GL_EXT_geometry_shader4 and ATI/OS X

I’m trying to get a fairly straightforward geometry shader to work in OS X (10.8.3), but I’ve run into a very strange problem that is causing artifacts on screen. This same program works just fine using a Windows computer with an Nvidia graphics card. Here is a video of the problem, where you can see random triangles appearing and disappearing.

I have narrowed down the problem to transferring vertex attributes between the geometry and fragment shader. It doesn’t matter if I use built-in attributes (gl_Vertex, gl_Normal) or generic vertex attributes.

// VERTEX SHADER----------------------------------------------------------------
#version 120
uniform mat4 modelView;
uniform mat4 projection;
varying vec3 vert_normal_eye;
void main()
vert_normal_eye = (modelView * vec4(gl_Normal, 0.0)).xyz;
gl_Position = projection * modelView * gl_Vertex;

// GEOMETRY SHADER ------------------------------------------------------------
#version 120
#extension GL_EXT_gpu_shader4 : enable
#extension GL_EXT_geometry_shader4 : enable
varying in vec3 vert_normal_eye[3];
varying out vec3 normal_eye;
void main()
for (int i = 0; i < 3; i++) {
gl_Position = gl_PositionIn[i];
normal_eye = vert_normal_eye[i];

// FRAGMENT SHADER ------------------------------------------------------------
#version 120
const vec3 light = vec3(0.0, 0.0, -1.0);
varying vec3 normal_eye;
void main()
vec3 n = normalize(normal_eye);
float diffuse = max(max(dot(n, light), dot(-n, light)), 0.35);
gl_FragColor = vec4(diffuse, diffuse, diffuse, 0.2);

If I use gl_FragColor = vec4(1.0, 1.0, 1.0, 0.2) in the fragment shader and remove all lines containing normal_eye the problem goes away. Note that I don’t really need a geometry shader for this example, but it’s only to illustrate the problem in the smallest example I can provide.


I don’t know how well the legacy OpenGL with geometry shader extensions is supported on Macs (the extensions you mentioned should be supported: but how well tested that is is another question). Is porting your code to OpenGL 3.2 core an option?

Hi menzel,

I would have to think about porting to 3.2 core. I’m using some deprecated things like display lists with immediate mode in some parts. Is there a place I can submit a bug report (not that Apple is likely to care)?


…where you can attach your system profile, so there is something more concrete to reproduce with than “ATI”, which is any of a dozen+ different GPUs.

Have you tried adding EndPrimitive() to the end of the geometry shader? Also, are you setting the maximum number of output vertices to at least 3 via glProgramParameteri()?

According to the specs, “it is not necessary to call EndPrimitive() if the geometry shader writes only a single primitive.” I did try this of course, but no change. I am also settings the propert states using glProgramParameteri(). I put together a very example that reproduces this bug for an Apple bug report: It should compile trivially and only uses OpenGL/GLUT calls. I get a flickering triangle in the center of the teapot on my machine (Radeon 6750M / OS X 10.8.3).

Hi jstoecker ,
did you manage to make any progress with this. I’m having the same problem, my shaders are in GLSL 150 with 3.2 core profile so I’m not sure its a version issue.


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