HLSL: Triangle-2-Points/Lines Geometry Shader issue - hlsl

Question

I'm trying extend a renderer (for TressFX) with a Geometry Shader, and therefore I'm taking babysteps in order to see that everything works as it should. Therefore I've created a simpel pass-through Geometry Shader, which works for triangles, but for some reason does not work for lines or points (transforming the triangle to lines and points), since I can't see the output. Result link
I would be glad if someone could point out why it doesn't work for lines and points.
code
ASetPrimitiveTopology is set to D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST
Vertex Shader
struct PS_INPUT_HAIR_AA
{
float4 Position : SV_POSITION;
float4 Tangent : Tangent;
float4 p0p1 : TEXCOORD0;
};
PS_INPUT_HAIR_AA VS_RenderHair( uint vertexId : SV_VertexID )
{
PS_INPUT_HAIR_AA Output = (PS_INPUT_HAIR_AA)0;
Calculate position etc...
Output.Position = mul(float4(v, 1), g_mViewProj);
Output.Tangent = float4(t, ratio);
Output.p0p1 = float4( v.xy, g_HairVertexPositions[vertexId+1].xy );
return Output;
}
Geometry Shader for triangles (which works)
[maxvertexcount(64)] // more than enough
void GS_RenderHairPassThrough( triangle PS_INPUT_HAIR_AA input[3], inout TriangleStream<PS_INPUT_HAIR_AA> OutputStream )
{
PS_INPUT_HAIR_AA output = (PS_INPUT_HAIR_AA)0;
for(uint i = 0; i < 3; ++i) {
output.Position = input[i].Position;
output.Tangent = input[i].Tangent;
output.p0p1 = input[i].p0p1;
OutputStream.Append( output );
}
OutputStream.RestartStrip();
}
Geometry Shader for points and lines (which does not work)
[maxvertexcount(64)] // more than enough
void GS_RenderHairPassThrough( triangle PS_INPUT_HAIR_AA input[3], inout PointStream<PS_INPUT_HAIR_AA> OutputStream )
{
PS_INPUT_HAIR_AA output = (PS_INPUT_HAIR_AA)0;
for(uint i = 0; i < 3; ++i) {
output.Position = input[i].Position;
output.Tangent = input[i].Tangent;
output.p0p1 = input[i].p0p1;
OutputStream.Append( output );
OutputStream.RestartStrip(); // Not sure if I need this
}
}
[maxvertexcount(64)] // more than enough
void GS_RenderHairPassThrough( triangle PS_INPUT_HAIR_AA input[3], inout LineStream<PS_INPUT_HAIR_AA> OutputStream )
{
PS_INPUT_HAIR_AA output = (PS_INPUT_HAIR_AA)0;
for(uint i = 0; i < 3; ++i) {
output.Position = input[i].Position;
output.Tangent = input[i].Tangent;
output.p0p1 = input[i].p0p1;
OutputStream.Append( output );
}
OutputStream.RestartStrip();
}
However, if I hard code the output.Position in the Point/Line pass-through Geometry Shader I can manage to get an output which I can see on the screen.

Answer 1

I don't think you can change the primitive topology in geometry shader. to render the mesh as lines/points, you might want to set that in your render function as below.
g_pd3dDevice->IASetPrimitiveTopology(D3D10_PRIMITIVE_TOPOLOGY_LINELIST);
or
g_pd3dDevice->IASetPrimitiveTopology(D3D10_PRIMITIVE_TOPOLOGY_POINTLIST);
another thing is if you want to change the primitive type in geometry shader, you should use
void GS_RenderHairPassThrough( line PS_INPUT_HAIR_AA input[3], inout PointStream<PS_INPUT_HAIR_AA> OutputStream )
or
void GS_RenderHairPassThrough( point PS_INPUT_HAIR_AA input[3], inout PointStream<PS_INPUT_HAIR_AA> OutputStream )
I see you use triangle for both of them as the first argument of GS_RenderHairPassThrough