步骤
1、初始化上下文;
2、设置缓冲区
3、设置着色器
4、确定顶点坐标，绘制
ps: 跟圆的绘制也只是顶点坐标的不同而已
1、初始化
_eaglContext =[[EAGLContext alloc]initWithAPI:kEAGLRenderingAPIOpenGLES2];
[EAGLContext setCurrentContext:_eaglContext];
_glLayer = (CAEAGLLayer*) self.layer;
// CALayer 默认是透明的，必须将它设为不透明才能让其可见
_glLayer.opaque = YES;
// 设置描绘属性，在这里设置不维持渲染内容以及颜色格式为 RGBA8
_glLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:NO], kEAGLDrawablePropertyRetainedBacking, kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];
kEAGLColorFormatRGBA8:使用8位来保存RGBA的值;
kEAGLDrawablePropertyRetainedBacking:设置NO不保留之前绘制的图像以用来重用;
2、绑定渲染缓冲及帧缓冲区
glGenRenderbuffers(1, &_colorRenderBuffer);
glBindRenderbuffer(GL_RENDERBUFFER, _colorRenderBuffer);
[_eaglContext renderbufferStorage:GL_RENDERBUFFER fromDrawable:_glLayer];
glGenFramebuffers(1,&_frameBuffer);
glBindFramebuffer(GL_FRAMEBUFFER,_frameBuffer);
glFramebufferRenderbuffer(GL_FRAMEBUFFER,GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, _frameBuffer);
渲染缓存:存储绘制结果的缓冲区
帧缓存:接收渲染结果的缓冲区，为GPU指定存储渲染结果的区域。
3、设置着色器
//shader
GLuint vertext =[self compileWithShaderName:@"Vertex" shaderType:GL_VERTEX_SHADER];
GLuint fragment =[self compileWithShaderName:@"Fragment" shaderType:GL_FRAGMENT_SHADER];
_glProgram =glCreateProgram();
glAttachShader(_glProgram, vertext);
glAttachShader(_glProgram, fragment);
//操作产生最后的可执行程序，它包含最后可以在硬件上执行的硬件指令。
glLinkProgram(_glProgram);
GLint linkSuccess = GL_TRUE;
glGetProgramiv(_glProgram, GL_LINK_STATUS,&linkSuccess);
if (linkSuccess ==GL_FALSE) {
GLchar glMessage[256];
glGetProgramInfoLog(_glProgram, sizeof(glMessage), 0, &glMessage[0]);
NSString *messageString = [NSString stringWithUTF8String:glMessage];
NSLog(@"program error %@", messageString);
exit(1);
}
//绑定着色器参数
glUseProgram(_glProgram);
_glPosition = glGetAttribLocation(_glProgram,"Position");
-(GLuint)compileWithShaderName:(NSString*)name shaderType:(GLenum)shaderType
{
//获取着色器文件
NSString *shaderPath =[[NSBundle mainBundle]pathForResource:name ofType:@"glsl"];
NSError *error;
NSString *strShader =[NSString stringWithContentsOfFile:shaderPath encoding:NSUTF8StringEncoding error:&error];
NSLog(@"strShader %@",strShader);
if (!strShader) {
NSLog(@"shader error %@",error.localizedDescription);
exit(1);
}
// 2 创建一个代表shader的OpenGL对象, 指定vertex或fragment shader
GLuint shaderHandler = glCreateShader(shaderType);
// 3 获取shader的source
const char* shaderString = [strShader UTF8String];
int shaderStringLength = (int)[strShader length];
glShaderSource(shaderHandler, 1, &shaderString, &shaderStringLength);
// 4 编译shader
glCompileShader(shaderHandler);
// 5 查询shader对象的信息
GLint compileSuccess;
glGetShaderiv(shaderHandler, GL_COMPILE_STATUS, &compileSuccess);
if (compileSuccess == GL_FALSE) {
GLchar messages[256];
glGetShaderInfoLog(shaderHandler, sizeof(messages), 0, &messages[0]);
NSString *messageString = [NSString stringWithUTF8String:messages];
NSLog(@"%@", messageString);
exit(1);
}
return shaderHandler;
}
着色器: 分为Vertex Shader 和Fragment Shader
-
顶点着色器(Vertex Shader):用于确定图形形状
attribute vec3 position;
attribute vec3 color;
varying vec3 outColor;
void main()
{
gl_Position = vec4(position, 1.0);
outColor = color;
}
-
片段着色器(Fragment Shader):用于确定图像绘制渲染的颜色
precision mediump float;
varying vec3 outColor;
void main()
{
gl_FragColor = vec4(outColor, 1.0);
}
这里推荐一个介绍GLSL语言的博客，讲的还是比较详细的
4、渲染绘制
-
确定顶点(构成绘制区域的连接点)
1、三边形
const GLfloat triangle[]={
-0.5f,0.0f,0,
0.0f,0.5f,0,
0.5f,0.0f,0
};
2、四边形
const GLfloat rectangle[]={
-0.5f,-0.5f,0,
-0.5f, 0.5f,0,
0.5f, 0.5f,0,
0.5f,-0.5f,0
};
3、五边形
const GLfloat pentagon[]={
-0.5f,-0.5f,0,
-0.5f, 0.0f,0,
0.0f, 0.5f,0,
0.5f, 0.0f,0,
0.5f,-0.5f,0
};
-
绘制
//清屏
glClearColor(0.0, 1.0, 1.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
glLineWidth(1.0);
//设置绘制区域
glViewport(0,0,self.frame.size.width,self.frame.size.height);
/**
*void glVertexAttribPointer(GLuint index,GLint size,GLenum type,GLboolean normalized,GLsizei
* stride,const void *ptr)
* index: 着色器脚本对应变量ID
* size : 此类型数据的个数
* type : 此类型的sizeof值
* normalized : 是否对非float类型数据转化到float时候进行归一化处理
* stride : 此类型数据在数组中的重复间隔宽度，byte类型计数
* ptr : 数据指针， 这个值受到VBO的影响
*/
glEnableVertexAttribArray(_glPosition);
glVertexAttribPointer(_glPosition, 3, GL_FLOAT, GL_FALSE, 0, pentagon);
//triangle->3 rectangle->4 pentagon->5
glDrawArrays(GL_TRIANGLE_FAN,0,5);
//将指定 renderbuffer 呈现在屏幕上，在这里我们指定的是前面已经绑定为当前 renderbuffer 的那个，在 renderbuffer 可以被呈现之前，必须调用renderbufferStorage:fromDrawable: 为之分配存储空间。
[_eaglContext presentRenderbuffer:GL_RENDERBUFFER];
效果如下:
三边形.png
四边形.png
五边形.png
具体代码详见OpenGLES
