Graphics Reference
In-Depth Information
Once you have a linked program object, there are number of queries that
you might want to do on it. First, you will likely need to find out about
the active uniforms in your program. Uniforms—as we detail more in the
next chapter on the shading language—are variables that store read-only
constant values that are passed in by the application through the OpenGL
ES 3.0 API to the shader.
Sets of uniforms are grouped into two categories of uniform blocks. The
first category is the named uniform block, where the uniform's value is
backed by a buffer object called a uniform buffer object (more on that
next). The named uniform block is assigned a uniform block index.
The following example declares a named uniform block with the name
TransformBlock
containing three uniforms (
matViewProj
,
matNormal
,
and
matTexGen
):
uniform TransformBlock
{
mat4 matViewProj;
mat3 matNormal;
mat3 matTexGen;
};
The second category is the default uniform block for uniforms that are
declared outside of a named uniform block. Unlike with the named
uniform block, there is no name or uniform block index for default
uniform blocks. The following example declares the same three uniforms
outside of a named uniform block:
uniform mat4 matViewProj;
uniform mat3 matNormal;
uniform mat3 matTexGen;
We describe uniform blocks in more detail in the section
Uniform Blocks
in
Chapter 5.
If a uniform is declared in both a vertex shader and a fragment shader, it
must have the same type, and its value will be the same in both shaders.
During the link phase, the linker will assign uniform locations to each
of the active uniforms associated with the default uniform block in the
program. These locations are the identifiers the application will use to
load the uniform with a value. The linker will also assign offsets and
strides (for array and matrix type uniforms) for active uniforms associated
with the named uniform blocks.
