glValidateProgram

glValidateProgram: man2/glValidateProgram.xml

glValidateProgram checks to see whether the executables contained in program can execute given the current OpenGL state. The information generated by the validation process will be stored in program 's information log. The validation information may consist of an empty string, or it may be a string containing information about how the current program object interacts with the rest of current OpenGL state. This provides a way for OpenGL implementers to convey more information about why the current program is inefficient, suboptimal, failing to execute, and so on. The status of the validation operation will be stored as part of the program object's state. This value will be set to GL_TRUE if the validation succeeded, and GL_FALSE otherwise. It can be queried by calling glGetProgram with arguments program and GL_VALIDATE_STATUS. If validation is successful, program is guaranteed to execute given the current state. Otherwise, program is guaranteed to not execute. This function is typically useful only during application development. The informational string stored in the information log is completely implementation dependent; therefore, an application should not expect different OpenGL implementations to produce identical information strings.

glValidateProgram is available only if the GL version is 2.0 or greater. This function mimics the validation operation that OpenGL implementations must perform when rendering commands are issued while programmable shaders are part of current state. The error GL_INVALID_OPERATION will be generated by glBegin, glRasterPos, or any command that performs an implicit call to glBegin if:

1. any two active samplers in the current program object are of different types, but refer to the same texture image unit,
2. any active sampler in the current program object refers to a texture image unit where fixed-function fragment processing accesses a texture target that does not match the sampler type, or
3. the sum of the number of active samplers in the program and the number of texture image units enabled for fixed-function fragment processing exceeds the combined limit on the total number of texture image units allowed.

It may be difficult or cause a performance degradation for applications to catch these errors when rendering commands are issued. Therefore, applications are advised to make calls to glValidateProgram to detect these issues during application development.