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25 lines
1.1 KiB
25 lines
1.1 KiB
# About
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Because ANGLE can only generate full HLSL programs after we known the signatures
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between the vertex and pixel stages, we can not immediately call the D3D
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compiler at GL shader compile time. Moreover, we can insert additional
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optimization code right at draw-time.
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ESSL 1.00 shaders treat all vertex inputs as floating point. We insert a
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conversion routine to transform un-normalized integer vertex attributes in the
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shader preamble to floating point, saving CPU conversion time.
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At draw-time, we also optimize out any unused render target outputs. This
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improved draw call performance significantly on lower spec and integrated
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devices. Changing render target setups may trigger a shader recompile at draw
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time.
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# Addendum
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ANGLE is not the only program to do this kind of draw-time optimization. A
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common complaint from application developers is that draw calls sometimes
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perform very slowly due to dynamic shader re-compilation. A future design
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direction for ANGLE, when targeting a more modern API, is to perform the vertex
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conversion in a separate shader pass, which would then be linked with another
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compiled shader.
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