68 lines
2.8 KiB
ReStructuredText
68 lines
2.8 KiB
ReStructuredText
NIR Texture Instructions
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========================
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Even though texture instructions *could* be supported as intrinsics, the vast
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number of combinations mean that doing so is practically impossible. Instead,
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NIR has a dedicated texture instruction. There are several texture operations:
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.. doxygenenum:: nir_texop
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As with other instruction types, there is still an array of sources, except
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that each source also has a *type* associated with it. There are various
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source types, each corresponding to a piece of information that the different
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texture operations require.
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.. doxygenenum:: nir_tex_src_type
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Of particular interest are the texture/sampler deref/index/handle source types.
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First, note that textures and samplers are specified separately in NIR. While
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not required for OpenGL, this is required for Vulkan and OpenCL. Some
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OpenGL [ES] drivers have to deal with hardware that does not have separate
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samplers and textures. While not recommended, an OpenGL-only driver may assume
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that the texture and sampler derefs will always point to the same resource, if
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needed. Note that this pretty well paints your compiler into a corner and
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makes any future port to Vulkan or OpenCL harder, so such assumptions should
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really only be made if targeting OpenGL ES 2.0 era hardware.
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Also, like a lot of other resources, there are multiple ways to represent a
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texture in NIR. It can be referenced by a variable dereference, an index, or a
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bindless handle. When using an index or a bindless handle, the texture type
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information is generally not available. To handle this, various information
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from the type is redundantly stored in the :cpp:struct:`nir_tex_instr` itself.
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.. doxygenstruct:: nir_tex_instr
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:members:
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.. doxygenstruct:: nir_tex_src
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:members:
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Texture instruction helpers
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---------------------------
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There are a number of helper functions for working with NIR texture
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instructions. They are documented here in no particular order.
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.. doxygenfunction:: nir_tex_instr_create
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.. doxygenfunction:: nir_tex_instr_need_sampler
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.. doxygenfunction:: nir_tex_instr_result_size
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.. doxygenfunction:: nir_tex_instr_dest_size
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.. doxygenfunction:: nir_tex_instr_is_query
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.. doxygenfunction:: nir_tex_instr_has_implicit_derivative
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.. doxygenfunction:: nir_tex_instr_src_type
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.. doxygenfunction:: nir_tex_instr_src_size
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.. doxygenfunction:: nir_tex_instr_src_index
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.. doxygenfunction:: nir_tex_instr_add_src
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.. doxygenfunction:: nir_tex_instr_remove_src
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Texture instruction lowering
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----------------------------
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Because most hardware only supports some subset of all possible GLSL/SPIR-V
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texture operations, NIR provides a quite powerful lowering pass which is able
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to implement more complex texture operations in terms of simpler ones.
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.. doxygenfunction:: nir_lower_tex
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.. doxygenstruct:: nir_lower_tex_options
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:members:
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.. doxygenenum:: nir_lower_tex_packing
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