Pro OpenGL ES for iOS

CHAPTER 10: OpenGL ES 2, Shaders, and... (^315)
if (_program)
{
glDeleteProgram(_program);
_program = 0;
}
return NO;
}
uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX] = //6
glGetUniformLocation(_program, "modelViewProjectionMatrix");
uniforms[UNIFORM_NORMAL_MATRIX] =
glGetUniformLocation(_program, "normalMatrix");
if (vertShader) //7
{
glDetachShader(_program, vertShader);
glDeleteShader(vertShader);
}
if (fragShader)
{
glDetachShader(_program, fragShader);
glDeleteShader(fragShader);
}
return YES;
}
Here’s what’s happening:
„ Line 1 generates a program handle and creates an empty program
object. You keep this handle around and use it to specify which
program you want to use for a specific piece of geometry, because
you can have multiple programs and swap them back and forth as
needed.
„ Now the shaders are compiled in lines 2ff.
„ Lines 3f bind the specific shader to the new program object. Each
program object must have one vertex and one fragment shader.
„ In lines 4ff, we bind whatever attributes we want to the program. In the
actual vertex shader code, you can see attributes by those names
defined for use:
attribute vec4 position;
attribute vec3 normal;
The names can be nearly anything you want; there is nothing special
about the use of position or normal.
„ Line 5 links both shaders.