Point to quad expansion with Geometry Shader - c++

Question

I am new to the geometry shader, so I am trying to make a geometry shader that will take a point and create a quad with texture coordinates, just as an example to see how the geometry shader works. Here is the code I have written:
Texture2D txDiffuse : register( t0 );
SamplerState samAnisotropic
{
Filter = ANISOTROPIC;
MaxAnisotropy = 4;
};
cbuffer cbFixed
{
//
// Compute texture coordinates to stretch texture over quad.
//
float2 gTexC[4] =
{
float2(0.0f, 1.0f),
float2(0.0f, 0.0f),
float2(1.0f, 1.0f),
float2(1.0f, 0.0f)
};
};
cbuffer ConstantBuffer : register( b0 )
{
matrix World;
matrix View;
matrix Projection;
}
struct VS_INPUT
{
float3 Pos : POSITION;
};
struct VertexOut
{
float3 Pos : POSITION;
};
struct GeoOut
{
float4 PosH : SV_POSITION;
float2 Tex : TEXCOORD;
uint PrimID : SV_PrimitiveID;
};
VertexOut VS( VS_INPUT input )
{
VertexOut output;
output.Pos = input.Pos;
return output;
}
[maxvertexcount(4)]
void GS(point VertexOut gin[1], uint primID : SV_PrimitiveID, inout TriangleStream<GeoOut> tristream)
{
float4 v[4];
v[0] = float4(gin[0].Pos + float3(1.0f, -1.0f, 0.0f), 1.0f);
v[1] = float4(gin[0].Pos + float3(1.0f, 1.0f, 0.0f), 1.0f);
v[2] = float4(gin[0].Pos + float3(-1.0f, -1.0f, 0.0f), 1.0f);
v[3] = float4(gin[0].Pos + float3(-1.0f, 1.0f, 0.0f), 1.0f);
GeoOut gout;
[unroll]
for (int i = 0; i < 4; i++)
{
gout.PosH = mul(v[i], World);
gout.PosH = mul(v[i], View);
gout.PosH = mul(v[i], Projection);
gout.Tex = gTexC[i];
gout.PrimID = primID;
tristream.Append(gout);
}
}
float4 PS( GeoOut input) : SV_Target
{
//return txDiffuse.Sample( samAnisotropic, input.Tex );
return float4( 1.0f, 1.0f, 1.0f, 1.0f );
}
When I compile this code, I get a blank screen. At first I thought it may be a texture problem, so I tried having the pixel shader output white, but it did not help. Next I thought it may not show because of the way the triangle is wound, so I disabled back face culling, but it still did not help. I'm not sure what to try next. Any ideas on the problem?

Answer 1

I have not ever worked with geometry shaders, but I think the way you're calculating gout.PosH is wrong. It should be
float4 p = mul(v[i], World);
p = mul(p, View);
p = mul(p, Projection);
gout.PosH = p;
See where you went wrong? Hope this helps.