macOS中如何使用OpenGL 3.2 Core Profile

从macOS Lion（10.7）开始，Apple支持了对OpenGL 3.2 Core Profile的支持。不过Core Profile与Compatible相比有比较大幅度的改变。从主机端的API到OpenGL接口，再到GLSL（OpenGL Shading Language），这些方面都有些变化。

在主机端接口方面，首先，必须用 <OpenGL/gl3.h> 来代替原来的 <OpenGL/gl.h>，这点很重要！

其次，在 NSOpenGLPixelFormatAttribute 对象中必须增加 NSOpenGLPFAOpenGLProfile 以及 NSOpenGLProfileVersion3_2Core 这两个属性。

在最后完成绘制后，需要调用CGL库的 CGLFlushDrawable 接口将所渲染的图形结果显示到视图或窗口上。

在OpenGL接口使用方面，必须使用VAO和VBO来存放顶点数据。然后，所有与固定功能流水线相关的接口都被移出，无法使用。因此这些被移除的功能只能通过Shader来实现。

在GLSL方面，必须显式地加上GLSL的版本号，并且至少为140（表示1.40），在基于Sandy Bridge的Intel HD Graphics 3000上默认为150（1.50）。然后，in、out 代替了原来的 attribute 和 varying 关键字。在Fragment shader中，gl_FragColor 内建变量被取消，你可以自己定义一个 out 变量作为最后像素的输出。

下面给出一个比较基本、简洁的代码样例：

以下是 MyGLView.h 头文件的内容

//
//  MyGLView.h
//  OpenGLShaderBasic
//
//  Created by Zenny Chen on 10/4/10.
//  Copyright 2010 GreenGames Studio. All rights reserved.
//
 
@import Cocoa;

 
@interface MyGLView : NSOpenGLView
{
    GLuint program;
     
    GLuint vbo, vao;
}
 
- (void)render;
 
@end

以下是 MyGLView.m 源文件的内容：

//
//  MyGLView.m
//  OpenGLShaderBasic
//
//  Created by Zenny Chen on 10/4/10.
//  Copyright 2010 GreenGames Studio. All rights reserved.
//
 
#import "MyGLView.h"
 
// 这里必须注意！<gl3.h>头文件必须被包含并取代<gl.h>，否则VAO接口会调用不正常，从而无法正确显示图形！
#import <OpenGL/gl3.h>
 
#define MY_PIXEL_WIDTH      128
#define MY_PIXEL_HEIGHT     128
 
@implementation MyGLView
 
// attribute index
enum
{
    ATTRIB_VERTEX,
    NUM_ATTRIBUTES
};

- (BOOL)compileShader:(GLuint *)shader type:(GLenum)type file:(NSString *)file
{
    GLint status;
    const GLchar *source;
     
    source = (GLchar *)[NSString stringWithContentsOfFile:file encoding:NSUTF8StringEncoding error:nil].UTF8String;
    if (source == NULL)
    {
        NSLog(@"Failed to load vertex shader");
        return NO;
    }
     
    *shader = glCreateShader(type);
    glShaderSource(*shader, 1, &source, NULL);
    glCompileShader(*shader);
     
    GLint logLength;
    glGetShaderiv(*shader, GL_INFO_LOG_LENGTH, &logLength);
    if (logLength > 0)
    {
        GLchar *log = (GLchar *)malloc(logLength);
        glGetShaderInfoLog(*shader, logLength, &logLength, log);
        NSLog(@"Shader compile log:\n%s", log);
        free(log);
    }
     
    glGetShaderiv(*shader, GL_COMPILE_STATUS, &status);
    if (status == 0)
    {
        glDeleteShader(*shader);
        return NO;
    }
     
    return YES;
}
 
- (BOOL)linkProgram:(GLuint)prog
{
    GLint status;
     
    glLinkProgram(prog);
     
    GLint logLength;
    glGetProgramiv(prog, GL_INFO_LOG_LENGTH, &logLength);
    if (logLength > 0)
    {
        GLchar *log = (GLchar *)malloc(logLength);
        glGetProgramInfoLog(prog, logLength, &logLength, log);
        NSLog(@"Program link log:\n%s", log);
        free(log);
    }
     
    glGetProgramiv(prog, GL_LINK_STATUS, &status);
    if (status == 0) return NO;
    
    return YES;
}

- (BOOL)validateProgram:(GLuint)prog
{
    GLint logLength, status;
     
    glValidateProgram(prog);
    glGetProgramiv(prog, GL_INFO_LOG_LENGTH, &logLength);
    if (logLength > 0)
    {
        GLchar *log = (GLchar *)malloc(logLength);
        glGetProgramInfoLog(prog, logLength, &logLength, log);
        NSLog(@"Program validate log:\n%s", log);
        free(log);
    }
     
    glGetProgramiv(prog, GL_VALIDATE_STATUS, &status);
    if (status == 0) return NO;
     
    return YES;
}
 
- (BOOL)loadShaders
{
    GLuint vertShader, fragShader;
    NSString *vertShaderPathname, *fragShaderPathname;
     
    // create shader program
    program = glCreateProgram();
     
    // bind attribute locations
    // this needs to be done prior to linking
    glBindAttribLocation(program, ATTRIB_VERTEX, "inPos");
     
    // create and compile vertex shader
    vertShaderPathname = [NSBundle.mainBundle pathForResource:@"Shader" ofType:@"vsh"];
    if (![self compileShader:&vertShader type:GL_VERTEX_SHADER file:vertShaderPathname])
    {
        NSLog(@"Failed to compile vertex shader");
        return NO;
    }
     
    // create and compile fragment shader
    fragShaderPathname = [NSBundle.mainBundle pathForResource:@"Shader" ofType:@"fsh"];
    if (![self compileShader:&fragShader type:GL_FRAGMENT_SHADER file:fragShaderPathname])
    {
        NSLog(@"Failed to compile fragment shader");
        return NO;
    }
     
    // attach vertex shader to program
    glAttachShader(program, vertShader);
     
    // attach fragment shader to program
    glAttachShader(program, fragShader);
     
    //glBindFragDataLocationEXT(program, 0, "myOutput");
     
    // link program
    if (![self linkProgram:program])
    {
        NSLog(@"Failed to link program: %d", program);
        return NO;
    }
     
    // release vertex and fragment shaders
    if (vertShader) {
        glDeleteShader(vertShader);
    }
    if (fragShader) {
        glDeleteShader(fragShader);
    }
    return YES;
}

- (instancetype)initWithFrame:(NSRect)frameRect
{
    self = [super initWithFrame:frameRect];
     
    const NSOpenGLPixelFormatAttribute attrs[] =
    {
        NSOpenGLPFADoubleBuffer,    // 可选地，可以使用双缓冲
        NSOpenGLPFAOpenGLProfile,   // Must specify the 3.2 Core Profile to use OpenGL 3.2
        NSOpenGLProfileVersion3_2Core,
        0
    };
     
    NSOpenGLPixelFormat *pf = [NSOpenGLPixelFormat.alloc initWithAttributes:attrs];
     
    if (pf == nil) {
        NSLog(@"No OpenGL pixel format");
    }
    
    NSOpenGLContext* context = [NSOpenGLContext.alloc initWithFormat:pf shareContext:nil];
    
    [self setPixelFormat:pf];
    [pf release];
     
    [self setOpenGLContext:context];
    [context release];
     
    return self;
}
 
- (void)dealloc
{
    if(vbo != 0) {
        glDeleteFramebuffers(1, &vbo);
    }
    if(vao != 0) {
        glDeleteRenderbuffers(1, &vao);
    }
    [super dealloc];
}

- (void)prepareOpenGL
{
    [super prepareOpenGL];
     
    [self.openGLContext makeCurrentContext];
     
    // Synchronize buffer swaps with vertical refresh rate
    GLint swapInt = 1;
    [self.openGLContext setValues:&swapInt forParameter:NSOpenGLCPSwapInterval];
    
    // Drawing code here.
    static const GLfloat squareVertices[] = {
        -1.0f,  1.0f, 0.0f, 1.0f,
        -1.0f, -1.0f, 0.0f, 1.0f,
        1.0f,  1.0f, 0.0f, 1.0f,
        1.0f, -1.0f, 0.0f, 1.0f
    };
     
    // In OpenGL 3.2 core profile, vertex buffer object and vertex array object must be used!
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
     
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(squareVertices), squareVertices, GL_STATIC_DRAW);
     
    // Update attribute values
    glEnableVertexAttribArray(ATTRIB_VERTEX);
    glVertexAttribPointer(ATTRIB_VERTEX, 4, GL_FLOAT, 0, 0, (const GLvoid*)0);
     
    // Load shaders and build the program
    if(![self loadShaders]) return;
    
    // Use shader program
    glUseProgram(program);
     
    glViewport(0, 0, MY_PIXEL_WIDTH, MY_PIXEL_HEIGHT);
    glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
}

- (void)render
{    
    // render
    glClear(GL_COLOR_BUFFER_BIT);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    glFlush();
     
    CGLFlushDrawable([[self openGLContext] CGLContextObj]);
}
 
@end

以上两个文件是主要的使用OpenGL接口的样例头文件和源文件。在这个例子中，OpenGL的上下文基于一个视图（NSOpenGLView的子类）。

下面将给出Shader源代码。

先是顶点着色器：

//
//  Shader.vsh
//  GLSLTest
//
//  Created by Zenny Chen on 4/11/10.
//  Copyright GreenGames Studio 2010. All rights reserved.
//
 
// 在OpenGL3.2 Core Profile中，版本号必须显式地给出
#version 150
 
in vec4 inPos;
 
void main(void)
{
    gl_Position = inPos;
}

其次是片段着色器：

//
//  Shader.fsh
//  GLSLTest
//
//  Created by Zenny Chen on 4/11/10.
//  Copyright GreenGames Studio 2010. All rights reserved.
//
 
// 在OpenGL3.2 Core Profile中，版本号必须显式地给出
#version 150
 
out vec4 myOutput;
 
void main(void)
{
    //gl_FragColor = vec4(0.1, 0.8, 0.5, 1.0);
    myOutput = vec4(0.1, 0.8, 0.5, 1.0);
}

下面给出 AppDelegate 中对 MyGLView 对象的具体调用。

先是 AppDelegate.h 头文件：

@import Cocoa;
 
@class MyGLView;
 
@interface AppDelegate : NSObject <NSApplicationDelegate>
{
    MyGLView *glComputeObj;
}
 
@property (assign) IBOutlet NSWindow *window;
 
@end

其次是 AppDelegate.m 源文件内容：

//
//  AppDelegate.m
//  OpenGL4Compute
//
//  Created by zenny_chen on 12-12-9.
//  Copyright (c) 2012年 zenny_chen. All rights reserved.
//
 
#import "AppDelegate.h"
#import "MyGLView.h"
 
@implementation AppDelegate
 
- (void)dealloc
{
    [super dealloc];
}
 
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    // Insert code here to initialize your application
    NSView *baseView = self.window.contentView;
    CGSize viewSize = baseView.frame.size;
     
    NSButton *button = [[NSButton alloc] initWithFrame:CGRectMake(20.0f, viewSize.height - 60.0f, 60.0f, 30.0f)];
    [button setButtonType:NSMomentaryPushInButton];
    [button setBezelStyle:NSRoundedBezelStyle];
    [button setTitle:@"Show"];
    [button setTarget:self];
    [button setAction:@selector(computeButtonTouched:)];
    [baseView addSubview:button];
    [button release];
     
    NSLog(@"The view is: %@", [self.window.contentView class]);
}
 
- (void)computeButtonTouched:(id)sender
{
    if(glComputeObj == nil)
    {
        NSView *baseView = self.window.contentView;
        CGSize viewSize = baseView.frame.size;
        glComputeObj = [[MyGLView alloc] initWithFrame:CGRectMake((viewSize.width - 128.0f) * 0.5f, (viewSize.height - 128.0f) * 0.5f, 128.0f, 128.0f)];
        [baseView addSubview:glComputeObj];
        [glComputeObj release];
    }
     
    [glComputeObj performSelector:@selector(render) withObject:nil afterDelay:0.1];
}
 
@end

由于此篇博文写于2012年，因此用了一些老旧的方式，比如XIB这种基于GUI的拖拽方式，而不是纯代码。不过主要逻辑都在 MyGLView.m 源文件中，各位直接参考这里头的代码即可。