前言

上篇只是簡(jiǎn)單介紹了一點(diǎn)清屏出現(xiàn)的效果，今天該講正式的渲染效果了。

正文

1、初始化

_eaglContext =[[EAGLContext alloc]initWithAPI:kEAGLRenderingAPIOpenGLES2];
[EAGLContext setCurrentContext:_eaglContext];

_glLayer = (CAEAGLLayer*) self.layer;
// CALayer 默認(rèn)是透明的，必須將它設(shè)為不透明才能讓其可見(jiàn)
_glLayer.opaque = YES;
// 設(shè)置描繪屬性，在這里設(shè)置不維持渲染內(nèi)容以及顏色格式為 RGBA8
_glLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:
                                     [NSNumber numberWithBool:NO], kEAGLDrawablePropertyRetainedBacking, kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];

kEAGLColorFormatRGBA8:使用8位來(lái)保存RGBA的值;
kEAGLDrawablePropertyRetainedBacking:設(shè)置NO不保留之前繪制的圖像以用來(lái)重用;

2、綁定渲染緩沖及幀緩沖區(qū)

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);

渲染緩存:存儲(chǔ)繪制結(jié)果的緩沖區(qū)
幀緩存:接收渲染結(jié)果的緩沖區(qū)，為GPU指定存儲(chǔ)渲染結(jié)果的區(qū)域。

3、設(shè)置著色器

//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);

//操作產(chǎn)生最后的可執(zhí)行程序，它包含最后可以在硬件上執(zhí)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);
}
    
//綁定著色器參數(shù)
glUseProgram(_glProgram);
_glPosition = glGetAttribLocation(_glProgram,"Position");

-(GLuint)compileWithShaderName:(NSString*)name shaderType:(GLenum)shaderType
{
    //獲取著色器文件
    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 創(chuàng)建一個(gè)代表shader的OpenGL對(duì)象, 指定vertex或fragment shader
    GLuint shaderHandler = glCreateShader(shaderType);
    
    // 3 獲取shader的source
    const char* shaderString = [strShader UTF8String];
    int shaderStringLength = (int)[strShader length];
    glShaderSource(shaderHandler, 1, &shaderString, &shaderStringLength);
    
    // 4 編譯shader
    glCompileShader(shaderHandler);
    
    // 5 查詢shader對(duì)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;
}

著色器: 分為Vertex Shader 和Fragment Shader

• 頂點(diǎn)著色器(Vertex Shader):用于確定圖形形狀

attribute  vec4  Position;
void main(void){
      gl_Position = Position;
}

• 片段著色器(Fragment Shader):用于確定圖像繪制渲染的顏色

void main(void){
    gl_FragColor =vec4(0,1,1,1);
}

這里推薦一個(gè)介紹GLSL語(yǔ)言的博客，講的還是比較詳細(xì)的

4、渲染繪制

• 確定頂點(diǎn)(構(gòu)成繪制區(qū)域的連接點(diǎn))

const GLfloat vertices[]={
    -0.5f,-0.5f, 0,        //左下
     0.5f,-0.5f, 0,        //右下
    -0.5f, 0.5f, 0,        //左上
     0.5f, 0.5f, 0         //右上
};

• 繪制

//清屏
glClearColor(1.0,1.0,1.0,1.0);
glClear(GL_COLOR_BUFFER_BIT);
    
//設(shè)置繪制區(qū)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: 著色器腳本對(duì)應(yīng)變量ID
  *     size : 此類型數(shù)據(jù)的個(gè)數(shù)
  *     type : 此類型的sizeof值
  *     normalized : 是否對(duì)非float類型數(shù)據(jù)轉(zhuǎn)化到float時(shí)候進(jìn)行歸一化處理
  *     stride : 此類型數(shù)據(jù)在數(shù)組中的重復(fù)間隔寬度，byte類型計(jì)數(shù)
  *     ptr    : 數(shù)據(jù)指針， 這個(gè)值受到VBO的影響 
  */
//傳入頂點(diǎn)參數(shù)
glVertexAttribPointer(_glPosition, 3, GL_FLOAT, GL_FALSE, 0, vertices);
glEnableVertexAttribArray(_glPosition);
    
//繪制
glDrawArrays(GL_TRIANGLE_STRIP,0, 4);
[_eaglContext presentRenderbuffer:GL_RENDERBUFFER];

效果如下:

效果.png

具體代碼詳見(jiàn)OpenGLES