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Journeyman III

[DX9] hlsl lerp weird bug. SM3.0 pixel shader


I've got weird result on some pixel shader output.

I  sample R16G16 four times (using point sampling) to compute a manual bilinear filtering on a R16G16 surface. (I can't use bilinear filetring as I'm packing different kind of data in this surface). The result is put in a ARGB16F render target.

Screen :

shader sample :

 float f1 = tex2D(ShadowSampler, _texcoord.xy).g;

float f2 = tex2D(ShadowSampler, _texcoord.xy + o.xw).g;  

float f3 = tex2D(ShadowSampler, _texcoord.xy + o.wy).g; 

float f4 = tex2D(ShadowSampler, _texcoord.xy + o.xy).g; 

 float fV0 = UnpackFade(f1);


float fV1 = UnpackFade(f2);

 float fV2 = UnpackFade(f3);

float fV3 = UnpackFade(f4);

// Bilinear filter on fade value

 fFade = lerp( lerp( fV0, fV1, d.x ), lerp( fV2, fV3, d.x ), d.y );


When debugging the weird pixel in PIX, the oC0 register reports a correct computation (mean wanted computation). But pixel written in render target are not.

I can send a PIX capture of this problem. I've tested it on 2900XT and 3850. The problem doesn't exist on Nvidia 8800 GTS card. Maybe someone could confirm that it's a driver problem or point me to a workaround solution...

Thanks for any help !

Driver Packaging Version 8.702-100202a-095692C-ATI 
Catalyst™ Version 10.2 
Provider ATI Technologies Inc. 
2D Driver Version 
2D Driver File Path /REGISTRY/MACHINE/SYSTEM/ControlSet001/Control/Class/{4D36E968-E325-11CE-BFC1-08002BE10318}/0000 
Direct3D Version 
OpenGL Version 
Catalyst™ Control Center Version 2010.0202.2335.42270 
AV Stream (T200) Driver Version 


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