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 )
- Page 21 and 22: HLSL and Conditionals • Initial r
- Page 23 and 24: Original HLSL Compiler Results vs_2
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- Page 39 and 40: 2.0 Pixel Shader Instruction Set
- Page 41 and 42: Argument Swizzles •.r, .rrrr, .xx
- Page 43 and 44: ps.2.0 Review - Comparison with ps.
- Page 45 and 46: Caps for Pixel Shader 2.x D3DCAPS9
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- Page 49 and 50: Single Pass Lighting? • Sometimes
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Why use fp16 precision?<br />
• SPEED<br />
– On some HW, using fewer registers leads <strong>to</strong> faster<br />
performance<br />
– fp16 takes half <strong>the</strong> register space of fp32, so can be 2x<br />
faster<br />
• That said, <strong>the</strong> first rule of optimization is : DON’T<br />
• If your shaders are fast enough at full precision,<br />
great<br />
– But make sure you test on low-end <strong>DirectX</strong>9 cards, <strong>to</strong>o<br />
• O<strong>the</strong>rwise, here is how <strong>to</strong> optimize your shaders<br />
for precision
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