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How do you pass a float to a shader program?

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Hi Guys,

I am new to shader programming (like 1 Hr new :) and I can't work out how to send a float value from C++ to my shader.

The shader itself is working fine. If I set the 'nTest' value manually from within the shader I can make my object lighter of darker. But, I cant seem to get a value over to the shader from my app.

I am trying to send the value over using the following lines.

D3DXHANDLE nTest=mFX->GetParameterByName(0,"nTest");

This is my shader;
uniform extern float4x4 gWVP;
uniform extern float fTest;

struct OutputVS
float4 posH : POSITION0;

OutputVS TransformVS(float3 posL : POSITION0)
OutputVS outVS = (OutputVS)0;
outVS.posH = mul(float4(posL, 1.0f), gWVP);
return outVS;

float4 TransformPS() : COLOR
float4 AmbientColor = float4(1.0f,1.0f,1.0f,1.0f);

return AmbientColor * fTest;

technique TransformTech
pass P0
vertexShader = compile vs_2_0 TransformVS();
pixelShader = compile ps_2_0 TransformPS();
FillMode = Wireframe;

Be gentle, I am a complete newcomer to shaders :)

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