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I am writing a program that uses two different shaders for different primitives. My question is: if I bind a program, send it uniform variables, then use another shader program and come back to the first one, will the passed uniform values remain? Here is some pseudocode:
glUseProgram(shader1);
glUniform(shader1,...);
//stuff
for(elements in a list) {
if(element.type = 1) {
glUseProgram(shader2);
element.draw();
} else {
glUseProgram(shader1); //Here, do the uniforms from above remain, if shader2 was bound before?
element.draw();
}
}
809
A uniform is a global Shader variable declared with the "uniform" storage qualifier. These act as parameters that the user of a shader program can pass to that program. Their values are stored in a program object.
Fragment shader reads a value from the same variable, automatically interpolated to that fragment. No need to declare these in the Java program.
Shaders use GLSL (OpenGL Shading Language), a special OpenGL Shading Language with syntax similar to C. GLSL is executed directly by the graphics pipeline. There are several kinds of shaders, but two are commonly used to create graphics on the web: Vertex Shaders and Fragment (Pixel) Shaders.
One way to speed up GLSL code, is by marking some variables constant at compile-time. This way the compiler may optimize code (e.g. unroll loops) and remove unused code (e.g. if hard shadows are disabled). The drawback is that changing these constant variables requires that the GLSL code is compiled again.
Yes, uniforms are specific to a program, and will be persistent if you unbind and rebind it.
Also, if you want, you could easily verify this yourself in that sample with glGetUniform.
From the OpenGL 4.1 Specification:
2.11.7 Uniform Variables
... Uniforms are program object-specific state. They retain their values once loaded, and their values are restored whenever a program object is used, as long as the program object has not been re-linked. ...
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