this glsl 1.3 thing

[martinsm]

But how the hell can we know in which texture data is written.

GL3.0 spec says it clearly Read section 3.12.2 Shader Outputs.

You bind output variables from fragment shader with glBindFragDataLocation before linking your program:

glBindFragDataLocation(programId, 0, "myVec41");
glBindFragDataLocation(programId, 1, "myVec42");
glLinkProgram(programId);

This means myVec41 will go to first draw buffer and myVec42 will go to second. You specifiy draw buffers with glDrawBuffers function.

[bakura]

Oh yes, this is because I only read GLSL specs... Thank you . I'll read the whole OpenGL 3.0 specs too.