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77 lines
4.0 KiB
77 lines
4.0 KiB
4 months ago
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# Vertex Texture Fetch
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This page details the steps necessary to implement vertex texture fetch in ANGLE
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and documents some of the pitfalls that may be encountered along the way.
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# Details
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Tasks to implement vertex texture support.
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1. add/enable vertex shader texture look up functions in compiler & HLSL
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translator.
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* add texture2DLod, texture2DProjLod (2 variants), textureCubeLod (these
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are **only** valid in vertex shaders)
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* ensure other (non-bias/non-LOD) texture functions work in vertex shaders
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* non-mipmapped textures use the only level available
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* mipmapped textures use only the base level (ie level 0).
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2. update implementation-dependent constants in Context.h
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* MAX\_VERTEX\_TEXTURE\_IMAGE\_UNITS = 4
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* MAX\_COMBINED\_TEXTURE\_IMAGE\_UNITS =
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MAX\_VERTEX\_TEXTURE\_IMAGE\_UNITS + MAX\_TEXTURE\_IMAGE\_UNITS (ie 20).
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* these limits have to change based on the d3d device characteristics. For
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example we likely don't want to advertise vertex image units on SM2.0
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cards (unless we end up using software vertex processing).
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* detection of hardware support for various formats, types, etc.
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* As a first pass, use the "hasVertexTextures" check that Aras suggested
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to only enable VTF on DX10 NVIDIA and AMD parts, and SM3 Intel parts.
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* If this proves insufficient, there are other things we can do, but it
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involves using software vertex processing for unsupported formats and
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system memory copies of textures -- all stuff which is rather annoying
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and likely to hurt performance (see point 4. below).
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3. add support and handling for vertex textures/samplers in the API.
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* any textures used in a vertex shader need to get assigned to the special
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samplers in d3d9
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* there are only 4 of them (D3DVERTEXTEXTURESAMPLER0..
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D3DVERTEXTEXTURESAMPLER3)
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* if a texture is used in both vertex & fragment it counts twice against
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the "MAX\_COMBINED" limit (validated in Program::validateSamplers)
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* there are a number of places in our code where we have arrays of size,
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or iterate over, MAX\_TEXTURE\_IMAGE\_UNITS. These will need to be
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changed to operate on MAX\_COMBINED\_TEXTURE\_IMAGE\_UNITS instead. A
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(possibly incomplete & outdated) list of areas that need to be updated
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is as follows:
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* Program.h - increase size of mSamplers
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* Context.h - increase size of samplerTexture
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* glActiveTexture needs accept values in the range
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0..MAX\_COMBINED\_TEXTURE\_IMAGE\_UNITS-1
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* Context::~Context
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* GetIntegerv (2D\_BINDING, CUBE\_BINDING)
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* Context::applyTextures
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* Context::detachTexture
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* Program::getSamplerMapping
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* Program::dirtyAllSamplers
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* Program::applyUniform1iv
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* Program::unlink
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* Program::validateSamplers
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4. handling the nasty corner cases: texture formats, filtering and cube
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textures.
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* OpenGL doesn't provide any restrictions on what formats and/or types of
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textures can used for vertex textures, or if filtering can be enabled,
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whereas D3D9 does.
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* Reference Rasterizer / Software Vertex Processing: all formats & types
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supported (including filtering)
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* ATI R500 (on Google Code) cards do not support VTF (even though they are
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SM 3.0)
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* ATI R600 (on Google Code) (and later) and in theory the Intel 965+,
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claim to support all texture formats/types we care about and some with
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filtering
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* NVIDIA cards fall into two camps:
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* dx9 SM3 (6&7 series): only R32F & A32B32G32R32F supported for 2D and no
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filtering, CUBE or VOL texture support
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* dx10 (8+ series): only float texture formats for 2D, CUBE & VOLUME. no
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filtering (according to caps)
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* further info from Aras P. suggests that all formats are supported on
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DX10 hardware, but are just not advertised.
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* unsure what they do on these cards under OpenGL. Need to do more
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testing, but suspect software fallback.
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