OpenGL 4 Shading Language Cookbook - Third Edition

Executing the compute shader

When we execute the compute shader, we define the compute space. The number of work groups are determined by the parameters to glDispatchCompute. For example, to execute the compute shader with a two-dimensional compute space with 4 work groups in the x dimension and 5 work groups in the y dimension (matching the preceding diagram), we'd use the following call:

glDispatchCompute( 4, 5, 1 ); 

The number of local invocations within each work group is not specified on the OpenGL side. Instead, it is specified within the compute shader itself with a layout specifier. For example, here, we specify nine local invocations per work group, 3 in the x direction and 3 in the y direction:

layout (local_size_x = 3, local_size_y ...