static void vrend_use_program(struct vrend_sub_context *sub_ctx, GLuint program_id)
{
   if (sub_ctx->program_id != program_id) {
      glUseProgram(program_id);
      sub_ctx->program_id = program_id;
   }
}
static void vrend_use_program(struct vrend_sub_context *sub_ctx, GLuint program_id)
{
   if (sub_ctx->program_id != program_id) {
      glUseProgram(program_id);
      sub_ctx->program_id = program_id;
   }
}