C++ Nvidia Cg question

Question

I started using Nvidia Cg shaders recently and everything looks and works fine if I'm doing it on the Nvidia GPU (GTS250 in my case).

I tried launching the same (my own test application) on ATI HD4650 and saw no output. Right after that I started experimenting with test examples (provided with Nvidia Cg 3.0) and 6/7 work, but the first one (which seems to be the simpliest) doesn't.

Here is the shader code:

// This is C2E1v_green from "The Cg Tutorial" (Addison-Wesley, ISBN
// 0321194969) by Randima Fernando and Mark J. Kilgard.  See page 38.

struct C2E1v_Output {
  float4 position : POSITION;
  float3 color    : COLOR;
};

C2E1v_Output C2E1v_green(float2 position : POSITION)
{ 
  C2E1v_Output OUT;

  OUT.position = float4(position,0,1);
  OUT.color = float3(0,1,0);

  return OUT; 
}

I have no ideas why doesn't this simple shader work, while for example the same shader paired with the following passthru-shader does work (example 2 from the Nvidia Cg SDK):

// This is C2E2f_passthru from "The Cg Tutorial" (Addison-Wesley, ISBN
// 0321194969) by Randima Fernando and Mark J. Kilgard.  See page 53.

struct C2E2f_Output {
  float4 color : COLOR;
};

C2E2f_Output C2E2f_passthru(float4 color : COLOR)
{
  C2E2f_Output OUT;
  OUT.color = color;
  return OUT;
}

Did someone face the same troubles? Any ideas?

Thank you.

---

Update here: Turning on maximum debug output made the problem obvious:

vs_3_0 shader executed in hardware vertex processing mode can only be paired
with at least a ps_3_0 shader

The first example in that package was the only one which had ONLY vertex shader in it, without any (even simple passthrough) pixel shader. I have no idea why does Nvidia Cg runtime generates incompatible shader in this case, but it obviously failed only on a somewhat old GPU (ATI HD4650).

Anyway, I was stupid enough to work without turning the debug output on.

2 Alex Farber: I guess you can post a dummy answer, so that I can award bounty to you, because you helped me realize that I forgot to turn debugging on. Thank you.

Answer 1

Set Debug DirectX version in the DirectX control panel and see trace output to get the reason of this failure.

BTW, I had the same situation with my pixel shader and got help in GameDev.net DirectX forum. I remember that finally I converted the shader to lowest version using SDK conversion tool, and it worked without pixel shader. According to GPU provider, this behavior is according to DirectX specification.