View Full Version : GLSL 1.5 Geometry shader issue

Joel Graff
12-09-2010, 08:27 PM

I've been playing with shaders using OpenSceneGraph and as an experiment, I thought I'd try implementing vertex normals using a geometry shader.

What's odd is that I can get the shader to output only two of the three normals at a time and I have no idea why. If I comment out any one of the three normals, the other two are rendered fine. If, however, I try to render all three, the shader fails.

Unfortunately, I'm having a difficult time extracting the log in OSG, so I don't have compile error information (working on that, though).

That said, I have no idea why the code doesn't work for all three normals, nor am I sure that the problem is in the shader code (it could be something with OSG, I suppose).

Anyway, the shader code follows. Any thoughts would be appreciated.

vertex shader:

#version 150
uniform mat4 osg_ModelViewMatrix; //from application program.
uniform mat4 osg_ModelViewProjectionMatrix;
in vec4 osg_Vertex; //from vertex buffer from app pgm.

void main (void) {
gl_Position = osg_ModelViewMatrix * osg_Vertex;

geometry shader:

#version 150
layout (triangles) in;
layout (line_strip, max_vertices = 6) out;
uniform mat4 osg_ProjectionMatrix; //from application program.
out vec3 normal;

void main (void) {
vec3 vector1;
vec3 vector2;

vector1 = gl_in[1].gl_Position.xyz - gl_in[0].gl_Position.xyz;
vector2 = gl_in[2].gl_Position.xyz - gl_in[0].gl_Position.xyz;

normal = normalize (cross (vector1, vector2));

gl_Position = osg_ProjectionMatrix * gl_in[0].gl_Position;
EmitVertex ();

gl_Position = osg_ProjectionMatrix * (gl_in[0].gl_Position + vec4(normal, 0.0));
EmitVertex ();


gl_Position = osg_ProjectionMatrix * gl_in[1].gl_Position;
EmitVertex ();

gl_Position = osg_ProjectionMatrix * (gl_in[1].gl_Position + vec4(normal, 0.0));
EmitVertex ();

EndPrimitve ();

gl_Position = osg_ProjectionMatrix * gl_in[2].gl_Position;
EmitVertex ();

gl_Position = osg_ProjectionMatrix * (gl_in[2].gl_Position + vec4(normal, 0.0));
EmitVertex ();

frag shader:

#version 150
in vec3 normal; //from geometry shader.
out vec4 color; //to framebuffer.

void main (void) {
gl_FragColor = vec4 (normal, 1.0);

12-09-2010, 10:34 PM
When I compile to check your shaders, a log error is generated:

OpenGL Version: 4.1.0 NVIDIA 260.19.21
Can't compile Fluid.zG:
0(243) : error C1008: undefined variable "EndPrimitve"

Hence, you have a typo in your geometry shader
replace "EndPrimitve" with "EndPrimitive".

Joel Graff
12-10-2010, 05:59 AM
Ya know, I reread that code several times trying to find typos - that's happened to me before. :o Anyway, I've gotta figure
out how to get the logs out of OSG - much less embarrassing to have a compiler tell me that I can't type...

Thanks for catching that.