiveScissorStateCreateInfoNV-exclusiveScissorCount-02029]] pname:exclusiveScissorCount must: be `0` or identical to the pname:viewportCount member of sname:VkPipelineViewportStateCreateInfo * [[VUID-VkPipelineViewportExclusiveScissorStateCreateInfoNV-pDynamicStates-02030]] If no element of the pname:pDynamicStates member of pname:pDynamicState is ename:VK_DYNAMIC_STATE_EXCLUSIVE_SCISSOR_NV and pname:exclusiveScissorCount is not `0`, pname:pExclusiveScissors must: be a valid pointer to an array of pname:exclusiveScissorCount sname:VkRect2D structures **** include::../validity/structs/VkPipelineViewportExclusiveScissorStateCreateInfoNV.txt[] -- [open,refpage='vkCmdSetExclusiveScissorNV',desc='Set the dynamic exclusive scissor rectangles on a command buffer',type='protos'] -- If the pipeline state object is created with ename:VK_DYNAMIC_STATE_EXCLUSIVE_SCISSOR_NV enabled, then the exclusive scissor rectangles are set by: include::../api/protos/vkCmdSetExclusiveScissorNV.txt[] * pname:commandBuffer is the command buffer into which the command will be recorded. * pname:firstExclusiveScissor is the index of the first exclusive scissor rectangle whose state is updated by the command. * pname:exclusiveScissorCount is the number of exclusive scissor rectangles updated by the command. * pname:pExclusiveScissors is a pointer to an array of slink:VkRect2D structures defining exclusive scissor rectangles. The scissor rectangles taken from element [eq]#i# of pname:pExclusiveScissors replace the current state for the scissor index [eq]#pname:firstExclusiveScissor {plus} i#, for [eq]#i# in [eq]#[0, pname:exclusiveScissorCount)#. Each scissor rectangle is described by a slink:VkRect2D structure, with the pname:offset.x and pname:offset.y values determining the upper left corner of the scissor rectangle, and the pname:extent.width and pname:extent.height values determining the size in pixels. .Valid Usage **** * [[VUID-vkCmdSetExclusiveScissorNV-None-02031]] The <> feature must: be enabled. * [[VUID-vkCmdSetExclusiveScissorNV-None-02032]] The bound graphics pipeline must: have been created with the ename:VK_DYNAMIC_STATE_EXCLUSIVE_SCISSOR_NV dynamic state enabled * [[VUID-vkCmdSetExclusiveScissorNV-firstExclusiveScissor-02033]] pname:firstExclusiveScissor must: be less than sname:VkPhysicalDeviceLimits::pname:maxViewports * [[VUID-vkCmdSetExclusiveScissorNV-firstExclusiveScissor-02034]] The sum of pname:firstExclusiveScissor and pname:exclusiveScissorCount must: be between `1` and sname:VkPhysicalDeviceLimits::pname:maxViewports, inclusive * [[VUID-vkCmdSetExclusiveScissorNV-firstExclusiveScissor-02035]] If the <> feature is not enabled, pname:firstExclusiveScissor must: be `0` * [[VUID-vkCmdSetExclusiveScissorNV-exclusiveScissorCount-02036]] If the <> feature is not enabled, pname:exclusiveScissorCount must: be `1` * [[VUID-vkCmdSetExclusiveScissorNV-x-02037]] The pname:x and pname:y members of pname:offset in each member of pname:pExclusiveScissors must: be greater than or equal to `0` * [[VUID-vkCmdSetExclusiveScissorNV-offset-02038]] Evaluation of [eq]#(pname:offset.x {plus} pname:extent.width)# for each member of pname:pExclusiveScissors must: not cause a signed integer addition overflow * [[VUID-vkCmdSetExclusiveScissorNV-offset-02039]] Evaluation of [eq]#(pname:offset.y {plus} pname:extent.height)# for each member of pname:pExclusiveScissors must: not cause a signed integer addition overflow **** include::../validity/protos/vkCmdSetExclusiveScissorNV.txt[] -- If [eq]#pname:offset.x {leq} x~f~ < pname:offset.x {plus} pname:extent.width# and [eq]#pname:offset.y {leq} y~f~ < pname:offset.y {plus} pname:extent.height# for the selected exclusive scissor rectangle, then the exclusive scissor test fails and the fragment is discarded. Otherwise, the exclusive scissor test passes. For points, lines, and polygons, the exclusive scissor rectangle for a primitive is selected in the same manner as the viewport (see <>). The exclusive scissor test only applies to <>, not to other commands like clears or copies. It is legal for [eq]#pname:offset.x {plus} pname:extent.width# or [eq]#pname:offset.y {plus} pname:extent.height# to exceed the dimensions of the framebuffer - the exclusive scissor test still applies as defined above. Rasterization does not produce fragments outside of the framebuffer, so such fragments never have the exclusive scissor test performed on them. The exclusive scissor test is performed if and only if the current pipeline was created with a non-zero pname:exclusiveScissorCount. Applications can: effectively disable the exclusive scissor test for specific viewports by specifying a scissor rectangle with a width or height of zero. ifdef::VK_NV_shading_rate_image[] When the use of a shading rate image results in a fragment covering multiple pixels, the exclusive scissor test is performed independently for each pixel in the fragment. If a pixel covered by a fragment fails the exclusive scissor test, all samples in the fragment associated with that pixel are treated as not covered. If the exclusive scissor test results in a fragment with no samples covered, that fragment is discarded. endif::VK_NV_shading_rate_image[] endif::VK_NV_scissor_exclusive[] [[fragops-samplemask]] == Sample Mask This step modifies fragment coverage values based on the values in the pname:pSampleMask array member of slink:VkPipelineMultisampleStateCreateInfo, as described previously in section <>. pname:pSampleMask contains an array of static coverage information that is code:ANDed with the coverage information generated during rasterization. Bits that are zero disable coverage for the corresponding sample. Bit [eq]#B# of mask word [eq]#M# corresponds to sample [eq]#32 {times} M {plus} B#. The array is sized to a length of [eq]#{lceil} pname:rasterizationSamples / 32 {rceil}# words. If pname:pSampleMask is `NULL`, it is treated as if the mask has all bits enabled, i.e. no coverage is removed from fragments. [open,refpage='VkSampleMask',desc='Mask of sample coverage information',type='basetypes',xrefs='VkPipelineMultisampleStateCreateInfo'] -- The elements of the sample mask array are of type basetype:VkSampleMask, each representing 32 bits of coverage information: include::../api/basetypes/VkSampleMask.txt[] -- [[fragops-early-mode]] == Early Fragment Test Mode The depth bounds test, stencil test, depth test, ifdef::VK_NV_representative_fragment_test[] representative fragment test, endif::VK_NV_representative_fragment_test[] and occlusion query sample counting are performed before fragment shading if and only if early fragment tests are enabled by the fragment shader (see <>). When early per-fragment operations are enabled, these operations are performed prior to fragment shader execution, and the stencil buffer, depth buffer, and occlusion query sample counts will be updated accordingly; these operations will not be performed again after fragment shader execution. If a pipeline's fragment shader has early fragment tests disabled, these operations are performed only after fragment program execution, in the order described below. If a pipeline does not contain a fragment shader, these operations are performed only once. If early fragment tests are enabled, any depth value computed by the fragment shader has no effect. Additionally, the depth test (including depth writes), stencil test (including stencil writes) and sample counting operations are performed even for fragments or samples that would be discarded after fragment shader execution due to per-fragment operations such as alpha-to-coverage tests, or due to the fragment being discarded by the shader itself. [[fragops-late]] == Late Per-Fragment Tests After programmable fragment processing, per-fragment operations are performed before blending and color output to the framebuffer. A fragment is produced by rasterization with framebuffer coordinates of [eq]#(x~f~,y~f~)# and depth [eq]#z#, as described in <>. The fragment is then modified by programmable fragment processing, which adds associated data as described in <>. The fragment is then further modified, and possibly discarded by the late per-fragment operations described in this chapter. Finally, if the fragment was not discarded, it is used to update the framebuffer at the fragment's framebuffer coordinates for any samples that remain covered. The depth bounds test, stencil test, and depth test are performed for each pixel sample, rather than just once for each fragment. Stencil and depth operations are performed for a pixel sample only if that sample's fragment coverage bit is a value of 1 when the fragment executes the corresponding stage of the graphics pipeline. If the corresponding coverage bit is 0, no operations are performed for that sample. Failure of the depth bounds, stencil, or depth test results in termination of the processing of that sample by means of disabling coverage for that sample, rather than discarding of the fragment. If, at any point, a fragment's coverage becomes zero for all samples, then the fragment is discarded. All operations are performed on the depth and stencil values stored in the depth/stencil attachment of the framebuffer. The contents of the color attachments are not modified at this point. The depth bounds test, stencil test, depth test, and occlusion query operations described in <>, <>, <>, <> are instead performed prior to fragment processing, as described in <>, if requested by the fragment shader. ifdef::VK_AMD_mixed_attachment_samples[] [[fragops-mixed-attachment-samples]] == Mixed attachment samples Special rules apply to per-fragment operations when the number of samples of the color attachments differs from the number of samples of the depth/stencil attachment used in a subpass. Let [eq]#C# be the number of color attachment samples and [eq]#D# be the number of depth/stencil attachment samples used by a given subpass. If [eq]#C < D# then only the first [eq]#C# number of samples are guaranteed to have a corresponding fragment shader invocation and thus a corresponding color output value, unless the fragment shaders produce inputs to the late per-fragment tests (e.g. by outputting to a variable decorated with the code:FragDepth built-in decoration). Implementations are allowed to produce fragment shader invocations for samples with indices greater than or equal to [eq]#C# but (other than potential side effects) the color outputs of fragment shader invocations corresponding to such samples are discarded. endif::VK_AMD_mixed_attachment_samples[] [[fragops-covg]] == Multisample Coverage ifndef::VK_NV_sample_mask_override_coverage[] If a fragment shader is active and its entry point's interface includes a built-in output variable decorated with code:SampleMask, the fragment coverage is code:ANDed with the bits of the sample mask to generate a new fragment coverage value. endif::VK_NV_sample_mask_override_coverage[] ifdef::VK_NV_sample_mask_override_coverage[] If a fragment shader is active and its entry point's interface includes a built-in output variable decorated with code:SampleMask and also decorated with code:OverrideCoverageNV the fragment coverage is replaced with the sample mask bits set in the shader. Otherwise if the built-in output variable decorated with code:SampleMask is not also decorated with code:OverrideCoverageNV then the fragment coverage is code:ANDed with the bits of the sample mask to generate a new fragment coverage value. endif::VK_NV_sample_mask_override_coverage[] If such a fragment shader did not assign a value to code:SampleMask due to flow of control, the value code:ANDed with the fragment coverage is undefined. If no fragment shader is active, or if the active fragment shader does not include code:SampleMask in its interface, the fragment coverage is not modified. Next, the fragment alpha and coverage values are modified based on the pname:alphaToCoverageEnable and pname:alphaToOneEnable members of the slink:VkPipelineMultisampleStateCreateInfo structure. All alpha values in this section refer only to the alpha component of the fragment shader output that has a code:Location and code:Index decoration of zero (see the <> section). If that shader output has an integer or unsigned integer type, then these operations are skipped. If pname:alphaToCoverageEnable is enabled, a temporary coverage value with pname:rasterizationSamples bits is generated where each bit is determined by the fragment's alpha value. The temporary coverage value is then ANDed with the fragment coverage value to generate a new fragment coverage value. No specific algorithm is specified for converting the alpha value to a temporary coverage mask. It is intended that the number of 1's in this value be proportional to the alpha value (clamped to [eq]#[0,1]#), with all 1's corresponding to a value of 1.0 and all 0's corresponding to 0.0. The algorithm may: be different at different pixel locations. [NOTE] .Note ==== Using different algorithms at different pixel location may: help to avoid artifacts caused by regular coverage sample locations. ==== Next, if pname:alphaToOneEnable is enabled, each alpha value is replaced by the maximum representable alpha value for fixed-point color buffers, or by 1.0 for floating-point buffers. Otherwise, the alpha values are not changed. [[fragops-ds-state]] == Depth and Stencil Operations Pipeline state controlling the <>, <>, and <> is specified through the members of the sname:VkPipelineDepthStencilStateCreateInfo structure. [open,refpage='VkPipelineDepthStencilStateCreateInfo',desc='Structure specifying parameters of a newly created pipeline depth stencil state',type='structs'] -- The sname:VkPipelineDepthStencilStateCreateInfo structure is defined as: include::../api/structs/VkPipelineDepthStencilStateCreateInfo.txt[] * pname:sType is the type of this structure. * pname:pNext is `NULL` or a pointer to an extension-specific structure. * pname:flags is reserved for future use. * pname:depthTestEnable controls whether <> is enabled. * pname:depthWriteEnable controls whether <> are enabled when pname:depthTestEnable is ename:VK_TRUE. Depth writes are always disabled when pname:depthTestEnable is ename:VK_FALSE. * pname:depthCompareOp is the comparison operator used in the <>. * pname:depthBoundsTestEnable controls whether <> is enabled. * pname:stencilTestEnable controls whether <> is enabled. * pname:front and pname:back control the parameters of the <>. * pname:minDepthBounds and pname:maxDepthBounds define the range of values used in the <>. .Valid Usage **** * [[VUID-VkPipelineDepthStencilStateCreateInfo-depthBoundsTestEnable-00598]] If the <> feature is not enabled, pname:depthBoundsTestEnable must: be ename:VK_FALSE **** include::../validity/structs/VkPipelineDepthStencilStateCreateInfo.txt[] -- [open,refpage='VkPipelineDepthStencilStateCreateFlags',desc='Reserved for future use',type='enums'] -- include::../api/flags/VkPipelineDepthStencilStateCreateFlags.txt[] sname:VkPipelineDepthStencilStateCreateFlags is a bitmask type for setting a mask, but is currently reserved for future use. -- [[fragops-dbt]] == Depth Bounds Test [open,refpage='vkCmdSetDepthBounds',desc='Set the depth bounds test values for a command buffer',type='protos'] -- The depth bounds test conditionally disables coverage of a sample based on the outcome of a comparison between the value [eq]#z~a~# in the depth attachment at location [eq]#(x~f~,y~f~)# (for the appropriate sample) and a range of values. The test is enabled or disabled by the pname:depthBoundsTestEnable member of slink:VkPipelineDepthStencilStateCreateInfo: If the pipeline state object is created without the ename:VK_DYNAMIC_STATE_DEPTH_BOUNDS dynamic state enabled then the range of values used in the depth bounds test are defined by the pname:minDepthBounds and pname:maxDepthBounds members of the slink:VkPipelineDepthStencilStateCreateInfo structure. Otherwise, to dynamically set the depth bounds range values call: include::../api/protos/vkCmdSetDepthBounds.txt[] * pname:commandBuffer is the command buffer into which the command will be recorded. * pname:minDepthBounds is the lower bound of the range of depth values used in the depth bounds test. * pname:maxDepthBounds is the upper bound of the range. .Valid Usage **** * [[VUID-vkCmdSetDepthBounds-None-00599]] The bound graphics pipeline must: have been created with the ename:VK_DYNAMIC_STATE_DEPTH_BOUNDS dynamic state enabled ifdef::VK_EXT_depth_range_unrestricted[] * [[VUID-vkCmdSetDepthBounds-minDepthBounds-00600]] Unless the `<>` extension is enabled pname:minDepthBounds must: be between `0.0` and `1.0`, inclusive endif::VK_EXT_depth_range_unrestricted[] ifndef::VK_EXT_depth_range_unrestricted[] * [[VUID-vkCmdSetDepthBounds-minDepthBounds-00600]] pname:minDepthBounds must: be between `0.0` and `1.0`, inclusive endif::VK_EXT_depth_range_unrestricted[] ifdef::VK_EXT_depth_range_unrestricted[] * [[VUID-vkCmdSetDepthBounds-maxDepthBounds-00601]] Unless the `<>` extension is enabled pname:maxDepthBounds must: be between `0.0` and `1.0`, inclusive endif::VK_EXT_depth_range_unrestricted[] ifndef::VK_EXT_depth_range_unrestricted[] * [[VUID-vkCmdSetDepthBounds-maxDepthBounds-00601]] pname:maxDepthBounds must: be between `0.0` and `1.0`, inclusive endif::VK_EXT_depth_range_unrestricted[] **** include::../validity/protos/vkCmdSetDepthBounds.txt[] -- If [eq]#pname:minDepthBounds {leq} z~a~ {leq} pname:maxDepthBounds}#, then the depth bounds test passes. Otherwise, the test fails and the sample's coverage bit is cleared in the fragment. If there is no depth framebuffer attachment or if the depth bounds test is disabled, it is as if the depth bounds test always passes. [[fragops-stencil]] == Stencil Test The stencil test conditionally disables coverage of a sample based on the outcome of a comparison between the stencil value in the depth/stencil attachment at location [eq]#(x~f~,y~f~)# (for the appropriate sample) and a reference value. The stencil test also updates the value in the stencil attachment, depending on the test state, the stencil value and the stencil write masks. The test is enabled or disabled by the pname:stencilTestEnable member of slink:VkPipelineDepthStencilStateCreateInfo. When disabled, the stencil test and associated modifications are not made, and the sample's coverage is not modified. The stencil test is controlled with the pname:front and pname:back members of sname:VkPipelineDepthStencilStateCreateInfo which are of type sname:VkStencilOpState. [open,refpage='VkStencilOpState',desc='Structure specifying stencil operation state',type='structs'] -- The sname:VkStencilOpState structure is defined as: include::../api/structs/VkStencilOpState.txt[] * pname:failOp is a elink:VkStencilOp value specifying the action performed on samples that fail the stencil test. * pname:passOp is a elink:VkStencilOp value specifying the action performed on samples that pass both the depth and stencil tests. * pname:depthFailOp is a elink:VkStencilOp value specifying the action performed on samples that pass the stencil test and fail the depth test. * pname:compareOp is a elink:VkCompareOp value specifying the comparison operator used in the stencil test. * pname:compareMask selects the bits of the unsigned integer stencil values participating in the stencil test. * pname:writeMask selects the bits of the unsigned integer stencil values updated by the stencil test in the stencil framebuffer attachment. * pname:reference is an integer reference value that is used in the unsigned stencil comparison. include::../validity/structs/VkStencilOpState.txt[] -- There are two sets of stencil-related state, the front stencil state set and the back stencil state set. Stencil tests and writes use the front set of stencil state when processing front-facing fragments and use the back set of stencil state when processing back-facing fragments. Fragments rasterized from non-polygon primitives (points and lines) are always considered front-facing. Fragments rasterized from polygon primitives inherit their facingness from the polygon, even if the polygon is rasterized as points or lines due to the current elink:VkPolygonMode. Whether a polygon is front- or back-facing is determined in the same manner used for face culling (see <>). The operation of the stencil test is also affected by the pname:compareMask, pname:writeMask, and pname:reference members of sname:VkStencilOpState set in the pipeline state object if the pipeline state object is created without the ename:VK_DYNAMIC_STATE_STENCIL_COMPARE_MASK, ename:VK_DYNAMIC_STATE_STENCIL_WRITE_MASK, and ename:VK_DYNAMIC_STATE_STENCIL_REFERENCE dynamic states enabled, respectively. [open,refpage='vkCmdSetStencilCompareMask',desc='Set the stencil compare mask dynamic state',type='protos'] -- If the pipeline state object is created with the ename:VK_DYNAMIC_STATE_STENCIL_COMPARE_MASK dynamic state enabled, then to dynamically set the stencil compare mask call: include::../api/protos/vkCmdSetStencilCompareMask.txt[] * pname:commandBuffer is the command buffer into which the command will be recorded. * pname:faceMask is a bitmask of elink:VkStencilFaceFlagBits specifying the set of stencil state for which to update the compare mask. * pname:compareMask is the new value to use as the stencil compare mask. .Valid Usage **** * [[VUID-vkCmdSetStencilCompareMask-None-00602]] The bound graphics pipeline must: have been created with the ename:VK_DYNAMIC_STATE_STENCIL_COMPARE_MASK dynamic state enabled **** include::../validity/protos/vkCmdSetStencilCompareMask.txt[] -- [open,refpage='VkStencilFaceFlagBits',desc='Bitmask specifying sets of stencil state for which to update the compare mask',type='enums'] -- Bits which can: be set in the flink:vkCmdSetStencilCompareMask::pname:faceMask parameter, and similar parameters of other commands specifying which stencil state to update stencil masks for, are: include::../api/enums/VkStencilFaceFlagBits.txt[] * ename:VK_STENCIL_FACE_FRONT_BIT specifies that only the front set of stencil state is updated. * ename:VK_STENCIL_FACE_BACK_BIT specifies that only the back set of stencil state is updated. * ename:VK_STENCIL_FRONT_AND_BACK is the combination of ename:VK_STENCIL_FACE_FRONT_BIT and ename:VK_STENCIL_FACE_BACK_BIT, and specifies that both sets of stencil state are updated. -- [open,refpage='VkStencilFaceFlags',desc='Bitmask of VkStencilFaceFlagBits',type='enums'] -- include::../api/flags/VkStencilFaceFlags.txt[] sname:VkStencilFaceFlags is a bitmask type for setting a mask of zero or more slink:VkStencilFaceFlagBits. -- [open,refpage='vkCmdSetStencilWriteMask',desc='Set the stencil write mask dynamic state',type='protos'] -- If the pipeline state object is created with the ename:VK_DYNAMIC_STATE_STENCIL_WRITE_MASK dynamic state enabled, then to dynamically set the stencil write mask call: include::../api/protos/vkCmdSetStencilWriteMask.txt[] * pname:commandBuffer is the command buffer into which the command will be recorded. * pname:faceMask is a bitmask of elink:VkStencilFaceFlagBits specifying the set of stencil state for which to update the write mask, as described above for flink:vkCmdSetStencilCompareMask. * pname:writeMask is the new value to use as the stencil write mask. .Valid Usage **** * [[VUID-vkCmdSetStencilWriteMask-None-00603]] The bound graphics pipeline must: have been created with the ename:VK_DYNAMIC_STATE_STENCIL_WRITE_MASK dynamic state enabled **** include::../validity/protos/vkCmdSetStencilWriteMask.txt[] -- [open,refpage='vkCmdSetStencilReference',desc='Set the stencil reference dynamic state',type='protos'] -- If the pipeline state object is created with the ename:VK_DYNAMIC_STATE_STENCIL_REFERENCE dynamic state enabled, then to dynamically set the stencil reference value call: include::../api/protos/vkCmdSetStencilReference.txt[] * pname:commandBuffer is the command buffer into which the command will be recorded. * pname:faceMask is a bitmask of elink:VkStencilFaceFlagBits specifying the set of stencil state for which to update the reference value, as described above for flink:vkCmdSetStencilCompareMask. * pname:reference is the new value to use as the stencil reference value. .Valid Usage **** * [[VUID-vkCmdSetStencilReference-None-00604]] The bound graphics pipeline must: have been created with the ename:VK_DYNAMIC_STATE_STENCIL_REFERENCE dynamic state enabled **** include::../validity/protos/vkCmdSetStencilReference.txt[] -- pname:reference is an integer reference value that is used in the unsigned stencil comparison. The reference value used by stencil comparison must be within the range [eq]#[0,2^s^-1]# , where [eq]#s# is the number of bits in the stencil framebuffer attachment, otherwise the reference value is considered undefined. The [eq]#s# least significant bits of pname:compareMask are bitwise code:ANDed with both the reference and the stored stencil value, and the resulting masked values are those that participate in the comparison controlled by pname:compareOp. Let [eq]#R# be the masked reference value and [eq]#S# be the masked stored stencil value. [open,refpage='VkCompareOp',desc='Stencil comparison function',type='enums'] -- Possible values of slink:VkStencilOpState::pname:compareOp, specifying the stencil comparison function, are: include::../api/enums/VkCompareOp.txt[] * ename:VK_COMPARE_OP_NEVER specifies that the test never passes. * ename:VK_COMPARE_OP_LESS specifies that the test passes when [eq]#R < S#. * ename:VK_COMPARE_OP_EQUAL specifies that the test passes when [eq]#R = S#. * ename:VK_COMPARE_OP_LESS_OR_EQUAL specifies that the test passes when [eq]#R {leq} S#. * ename:VK_COMPARE_OP_GREATER specifies that the test passes when [eq]#R > S#. * ename:VK_COMPARE_OP_NOT_EQUAL specifies that the test passes when [eq]#R {neq} S#. * ename:VK_COMPARE_OP_GREATER_OR_EQUAL specifies that the test passes when [eq]#R {geq} S#. * ename:VK_COMPARE_OP_ALWAYS specifies that the test always passes. -- [open,refpage='VkStencilOp',desc='Stencil comparison function',type='enums'] -- Possible values of the pname:failOp, pname:passOp, and pname:depthFailOp members of slink:VkStencilOpState, specifying what happens to the stored stencil value if this or certain subsequent tests fail or pass, are: include::../api/enums/VkStencilOp.txt[] * ename:VK_STENCIL_OP_KEEP keeps the current value. * ename:VK_STENCIL_OP_ZERO sets the value to 0. * ename:VK_STENCIL_OP_REPLACE sets the value to pname:reference. * ename:VK_STENCIL_OP_INCREMENT_AND_CLAMP increments the current value and clamps to the maximum representable unsigned value. * ename:VK_STENCIL_OP_DECREMENT_AND_CLAMP decrements the current value and clamps to 0. * ename:VK_STENCIL_OP_INVERT bitwise-inverts the current value. * ename:VK_STENCIL_OP_INCREMENT_AND_WRAP increments the current value and wraps to 0 when the maximum value would have been exceeded. * ename:VK_STENCIL_OP_DECREMENT_AND_WRAP decrements the current value and wraps to the maximum possible value when the value would go below 0. For purposes of increment and decrement, the stencil bits are considered as an unsigned integer. If the stencil test fails, the sample's coverage bit is cleared in the fragment. If there is no stencil framebuffer attachment, stencil modification cannot: occur, and it is as if the stencil tests always pass. If the stencil test passes, the pname:writeMask member of the slink:VkStencilOpState structures controls how the updated stencil value is written to the stencil framebuffer attachment. The least significant [eq]#s# bits of pname:writeMask, where [eq]#s# is the number of bits in the stencil framebuffer attachment, specify an integer mask. Where a [eq]#1# appears in this mask, the corresponding bit in the stencil value in the depth/stencil attachment is written; where a [eq]#0# appears, the bit is not written. The pname:writeMask value uses either the front-facing or back-facing state based on the facingness of the fragment. Fragments generated by front-facing primitives use the front mask and fragments generated by back-facing primitives use the back mask. -- [[fragops-depth]] == Depth Test The depth test conditionally disables coverage of a sample based on the outcome of a comparison between the fragment's depth value at the sample location and the sample's depth value in the depth/stencil attachment at location [eq]#(x~f~,y~f~)#. The comparison is enabled or disabled with the pname:depthTestEnable member of the slink:VkPipelineDepthStencilStateCreateInfo structure. When disabled, the depth comparison and subsequent possible updates to the value of the depth component of the depth/stencil attachment are bypassed and the fragment is passed to the next operation. The stencil value, however, can: be modified as indicated above as if the depth test passed. If enabled, the comparison takes place and the depth/stencil attachment value can: subsequently be modified. The comparison is specified with the pname:depthCompareOp member of slink:VkPipelineDepthStencilStateCreateInfo. Let [eq]#pname:z~f~# be the incoming fragment's depth value for a sample, and let [eq]#z~a~# be the depth/stencil attachment value in memory for that sample. The depth test passes under the following conditions: * ename:VK_COMPARE_OP_NEVER: the test never passes. * ename:VK_COMPARE_OP_LESS: the test passes when [eq]#z~f~ < z~a~#. * ename:VK_COMPARE_OP_EQUAL: the test passes when [eq]#z~f~ = z~a~#. * ename:VK_COMPARE_OP_LESS_OR_EQUAL: the test passes when [eq]#z~f~ {leq} z~a~#. * ename:VK_COMPARE_OP_GREATER: the test passes when [eq]#z~f~ > z~a~#. * ename:VK_COMPARE_OP_NOT_EQUAL: the test passes when [eq]#z~f~ {neq} z~a~#. * ename:VK_COMPARE_OP_GREATER_OR_EQUAL: the test passes when [eq]#z~f~ {geq} z~a~#. * ename:VK_COMPARE_OP_ALWAYS: the test always passes. If slink:VkPipelineRasterizationStateCreateInfo::pname:depthClampEnable is enabled, before the incoming fragment's [eq]#pname:z~f~# is compared to [eq]#pname:z~a~#, [eq]#pname:z~f~# is clamped to [eq]#[min(n,f),max(n,f)]#, where [eq]#n# and [eq]#f# are the pname:minDepth and pname:maxDepth depth range values of the viewport used by this fragment, respectively. If the depth test fails, the sample's coverage bit is cleared in the fragment. The stencil value at the sample's location is updated according to the function currently in effect for depth test failure. [[fragops-depth-write]] If the depth test passes, the sample's (possibly clamped) [eq]#pname:z~f~# value is conditionally written to the depth framebuffer attachment based on the pname:depthWriteEnable member of slink:VkPipelineDepthStencilStateCreateInfo. If pname:depthWriteEnable is ename:VK_TRUE the value is written, and if it is ename:VK_FALSE the value is not written. ifdef::VK_EXT_depth_range_unrestricted[] If the depth framebuffer attachment is a fixed-point format and the depth value is outside of the `0.0` to `1.0` range the depth value is clamped between `0.0` and `1.0` inclusive before writing. endif::VK_EXT_depth_range_unrestricted[] The stencil value at the sample's location is updated according to the function currently in effect for depth test success. If there is no depth framebuffer attachment, it is as if the depth test always passes. ifdef::VK_NV_representative_fragment_test[] [[fragops-rep-frag-test]] == Representative Fragment Test The representative fragment test allows implementations to reduce the amount of rasterization and fragment processing work performed for each point, line, or triangle primitive. For any primitive that produces one or more fragments that pass all prior early fragment tests, the implementation may: choose one or more "representative" fragments for processing and discard all other fragments. For draw calls rendering multiple points, lines, or triangles arranged in lists, strips, or fans, the representative fragment test is performed independently for each of those primitives. The set of fragments discarded by the representative fragment test is implementation-dependent. In some cases, the representative fragment test may not discard any fragments for a given primitive. [open,refpage='VkPipelineRepresentativeFragmentTestStateCreateInfoNV',desc='Structure specifying representative fragment test',type='structs'] -- If the pname:pNext chain of slink:VkGraphicsPipelineCreateInfo includes a sname:VkPipelineRepresentativeFragmentTestStateCreateInfoNV structure, then that structure includes parameters that control the representative fragment test. The sname:VkPipelineRepresentativeFragmentTestStateCreateInfoNV structure is defined as: include::../api/structs/VkPipelineRepresentativeFragmentTestStateCreateInfoNV.txt[] * pname:sType is the type of this structure. * pname:pNext is `NULL` or a pointer to an extension-specific structure. * pname:representativeFragmentTestEnable controls whether the representative fragment test is enabled. If this structure is not present, pname:representativeFragmentTestEnable is considered to be ename:VK_FALSE, and the representative fragment test is disabled. If <> are not enabled in the active fragment shader, the representative fragment shader test has no effect, even if enabled. include::../validity/structs/VkPipelineRepresentativeFragmentTestStateCreateInfoNV.txt[] -- endif::VK_NV_representative_fragment_test[] [[fragops-samplecount]] == Sample Counting Occlusion queries use query pool entries to track the number of samples that pass all the per-fragment tests. The mechanism of collecting an occlusion query value is described in <>. The occlusion query sample counter increments by one for each sample with a coverage value of 1 in each fragment that survives all the per-fragment tests, including scissor, ifdef::VK_NV_scissor_exclusive[] exclusive scissor, endif::VK_NV_scissor_exclusive[] sample mask, alpha to coverage, stencil, and depth tests. ifdef::VK_NV_fragment_coverage_to_color[] [[fragops-coverage-to-color]] == Fragment Coverage To Color [open,refpage='VkPipelineCoverageToColorStateCreateInfoNV',desc='Structure specifying whether fragment coverage replaces a color',type='structs'] -- If the pname:pNext chain of slink:VkPipelineMultisampleStateCreateInfo includes a sname:VkPipelineCoverageToColorStateCreateInfoNV structure, then that structure controls whether the fragment coverage is substituted for a fragment color output and, if so, which output is replaced. The sname:VkPipelineCoverageToColorStateCreateInfoNV structure is defined as: include::../api/structs/VkPipelineCoverageToColorStateCreateInfoNV.txt[] * pname:sType is the type of this structure * pname:pNext is `NULL` or a pointer to an extension-specific structure * pname:flags is reserved for future use. * pname:coverageToColorEnable controls whether the fragment coverage value replaces a fragment color output. * pname:coverageToColorLocation controls which fragment shader color output value is replaced. If pname:coverageToColorEnable is ename:VK_TRUE, the fragment coverage information is treated as a bitmask with one bit for each sample (as in the <> section), and this bitmask replaces the first component of the color value corresponding to the fragment shader output location with code:Location equal to pname:coverageToColorLocation and code:Index equal to zero. If the color attachment format has fewer bits than the sample coverage, the low bits of the sample coverage bitmask are taken without any clamping. If the color attachment format has more bits than the sample coverage, the high bits of the sample coverage bitmask are filled with zeros. If <> is in use, the coverage bitmask only has bits set for samples that correspond to the fragment shader invocation that shades those samples. This pipeline stage occurs after sample counting and before blending, and is always performed after fragment shading regardless of the setting of code:EarlyFragmentTests. If pname:coverageToColorEnable is ename:VK_FALSE, these operations are skipped. If this structure is not present, it is as if pname:coverageToColorEnable is ename:VK_FALSE. .Valid Usage **** * [[VUID-VkPipelineCoverageToColorStateCreateInfoNV-coverageToColorEnable-01404]] If pname:coverageToColorEnable is ename:VK_TRUE, then the render pass subpass indicated by slink:VkGraphicsPipelineCreateInfo::pname:renderPass and slink:VkGraphicsPipelineCreateInfo::pname:subpass must: have a color attachment at the location selected by pname:coverageToColorLocation, with a elink:VkFormat of ename:VK_FORMAT_R8_UINT, ename:VK_FORMAT_R8_SINT, ename:VK_FORMAT_R16_UINT, ename:VK_FORMAT_R16_SINT, ename:VK_FORMAT_R32_UINT, or ename:VK_FORMAT_R32_SINT **** include::../validity/structs/VkPipelineCoverageToColorStateCreateInfoNV.txt[] -- [open,refpage='VkPipelineCoverageToColorStateCreateFlagsNV',desc='Reserved for future use',type='enums'] -- include::../api/flags/VkPipelineCoverageToColorStateCreateFlagsNV.txt[] sname:VkPipelineCoverageToColorStateCreateFlagsNV is a bitmask type for setting a mask, but is currently reserved for future use. -- endif::VK_NV_fragment_coverage_to_color[] [[fragops-coverage-reduction]] == Coverage Reduction Coverage reduction generates a _color sample mask_ from the coverage mask, with one bit for each sample in the color attachment(s) for the subpass. If a bit in the color sample mask is 0, then blending and writing to the framebuffer are not performed for that sample. ifndef::VK_NV_framebuffer_mixed_samples[] Each color sample is associated with a unique rasterization sample, and the value of the coverage mask is assigned to the color sample mask. endif::VK_NV_framebuffer_mixed_samples[] ifdef::VK_NV_framebuffer_mixed_samples[] If the pipeline's slink:VkPipelineMultisampleStateCreateInfo::pname:rasterizationSamples is greater than one and the slink:VkAttachmentDescription::pname:samples of the color attachments is one, then the fragment's coverage is reduced from pname:rasterizationSamples bits to a single bit, where the color sample mask is 1 if any bit in the fragment's coverage is on, and 0 otherwise. If the pipeline's slink:VkPipelineMultisampleStateCreateInfo::pname:rasterizationSamples is greater than the slink:VkAttachmentDescription::pname:samples of the color attachments in the subpass, then the fragment's coverage is reduced from pname:rasterizationSamples bits to a color sample mask with slink:VkAttachmentDescription::pname:samples bits. There is an implementation-dependent association of raster samples to color samples. The reduced color sample mask is computed such that the bit for each color sample is 1 if any of the associated bits in the fragment's coverage is on, and 0 otherwise. [[fragops-coverage-modulation]] === Coverage Modulation [open,refpage='VkPipelineCoverageModulationStateCreateInfoNV',desc='Structure specifying parameters controlling coverage modulation',type='structs'] -- As part of coverage reduction, fragment color values can: also be modulated (multiplied) by a value that is a function of fraction of covered rasterization samples associated with that color sample. Pipeline state controlling coverage reduction is specified through the members of the sname:VkPipelineCoverageModulationStateCreateInfoNV structure. The sname:VkPipelineCoverageModulationStateCreateInfoNV structure is defined as: include::../api/structs/VkPipelineCoverageModulationStateCreateInfoNV.txt[] * pname:sType is the type of this structure. * pname:pNext is `NULL` or a pointer to an extension-specific structure. * pname:flags is reserved for future use. * pname:coverageModulationMode controls which color components are modulated and is of type elink:VkCoverageModulationModeNV. * pname:coverageModulationTableEnable controls whether the modulation factor is looked up from a table in pname:pCoverageModulationTable. * pname:coverageModulationTableCount is the number of elements in pname:pCoverageModulationTable. * pname:pCoverageModulationTable is a table of modulation factors containing a value for each number of covered samples. If pname:coverageModulationTableEnable is ename:VK_FALSE, then for each color sample the associated bits of the fragment's coverage are counted and divided by the number of associated bits to produce a modulation factor [eq]#R# in the range [eq]#(0,1]# (a value of zero would have been killed due to a color coverage of 0). Specifically: * [eq]#N# = value of pname:rasterizationSamples * [eq]#M# = value of slink:VkAttachmentDescription::pname:samples for any color attachments * [eq]#R = popcount(associated coverage bits) / (N / M)# If pname:coverageModulationTableEnable is ename:VK_TRUE, the value [eq]#R# is computed using a programmable lookup table. The lookup table has [eq]#N / M# elements, and the element of the table is selected by: * [eq]#R = pname:pCoverageModulationTable[popcount(associated coverage bits)-1]# Note that the table does not have an entry for [eq]#popcount(associated coverage bits) = 0#, because such samples would have been killed. The values of pname:pCoverageModulationTable may: be rounded to an implementation-dependent precision, which is at least as fine as [eq]#1 / N#, and clamped to [eq]#[0,1]#. For each color attachment with a floating point or normalized color format, each fragment output color value is replicated to [eq]#M# values which can: each be modulated (multiplied) by that color sample's associated value of [eq]#R#. Which components are modulated is controlled by pname:coverageModulationMode. If this structure is not present, it is as if coverageModulationMode is ename:VK_COVERAGE_MODULATION_MODE_NONE_NV. .Valid Usage **** * [[VUID-VkPipelineCoverageModulationStateCreateInfoNV-coverageModulationTableEnable-01405]] If pname:coverageModulationTableEnable is ename:VK_TRUE, pname:coverageModulationTableCount must: be equal to the number of rasterization samples divided by the number of color samples in the subpass. **** include::../validity/structs/VkPipelineCoverageModulationStateCreateInfoNV.txt[] -- [open,refpage='VkPipelineCoverageModulationStateCreateFlagsNV',desc='Reserved for future use',type='enums'] -- include::../api/flags/VkPipelineCoverageModulationStateCreateFlagsNV.txt[] sname:VkPipelineCoverageModulationStateCreateFlagsNV is a bitmask type for setting a mask, but is currently reserved for future use. -- [open,refpage='VkCoverageModulationModeNV',desc='Specify the discard rectangle mode',type='enums'] -- Possible values of slink:VkPipelineCoverageModulationStateCreateInfoNV::pname:coverageModulationMode, specifying which color components are modulated, are: include::../api/enums/VkCoverageModulationModeNV.txt[] * ename:VK_COVERAGE_MODULATION_MODE_NONE_NV specifies that no components are multiplied by the modulation factor. * ename:VK_COVERAGE_MODULATION_MODE_RGB_NV specifies that the red, green, and blue components are multiplied by the modulation factor. * ename:VK_COVERAGE_MODULATION_MODE_ALPHA_NV specifies that the alpha component is multiplied by the modulation factor. * ename:VK_COVERAGE_MODULATION_MODE_RGBA_NV specifies that all components are multiplied by the modulation factor. -- endif::VK_NV_framebuffer_mixed_samples[]