View more

View more

View more

### Image of the Day Submit

IOTD | Top Screenshots

### The latest, straight to your Inbox.

Subscribe to GameDev.net Direct to receive the latest updates and exclusive content.

Sign up now

# Geometry Shader Only Outputs 3 Vertices

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.

1 reply to this topic

### #1vv4r10ck  Members

Posted 19 July 2012 - 01:36 AM

I'm having troubles rendering a billboard quad, that's generated from a single vertex in the geometry shader. For some reason I can only emit 3 vertices. Here's my shader:

[source lang="cpp"]struct QuadVertexInput { float4 position_local : POSITION0; float4 color : COLOR0;};struct QuadVertexOutput { float4 position_projection : POSITION0; float4 color : COLOR0;};struct QuadGeometryOut { float4 position_screen : SV_Position; float4 color : COLOR0;}; struct QuadPixelOutput { float4 color : SV_TARGET;};QuadVertexOutput QuadVertexMain(QuadVertexInput input) { QuadVertexOutput output; output.position_projection = mul(input.position_local, world_matrix); output.color = input.color; return output;}[maxvertexcount(4)]void QuadGeometryMain(point QuadVertexOutput input[1], inout TriangleStream<QuadGeometryOut> stream) { QuadGeometryOut output = (QuadGeometryOut)0; float3 y_axis = float3(0.0f, 1.0f, 0.0f); float3 right = cross(y_axis, camera_direction); float3 up = cross(camera_direction, right); float3 center = input[0].position_projection; float4 vertex0 = float4(center + up * 0.5f + right * 0.5f, 1.0f); float4 vertex1 = float4(center - up * 0.5f + right * 0.5f, 1.0f); float4 vertex2 = float4(center - up * 0.5f - right * 0.5f, 1.0f); float4 vertex3 = float4(center + up * 0.5f - right * 0.5f, 1.0f); vertex0 = mul(mul(vertex0, view_matrix), projection_matrix); vertex1 = mul(mul(vertex1, view_matrix), projection_matrix); vertex2 = mul(mul(vertex2, view_matrix), projection_matrix); vertex3 = mul(mul(vertex3, view_matrix), projection_matrix); output.position_screen = vertex0; output.color = float4(1.0f, 0.0f, 0.0f, 1.0f); stream.Append(output); output.position_screen = vertex1; output.color = float4(0.0f, 1.0f, 0.0f, 1.0f); stream.Append(output); output.position_screen = vertex2; output.color = float4(0.0f, 0.0f, 1.0f, 1.0f); stream.Append(output); output.position_screen = vertex3; output.color = float4(1.0f, 1.0f, 0.0f, 1.0f); stream.Append(output);}QuadPixelOutput QuadPixelMain(QuadGeometryOut input) { QuadPixelOutput output; output.color = input.color; return output;}technique10 Quad { pass P0 { SetVertexShader(CompileShader(vs_4_0, QuadVertexMain())); SetGeometryShader(CompileShader(gs_4_0, QuadGeometryMain())); SetPixelShader(CompileShader(ps_4_0, QuadPixelMain())); }}[/source]

Can anyone help me out with what I'm doing wrong?

Here's an image of what it looks like:

http://imageshack.us/photo/my-images/836/picnj.png/

### #2streamer  Members

Posted 20 July 2012 - 12:58 AM

I am not familiar with geometry shaders but here are few thoughts:
- you are using two triangles with unappropriated culling, switch culling off if there is a second triangle shown (easy to debug)
- you are try to render triangles with triangle fan method, and output is expected to be two triangles. Add two more vertices, or render with triangle fan

Anyway 3d APIs usually work with triangles not quads. However, OpenGL have GL_QUADS rendering method, but that is not geometry shader.

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.