GLSL share uniforms among programs #130

i'm currently trying to figure out, how I share a uniform between shaders in old GLSL. Sticking 'shared' in front of the uniform didn't compile. Edit: I know the scope of a uniform is one program. An example for this could be the modeliew-projection-matrix. One wouldn't want to set it for each program individually but only once.

Is there a way to do it?

This is the (vertex-)shader code:

#version 130
in vec4 position;
in float size;
in vec4 incol;
out vec4 color;
shared uniform ivec4 relWorldOffset;
uniform vec4[14] cubestrip;
uint cubeindex;
void main()
{
  gl_Position = gl_ModelViewProjectionMatrix
   * (cubestrip[cubeindex] * size
   + relWorldOffset + position);
  cubeindex++;
  color = incol;
  cubeindex %= 14U;

This is the error:

0:6(1): error: syntax error, unexpected NEW_IDENTIFIER, expecting $end

Solution

There's no shared keyword like that in GLSL. You are probably looking for uniform blocks or uniform buffer objects (UBO). According to OpenGL wiki, they require OpenGL version 3.1 (so GLSL #version 140 or higher is required). If that's not a problem, the GLSL syntax would be as follows:

uniform MatrixBlock
{
    mat4 projection;
    mat4 modelview;
};

Also, take a look at this tutorial and GLSL 1.40 specification (chapter 4.3.5.1) for more pointers.

(EDIT: Actually, shared keyword is defined in most recent OpenGL versions, but it is only used as a layout qualifier in compute shaders to make variable shared within a workgroup.)