Hi All,

I've been porting my openGL ES 1.1 game over to 2.0. I've got a number of vertex shader programs now that all need to take a uniform for the model view projection matrix.

Can I give this uniform the same name in each shader program?

If I do give the uniform the same name in the vertex shader programs, when I call glGetUniformLocation will I get the same uniform location for each program or will I get a different location for each one?

Assuming I get the same location, when I set the value for the mvp uniform do I need to set it for each program I use or can I set it at the start of my rendering and will all the programs get the same value?

Sorry if these are all obvious questions - but I've looked through the gold book and it didn't really seem to say.

(Sep 3, 2010 08:39 AM)iamflimflam1 Wrote:  Can I give this uniform the same name in each shader program

Yes.

Quote:If I do give the uniform the same name in the vertex shader programs, when I call glGetUniformLocation will I get the same uniform location for each program or will I get a different location for each one?

Undefined. The compiler can assign any location it wants. Don't depend on it being the same.

Quote:Assuming I get the same location, when I set the value for the mvp uniform do I need to set it for each program I use or can I set it at the start of my rendering and will all the programs get the same value?

You need to set it for each program.

Thanks arekkusu,, so uniforms are pretty much tied to the program.

I seem to remember reading somewhere that if you set a uniform on a program, change programs, then switch back to the original program the uniform's value is still valid - is that definitely the case?

Thanks
Chris.

Yes. Uniforms are program state.

Uniforms are initialized to zero when you (re)link.

(Sep 3, 2010 10:39 AM)arekkusu Wrote:  Yes. Uniforms are program state.

Uniforms are initialized to zero when you (re)link.

Yes, but they retain their values at other times (such as in the UseProgram(A); UseProgram(B); UseProgram(A)) example.