Skip to content

Latest commit

 

History

History
83 lines (57 loc) · 2.87 KB

tex.rst

File metadata and controls

83 lines (57 loc) · 2.87 KB

NIR Texture Instructions

Even though texture instructions could be supported as intrinsics, the vast number of combinations mean that doing so is practically impossible. Instead, NIR has a dedicated texture instruction. There are several texture operations:

.. c:autoenum:: nir_texop
   :file: src/compiler/nir/nir.h
   :members:

As with other instruction types, there is still an array of sources, except that each source also has a type associated with it. There are various source types, each corresponding to a piece of information that the different texture operations require.

.. c:autoenum:: nir_tex_src_type
   :members:

Of particular interest are the texture/sampler deref/index/handle source types. First, note that textures and samplers are specified separately in NIR. While not required for OpenGL, this is required for Vulkan and OpenCL. Some OpenGL [ES] drivers have to deal with hardware that does not have separate samplers and textures. While not recommended, an OpenGL-only driver may assume that the texture and sampler derefs will always point to the same resource, if needed. Note that this pretty well paints your compiler into a corner and makes any future port to Vulkan or OpenCL harder, so such assumptions should really only be made if targeting OpenGL ES 2.0 era hardware.

Also, like a lot of other resources, there are multiple ways to represent a texture in NIR. It can be referenced by a variable dereference, an index, or a bindless handle. When using an index or a bindless handle, the texture type information is generally not available. To handle this, various information from the type is redundantly stored in the :c:struct:`nir_tex_instr` itself.

.. c:autostruct:: nir_tex_instr
   :members:


.. c:autostruct:: nir_tex_src
   :members:

Texture instruction helpers

There are a number of helper functions for working with NIR texture instructions. They are documented here in no particular order.

.. c:autofunction:: nir_tex_instr_create


.. c:autofunction:: nir_tex_instr_need_sampler


.. c:autofunction:: nir_tex_instr_result_size


.. c:autofunction:: nir_tex_instr_dest_size


.. c:autofunction:: nir_tex_instr_is_query


.. c:autofunction:: nir_tex_instr_has_implicit_derivative


.. c:autofunction:: nir_tex_instr_src_type


.. c:autofunction:: nir_tex_instr_src_size


.. c:autofunction:: nir_tex_instr_src_index


.. c:autofunction:: nir_tex_instr_add_src


.. c:autofunction:: nir_tex_instr_remove_src

Texture instruction lowering

Because most hardware only supports some subset of all possible GLSL/SPIR-V texture operations, NIR provides a quite powerful lowering pass which is able to implement more complex texture operations in terms of simpler ones.

.. c:autofunction:: nir_lower_tex


.. c:autostruct:: nir_lower_tex_options
   :members:


.. c:autoenum:: nir_lower_tex_packing
   :members: