GLSL中对Shader的编译、链接、使用流程：
创建编写shader程序
顶点着色器程序：
//文件名：shaderv.vsh 后面会使用
attribute vec4 position;
attribute vec2 textureCoor;
varying lowp vec2 varyTextCoor;
void main() {
varyTextCoor = textureCoor;
gl_Position = position;
}
片元着色器程序：
// 文件名 ： shaderf.fsh 后面会使用
uniform sampler2D colorMap;
varying lowp vec2 varyTextCoor;
void main() {
lowp vec4 temp = texture2D(colorMap,varyTextCoor);
gl_FragColor = temp;
}
核心代码
传入顶点着色器的路径和片元着色器的路径来生成最终可执行的program
- (GLuint)loadShaders:(NSString *)verFile :(NSString *)fragFile {
GLuint verShader,fragShader;
GLuint programe = glCreateProgram();
//开始编译shader
[self compileShader:&verShader path:verFile type:GL_VERTEX_SHADER];
[self compileShader:&fragShader path:fragFile type:GL_FRAGMENT_SHADER];
//将编译完的shader附着到program上
glAttachShader(programe, verShader);
glAttachShader(programe, fragShader);
//附着完成后删除shader
glDeleteShader(verShader);
glDeleteShader(fragShader);
//返回可供使用的program
return programe;
}
- (void)compileShader:(GLuint *)shader path:(NSString *)path type:(GLenum)type {
//读取shader文件信息
NSString *str = [[NSString alloc]initWithContentsOfFile:path encoding:NSUTF8StringEncoding error:nil];
const GLchar *source = (GLchar *)[str UTF8String];
//创建一个shader
*shader = glCreateShader(type);
//将着色器源码附加到着色器对象上。
//参数1：shader,要编译的着色器对象 *shader
//参数2：numOfStrings,传递的源码字符串数量 1个
//参数3：strings,着色器程序的源码（真正的着色器程序源码）
//参数4：lenOfStrings,长度，具有每个字符串长度的数组，或NULL，这意味着字符串是NULL终止的
glShaderSource(*shader, 1, &source, NULL);
//glCompileShader编译shader
glCompileShader(*shader);
}
使用GLSL实现一张图片的加载
实现流程：
初始化的一些属性数据：
@property (strong,nonatomic) CAEAGLLayer *myEagLayer;
@property (strong,nonatomic) EAGLContext *myContext;
@property (assign,nonatomic) GLuint myColorRenderBuffer;
@property (assign,nonatomic) GLuint myColorFrameBuffer;
@property (assign,nonatomic) GLuint myPrograme;
- 初始化 CAEAGLLayer
self.myEagLayer = (CAEAGLLayer *)self.layer;
[self setContentScaleFactor:[[UIScreen mainScreen]scale]];
self.myEagLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:@false,kEAGLDrawablePropertyRetainedBacking, kEAGLColorFormatRGBA8,kEAGLDrawablePropertyColorFormat,nil];
- 设置EAGLContext
EAGLRenderingAPI api = kEAGLRenderingAPIOpenGLES2;
EAGLContext *context = [[EAGLContext alloc]initWithAPI:api];
if (!context) {
NSLog(@"Create context failed!");
return;
}
if (![EAGLContext setCurrentContext:context]) {
NSLog(@"setCurrentContext failed!");
return;
}
self.myContext = context;
- 创建之前清空RenderBuffer和FrameBuffer，也可以不写，习惯问题
glDeleteBuffers(1, &_myColorRenderBuffer);
self.myColorRenderBuffer = 0;
glDeleteBuffers(1, &_myColorFrameBuffer);
self.myColorFrameBuffer = 0;
- 创建RenderBuffer
glGenRenderbuffers(1, &_myColorRenderBuffer);
glBindRenderbuffer(GL_RENDERBUFFER, self.myColorRenderBuffer);
//将可绘制对象drawable object's CAEAGLLayer的存储绑定到OpenGL ES renderBuffer对象
[self.myContext renderbufferStorage:GL_RENDERBUFFER fromDrawable:self.myEagLayer];
- 创建FrameBuffer
glGenBuffers(1, &_myColorFrameBuffer);
glBindFramebuffer(GL_FRAMEBUFFER, self.myColorFrameBuffer);
/*生成帧缓存区之后，则需要将renderbuffer跟framebuffer进行绑定，
调用glFramebufferRenderbuffer函数进行绑定到对应的附着点上，后面的绘制才能起作用
*/
//将渲染缓存区myColorRenderBuffer 通过glFramebufferRenderbuffer函数绑定到 GL_COLOR_ATTACHMENT0上。
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, self.myColorRenderBuffer);
- 开始渲染
glClearColor(0.3f, 0.45f, 0.5f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
//设置视口
CGFloat scale = [[UIScreen mainScreen]scale];
glViewport(self.frame.origin.x * scale, self.frame.origin.y * scale, self.frame.size.width * scale, self.frame.size.height * scale);
NSString *vertFile = [NSBundle.mainBundle pathForResource:@"shaderv" ofType:@"vsh"];
NSString *fragFile = [NSBundle.mainBundle pathForResource:@"shaderf" ofType:@"fsh"];
self.myPrograme = [self loadShaders:vertFile :fragFile];
//链接
glLinkProgram(self.myPrograme);
GLint linkStatus;
glGetProgramiv(self.myPrograme, GL_LINK_STATUS, &linkStatus);
if (linkStatus == GL_FALSE) {
GLchar message[1024] ;
glGetProgramInfoLog(self.myPrograme, sizeof(message), 0, message);
NSString * str = [NSString stringWithUTF8String:message];
NSLog(@"programe link error = %@",str);
return;
}
NSLog(@"programe link success !");
//link成功就可以开始使用了
glUseProgram(self.myPrograme);
后面的流程跟上一篇的OpenGL ES - GLKit初探 配置顶点数据的流程 类似，只是GLKit对着色器程序进行了封装并有了固定的键来表示顶点和纹理（GLKVertexAttribPosition和GLKVertexAttribTexCoord0），而在GLSL中需要我们自己来获取这条通道ID。GLKit中可以通过GLBaseEffect来加载纹理，而在GLSL中也是需要自己去加载纹理。
通过glGetAttribLocation来获取attribute修饰的变量通道
//传递顶点
GLuint position = glGetAttribLocation(self.myPrograme, "position");
glEnableVertexAttribArray(position);
glVertexAttribPointer(position, 3, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 5, NULL);
//传递纹理
GLuint textCoor = glGetAttribLocation(self.myPrograme, "textureCoor");
glEnableVertexAttribArray(textCoor);
glVertexAttribPointer(textCoor, 2, GL_FLOAT, GL_FALSE, sizeof(GLfloat)*5, (float *)NULL + 3);
加载纹理
[self setupTexture:@"memory.jpg"];
//设置纹理采样
glUniform1f(glGetUniformLocation(self.myPrograme, "colorMap"), 0);
glDrawArrays(GL_TRIANGLES, 0, 6);
[self.myContext presentRenderbuffer:GL_RENDERBUFFER];
//读取纹理
- (void)setupTexture:(NSString *)name {
CGImageRef imgRef = [UIImage imageNamed:name].CGImage;
if (imgRef == nil) {
return;
}
size_t width = CGImageGetWidth(imgRef);
size_t height = CGImageGetHeight(imgRef);
//获取图片总字节数
GLubyte *imgData = calloc(width * height * 4, sizeof(GLubyte));
CGContextRef imgContext = CGBitmapContextCreate(imgData, width, height, 8, width * 4, CGImageGetColorSpace(imgRef), kCGImageAlphaPremultipliedLast);
CGRect rect = CGRectMake(0, 0, width, height);
CGContextDrawImage(imgContext, rect, imgRef);
CGContextRelease(imgContext);
//开始绑定纹理
glBindTexture(GL_TEXTURE_2D, 0);
//设置属性
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
float fw = width,fh = height;
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, fw, fh, 0, GL_RGBA, GL_UNSIGNED_BYTE, imgData);
free(imgData);
}
