步驟
1、初始化上下文;
2、設(shè)置緩沖區(qū)
3、設(shè)置著色器
4、確定頂點坐標，繪制
1、初始化
_eaglContext =[[EAGLContext alloc]initWithAPI:kEAGLRenderingAPIOpenGLES2];
[EAGLContext setCurrentContext:_eaglContext];
_glLayer = (CAEAGLLayer*) self.layer;
// CALayer 默認是透明的，必須將它設(shè)為不透明才能讓其可見
_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位來保存RGBA的值;
kEAGLDrawablePropertyRetainedBacking:設(shè)置NO不保留之前繪制的圖像以用來重用;
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)建一個代表shader的OpenGL對象, 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
-
頂點著色器(Vertex Shader):用于確定圖形形狀
attribute vec3 position;
attribute vec3 color;
varying vec3 outColor;
void main()
{
gl_Position = vec4(position, 1.0);
outColor = color;
}
-
片段著色器(Fragment Shader):用于確定圖像繪制渲染的顏色
precision mediump float;
varying vec3 outColor;
void main()
{
gl_FragColor = vec4(outColor, 1.0);
}
這里推薦一個介紹GLSL語言的博客，講的還是比較詳細的
4、渲染繪制
-
確定頂點(構(gòu)成繪制區(qū)域的連接點)
圓頂點主要運用圓弧的計算公式獲得，已知圓心坐標(a,b)，半徑為r
x=a+r * cosθ
y=b+r * sinθ
typedef struct {
GLfloat x,y,z;
GLfloat r,g,b;
} Vertex;
int segCount = 10000; // 分割份數(shù)
Vertex *vertext = (Vertex *)malloc(sizeof(Vertex) * segCount);
memset(vertext, 0x00, sizeof(Vertex) * segCount);
float a = 0.8; // 水平方向的半徑
float b = a * self.frame.size.width / self.frame.size.height;
float delta = 2.0*M_PI/segCount;
for (int i = 0; i < segCount; i++) {
GLfloat x = a * cos(delta * i);
GLfloat y = b * sin(delta * i);
GLfloat z = 0.0;
vertext[i] = (Vertex){x, y, z, x, y, x+y};
printf("%f , %f\n", x, y);
}
-
繪制
//清屏
glClearColor(1.0, 1.0, 1.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
glLineWidth(2.0);
//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: 著色器腳本對應(yīng)變量ID
* size : 此類型數(shù)據(jù)的個數(shù)
* type : 此類型的sizeof值
* normalized : 是否對非float類型數(shù)據(jù)轉(zhuǎn)化到float時候進行歸一化處理
* stride : 此類型數(shù)據(jù)在數(shù)組中的重復(fù)間隔寬度，byte類型計數(shù)
* ptr : 數(shù)據(jù)指針， 這個值受到VBO的影響
*/
glEnableVertexAttribArray(glGetAttribLocation(_glProgram, "position"));
glVertexAttribPointer(glGetAttribLocation(_glProgram, "position"), 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), vertext);
glEnableVertexAttribArray(glGetAttribLocation(_glProgram, "color"));
glVertexAttribPointer(glGetAttribLocation(_glProgram, "color"), 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), vertext+sizeof(GLfloat)*3);
glDrawArrays(GL_TRIANGLE_FAN, 0, segCount);
//將指定 renderbuffer 呈現(xiàn)在屏幕上，在這里我們指定的是前面已經(jīng)綁定為當前 renderbuffer 的那個，在 renderbuffer 可以被呈現(xiàn)之前，必須調(diào)用renderbufferStorage:fromDrawable: 為之分配存儲空間。
[_eaglContext presentRenderbuffer:GL_RENDERBUFFER];
free(vertext);
vertext = NULL;
效果如下:
效果圖.png
具體代碼詳見OpenGLES
