OpenGL绘制一个三角形

应该建立一个vertex shader文件和一个pixel shader文件，分别命名为shader.vsh和shader.fsh。

shader.vsh:

attribute vec3 position;   //入参，主程序会将数值传入
void main()
{
    gl_Position = vec4(position,1);  //顶点经过投影变换变换后的位置
}

shader.fsh:

void main()
{
    gl_FragColor = vec4(0.5,0.5,0.5,1);   //顶点的颜色
}

ViewController.m中的代码如下：

//
//  ViewController.m
//  OpenGL学习Demo
//
//  Created by 孙建飞 on 16/7/9.
//  Copyright © 2016年 sjf. All rights reserved.
//

#import "ViewController.h"

#import <OpenGLES/ES3/gl.h>
#import <OpenGLES/ES3/glext.h>

@interface ViewController ()
{
    EAGLContext *context; //EAGLContent是苹果在ios平台下实现的opengles渲染层，用于渲染结果在目标surface上的更新。
    GLuint program;//？？？？？？？？
    GLuint vertexID;
  //  GLvoid *vec;
    
}
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    //三点的坐标：
    GLKVector3 vec[3]={
        {0.5,0.5,0},
        {-0.5,-0.5,0},
        {0.5,-0.5,0},
        
    };
    //初始化EAGLContext时指定ES版本号OPenGLES3
    context=[[EAGLContext alloc]initWithAPI:kEAGLRenderingAPIOpenGLES3];
    if (!context) {
        NSLog(@"failed to create ES context !")
        ;
    }
    //
    GLKView *view=(GLKView *)self.view;
    view.context=context;
    view.drawableDepthFormat=GLKViewDrawableDepthFormat24;
    [EAGLContext setCurrentContext:context];
    glEnable(GL_DEPTH_TEST);//开启深度测试，就是让离你近的物体可以遮挡离你远的物体
    glClearColor(0.1, 0.2, 0.3, 1); //设置surface的清除颜色，也就是渲染到屏幕上的背景色。
    //
    [self loadShaders];
    glEnable(GL_DEPTH_TEST);
    glClearColor(0.1, 0.2, 0.3, 1);
   // glGenVertexArrays(<#GLsizei n#>, <#GLuint *arrays#>)
    glGenVertexArrays(1, &vertexID);//生成一个vao对象
    glBindVertexArray(vertexID); //绑定vao
    GLuint bufferID;
    glGenBuffers(1, &bufferID);  //生成vbo
    //
    glBindBuffer(GL_ARRAY_BUFFER, bufferID);  //绑定
   // glBufferData(<#GLenum target#>, <#GLsizeiptr size#>, <#const GLvoid *data#>, <#GLenum usage#>)
    glBufferData(GL_ARRAY_BUFFER, sizeof(vec), vec, GL_STATIC_DRAW); //填充缓冲对象
    GLuint loc=glGetAttribLocation(program, "position");   //获得shader里position变量的索引
    glEnableVertexAttribArray(loc);     //启用这个索引
    glVertexAttribPointer(loc, 3, GL_FLOAT, GL_FALSE, sizeof(GLKVector3), 0);  //设置这个索引需要填充的内容
    glBindVertexArray(0);   //释放vao
    glBindBuffer(GL_ARRAY_BUFFER, 0);  //释放vbo
}
//隐藏状态栏
- (BOOL)prefersStatusBarHidden {
    return YES;
}
//
-(void)glkView:(GLKView *)view drawInRect:(CGRect)rect
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);  //清除surface内容，恢复至初始状态。
    glBindVertexArray(vertexID);
    glUseProgram(program);      //使用shader
    glDrawArrays(GL_TRIANGLES, 0, 3);     //绘制三角形
    glBindVertexArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
/***************************加载shader***************************/
- (BOOL)loadShaders
{
    GLuint vertShader, fragShader;
    NSString *vertShaderPathname, *fragShaderPathname;
    
    // Create shader program.
    program = glCreateProgram();
    
    // 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);
    
    // Link program.
    if (![self linkProgram:program]) {
        NSLog(@"Failed to link program: %d", program);
        
        if (vertShader) {
            glDeleteShader(vertShader);
            vertShader = 0;
        }
        if (fragShader) {
            glDeleteShader(fragShader);
            fragShader = 0;
        }
        if (program) {
            glDeleteProgram(program);
            program = 0;
        }
        
        return NO;
    }
    // Release vertex and fragment shaders.
    if (vertShader) {
        glDetachShader(program, vertShader);
        glDeleteShader(vertShader);
    }
    if (fragShader) {
        glDetachShader(program, fragShader);
        glDeleteShader(fragShader);
    }
    
    return YES;
}

- (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) {
        NSLog(@"Failed to load vertex shader");
        return NO;
    }
    
    *shader = glCreateShader(type);
    glShaderSource(*shader, 1, &source, NULL);
    glCompileShader(*shader);
    
#if defined(DEBUG)
    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:
%s", log);
        free(log);
    }
#endif
    
    glGetShaderiv(*shader, GL_COMPILE_STATUS, &status);
    if (status == 0) {
        glDeleteShader(*shader);
        return NO;
    }
    
    return YES;
}

- (BOOL)linkProgram:(GLuint)prog
{
    GLint status;
    glLinkProgram(prog);
    
#if defined(DEBUG)
    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:
%s", log);
        free(log);
    }
#endif
    
    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:
%s", log);
        free(log);
    }
    
    glGetProgramiv(prog, GL_VALIDATE_STATUS, &status);
    if (status == 0) {
        return NO;
    }
    
    return YES;
}

@end

运行后得到如下：

 参考文献：

                http://blog.csdn.net/sx1989827/article/details/47974595