185 lines
8.3 KiB
Plaintext
185 lines
8.3 KiB
Plaintext
// Copyright (c) 2015-2016 The Khronos Group Inc.
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// Copyright notice at https://www.khronos.org/registry/speccopyright.html
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[[samplers]]
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= Samplers
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sname:VkSampler objects encapsulate the state of an image sampler which is
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used by the implementation to read image data and apply filtering and other
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transformations for the shader.
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To create a sampler object, call:
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include::../protos/vkCreateSampler.txt[]
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* pname:device is the logical device that creates the sampler.
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* pname:pCreateInfo is a pointer to an instance of the
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slink:VkSamplerCreateInfo structure specifying the state of the sampler
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object.
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* pname:pAllocator controls host memory allocation as described in the
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<<memory-allocation, Memory Allocation>> chapter.
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* pname:pSampler points to a sname:VkSampler handle in which the resulting
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sampler object is returned.
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include::../validity/protos/vkCreateSampler.txt[]
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The sname:VkSamplerCreateInfo structure is defined as follows:
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include::../structs/VkSamplerCreateInfo.txt[]
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The members of sname:VkSamplerCreateInfo are described as follows:
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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:magFilter is the magnification filter to apply to lookups, and
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is of type:
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+
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--
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include::../enums/VkFilter.txt[]
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--
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* pname:minFilter is the minification filter to apply to lookups, and is
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of type elink:VkFilter.
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* pname:mipmapMode is the mipmap filter to apply to lookups as described
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in the <<textures-texel-filtering, Texel Filtering>> section, and is of
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type:
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+
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--
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include::../enums/VkSamplerMipmapMode.txt[]
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--
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+
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* pname:addressModeU is the addressing mode for outside [0..1] range for U
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coordinate. See elink:VkSamplerAddressMode.
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* pname:addressModeV is the addressing mode for outside [0..1] range for V
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coordinate. See elink:VkSamplerAddressMode.
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* pname:addressModeW is the addressing mode for outside [0..1] range for W
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coordinate. See elink:VkSamplerAddressMode.
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* [[samplers-mipLodBias]] pname:mipLodBias is the bias to be added to
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mipmap LOD calculation and bias provided by image sampling functions in
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SPIR-V, as described in the <<textures-level-of-detail-operation,
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Level-of-Detail Operation>> section.
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* [[samplers-maxAnisotropy]] pname:anisotropyEnable is ename:VK_TRUE to
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enable anisotropic filtering, as described in the
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<<textures-texel-anisotropic-filtering, Texel Anisotropic Filtering>>
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section, or ename:VK_FALSE otherwise.
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* pname:maxAnisotropy is the anisotropy value clamp.
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* pname:compareEnable is ename:VK_TRUE to enable comparison against a
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reference value during lookups, or ename:VK_FALSE otherwise.
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** Note: Some implementations will default to shader state if this member
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does not match.
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* pname:compareOp is the comparison function to apply to fetched data
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before filtering as described in the <<textures-depth-compare-operation,
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Depth Compare Operation>> section. See elink:VkCompareOp.
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* pname:minLod and pname:maxLod are the values used to clamp the computed
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level-of-detail value, as described in the
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<<textures-level-of-detail-operation, Level-of-Detail Operation>>
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section. pname:maxLod must: be greater than or equal to pname:minLod.
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* pname:borderColor is the predefined border color to use, as described
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in the <<textures-texel-replacement, Texel Replacement>>
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section, and is of type:
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+
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--
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include::../enums/VkBorderColor.txt[]
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--
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* [[samplers-unnormalizedCoordinates]] pname:unnormalizedCoordinates
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controls whether to use unnormalized or normalized texel coordinates to
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address texels of the image. When set to ename:VK_TRUE, the range of the
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image coordinates used to lookup the texel is in the range of zero to
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the image dimensions for x, y and z. When set to ename:VK_FALSE the
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range of image coordinates is zero to one. When
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pname:unnormalizedCoordinates is ename:VK_TRUE, samplers have the
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following requirements:
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** pname:minFilter and pname:magFilter must: be equal.
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** pname:mipmapMode must: be ename:VK_SAMPLER_MIPMAP_MODE_NEAREST.
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** pname:minLod and pname:maxLod must: be zero.
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** pname:addressModeU and pname:addressModeV must: each
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be either ename:VK_SAMPLER_ADDRESS_MODE_CLAMP_TO_EDGE or
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ename:VK_SAMPLER_ADDRESS_MODE_CLAMP_TO_BORDER.
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** pname:anisotropyEnable must: be ename:VK_FALSE.
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** pname:compareEnable must: be ename:VK_FALSE.
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* When pname:unnormalizedCoordinates is ename:VK_TRUE, images the sampler
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is used with in the shader have the following requirements:
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** The pname:viewType must: be either ename:VK_IMAGE_VIEW_TYPE_1D or
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ename:VK_IMAGE_VIEW_TYPE_2D.
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** The image view must: have a single layer and a single mip level.
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* When pname:unnormalizedCoordinates is ename:VK_TRUE, image built-in
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functions in the shader that use the sampler have the following
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requirements:
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** The functions mustnot: use projection.
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** The functions mustnot: use offsets.
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[NOTE]
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.Mapping of OpenGL to {apiname} filter modes
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==================
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pname:magFilter values of ename:VK_FILTER_NEAREST and ename:VK_FILTER_LINEAR
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directly correspond to code:GL_NEAREST and code:GL_LINEAR magnification
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filters. pname:minFilter and pname:mipmapMode combine to correspond to the
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similarly named OpenGL minification filter of
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code:GL_minFilter_MIPMAP_mipmapMode (e.g. pname:minFilter of
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ename:VK_FILTER_LINEAR and pname:mipmapMode of
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ename:VK_SAMPLER_MIPMAP_MODE_NEAREST correspond to
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code:GL_LINEAR_MIPMAP_NEAREST).
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There are no {apiname} filter modes that directly correspond to OpenGL
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minification filters of code:GL_LINEAR or code:GL_NEAREST, but they can be
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emulated using ename:VK_SAMPLER_MIPMAP_MODE_NEAREST, pname:minLod = 0, and
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pname:maxLod = 0.25, and using pname:minFilter = ename:VK_FILTER_LINEAR or
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pname:minFilter = ename:VK_FILTER_NEAREST, respectively.
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Note that using a pname:maxLod of zero would cause
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<<textures-texel-filtering,magnification>> to always be performed, and the
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pname:magFilter to always be used. This is valid, just not an exact match
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for OpenGL behavior. Clamping the maximum lod to 0.25 allows the
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latexmath:[$\lambda$] value to be non-zero and minification to be performed,
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while still always rounding down to the base level. If the pname:minFilter
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and pname:magFilter are equal, then using a pname:maxLod of zero also works.
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==================
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include::../validity/structs/VkSamplerCreateInfo.txt[]
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pname:addressModeU, pname:addressModeV, and pname:addressModeW must: each
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have one of the following values:
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include::../enums/VkSamplerAddressMode.txt[]
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These values control the behavior of sampling with coordinates outside the
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range [0,1] for the respective u, v, or w coordinate as defined in the
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<<textures-wrapping-operation, Wrapping Operation>> section.
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* ename:VK_SAMPLER_ADDRESS_MODE_REPEAT indicates that the repeat wrap mode
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will be used.
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* ename:VK_SAMPLER_ADDRESS_MODE_MIRRORED_REPEAT indicates that the
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mirrored repeat wrap mode will be used.
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* ename:VK_SAMPLER_ADDRESS_MODE_CLAMP_TO_EDGE indicates that the clamp to
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edge wrap mode will be used.
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* ename:VK_SAMPLER_ADDRESS_MODE_CLAMP_TO_BORDER indicates that the clamp
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to border wrap mode will be used.
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* ename:VK_SAMPLER_ADDRESS_MODE_MIRROR_CLAMP_TO_EDGE indicates that
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the mirror clamp to edge wrap mode will be used. This is only valid
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if the VK_KHR_mirror_clamp_to_edge extension is enabled.
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The maximum number of sampler objects which can: be simultaneously created
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on a device is implementation-dependent and specified by the
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<<features-limits-maxSamplerAllocationCount,pname:maxSamplerAllocationCount>>
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member of the sname:VkPhysicalDeviceLimits structure. If
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pname:maxSamplerAllocationCount is exceeded, fname:vkCreateSampler will
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return ename:VK_ERROR_TOO_MANY_OBJECTS.
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Since sname:VkSampler is a non-dispatchable handle type, implementations
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may: return the same handle for sampler state vectors that are identical. In
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such cases, all such objects would only count once against the
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pname:maxSamplerAllocationCount limit.
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To destroy a sampler, call:
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include::../protos/vkDestroySampler.txt[]
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* pname:device is the logical device that destroys the sampler.
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* pname:sampler is the sampler to destroy.
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* pname:pAllocator controls host memory allocation as described in the
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<<memory-allocation, Memory Allocation>> chapter.
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include::../validity/protos/vkDestroySampler.txt[]
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