Introduction to the DirectX 9 Shader Models - Nvidia
Introduction to the DirectX 9 Shader Models - Nvidia Introduction to the DirectX 9 Shader Models - Nvidia
Why use fp16 precision? • SPEED – On some HW, using fewer registers leads to faster performance – fp16 takes half the register space of fp32, so can be 2x faster • That said, the first rule of optimization is : DON’T • If your shaders are fast enough at full precision, great – But make sure you test on low-end DirectX9 cards, too • Otherwise, here is how to optimize your shaders for precision
How to use fp16 • In HLSL or Cg, use the half keyword instead of float • Because the spec requires high-precision when mixing high & low precision, you may have to use extra casts or temporaries at times • Assuming s0 maps to a 32bit fp texture : – Original : float3 a = tex2d( s0, tex0 ) – Optimized : half3 a = tex2d( s0, (half3)tex0 )
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How <strong>to</strong> use fp16<br />
• In HLSL or Cg, use <strong>the</strong> half keyword instead of<br />
float<br />
• Because <strong>the</strong> spec requires high-precision when<br />
mixing high & low precision, you may have <strong>to</strong> use<br />
extra casts or temporaries at times<br />
• Assuming s0 maps <strong>to</strong> a 32bit fp texture :<br />
– Original :<br />
float3 a = tex2d( s0, tex0 )<br />
– Optimized :<br />
half3 a = tex2d( s0, (half3)tex0 )
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