rez_demo/sources/GL_STUFF/GLES_3_1_compatibility.c

#include "GLES_3_1_compatibility.h"

/* fails at link time, 
resorting to eglGetProcAddress

#define GL_GLEXT_PROTOTYPES 1
#include <GLES2/gl2ext.h>
*/

#include <EGL/egl.h>

PFNGLGENVERTEXARRAYSOESPROC glGenVertexArraysOES;
PFNGLBINDVERTEXARRAYOESPROC glBindVertexArrayOES;
PFNGLDRAWBUFFERSEXTPROC glDrawBuffersEXT;

void glGenVertexArrays( GLuint n, GLuint *arrays_ptr) {
	glGenVertexArraysOES( n, arrays_ptr);
}

void glBindVertexArray( GLuint array_ptr) {
	glBindVertexArrayOES( array_ptr);
}

/* https://registry.khronos.org/OpenGL/extensions/OES/OES_framebuffer_object.txt */
void glDrawBuffers( GLsizei n,GLenum *buffers_ptr) {
	glDrawBuffersEXT( n, buffers_ptr);
}

void GLES_3_1_comp_init(){
	glGenVertexArraysOES = (PFNGLGENVERTEXARRAYSOESPROC)eglGetProcAddress("glGenVertexArraysOES");
	glBindVertexArrayOES = (PFNGLBINDVERTEXARRAYOESPROC)eglGetProcAddress("glBindVertexArrayOES");
	glDrawBuffersEXT = (PFNGLDRAWBUFFERSEXTPROC)eglGetProcAddress("glDrawBuffersEXT");
}