一、效果图
入门实践，做的东西比较简单，效果如下：
二、关于顶点坐标和纹理坐标
绘制图片需要设置顶点坐标和纹理坐标并加载像素数据，之所以要指定两组坐标是因为纹理和顶点使用不同的坐标系，就是告诉OpenGL：把图像的某一区域绘制到屏幕的某一区域，3个点能确定一个三角形区域，我们把一张图分成4个三角形，分别是中心点和每条边点两个顶点组成的三角形，如下图，它图能够帮助你理解后面代码 GLImage.m 中的两组顶点为什么是那样子设置的
三、关于坐标轴方向、投影和坐标映射
具体参考我的另一篇文章Android OpenGL ES 2.0入门实践，主要也是参考的Android官方文档，好在iOS都有对应的函数，就没再仔细看iOS官方文档了。
四、代码
OpenGL在iOS12 就已经不推荐使用了，官方推荐使用Metal，最近在学习OpenGL ES就在Android和iOS上分别实践了一下，iOS端最简单的方式就是使用GLKit，主要使用GLKViewController这个现成的绘制环境，有了这个环境，就可以直接使用OpenGL的接口进行编码了，平台有更简单易用的 GLKBaseEffect，我没有使用，还是沿用了最基本的流程，使用GL着色器，下面是主要代码：
GlUtil.h
#import <Foundation/Foundation.h>
#import <GLKit/GLKit.h>NS_ASSUME_NONNULL_BEGIN@interface GLUtil : NSObject+(GLuint)createProgram:(NSString*)vertexShaderCode :(NSString*)fragmentShaderCode;+(void)printActiveUniforms:(GLuint)program;@endNS_ASSUME_NONNULL_ENDGLUtil.m
#import "GLUtil.h"@implementation GLUtil+ (NSString *)readShaderSource:(NSString *)bundleFileName {NSString* path = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:bundleFileName];NSString* content = [NSString stringWithContentsOfFile:path encoding:NSUTF8StringEncoding error:nil];
// NSLog(@"%@", content);return content;
}+ (GLuint)loadShader:(GLenum)type :(const char *)shaderCode {GLuint shader = glCreateShader(type);glShaderSource(shader, 1, &shaderCode, NULL);glCompileShader(shader);GLint commpiled;glGetShaderiv(shader, GL_COMPILE_STATUS, &commpiled);if(!commpiled) {GLint infoLen = 0;glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &infoLen);if(infoLen > 0) {char* infoLog = malloc(infoLen);glGetShaderInfoLog(shader, infoLen, NULL, infoLog);NSLog(@"%s", infoLog);free(infoLog);glDeleteShader(shader);return 0;}}return shader;
}+ (GLuint)createProgram:(NSString *)vertexShaderFileName :(NSString *)fragmentShaderFileName {GLuint program = glCreateProgram();const char* vertexShaderCode = [[GLUtil readShaderSource:vertexShaderFileName] UTF8String];const char* fragmentShaderCode = [[GLUtil readShaderSource:fragmentShaderFileName] UTF8String];GLuint vertexShader = [self loadShader:GL_VERTEX_SHADER:vertexShaderCode];GLuint fragmentShader = [self loadShader:GL_FRAGMENT_SHADER:fragmentShaderCode];if (vertexShader == 0 || fragmentShader == 0) {return 0;}glAttachShader(program, vertexShader);glAttachShader(program, fragmentShader);glLinkProgram(program);GLint linked;glGetProgramiv(program, GL_LINK_STATUS, &linked);if(!linked) {GLint infoLen = 0;glGetProgramiv(program, GL_INFO_LOG_LENGTH, &infoLen);if(infoLen > 0) {char* infoLog = malloc(infoLen);glGetProgramInfoLog(program, infoLen, NULL, infoLog);NSLog(@"%s", infoLog);free(infoLog);glDeleteProgram(program);return 0;}}glDeleteShader(vertexShader);glDeleteShader(fragmentShader);return program;
}+ (void)printActiveUniforms:(GLuint)program {GLint maxUniformLen;//变量名的最大长度GLint numUniforms;//变量个数char* uniformName;//变量名glGetProgramiv(program, GL_ACTIVE_UNIFORMS, &numUniforms);glGetProgramiv(program, GL_ACTIVE_UNIFORM_MAX_LENGTH, &maxUniformLen);uniformName = malloc(maxUniformLen);for (GLint index = 0; index < numUniforms; index++) {GLint size;GLenum type;GLint location;glGetActiveUniform(program, index, maxUniformLen, NULL, &size, &type, uniformName);location = glGetUniformLocation(program, uniformName);NSString* typeStr;switch (type) {case GL_FLOAT:typeStr = (@"GL_FLOAT");break;case GL_FLOAT_VEC2:typeStr = (@"GL_FLOAT_VEC2");break;case GL_FLOAT_VEC3:typeStr = (@"GL_FLOAT_VEC3");break;case GL_FLOAT_VEC4:typeStr = (@"GL_FLOAT_VEC4");break;case GL_FLOAT_MAT4:typeStr = (@"GL_FLOAT_MAT4");break;case GL_BOOL:typeStr = (@"GL_BOOL");break;case GL_SAMPLER_2D:typeStr = (@"GL_SAMPLER_2D");break;default:typeStr = [NSString stringWithFormat:@"变量类型：0x%X", type];break;}NSLog(@"index=%d, name=%s, size=%d, type=%@, location=%d", index, uniformName, size, typeStr, location);}free(uniformName);
}@endvertexShader.glsl
顶点着色器代码 vertexShader.glsl
#version 300 es
uniform mat4 uMVPMatrix;
uniform mat4 translateMatrix;
uniform bool isTranslate;
layout(location = 0) in vec4 vPosition;
layout(location = 1) in vec2 aTextureCoord;
out vec2 vTexCoord;
void main() {if (isTranslate) {gl_Position = uMVPMatrix * translateMatrix * vPosition;} else {gl_Position = uMVPMatrix * vPosition;}vTexCoord = aTextureCoord;
}fragmentShader.glsl
片段着色器代码 fragmentShader.glsl
#version 300 es
precision mediump float;
uniform bool isTexture;
uniform vec4 vColor;
uniform sampler2D uTextureUnit;
in vec2 vTexCoord;
out vec4 fragColor;
void main() {if(isTexture) {fragColor = texture(uTextureUnit,vTexCoord);} else {fragColor = vColor;}
}绘制2D纹理的类 GLImage
GLImage.h
#import <GLKit/GLKit.h>NS_ASSUME_NONNULL_BEGIN@interface GLImage : NSObject-(void)loadTexture:(NSString*)imageName;-(void)draw:(int)positionHandle :(int)textureHandle :(GLuint*)vbo;@endNS_ASSUME_NONNULL_ENDGLImage.m
#import "GLImage.h"
#import <UIKit/UIKit.h>//原文链接：https://blog.csdn.net/gongxiaoou/article/details/89344561//图片尺寸：2385 × 3623
static const float POSITION_VERTEX[] = {0.0f, 0.0f, //顶点坐标V01.0f, 1.52f, //顶点坐标V1-1.0f, 1.52f, //顶点坐标V2-1.0f, -1.52f, //顶点坐标V31.0f, -1.52f //顶点坐标V4
};static const float TEX_VERTEX[] = {0.5f, 0.5f, //纹理坐标V01.0f, 1.0f, //纹理坐标V10.0f, 1.0f, //纹理坐标V20.0f, 0.0f, //纹理坐标V31.0f, 0.0f //纹理坐标V4
};static const short VERTEX_INDEX[] = {0, 1, 2, //V0,V1,V2 三个顶点组成一个三角形0, 2, 3, //V0,V2,V3 三个顶点组成一个三角形0, 3, 4, //V0,V3,V4 三个顶点组成一个三角形0, 4, 1 //V0,V4,V1 三个顶点组成一个三角形
};@interface GLImage()
{GLuint textureID;
}@end@implementation GLImage//原文链接：https://blog.csdn.net/qq_30513483/article/details/101538967
- (void)loadTexture:(NSString *)imageName {UIImage *image = [UIImage imageNamed:imageName];// 将 UIImage 转换为 CGImageRefCGImageRef cgImageRef = [image CGImage];GLuint width = (GLuint)CGImageGetWidth(cgImageRef);GLuint height = (GLuint)CGImageGetHeight(cgImageRef);CGRect rect = CGRectMake(0, 0, width, height);// 绘制图片CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();void *imageData = malloc(width * height * 4);CGContextRef context = CGBitmapContextCreate(imageData, width, height, 8, width * 4, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);CGContextTranslateCTM(context, 0, height);CGContextScaleCTM(context, 1.0f, -1.0f);CGColorSpaceRelease(colorSpace);CGContextClearRect(context, rect);CGContextDrawImage(context, rect, cgImageRef);// 生成纹理glGenTextures(1, &textureID);glBindTexture(GL_TEXTURE_2D, textureID);// 将图片数据写入纹理缓存glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData);// 设置如何把纹素映射成像素glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);// 解绑glBindTexture(GL_TEXTURE_2D, 0);// 释放内存CGContextRelease(context);free(imageData);
}- (void)draw:(int)positionHandle :(int)textureHandle :(GLuint*)vbo {//顶点坐标glEnableVertexAttribArray(positionHandle);glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);glBufferData(GL_ARRAY_BUFFER, sizeof(POSITION_VERTEX), POSITION_VERTEX, GL_STATIC_DRAW);glVertexAttribPointer(positionHandle, 2, GL_FLOAT, GL_FALSE, 0, 0);//纹理坐标glEnableVertexAttribArray(textureHandle);glBindBuffer(GL_ARRAY_BUFFER, vbo[1]);glBufferData(GL_ARRAY_BUFFER, sizeof(TEX_VERTEX), TEX_VERTEX, GL_STATIC_DRAW);glVertexAttribPointer(textureHandle, 2, GL_FLOAT, GL_FALSE, 0, 0);//激活纹理glActiveTexture(GL_TEXTURE0);//绑定纹理glBindTexture(GL_TEXTURE_2D, textureID);//绘制glDrawElements(GL_TRIANGLES, sizeof(VERTEX_INDEX)/sizeof(short), GL_UNSIGNED_SHORT, VERTEX_INDEX);
}@endGLViewController.h
#import <GLKit/GLKit.h>NS_ASSUME_NONNULL_BEGIN@interface GLViewController : GLKViewController {
}@endNS_ASSUME_NONNULL_ENDGLViewController.m
#import "GLViewController.h"
#import "GLUtil.h"
#import "GLImage.h"const int VBO_NUM = 2;static const GLfloat vertices[] = {0.0f, 0.5f, 0.0f,-0.5f, -0.5f, 0.0f,0.5f, -0.5f, 0.0f};@interface GLViewController ()
{GLuint program;int muMVPMatrixHandle;int translateMatrixHandle;int isTranslateHandle;int isTextureHandle;int colorHandle;GLKMatrix4 vMatrix;GLKMatrix4 projMatrix;GLKMatrix4 vPMatrix;GLKMatrix4 translateMatrix;GLuint vbo[VBO_NUM];GLImage* glImage;
}@end@implementation GLViewController- (void)initGL{program = [GLUtil createProgram:@"vertexShader.glsl" :@"fragmentShader.glsl"];glUseProgram(program);muMVPMatrixHandle = glGetUniformLocation(program, "uMVPMatrix");translateMatrixHandle = glGetUniformLocation(program, "translateMatrix");isTranslateHandle = glGetUniformLocation(program, "isTranslate");isTextureHandle = glGetUniformLocation(program, "isTexture");colorHandle = glGetUniformLocation(program, "vColor");glGenBuffers(VBO_NUM, vbo);[GLUtil printActiveUniforms:program];
}- (void)viewDidLoad {[super viewDidLoad];// Do any additional setup after loading the view.GLKView* glView = (GLKView*)self.view;glView.context = [[EAGLContext alloc]initWithAPI:kEAGLRenderingAPIOpenGLES3];[EAGLContext setCurrentContext:glView.context];//这句必须得有，不然画不出来图形[self initGL];glImage = [GLImage new];[glImage loadTexture:@"dog.jpg"];// Combine the projection and camera view matricesvMatrix = GLKMatrix4MakeLookAt(0.0f, 0.0f, 3.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f);
}- (void) onSurfaceChange:(float)width :(float)height {NSLog(@"%fx%f", width, height);glViewport(0, 0, width, height);//投影矩阵if (width > height) {float ratio = width / height;projMatrix = GLKMatrix4MakeFrustum(-ratio, ratio, -1.0f, 1.0f, 3.0f, 7.0f);} else {float ratio = height / width;projMatrix = GLKMatrix4MakeFrustum(-1.0f, 1.0f, -ratio, ratio, 3.0f, 7.0f);}// Combine the projection and camera view matricesvPMatrix = GLKMatrix4Multiply(projMatrix, vMatrix);
}- (void)viewWillLayoutSubviews {[super viewWillLayoutSubviews];float width = self.view.frame.size.width;float height = self.view.frame.size.height;NSLog(@"%s %fx%f", __func__, width, height);[self onSurfaceChange:width :height];
}- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect {
// NSLog(@"%s %f", __func__, [[NSDate new] timeIntervalSince1970]);// Apply the combined projection and camera view transformationsglUniformMatrix4fv(muMVPMatrixHandle, 1, false, (float*)&vPMatrix);glClearColor(0.9f, 0.9f, 0.9f, 1.0f);//背景色glClear(GL_COLOR_BUFFER_BIT);//画图片glUniform1i(isTranslateHandle, 0);//禁用矩阵偏移glUniform1i(isTextureHandle, 1);//启用纹理[glImage draw:0 :1 :vbo];double degrees = (long)([[NSDate new] timeIntervalSince1970] * 50) % 360;double radians = degrees * M_PI / 180.0;
// NSLog(@"degrees=%f", degrees);translateMatrix = GLKMatrix4Translate(GLKMatrix4Identity, cos(radians), sin(radians), 0.0f);glUniformMatrix4fv(translateMatrixHandle, 1, GL_FALSE, (float*)&translateMatrix);glUniform1i(isTranslateHandle, 1);//启用矩阵偏移glUniform1i(isTextureHandle, 0);//禁用纹理glUniform4f(colorHandle, 0.0f, 0.5f, 1.0f, 1.0f);glEnableVertexAttribArray(0);glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);glDrawArrays(GL_TRIANGLES, 0, 3);
}@end
