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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sname: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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|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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|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
|
|
| [eq]#R = R~s0~ {times} S~r~ - R~d~ {times} D~r~# +
|
|
[eq]#G = G~s0~ {times} S~g~ - G~d~ {times} D~g~# +
|
|
[eq]#B = B~s0~ {times} S~b~ - B~d~ {times} D~b~#
|
|
| [eq]#A = A~s0~ {times} S~a~ - A~d~ {times} D~a~#
|
|
|
|
|ename:VK_BLEND_OP_REVERSE_SUBTRACT
|
|
| [eq]#R = R~d~ {times} D~r~ - R~s0~ {times} S~r~# +
|
|
[eq]#G = G~d~ {times} D~g~ - G~s0~ {times} S~g~# +
|
|
[eq]#B = B~d~ {times} D~b~ - B~s0~ {times} S~b~#
|
|
| [eq]#A = A~d~ {times} D~a~ - A~s0~ {times} S~a~#
|
|
|
|
|ename:VK_BLEND_OP_MIN
|
|
| [eq]#R = min(R~s0~,R~d~)# +
|
|
[eq]#G = min(G~s0~,G~d~)# +
|
|
[eq]#B = min(B~s0~,B~d~)#
|
|
| [eq]#A = min(A~s0~,A~d~)#
|
|
|
|
|ename:VK_BLEND_OP_MAX
|
|
| [eq]#R = max(R~s0~,R~d~)# +
|
|
[eq]#G = max(G~s0~,G~d~)# +
|
|
[eq]#B = max(B~s0~,B~d~)#
|
|
| [eq]#A = max(A~s0~,A~d~)#
|
|
|====
|
|
|
|
In this table, the following conventions are used:
|
|
|
|
* [eq]#R~s0~, G~s0~, B~s0~# and [eq]#A~s0~# represent the first source
|
|
color R, G, B, and A components, respectively.
|
|
* [eq]#R~d~, G~d~, B~d~# and [eq]#A~d~# represent the R, G, B, and A
|
|
components of the destination color.
|
|
That is, the color currently in the corresponding color attachment for
|
|
this fragment/sample.
|
|
* [eq]#S~r~, S~g~, S~b~# and [eq]#S~a~# represent the source blend factor
|
|
R, G, B, and A components, respectively.
|
|
* [eq]#D~r~, D~g~, D~b~# and [eq]#D~a~# represent the destination blend
|
|
factor R, G, B, and A components, respectively.
|
|
|
|
The blending operation produces a new set of values [eq]#R, G, B# and
|
|
[eq]#A#, which are written to the framebuffer attachment.
|
|
If blending is not enabled for this attachment, then [eq]#R, G, B# and
|
|
[eq]#A# are assigned [eq]#R~s0~, G~s0~, B~s0~# and [eq]#A~s0~#,
|
|
respectively.
|
|
|
|
If the color attachment is fixed-point, the components of the source and
|
|
destination values and blend factors are each clamped to [eq]#[0,1]# or
|
|
[eq]#[-1,1]# respectively for an unsigned normalized or signed normalized
|
|
color attachment prior to evaluating the blend operations.
|
|
If the color attachment is floating-point, no clamping occurs.
|
|
|
|
--
|
|
|
|
If the numeric format of a framebuffer attachment uses sRGB encoding, the R,
|
|
G, and B destination color values (after conversion from fixed-point to
|
|
floating-point) are considered to be encoded for the sRGB color space and
|
|
hence are linearized prior to their use in blending.
|
|
Each R, G, and B component is converted from nonlinear to linear as
|
|
described in the "`sRGB EOTF`" section of the <<data-format,Khronos Data
|
|
Format Specification>>.
|
|
If the format is not sRGB, no linearization is performed.
|
|
|
|
If the numeric format of a framebuffer attachment uses sRGB encoding, then
|
|
the final R, G and B values are converted into the nonlinear sRGB
|
|
representation before being written to the framebuffer attachment as
|
|
described in the "`sRGB EOTF^ -1^`" section of the Khronos Data Format
|
|
Specification.
|
|
|
|
If the framebuffer color attachment numeric format is not sRGB encoded then
|
|
the resulting [eq]#c~s~# values for R, G and B are unmodified.
|
|
The value of A is never sRGB encoded.
|
|
That is, the alpha component is always stored in memory as linear.
|
|
|
|
If the framebuffer color attachment is ename:VK_ATTACHMENT_UNUSED, no writes
|
|
are performed through that attachment.
|
|
Framebuffer color attachments greater than or equal to
|
|
sname:VkSubpassDescription::pname:colorAttachmentCount perform no writes.
|
|
|
|
ifdef::VK_EXT_blend_operation_advanced[]
|
|
include::VK_EXT_blend_operation_advanced/advanced_blend.txt[]
|
|
endif::VK_EXT_blend_operation_advanced[]
|
|
|
|
[[framebuffer-logicop]]
|
|
== Logical Operations
|
|
|
|
The application can: enable a _logical operation_ between the fragment's
|
|
color values and the existing value in the framebuffer attachment.
|
|
This logical operation is applied prior to updating the framebuffer
|
|
attachment.
|
|
Logical operations are applied only for signed and unsigned integer and
|
|
normalized integer framebuffers.
|
|
Logical operations are not applied to floating-point or sRGB format color
|
|
attachments.
|
|
|
|
[open,refpage='VkLogicOp',desc='Framebuffer logical operations',type='enums']
|
|
--
|
|
|
|
Logical operations are controlled by the pname:logicOpEnable and
|
|
pname:logicOp members of slink:VkPipelineColorBlendStateCreateInfo.
|
|
If pname:logicOpEnable is ename:VK_TRUE, then a logical operation selected
|
|
by pname:logicOp is applied between each color attachment and the fragment's
|
|
corresponding output value, and blending of all attachments is treated as if
|
|
it were disabled.
|
|
Any attachments using color formats for which logical operations are not
|
|
supported simply pass through the color values unmodified.
|
|
The logical operation is applied independently for each of the red, green,
|
|
blue, and alpha components.
|
|
The pname:logicOp is selected from the following operations:
|
|
|
|
include::../api/enums/VkLogicOp.txt[]
|
|
|
|
<<<
|
|
|
|
The logical operations supported by Vulkan are summarized in the following
|
|
table in which
|
|
|
|
* [eq]#{lnot}# is bitwise invert,
|
|
* [eq]#{land}# is bitwise and,
|
|
* [eq]#{lor}# is bitwise or,
|
|
* [eq]#{oplus}# is bitwise exclusive or,
|
|
* [eq]#s# is the fragment's [eq]#R~s0~, G~s0~, B~s0~# or [eq]#A~s0~#
|
|
component value for the fragment output corresponding to the color
|
|
attachment being updated, and
|
|
* [eq]#d# is the color attachment's [eq]#R, G, B# or [eq]#A# component
|
|
value:
|
|
|
|
.Logical Operations
|
|
[width="75%",options="header",align="center"]
|
|
|====
|
|
|Mode | Operation
|
|
|ename:VK_LOGIC_OP_CLEAR | [eq]#0#
|
|
|ename:VK_LOGIC_OP_AND | [eq]#s {land} d#
|
|
|ename:VK_LOGIC_OP_AND_REVERSE | [eq]#s {land} {lnot} d#
|
|
|ename:VK_LOGIC_OP_COPY | [eq]#s#
|
|
|ename:VK_LOGIC_OP_AND_INVERTED | [eq]#{lnot} s {land} d#
|
|
|ename:VK_LOGIC_OP_NO_OP | [eq]#d#
|
|
|ename:VK_LOGIC_OP_XOR | [eq]#s {oplus} d#
|
|
|ename:VK_LOGIC_OP_OR | [eq]#s {lor} d#
|
|
|ename:VK_LOGIC_OP_NOR | [eq]#{lnot} (s {lor} d)#
|
|
|ename:VK_LOGIC_OP_EQUIVALENT | [eq]#{lnot} (s {oplus} d)#
|
|
|ename:VK_LOGIC_OP_INVERT | [eq]#{lnot} d#
|
|
|ename:VK_LOGIC_OP_OR_REVERSE | [eq]#s {lor} {lnot} d#
|
|
|ename:VK_LOGIC_OP_COPY_INVERTED | [eq]#{lnot} s#
|
|
|ename:VK_LOGIC_OP_OR_INVERTED | [eq]#{lnot} s {lor} d#
|
|
|ename:VK_LOGIC_OP_NAND | [eq]#{lnot} (s {land} d)#
|
|
|ename:VK_LOGIC_OP_SET | all 1s
|
|
|====
|
|
|
|
The result of the logical operation is then written to the color attachment
|
|
as controlled by the component write mask, described in
|
|
<<framebuffer-blendoperations,Blend Operations>>.
|
|
|
|
--
|
|
|
|
|
|
[[framebuffer-color-write-mask]]
|
|
== Color Write Mask
|
|
|
|
[open,refpage='VkColorComponentFlagBits',desc='Bitmask controlling which components are written to the framebuffer',type='enums']
|
|
--
|
|
|
|
Bits which can: be set in
|
|
slink:VkPipelineColorBlendAttachmentState::pname:colorWriteMask to determine
|
|
whether the final color values [eq]#R, G, B# and [eq]#A# are written to the
|
|
framebuffer attachment are:
|
|
|
|
include::../api/enums/VkColorComponentFlagBits.txt[]
|
|
|
|
* ename:VK_COLOR_COMPONENT_R_BIT specifies that the [eq]#R# value is
|
|
written to the color attachment for the appropriate sample.
|
|
Otherwise, the value in memory is unmodified.
|
|
* ename:VK_COLOR_COMPONENT_G_BIT specifies that the [eq]#G# value is
|
|
written to the color attachment for the appropriate sample.
|
|
Otherwise, the value in memory is unmodified.
|
|
* ename:VK_COLOR_COMPONENT_B_BIT specifies that the [eq]#B# value is
|
|
written to the color attachment for the appropriate sample.
|
|
Otherwise, the value in memory is unmodified.
|
|
* ename:VK_COLOR_COMPONENT_A_BIT specifies that the [eq]#A# value is
|
|
written to the color attachment for the appropriate sample.
|
|
Otherwise, the value in memory is unmodified.
|
|
|
|
The color write mask operation is applied regardless of whether blending is
|
|
enabled.
|
|
|
|
--
|
|
|
|
[open,refpage='VkColorComponentFlags',desc='Bitmask of VkColorComponentFlagBits',type='enums']
|
|
--
|
|
include::../api/flags/VkColorComponentFlags.txt[]
|
|
|
|
sname:VkColorComponentFlags is a bitmask type for setting a mask of zero or
|
|
more slink:VkColorComponentFlagBits.
|
|
--
|