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279452463a
* Update release number to 92.
Public Issues:
* Move and modify valid usage statements dealing with pname:aspectMask in
flink:vkCmdClearColorImage, flink:vkCmdClearDepthStencilImage, and
slink:VkClearAttachment, so they are in places where all necessary
information is available (public issue 529).
* Fix math markup in <<textures-texel-anisotropic-filtering, Texel
Anisotropic Filtering>> (public pull request 840).
* Fix misspellings (public pull request 845).
Internal Issues:
* Add installation instructions and a Makefile "`chunked`" target for
chunked HTML generation (internal issue 1352).
* Fix pipeline mesh diagram style; also fix a minor bug in the classic
pipeline diagram where vertex/index buffers wrongly fed into the vertex
shader (internal issue 1436).
* Make asciidoctor ERROR output raise an error, and don't suppress
executed command output from CI make invocation (internal issue 1454).
* Minor typo fixes and clarifications for `VK_NV_raytracing`.
* Cleanup extension-specific properties
** Remove duplicated documentation for pname:maxDiscardRectangles,
pname:pointClippingBehavior, and pname:maxVertexAttribDivisor (they
shouldn't be documented with the other members of
slink:VkPhysicalDeviceLimits at all).
** Remove duplicate anchor for pname:maxVertexAttribDivisor
** Consistently document stext:VkPhysicalDevice<Extension>PropertiesKHR
*** Always document pname:sType/pname:pNext (was inconsistent before)
*** Always mention chaining to slink:VkPhysicalDeviceProperties2 (and not
as slink:VkPhysicalDeviceProperties2KHR)
*** Always include Valid Usage statements last
* Update Makefile 'checklinks' target and associated scripts, and fix
markup problems identified by checkLinks.py, so that we can rely on the
checklinks script as part of Gitlab CI.
551 lines
25 KiB
Plaintext
551 lines
25 KiB
Plaintext
// Copyright (c) 2015-2018 Khronos Group. This work is licensed under a
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// Creative Commons Attribution 4.0 International License; see
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// http://creativecommons.org/licenses/by/4.0/
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[[framebuffer]]
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= The Framebuffer
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[[framebuffer-blending]]
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== Blending
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Blending combines the incoming _source_ fragment's R, G, B, and A values
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with the _destination_ R, G, B, and A values of each sample stored in the
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framebuffer at the fragment's [eq]#(x~f~,y~f~)# location.
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Blending is performed for each pixel sample, rather than just once for each
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fragment.
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Source and destination values are combined according to the
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<<framebuffer-blendoperations,blend operation>>, quadruplets of source and
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destination weighting factors determined by the <<framebuffer-blendfactors,
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blend factors>>, and a <<framebuffer-blendconstants,blend constant>>, to
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obtain a new set of R, G, B, and A values, as described below.
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Blending is computed and applied separately to each color attachment used by
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the subpass, with separate controls for each attachment.
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Prior to performing the blend operation, signed and unsigned normalized
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fixed-point color components undergo an implied conversion to floating-point
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as specified by <<fundamentals-fixedfpconv,Conversion from Normalized
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Fixed-Point to Floating-Point>>.
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Blending computations are treated as if carried out in floating-point, and
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basic blend operations are performed with a precision and dynamic range no
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lower than that used to represent destination components.
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ifdef::VK_EXT_blend_operation_advanced[]
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<<framebuffer-blend-advanced,Advanced blending operations>> are performed
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with a precision and dynamic range no lower than the smaller of that used to
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represent destination components or that used to represent 16-bit
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floating-point values.
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endif::VK_EXT_blend_operation_advanced[]
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Blending applies only to fixed-point and floating-point color attachments.
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If the color attachment has an integer format, blending is not applied.
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The pipeline blend state is included in the
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sname:VkPipelineColorBlendStateCreateInfo structure during graphics pipeline
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creation:
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[open,refpage='VkPipelineColorBlendStateCreateInfo',desc='Structure specifying parameters of a newly created pipeline color blend state',type='structs']
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--
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The sname:VkPipelineColorBlendStateCreateInfo structure is defined as:
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include::../api/structs/VkPipelineColorBlendStateCreateInfo.txt[]
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* pname:sType is the type of this structure.
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* pname:pNext is `NULL` or a pointer to an extension-specific structure.
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* pname:flags is reserved for future use.
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* pname:logicOpEnable controls whether to apply <<framebuffer-logicop,
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Logical Operations>>.
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* pname:logicOp selects which logical operation to apply.
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* pname:attachmentCount is the number of
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sname:VkPipelineColorBlendAttachmentState elements in
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pname:pAttachments.
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This value must: equal the pname:colorAttachmentCount for the subpass in
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which this pipeline is used.
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* pname:pAttachments: is a pointer to array of per target attachment
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states.
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* pname:blendConstants is an array of four values used as the R, G, B, and
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A components of the blend constant that are used in blending, depending
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on the <<framebuffer-blendfactors,blend factor>>.
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Each element of the pname:pAttachments array is a
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slink:VkPipelineColorBlendAttachmentState structure specifying per-target
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blending state for each individual color attachment.
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If the <<features-features-independentBlend,independent blending>> feature
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is not enabled on the device, all slink:VkPipelineColorBlendAttachmentState
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elements in the pname:pAttachments array must: be identical.
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.Valid Usage
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****
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* [[VUID-VkPipelineColorBlendStateCreateInfo-pAttachments-00605]]
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If the <<features-features-independentBlend,independent blending>>
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feature is not enabled, all elements of pname:pAttachments must: be
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identical
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* [[VUID-VkPipelineColorBlendStateCreateInfo-logicOpEnable-00606]]
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If the <<features-features-logicOp,logic operations>> feature is not
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enabled, pname:logicOpEnable must: be ename:VK_FALSE
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* [[VUID-VkPipelineColorBlendStateCreateInfo-logicOpEnable-00607]]
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If pname:logicOpEnable is ename:VK_TRUE, pname:logicOp must: be a valid
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elink:VkLogicOp value
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****
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include::../validity/structs/VkPipelineColorBlendStateCreateInfo.txt[]
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--
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[open,refpage='VkPipelineColorBlendStateCreateFlags',desc='Reserved for future use',type='enums']
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--
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include::../api/flags/VkPipelineColorBlendStateCreateFlags.txt[]
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tname:VkPipelineColorBlendStateCreateFlags is a bitmask type for setting a
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mask, but is currently reserved for future use.
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--
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[open,refpage='VkPipelineColorBlendAttachmentState',desc='Structure specifying a pipeline color blend attachment state',type='structs']
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--
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The sname:VkPipelineColorBlendAttachmentState structure is defined as:
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include::../api/structs/VkPipelineColorBlendAttachmentState.txt[]
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* pname:blendEnable controls whether blending is enabled for the
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corresponding color attachment.
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If blending is not enabled, the source fragment's color for that
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attachment is passed through unmodified.
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* pname:srcColorBlendFactor selects which blend factor is used to
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determine the source factors [eq]#(S~r~,S~g~,S~b~)#.
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* pname:dstColorBlendFactor selects which blend factor is used to
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determine the destination factors [eq]#(D~r~,D~g~,D~b~)#.
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* pname:colorBlendOp selects which blend operation is used to calculate
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the RGB values to write to the color attachment.
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* pname:srcAlphaBlendFactor selects which blend factor is used to
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determine the source factor [eq]#S~a~#.
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* pname:dstAlphaBlendFactor selects which blend factor is used to
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determine the destination factor [eq]#D~a~#.
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* pname:alphaBlendOp selects which blend operation is use to calculate the
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alpha values to write to the color attachment.
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* pname:colorWriteMask is a bitmask of elink:VkColorComponentFlagBits
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specifying which of the R, G, B, and/or A components are enabled for
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writing, as described for the <<framebuffer-color-write-mask,Color Write
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Mask>>.
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.Valid Usage
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****
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* [[VUID-VkPipelineColorBlendAttachmentState-srcColorBlendFactor-00608]]
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If the <<features-features-dualSrcBlend,dual source blending>> feature
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is not enabled, pname:srcColorBlendFactor must: not be
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ename:VK_BLEND_FACTOR_SRC1_COLOR,
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ename:VK_BLEND_FACTOR_ONE_MINUS_SRC1_COLOR,
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ename:VK_BLEND_FACTOR_SRC1_ALPHA, or
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ename:VK_BLEND_FACTOR_ONE_MINUS_SRC1_ALPHA
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* [[VUID-VkPipelineColorBlendAttachmentState-dstColorBlendFactor-00609]]
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If the <<features-features-dualSrcBlend,dual source blending>> feature
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is not enabled, pname:dstColorBlendFactor must: not be
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ename:VK_BLEND_FACTOR_SRC1_COLOR,
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ename:VK_BLEND_FACTOR_ONE_MINUS_SRC1_COLOR,
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ename:VK_BLEND_FACTOR_SRC1_ALPHA, or
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ename:VK_BLEND_FACTOR_ONE_MINUS_SRC1_ALPHA
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* [[VUID-VkPipelineColorBlendAttachmentState-srcAlphaBlendFactor-00610]]
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If the <<features-features-dualSrcBlend,dual source blending>> feature
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is not enabled, pname:srcAlphaBlendFactor must: not be
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ename:VK_BLEND_FACTOR_SRC1_COLOR,
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ename:VK_BLEND_FACTOR_ONE_MINUS_SRC1_COLOR,
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ename:VK_BLEND_FACTOR_SRC1_ALPHA, or
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ename:VK_BLEND_FACTOR_ONE_MINUS_SRC1_ALPHA
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* [[VUID-VkPipelineColorBlendAttachmentState-dstAlphaBlendFactor-00611]]
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If the <<features-features-dualSrcBlend,dual source blending>> feature
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is not enabled, pname:dstAlphaBlendFactor must: not be
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ename:VK_BLEND_FACTOR_SRC1_COLOR,
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ename:VK_BLEND_FACTOR_ONE_MINUS_SRC1_COLOR,
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ename:VK_BLEND_FACTOR_SRC1_ALPHA, or
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ename:VK_BLEND_FACTOR_ONE_MINUS_SRC1_ALPHA
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ifdef::VK_EXT_blend_operation_advanced[]
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* [[VUID-VkPipelineColorBlendAttachmentState-colorBlendOp-01406]]
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If either of pname:colorBlendOp or pname:alphaBlendOp is an
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<<framebuffer-blend-advanced,advanced blend operation>>, then
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pname:colorBlendOp must: equal pname:alphaBlendOp
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* [[VUID-VkPipelineColorBlendAttachmentState-advancedBlendIndependentBlend-01407]]
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If
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slink:VkPhysicalDeviceBlendOperationAdvancedPropertiesEXT::pname:advancedBlendIndependentBlend
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is ename:VK_FALSE and pname:colorBlendOp is an
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<<framebuffer-blend-advanced,advanced blend operation>>, then
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pname:colorBlendOp must: be the same for all attachments.
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* [[VUID-VkPipelineColorBlendAttachmentState-advancedBlendIndependentBlend-01408]]
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If
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slink:VkPhysicalDeviceBlendOperationAdvancedPropertiesEXT::pname:advancedBlendIndependentBlend
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is ename:VK_FALSE and pname:alphaBlendOp is an
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<<framebuffer-blend-advanced,advanced blend operation>>, then
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pname:alphaBlendOp must: be the same for all attachments.
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* [[VUID-VkPipelineColorBlendAttachmentState-advancedBlendAllOperations-01409]]
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If
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slink:VkPhysicalDeviceBlendOperationAdvancedPropertiesEXT::pname:advancedBlendAllOperations
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is ename:VK_FALSE, then pname:colorBlendOp must: not be
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ename:VK_BLEND_OP_ZERO_EXT, ename:VK_BLEND_OP_SRC_EXT,
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ename:VK_BLEND_OP_DST_EXT, ename:VK_BLEND_OP_SRC_OVER_EXT,
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ename:VK_BLEND_OP_DST_OVER_EXT, ename:VK_BLEND_OP_SRC_IN_EXT,
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ename:VK_BLEND_OP_DST_IN_EXT, ename:VK_BLEND_OP_SRC_OUT_EXT,
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ename:VK_BLEND_OP_DST_OUT_EXT, ename:VK_BLEND_OP_SRC_ATOP_EXT,
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ename:VK_BLEND_OP_DST_ATOP_EXT, ename:VK_BLEND_OP_XOR_EXT,
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ename:VK_BLEND_OP_INVERT_EXT, ename:VK_BLEND_OP_INVERT_RGB_EXT,
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ename:VK_BLEND_OP_LINEARDODGE_EXT, ename:VK_BLEND_OP_LINEARBURN_EXT,
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ename:VK_BLEND_OP_VIVIDLIGHT_EXT, ename:VK_BLEND_OP_LINEARLIGHT_EXT,
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ename:VK_BLEND_OP_PINLIGHT_EXT, ename:VK_BLEND_OP_HARDMIX_EXT,
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ename:VK_BLEND_OP_PLUS_EXT, ename:VK_BLEND_OP_PLUS_CLAMPED_EXT,
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ename:VK_BLEND_OP_PLUS_CLAMPED_ALPHA_EXT,
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ename:VK_BLEND_OP_PLUS_DARKER_EXT, ename:VK_BLEND_OP_MINUS_EXT,
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ename:VK_BLEND_OP_MINUS_CLAMPED_EXT, ename:VK_BLEND_OP_CONTRAST_EXT,
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ename:VK_BLEND_OP_INVERT_OVG_EXT, ename:VK_BLEND_OP_RED_EXT,
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ename:VK_BLEND_OP_GREEN_EXT, or ename:VK_BLEND_OP_BLUE_EXT
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* [[VUID-VkPipelineColorBlendAttachmentState-colorBlendOp-01410]]
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If pname:colorBlendOp or pname:alphaBlendOp is an
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<<framebuffer-blend-advanced,advanced blend operation>>, then
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slink:VkSubpassDescription::pname:colorAttachmentCount of the subpass
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this pipeline is compiled against must: be less than or equal to
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slink:VkPhysicalDeviceBlendOperationAdvancedPropertiesEXT::advancedBlendMaxColorAttachments
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endif::VK_EXT_blend_operation_advanced[]
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****
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include::../validity/structs/VkPipelineColorBlendAttachmentState.txt[]
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--
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[[framebuffer-blendfactors]]
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=== Blend Factors
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[open,refpage='VkBlendFactor',desc='Framebuffer blending factors',type='enums']
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--
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The source and destination color and alpha blending factors are selected
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from the enum:
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include::../api/enums/VkBlendFactor.txt[]
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The semantics of each enum value is described in the table below:
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.Blend Factors
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[width="100%",options="header",align="center",cols="59%,28%,13%"]
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|====
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|elink:VkBlendFactor | RGB Blend Factors [eq]#(S~r~,S~g~,S~b~)# or [eq]#(D~r~,D~g~,D~b~)# | Alpha Blend Factor ([eq]#S~a~# or [eq]#D~a~#)
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|ename:VK_BLEND_FACTOR_ZERO | [eq]#(0,0,0)# | [eq]#0#
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|ename:VK_BLEND_FACTOR_ONE | [eq]#(1,1,1)# | [eq]#1#
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|ename:VK_BLEND_FACTOR_SRC_COLOR | [eq]#(R~s0~,G~s0~,B~s0~)# | [eq]#A~s0~#
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|ename:VK_BLEND_FACTOR_ONE_MINUS_SRC_COLOR | [eq]#(1-R~s0~,1-G~s0~,1-B~s0~)# | [eq]#1-A~s0~#
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|ename:VK_BLEND_FACTOR_DST_COLOR | [eq]#(R~d~,G~d~,B~d~)# | [eq]#A~d~#
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|ename:VK_BLEND_FACTOR_ONE_MINUS_DST_COLOR | [eq]#(1-R~d~,1-G~d~,1-B~d~)# | [eq]#1-A~d~#
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|ename:VK_BLEND_FACTOR_SRC_ALPHA | [eq]#(A~s0~,A~s0~,A~s0~)# | [eq]#A~s0~#
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|ename:VK_BLEND_FACTOR_ONE_MINUS_SRC_ALPHA | [eq]#(1-A~s0~,1-A~s0~,1-A~s0~)# | [eq]#1-A~s0~#
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|ename:VK_BLEND_FACTOR_DST_ALPHA | [eq]#(A~d~,A~d~,A~d~)# | [eq]#A~d~#
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|ename:VK_BLEND_FACTOR_ONE_MINUS_DST_ALPHA | [eq]#(1-A~d~,1-A~d~,1-A~d~)# | [eq]#1-A~d~#
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|ename:VK_BLEND_FACTOR_CONSTANT_COLOR | [eq]#(R~c~,G~c~,B~c~)# | [eq]#A~c~#
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|ename:VK_BLEND_FACTOR_ONE_MINUS_CONSTANT_COLOR | [eq]#(1-R~c~,1-G~c~,1-B~c~)# | [eq]#1-A~c~#
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|ename:VK_BLEND_FACTOR_CONSTANT_ALPHA | [eq]#(A~c~,A~c~,A~c~)# | [eq]#A~c~#
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|ename:VK_BLEND_FACTOR_ONE_MINUS_CONSTANT_ALPHA | [eq]#(1-A~c~,1-A~c~,1-A~c~)# | [eq]#1-A~c~#
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|ename:VK_BLEND_FACTOR_SRC_ALPHA_SATURATE | [eq]#(f,f,f)#; [eq]#f = min(A~s0~,1-A~d~)# | [eq]#1#
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|ename:VK_BLEND_FACTOR_SRC1_COLOR | [eq]#(R~s1~,G~s1~,B~s1~)# | [eq]#A~s1~#
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|ename:VK_BLEND_FACTOR_ONE_MINUS_SRC1_COLOR | [eq]#(1-R~s1~,1-G~s1~,1-B~s1~)# | [eq]#1-A~s1~#
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|ename:VK_BLEND_FACTOR_SRC1_ALPHA | [eq]#(A~s1~,A~s1~,A~s1~)# | [eq]#A~s1~#
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|ename:VK_BLEND_FACTOR_ONE_MINUS_SRC1_ALPHA | [eq]#(1-A~s1~,1-A~s1~,1-A~s1~)# | [eq]#1-A~s1~#
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|====
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In this table, the following conventions are used:
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* [eq]#R~s0~,G~s0~,B~s0~# and [eq]#A~s0~# represent the first source color
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R, G, B, and A components, respectively, for the fragment output
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location corresponding to the color attachment being blended.
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* [eq]#R~s1~,G~s1~,B~s1~# and [eq]#A~s1~# represent the second source
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color R, G, B, and A components, respectively, used in dual source
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blending modes, for the fragment output location corresponding to the
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color attachment being blended.
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* [eq]#R~d~,G~d~,B~d~# and [eq]#A~d~# represent the R, G, B, and A
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components of the destination color.
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That is, the color currently in the corresponding color attachment for
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this fragment/sample.
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* [eq]#R~c~,G~c~,B~c~# and [eq]#A~c~# represent the blend constant R, G,
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B, and A components, respectively.
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--
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[[framebuffer-blendconstants]]
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If the pipeline state object is created without the
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ename:VK_DYNAMIC_STATE_BLEND_CONSTANTS dynamic state enabled then the _blend
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constant_ [eq]#(R~c~,G~c~,B~c~,A~c~)# is specified via the
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pname:blendConstants member of slink:VkPipelineColorBlendStateCreateInfo.
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[open,refpage='vkCmdSetBlendConstants',desc='Set the values of blend constants',type='protos']
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--
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Otherwise, to dynamically set and change the blend constant, call:
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include::../api/protos/vkCmdSetBlendConstants.txt[]
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* pname:commandBuffer is the command buffer into which the command will be
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recorded.
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* pname:blendConstants is an array of four values specifying the R, G, B,
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and A components of the blend constant color used in blending, depending
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on the <<framebuffer-blendfactors,blend factor>>.
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.Valid Usage
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****
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* [[VUID-vkCmdSetBlendConstants-None-00612]]
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The bound graphics pipeline must: have been created with the
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ename:VK_DYNAMIC_STATE_BLEND_CONSTANTS dynamic state enabled
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****
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include::../validity/protos/vkCmdSetBlendConstants.txt[]
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--
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[[framebuffer-dsb]]
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=== Dual-Source Blending
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Blend factors that use the secondary color input
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[eq]#(R~s1~,G~s1~,B~s1~,A~s1~)# (ename:VK_BLEND_FACTOR_SRC1_COLOR,
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ename:VK_BLEND_FACTOR_ONE_MINUS_SRC1_COLOR,
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ename:VK_BLEND_FACTOR_SRC1_ALPHA, and
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ename:VK_BLEND_FACTOR_ONE_MINUS_SRC1_ALPHA) may: consume implementation
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resources that could otherwise be used for rendering to multiple color
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attachments.
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Therefore, the number of color attachments that can: be used in a
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framebuffer may: be lower when using dual-source blending.
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Dual-source blending is only supported if the
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<<features-features-dualSrcBlend,pname:dualSrcBlend>> feature is enabled.
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The maximum number of color attachments that can: be used in a subpass when
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using dual-source blending functions is implementation-dependent and is
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reported as the pname:maxFragmentDualSrcAttachments member of
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sname:VkPhysicalDeviceLimits.
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When using a fragment shader with dual-source blending functions, the color
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outputs are bound to the first and second inputs of the blender using the
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code:Index decoration, as described in <<interfaces-fragmentoutput,Fragment
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Output Interface>>.
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If the second color input to the blender is not written in the shader, or if
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no output is bound to the second input of a blender, the result of the
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blending operation is not defined.
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[[framebuffer-blendoperations]]
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=== Blend Operations
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[open,refpage='VkBlendOp',desc='Framebuffer blending operations',type='enums']
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--
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Once the source and destination blend factors have been selected, they along
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with the source and destination components are passed to the blending
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operations.
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RGB and alpha components can: use different operations.
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Possible values of elink:VkBlendOp, specifying the operations, are:
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include::../api/enums/VkBlendOp.txt[]
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<<<
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The semantics of each basic blend operations is described in the table
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below:
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.Basic Blend Operations
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[width="100%",cols="45%,30%,25%",options="header",align="center"]
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|====
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|elink:VkBlendOp | RGB Components | Alpha Component
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|ename:VK_BLEND_OP_ADD
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| [eq]#R = R~s0~ {times} S~r~ {plus} R~d~ {times} D~r~# +
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[eq]#G = G~s0~ {times} S~g~ {plus} G~d~ {times} D~g~# +
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[eq]#B = B~s0~ {times} S~b~ {plus} B~d~ {times} D~b~#
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| [eq]#A = A~s0~ {times} S~a~ {plus} A~d~ {times} D~a~#
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|ename:VK_BLEND_OP_SUBTRACT
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| [eq]#R = R~s0~ {times} S~r~ - R~d~ {times} D~r~# +
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[eq]#G = G~s0~ {times} S~g~ - G~d~ {times} D~g~# +
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[eq]#B = B~s0~ {times} S~b~ - B~d~ {times} D~b~#
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| [eq]#A = A~s0~ {times} S~a~ - A~d~ {times} D~a~#
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|ename:VK_BLEND_OP_REVERSE_SUBTRACT
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| [eq]#R = R~d~ {times} D~r~ - R~s0~ {times} S~r~# +
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[eq]#G = G~d~ {times} D~g~ - G~s0~ {times} S~g~# +
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[eq]#B = B~d~ {times} D~b~ - B~s0~ {times} S~b~#
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| [eq]#A = A~d~ {times} D~a~ - A~s0~ {times} S~a~#
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|ename:VK_BLEND_OP_MIN
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| [eq]#R = min(R~s0~,R~d~)# +
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[eq]#G = min(G~s0~,G~d~)# +
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[eq]#B = min(B~s0~,B~d~)#
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| [eq]#A = min(A~s0~,A~d~)#
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|ename:VK_BLEND_OP_MAX
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| [eq]#R = max(R~s0~,R~d~)# +
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[eq]#G = max(G~s0~,G~d~)# +
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[eq]#B = max(B~s0~,B~d~)#
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| [eq]#A = max(A~s0~,A~d~)#
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|====
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In this table, the following conventions are used:
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* [eq]#R~s0~, G~s0~, B~s0~# and [eq]#A~s0~# represent the first source
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color R, G, B, and A components, respectively.
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* [eq]#R~d~, G~d~, B~d~# and [eq]#A~d~# represent the R, G, B, and A
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components of the destination color.
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That is, the color currently in the corresponding color attachment for
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this fragment/sample.
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* [eq]#S~r~, S~g~, S~b~# and [eq]#S~a~# represent the source blend factor
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R, G, B, and A components, respectively.
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* [eq]#D~r~, D~g~, D~b~# and [eq]#D~a~# represent the destination blend
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factor R, G, B, and A components, respectively.
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The blending operation produces a new set of values [eq]#R, G, B# and
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[eq]#A#, which are written to the framebuffer attachment.
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If blending is not enabled for this attachment, then [eq]#R, G, B# and
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[eq]#A# are assigned [eq]#R~s0~, G~s0~, B~s0~# and [eq]#A~s0~#,
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respectively.
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If the color attachment is fixed-point, the components of the source and
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destination values and blend factors are each clamped to [eq]#[0,1]# or
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[eq]#[-1,1]# respectively for an unsigned normalized or signed normalized
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color attachment prior to evaluating the blend operations.
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If the color attachment is floating-point, no clamping occurs.
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--
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If the numeric format of a framebuffer attachment uses sRGB encoding, the R,
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G, and B destination color values (after conversion from fixed-point to
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floating-point) are considered to be encoded for the sRGB color space and
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hence are linearized prior to their use in blending.
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Each R, G, and B component is converted from nonlinear to linear as
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described in the "`sRGB EOTF`" section of the <<data-format,Khronos Data
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Format Specification>>.
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If the format is not sRGB, no linearization is performed.
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If the numeric format of a framebuffer attachment uses sRGB encoding, then
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the final R, G and B values are converted into the nonlinear sRGB
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representation before being written to the framebuffer attachment as
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described in the "`sRGB EOTF^ -1^`" section of the Khronos Data Format
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Specification.
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If the framebuffer color attachment numeric format is not sRGB encoded then
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the resulting [eq]#c~s~# values for R, G and B are unmodified.
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The value of A is never sRGB encoded.
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That is, the alpha component is always stored in memory as linear.
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If the framebuffer color attachment is ename:VK_ATTACHMENT_UNUSED, no writes
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are performed through that attachment.
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Framebuffer color attachments greater than or equal to
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sname:VkSubpassDescription::pname:colorAttachmentCount perform no writes.
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ifdef::VK_EXT_blend_operation_advanced[]
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include::VK_EXT_blend_operation_advanced/advanced_blend.txt[]
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endif::VK_EXT_blend_operation_advanced[]
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[[framebuffer-logicop]]
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== Logical Operations
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The application can: enable a _logical operation_ between the fragment's
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color values and the existing value in the framebuffer attachment.
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This logical operation is applied prior to updating the framebuffer
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attachment.
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Logical operations are applied only for signed and unsigned integer and
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normalized integer framebuffers.
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Logical operations are not applied to floating-point or sRGB format color
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attachments.
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[open,refpage='VkLogicOp',desc='Framebuffer logical operations',type='enums']
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--
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Logical operations are controlled by the pname:logicOpEnable and
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pname:logicOp members of slink:VkPipelineColorBlendStateCreateInfo.
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If pname:logicOpEnable is ename:VK_TRUE, then a logical operation selected
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by pname:logicOp is applied between each color attachment and the fragment's
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corresponding output value, and blending of all attachments is treated as if
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it were disabled.
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Any attachments using color formats for which logical operations are not
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supported simply pass through the color values unmodified.
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The logical operation is applied independently for each of the red, green,
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blue, and alpha components.
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The pname:logicOp is selected from the following operations:
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include::../api/enums/VkLogicOp.txt[]
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<<<
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The logical operations supported by Vulkan are summarized in the following
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table in which
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* [eq]#{lnot}# is bitwise invert,
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* [eq]#{land}# is bitwise and,
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* [eq]#{lor}# is bitwise or,
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* [eq]#{oplus}# is bitwise exclusive or,
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* [eq]#s# is the fragment's [eq]#R~s0~, G~s0~, B~s0~# or [eq]#A~s0~#
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component value for the fragment output corresponding to the color
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attachment being updated, and
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* [eq]#d# is the color attachment's [eq]#R, G, B# or [eq]#A# component
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value:
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.Logical Operations
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[width="75%",options="header",align="center"]
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|====
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|Mode | Operation
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|ename:VK_LOGIC_OP_CLEAR | [eq]#0#
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|ename:VK_LOGIC_OP_AND | [eq]#s {land} d#
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|ename:VK_LOGIC_OP_AND_REVERSE | [eq]#s {land} {lnot} d#
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|ename:VK_LOGIC_OP_COPY | [eq]#s#
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|ename:VK_LOGIC_OP_AND_INVERTED | [eq]#{lnot} s {land} d#
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|ename:VK_LOGIC_OP_NO_OP | [eq]#d#
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|ename:VK_LOGIC_OP_XOR | [eq]#s {oplus} d#
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|ename:VK_LOGIC_OP_OR | [eq]#s {lor} d#
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|ename:VK_LOGIC_OP_NOR | [eq]#{lnot} (s {lor} d)#
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|ename:VK_LOGIC_OP_EQUIVALENT | [eq]#{lnot} (s {oplus} d)#
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|ename:VK_LOGIC_OP_INVERT | [eq]#{lnot} d#
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|ename:VK_LOGIC_OP_OR_REVERSE | [eq]#s {lor} {lnot} d#
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|ename:VK_LOGIC_OP_COPY_INVERTED | [eq]#{lnot} s#
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|ename:VK_LOGIC_OP_OR_INVERTED | [eq]#{lnot} s {lor} d#
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|ename:VK_LOGIC_OP_NAND | [eq]#{lnot} (s {land} d)#
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|ename:VK_LOGIC_OP_SET | all 1s
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|====
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The result of the logical operation is then written to the color attachment
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as controlled by the component write mask, described in
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<<framebuffer-blendoperations,Blend Operations>>.
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--
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[[framebuffer-color-write-mask]]
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== Color Write Mask
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[open,refpage='VkColorComponentFlagBits',desc='Bitmask controlling which components are written to the framebuffer',type='enums']
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--
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Bits which can: be set in
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slink:VkPipelineColorBlendAttachmentState::pname:colorWriteMask to determine
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whether the final color values [eq]#R, G, B# and [eq]#A# are written to the
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framebuffer attachment are:
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include::../api/enums/VkColorComponentFlagBits.txt[]
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* ename:VK_COLOR_COMPONENT_R_BIT specifies that the [eq]#R# value is
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written to the color attachment for the appropriate sample.
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Otherwise, the value in memory is unmodified.
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* ename:VK_COLOR_COMPONENT_G_BIT specifies that the [eq]#G# value is
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written to the color attachment for the appropriate sample.
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Otherwise, the value in memory is unmodified.
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* ename:VK_COLOR_COMPONENT_B_BIT specifies that the [eq]#B# value is
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written to the color attachment for the appropriate sample.
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Otherwise, the value in memory is unmodified.
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* ename:VK_COLOR_COMPONENT_A_BIT specifies that the [eq]#A# value is
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written to the color attachment for the appropriate sample.
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Otherwise, the value in memory is unmodified.
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The color write mask operation is applied regardless of whether blending is
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enabled.
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--
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[open,refpage='VkColorComponentFlags',desc='Bitmask of VkColorComponentFlagBits',type='enums']
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--
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include::../api/flags/VkColorComponentFlags.txt[]
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tname:VkColorComponentFlags is a bitmask type for setting a mask of zero or
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more elink:VkColorComponentFlagBits.
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--
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