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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build darwin && !ios
// +build darwin,!ios
package glutil
// TODO(crawshaw): Only used in glutil tests for now (cgo is not support in _test.go files).
// TODO(crawshaw): Export some kind of Context. Work out what we can offer, where. Maybe just for tests.
// TODO(crawshaw): Support android and windows.
#cgo LDFLAGS: -framework OpenGL
#import <OpenGL/OpenGL.h>
#import <OpenGL/gl3.h>
CGLError CGCreate(CGLContextObj* ctx) {
CGLError err;
CGLPixelFormatAttribute attributes[] = {
kCGLPFAOpenGLProfile, (CGLPixelFormatAttribute)kCGLOGLPVersion_3_2_Core,
kCGLPFAColorSize, (CGLPixelFormatAttribute)24,
kCGLPFAAlphaSize, (CGLPixelFormatAttribute)8,
kCGLPFADepthSize, (CGLPixelFormatAttribute)16,
(CGLPixelFormatAttribute) 0
CGLPixelFormatObj pix;
GLint num;
if ((err = CGLChoosePixelFormat(attributes, &pix, &num)) != kCGLNoError) {
return err;
if ((err = CGLCreateContext(pix, 0, ctx)) != kCGLNoError) {
return err;
if ((err = CGLDestroyPixelFormat(pix)) != kCGLNoError) {
return err;
if ((err = CGLSetCurrentContext(*ctx)) != kCGLNoError) {
return err;
if ((err = CGLLockContext(*ctx)) != kCGLNoError) {
return err;
return kCGLNoError;
import "C"
import (
// contextGL holds a copy of the OpenGL Context from thread-local storage.
// Do not move a contextGL between goroutines or OS threads.
type contextGL struct {
ctx C.CGLContextObj
// createContext creates an OpenGL context, binds it as the current context
// stored in thread-local storage, and locks the current goroutine to an os
// thread.
func createContext() (*contextGL, error) {
// The OpenGL active context is stored in TLS.
c := new(contextGL)
if cglErr := C.CGCreate(&c.ctx); cglErr != C.kCGLNoError {
return nil, fmt.Errorf("CGL: %v", C.GoString(C.CGLErrorString(cglErr)))
// Using attribute arrays in OpenGL 3.3 requires the use of a VBA.
// But VBAs don't exist in ES 2. So we bind a default one.
var id C.GLuint
C.glGenVertexArrays(1, &id)
return c, nil
// destroy destroys an OpenGL context and unlocks the current goroutine from
// its os thread.
func (c *contextGL) destroy() {
c.ctx = nil