Graphics Reference
In-Depth Information
This code declares a uniform block with the name
TransformBlock
containing three matrices. The name
TransformBlock
will be used by the
application as the
blockName
parameter to
glGetUniformBlockIndex
as described in Chapter 4, “Shaders and Programs,” for uniform buffer
objects. The variables in the uniform block declaration are then accessed
throughout the shader just as if they were declared as a regular uniform.
For example, the
matViewProj
matrix declared in
TransformBlock
would
be accessed as follows:
#version 300 es
uniform TransformBlock
{
mat4 matViewProj;
mat3 matNormal;
mat3 matTexGen;
};
layout(location = 0) in vec4 a_position;
void main()
{
gl_Position = matViewProj * a_position;
}
A number of optional layout qualifiers can be used to specify how the
uniform buffer object that backs the uniform block will be laid out in
memory. Layout qualifiers can be provided either for individual
uniform blocks or globally for all uniform blocks. At the global
scope, setting the default layout for all uniform blocks would look as
follows:
layout(shared, column_major) uniform; // default if not
// specified
layout(packed, row_major) uniform;
Individual uniform blocks can also set the layout by overriding the default
set at the global scope. In addition, individual uniforms within a uniform
block can specify a layout qualifier as shown here:
layout(std140) uniform TransformBlock
{
mat4 matViewProj;
layout(row_major) mat3 matNormal;
mat3 matTexGen;
};
Table 5-4 lists all of the layout qualifiers that can be provided for uniform
blocks.
