Often, one would like for the OpenGL client to pass values to shaders.  This can done by getting the memory location of the variable in the shader after the shader has been linked.  This can be achieved using:

GLint glGetUniformLocation(GLuint programID, const char *name);

where programID is the program ID and name is the variable name. The return value is the location of the variable, which can then be used to assign values from the client to the shader. 

Only communicate to shader programs that are activated, by calling glUseProgram() first.

A uniform variable can be passed from the client to the shader using the location.  There are a set of functions depending on whether the layout of the variable.

Uniform (float below, replace “f” with “i” for integer):

• void glUniform1f(GLint location, GLfloat v0);
• void glUniform2f(GLint location, GLfloat v0, GLfloat v1);
• void glUniform3f(GLint location, GLfloat v0, GLfloat v1, GLfloat v2);
• void glUniform4f(GLint location, GLfloat v0, GLfloat v1, GLfloat v2, GLfloat v3);
• GLint glUniform{1,2,3,4}fv(GLint location, GLsizei count, GLfloat *v);
• GLint glUniformMatrix{2,3,4}fv(GLint location, GLsizei count, GLboolean transpose, GLfloat *v);

High