上文我们讲解了如何构建一个hello world开发环境，那么这一篇我们就来画一个简单的三角形出来。
首先，我要向大家介绍下opengl es的渲染流程，在2.0之前，es的渲染采用的是固定管线，何为固定管线，就是一套固定的模板流程，局部坐标变换 -> 世界坐标变换 ->观察坐标变换->背面消除->光照->裁剪->投影->视口计算->光栅化，程序员只需要调用固定的api修改一些配置参数就可以完成整个渲染流程了。而到了2.0，固定管线改成了可编程管线，我们对整个渲染流程可以再编程，没有固定的api给你调用，一切都依靠shader来完成。那么什么是shader呢：
GLKVector3 vec[3]={
{0.5,0.5,0.5},
{-0.5,-0.5,0.5},
{0.5,-0.5,-0.5}
}; 然后，因为我们介绍的是opengl es3.0的编程，所以我们用的是可编程管线，那么我们就应该建立一个vertex shader文件和一个pixel shader文件，分别命名为shader.vsh和shader.fsh。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
} 可以看到，每一个着色器文件都一个类似于c语言的main函数入口，这个就是着色器的入口，所有的代码都从这里开始执行。- (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:\n%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:\n%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:\n%s", log);
free(log);
}
glGetProgramiv(prog, GL_VALIDATE_STATUS, &status);
if (status == 0) {
return NO;
}
return YES;
}
然后再viewdidload里面添加如下代码：[self loadShaders];
glEnable(GL_DEPTH_TEST);
glClearColor(0.1, 0.2, 0.3, 1);
glGenVertexArrays(1, &vertexID);//生成一个vao对象
glBindVertexArray(vertexID); //绑定vao
GLuint bufferID;
glGenBuffers(1, &bufferID); //生成vboglBindBuffer(GL_ARRAY_BUFFER, bufferID); //绑定
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 这里我们用到了es 3.0里面的新技术vao（vertex array object）以及2.0里面的vbo。关于vao和vbo，我们会专门展开一章来探讨，现在大家知道就行啦。-(void)glkView:(GLKView *)view drawInRect:(CGRect)rect
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //清除颜色缓冲和深度缓冲
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);
} 代码阶段便编写完成啦，保存运行，出现如下界面便大功告成啦。
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iOS下OpenGL ES 3.0编程入门（二 ）：画一个简单三角形
原文地址：http://blog.csdn.net/sx1989827/article/details/47974595
