samizzo / glgen

Minimal OpenGL extension loader

glgen

glgen is a minimal OpenGL extension loader that parses your project files and generates a header file based on the functions you actually use.

The definitions are extracted from header files provided by the Khronos OpenGL API registry.

The boilerplate code that initializes OpenGL and loads all function pointers is minimal and cross platform.

Usage

glgen requires an API registry header file that you can download from the Khronos OpenGL API registry. You must also specify the output file with the -o option, and one or more <inputfile> to parse.

Usage: glgen [-h] -gl <registryfile> -o <outputfile> <inputfiles...>

required arguments:
  -gl <filename>       OpenGL header file downloaded from https://www.opengl.org/registry/
  <inputfiles...>      One or more input C/C++ files
  -o <filename>        Generated file containing typedefs and boilerplate code

optional arguments:
  -h                   Prints this help and exits
  -p <prefix>          Function prefix for boilerplate code.
  -i <token1,token2>   Ignored tokens (comma separated).
  -no-b                Don't generate the OpenGL loading boilerplate code

Define GLGEN_IMPLEMENTATION and include the generated header file in ONE cpp file to compile in the code and data. Other files should include the generated header file directly without defining GLGEN_IMPLEMENTATION:

// In one cpp file
#define GLGEN_IMPLEMENTATION
#include "my_gl.h"

// In another cpp file
#include "my_gl.h"

The generated boilerplate code that initializes OpenGL can be used like so:

OpenGLVersion Version;
OpenGLInit(&Version);
if(Version.Major < 3)
{
  printf("OpenGL 3 or above required.\n");
  return 0;
}

This is the definition of the OpenGLVersion struct:

struct OpenGLVersion
{
  int Major;
  int Minor;
};

To avoid collisions with your code you can specify a prefix with the -p option like so:

glgen source1.h source1.cpp source2.cpp -gl glcorearb.h \
  -o opengl.generated.h -p PREFIX_\
  -i glfwGetFramebufferSize,glfwMakeContextCurrent,glfwSwapInterval

And the following code will be generated:

struct PREFIX_OpenGLVersion
{
  int Major;
  int Minor;
};

static void PREFIX_OpenGLInit(PREFIX_OpenGLVersion* Version);

Running as part of your build

You can run glgen just before your normal build to keep the generated header up to data. For example, you can add the following to your CMakeLists.txt and glgen will be integrated in your build:

set(PREPROCESS_OPENGL_SOURCES ${CMAKE_SOURCE_DIR}/src/file1.cpp ${CMAKE_SOURCE_DIR}/src/file1.h)
set(PREPROCESS_OPENGL_OUTPUT ${CMAKE_SOURCE_DIR}/src/opengl.generated.h)
add_custom_target(
  OpenGLPreprocess
  COMMENT "Preprocessing OpenGL"
  COMMAND glgen ${PREPROCESS_OPENGL_SOURCES} -gl ${CMAKE_SOURCE_DIR}/src/lib/glcorearb.h -o ${PREPROCESS_OPENGL_OUTPUT} -p PREFIX_ -i glfwGetFramebufferSize,glfwMakeContextCurrent,glfwSwapInterval
)
add_dependencies(${EXECUTABLE} OpenGLPreprocess)

License

glgen is in the public domain. See the file LICENSE for more information.

Copyright

OpenGL is a registered trademark of SGI.