OpenGL ES大长腿功能实现

效果图如下：

大长腿效果图.png

一、拉伸图片

第一次加载图片过程

第一次加载图片过程.png

Slider 拉伸调整方法调用过程

Slider 拉伸调整方法调用过程.png

从第一加载图片到拉伸图片，都离不开根据当前控件的尺寸和纹理的尺寸，计算初始纹理坐标这个方法。下面我们就来分析一下这个方法- (void) calculateOriginTextureCoordWithTextureSize：(CGSize)size startY:(CGFloat)startY endY:(CGFloat)endY newHeight:(CGFloat)newHeight

1. 计算拉伸后的宽高比：图片只进行高度拉伸，变化的只是self.bounds.size. height，所以我们就可以根据self.bounds.size. height得到宽高比ratio
2. 然后我们根据纹理本身的宽度self.currentTextureWidth就可以计算出纹理的高度textureHeight
3. 根据slider计算出来的 中间拉伸区域高度 newHeight - 中间区域高度(endY - startY) 得到拉伸量delta
4. 然后我们针对纹理4个角的顶点做了世界坐标系的调整，如图1，获得pointLT、pointRT、pointRT、pointRB
5. 同样根据图2，我们可以获得中间矩形区域的顶点tempStartYCoord、tempEndYCoord。图2中starY = 2 * textureHeight * startY
6. 对应拉伸区域4个角的坐标centerPointLT、centerPointRT、centerPointLB、centerPointRB

图1.png 图2.png

/**
 根据当前控件的尺寸和纹理的尺寸，计算初始纹理坐标
 
 @param size 原始纹理尺寸
 @param startY 中间区域的开始纵坐标位置 0~1
 @param endY 中间区域的结束纵坐标位置 0~1
 @param newHeight 新的中间区域的高度
 */
- (void)calculateOriginTextureCoordWithTextureSize:(CGSize)size
                                            startY:(CGFloat)startY
                                              endY:(CGFloat)endY
                                         newHeight:(CGFloat)newHeight {
    NSLog(@"%f,%f",size.height,size.width);
    
    //1. 计算拉伸后的宽高比;
    CGFloat ratio = (size.height / size.width) *
    (self.bounds.size.width / self.bounds.size.height);
    //2. 宽度=纹理本身宽度;
    CGFloat textureWidth = self.currentTextureWidth;
    //3. 高度=纹理高度*radio(宽高比)
    CGFloat textureHeight = textureWidth * ratio;
    
    NSLog(@"%f,%f,%f,%f",newHeight,endY,startY,textureHeight);
    //4. 拉伸量 (newHeight - (endY-startY)) * 纹理高度;
    CGFloat delta = (newHeight - (endY -  startY)) * textureHeight;
    
    //5. 判断纹理高度+拉伸量是否超出最大值1
    if (textureHeight + delta >= 1) {
        delta = 1 - textureHeight;
        newHeight = delta / textureHeight + (endY -  startY);
    }
    
    //6. 纹理4个角的顶点
    // 左上角
    GLKVector3 pointLT = {-textureWidth, textureHeight + delta, 0};
    // 右上角
    GLKVector3 pointRT = {textureWidth, textureHeight + delta, 0};
    // 左下角
    GLKVector3 pointLB = {-textureWidth, -textureHeight - delta, 0};
    // 右下角
    GLKVector3 pointRB = {textureWidth, -textureHeight - delta, 0};
    
    // 中间矩形区域的顶点
    //0.7 - 2 * 0.7 * 0.25
    CGFloat tempStartYCoord = textureHeight - 2 * textureHeight * startY;
    CGFloat tempEndYCoord = textureHeight - 2 * textureHeight * endY;
    
    CGFloat startYCoord = MIN(tempStartYCoord, textureHeight);
    CGFloat endYCoord = MAX(tempEndYCoord, -textureHeight);
   
    // 中间部分左上角
    GLKVector3 centerPointLT = {-textureWidth, startYCoord + delta, 0};
    // 中间部分右上角
    GLKVector3 centerPointRT = {textureWidth, startYCoord + delta, 0};
    // 中间部分左下角
    GLKVector3 centerPointLB = {-textureWidth, endYCoord - delta, 0};
    // 中间部分右下角
    GLKVector3 centerPointRB = {textureWidth, endYCoord - delta, 0};
    
    //--纹理的上面两个顶点
    //顶点V0的顶点坐标以及纹理坐标;
    self.vertices[0].positionCoord = pointRT;
    self.vertices[0].textureCoord = GLKVector2Make(1, 1);
    
    //顶点V1的顶点坐标以及纹理坐标;
    self.vertices[1].positionCoord = pointLT;
    self.vertices[1].textureCoord = GLKVector2Make(0, 1);
    
    //--中间区域的4个顶点
    //顶点V2的顶点坐标以及纹理坐标;
    self.vertices[2].positionCoord = centerPointRT;
    self.vertices[2].textureCoord = GLKVector2Make(1, 1 - startY);
    
    //顶点V3的顶点坐标以及纹理坐标;
    self.vertices[3].positionCoord = centerPointLT;
    self.vertices[3].textureCoord = GLKVector2Make(0, 1 - startY);
    
    //顶点V4的顶点坐标以及纹理坐标;
    self.vertices[4].positionCoord = centerPointRB;
    self.vertices[4].textureCoord = GLKVector2Make(1, 1 - endY);
    
    //顶点V5的顶点坐标以及纹理坐标;
    self.vertices[5].positionCoord = centerPointLB;
    self.vertices[5].textureCoord = GLKVector2Make(0, 1 - endY);
    
    // 纹理的下面两个顶点
    //顶点V6的顶点坐标以及纹理坐标;
    self.vertices[6].positionCoord = pointRB;
    self.vertices[6].textureCoord = GLKVector2Make(1, 0);
    
    //顶点V7的顶点坐标以及纹理坐标;
    self.vertices[7].positionCoord = pointLB;
    self.vertices[7].textureCoord = GLKVector2Make(0, 0);
    
    // 保存临时值
    self.currentTextureStartY = startY;
    self.currentTextureEndY = endY;
    self.currentNewHeight = newHeight;
}

二、保存图片

将拉伸后效果的图片保存到系统相册中.png

1. 根据拉伸图片原理获得图片纹理
2. 通过glReadPixels从当前的帧缓存中读取出纹理数据，将图片从显存读取到内存中，GLubyte -> CGImageRef -> UIImage
3. 将获取到的图片保存到系统相册中

从帧缓存区中获取纹理图片文件createResult

//从帧缓存区中获取纹理图片文件; 获取当前的渲染结果
- (UIImage *)createResult {
    //1. 根据屏幕上显示结果, 重新获取顶点/纹理坐标
    [self resetTextureWithOriginWidth:self.currentImageSize.width
                         originHeight:self.currentImageSize.height
                                 topY:self.currentTextureStartY
                              bottomY:self.currentTextureEndY
                            newHeight:self.currentNewHeight];
    
    //2.绑定帧缓存区;
    glBindFramebuffer(GL_FRAMEBUFFER, self.tmpFrameBuffer);
    //3.获取新的图片Size
    CGSize imageSize = [self newImageSize];
    //4.从帧缓存中获取拉伸后的图片;
    UIImage *image = [self imageFromTextureWithWidth:imageSize.width height:imageSize.height];
    //5. 将帧缓存绑定0,清空;
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    
    //6. 返回拉伸后的图片
    return image;
}

根据当前屏幕上的显示，来重新获取纹理、顶点坐标resetTextureWithOriginWidth: originHeight: topY: bottomY: newHeight:

/**
 根据当前屏幕上的显示，来重新创建纹理
 
 @param originWidth 纹理的原始实际宽度
 @param originHeight 纹理的原始实际高度
 @param topY 0 ~ 1，拉伸区域的顶边的纵坐标
 @param bottomY 0 ~ 1，拉伸区域的底边的纵坐标
 @param newHeight 0 ~ 1，拉伸区域的新高度
 */
- (void)resetTextureWithOriginWidth:(CGFloat)originWidth
                       originHeight:(CGFloat)originHeight
                               topY:(CGFloat)topY
                            bottomY:(CGFloat)bottomY
                          newHeight:(CGFloat)newHeight {
    //1.新的纹理尺寸(新纹理图片的宽高)
    GLsizei newTextureWidth = originWidth;
    GLsizei newTextureHeight = originHeight * (newHeight - (bottomY - topY)) + originHeight;
    
    //2.高度变化百分比
    CGFloat heightScale = newTextureHeight / originHeight;
    
    //3.在新的纹理坐标下，重新计算topY、bottomY
    CGFloat newTopY = topY / heightScale;
    CGFloat newBottomY = (topY + newHeight) / heightScale;
    
    //4.创建顶点数组与纹理数组(逻辑与calculateOriginTextureCoordWithTextureSize 中关于纹理坐标以及顶点坐标逻辑是一模一样的)
    SenceVertex *tmpVertices = malloc(sizeof(SenceVertex) * kVerticesCount);
    tmpVertices[0] = (SenceVertex){{-1, 1, 0}, {0, 1}};
    tmpVertices[1] = (SenceVertex){{1, 1, 0}, {1, 1}};
    tmpVertices[2] = (SenceVertex){{-1, -2 * newTopY + 1, 0}, {0, 1 - topY}};
    tmpVertices[3] = (SenceVertex){{1, -2 * newTopY + 1, 0}, {1, 1 - topY}};
    tmpVertices[4] = (SenceVertex){{-1, -2 * newBottomY + 1, 0}, {0, 1 - bottomY}};
    tmpVertices[5] = (SenceVertex){{1, -2 * newBottomY + 1, 0}, {1, 1 - bottomY}};
    tmpVertices[6] = (SenceVertex){{-1, -1, 0}, {0, 0}};
    tmpVertices[7] = (SenceVertex){{1, -1, 0}, {1, 0}};
    
    
    ///下面开始渲染到纹理的流程
    
    //1. 生成帧缓存区;
    GLuint frameBuffer;
    GLuint texture;
    //glGenFramebuffers 生成帧缓存区对象名称;
    glGenFramebuffers(1, &frameBuffer);
    //glBindFramebuffer 绑定一个帧缓存区对象;
    glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);
    
    //2. 生成纹理ID,绑定纹理;
    //glGenTextures 生成纹理ID
    glGenTextures(1, &texture);
    //glBindTexture 将一个纹理绑定到纹理目标上;
    glBindTexture(GL_TEXTURE_2D, texture);
    //glTexImage2D 指定一个二维纹理图像;
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, newTextureWidth, newTextureHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
    
    //3. 设置纹理相关参数
    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_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    
    //4. 将纹理图像加载到帧缓存区对象上;
    /*
     glFramebufferTexture2D (GLenum target, GLenum attachment, GLenum textarget, GLuint texture, GLint level)
     target: 指定帧缓冲目标,符合常量必须是GL_FRAMEBUFFER;
     attachment: 指定附着纹理对象的附着点GL_COLOR_ATTACHMENT0
     textarget: 指定纹理目标, 符合常量:GL_TEXTURE_2D
     teture: 指定要附加图像的纹理对象;
     level: 指定要附加的纹理图像的mipmap级别，该级别必须为0。
     */
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);
    
    //5. 设置视口尺寸
    glViewport(0, 0, newTextureWidth, newTextureHeight);
    
    //6. 获取着色器程序
    GLuint program = [LongLegHelper programWithShaderName:@"spring"];
    glUseProgram(program);
    
    //7. 获取参数ID
    GLuint positionSlot = glGetAttribLocation(program, "Position");
    GLuint textureSlot = glGetUniformLocation(program, "Texture");
    GLuint textureCoordsSlot = glGetAttribLocation(program, "TextureCoords");
    
    //8. 传值
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, self.baseEffect.texture2d0.name);
    glUniform1i(textureSlot, 0);
    
    //9.初始化缓存区
    LongLegVertexAttribArrayBuffer *vbo = [[LongLegVertexAttribArrayBuffer alloc] initWithAttribStride:sizeof(SenceVertex) numberOfVertices:kVerticesCount data:tmpVertices usage:GL_STATIC_DRAW];
    
    //10.准备绘制,将纹理/顶点坐标传递进去;
    [vbo prepareToDrawWithAttrib:positionSlot numberOfCoordinates:3 attribOffset:offsetof(SenceVertex, positionCoord) shouldEnable:YES];
    [vbo prepareToDrawWithAttrib:textureCoordsSlot numberOfCoordinates:2 attribOffset:offsetof(SenceVertex, textureCoord) shouldEnable:YES];
    
    //11. 绘制
    [vbo drawArrayWithMode:GL_TRIANGLE_STRIP startVertexIndex:0 numberOfVertices:kVerticesCount];
    
    //12.解绑缓存
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    //13.释放顶点数组
    free(tmpVertices);
    
    //14.保存临时的纹理对象/帧缓存区对象;
    self.tmpTexture = texture;
    self.tmpFrameBuffer = frameBuffer;
}

从某个纹理对象获取UIImage对象

// 返回某个纹理对应的 UIImage，调用前先绑定对应的帧缓存
- (UIImage *)imageFromTextureWithWidth:(int)width height:(int)height {
    
    //1.绑定帧缓存区;
    glBindFramebuffer(GL_FRAMEBUFFER, self.tmpFrameBuffer);
    
    //2.将帧缓存区内的图片纹理绘制到图片上;
    int size = width * height * 4;
    GLubyte *buffer = malloc(size);
    
    /*
     
     glReadPixels (GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, GLvoid* pixels);
     @功能: 读取像素(理解为将已经绘制好的像素,从显存中读取到内存中;)
     @参数解读:
     参数x,y,width,height: xy坐标以及读取的宽高;
     参数format: 颜色格式; GL_RGBA;
     参数type: 读取到的内容保存到内存所用的格式;GL_UNSIGNED_BYTE 会把数据保存为GLubyte类型;
     参数pixels: 指针,像素数据读取后, 将会保存到该指针指向的地址内存中;
     
     注意: pixels指针,必须保证该地址有足够的可以使用的空间, 以容纳读取的像素数据; 例如一副256 * 256的图像,如果读取RGBA 数据, 且每个数据保存在GLUbyte. 总大小就是 256 * 256 * 4 = 262144字节, 即256M;
     int size = width * height * 4;
     GLubyte *buffer = malloc(size);
     */
    glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
    
    //使用data和size 数组来访问buffer数据;
    /*
     CGDataProviderRef CGDataProviderCreateWithData(void *info, const void *data, size_t size, CGDataProviderReleaseDataCallback releaseData);
     @功能: 新的数据类型, 方便访问二进制数据;
     @参数:
     参数info: 指向任何类型数据的指针, 或者为Null;
     参数data: 数据存储的地址,buffer
     参数size: buffer的数据大小;
     参数releaseData: 释放的回调,默认为空;
     
     */
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, size, NULL);
    //每个组件的位数;
    int bitsPerComponent = 8;
    //像素占用的比特数4 * 8 = 32;
    int bitsPerPixel = 32;
    //每一行的字节数
    int bytesPerRow = 4 * width;
    //颜色空间格式;
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    //位图图形的组件信息 - 默认的
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
    //颜色映射
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
    
    //3.将帧缓存区里像素点绘制到一张图片上;
    /*
     CGImageCreate(size_t width, size_t height,size_t bitsPerComponent, size_t bitsPerPixel, size_t bytesPerRow,CGColorSpaceRef space, CGBitmapInfo bitmapInfo, CGDataProviderRef provider,const CGFloat decode[], bool shouldInterpolate,CGColorRenderingIntent intent);
     @功能:根据你提供的数据创建一张位图;
     注意:size_t 定义的是一个可移植的单位,在64位机器上为8字节,在32位机器上是4字节;
     参数width: 图片的宽度像素;
     参数height: 图片的高度像素;
     参数bitsPerComponent: 每个颜色组件所占用的位数, 比如R占用8位;
     参数bitsPerPixel: 每个颜色的比特数, 如果是RGBA则是32位, 4 * 8 = 32位;
     参数bytesPerRow :每一行占用的字节数;
     参数space:颜色空间模式,CGColorSpaceCreateDeviceRGB
     参数bitmapInfo:kCGBitmapByteOrderDefault 位图像素布局;
     参数provider: 图片数据源提供者, 在CGDataProviderCreateWithData ,将buffer 转为 provider 对象;
     参数decode: 解码渲染数组, 默认NULL
     参数shouldInterpolate: 是否抗锯齿;
     参数intent: 图片相关参数;kCGRenderingIntentDefault
     
     */
    CGImageRef imageRef = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
    
    //4. 此时的 imageRef 是上下颠倒的，调用 CG 的方法重新绘制一遍，刚好翻转过来
    //创建一个图片context
    UIGraphicsBeginImageContext(CGSizeMake(width, height));
    CGContextRef context = UIGraphicsGetCurrentContext();
    //将图片绘制上去
    CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
    //从context中获取图片
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    //结束图片context处理
    UIGraphicsEndImageContext();
    
    //释放buffer
    free(buffer);
    //返回图片
    return image;
}

将图片保存到系统相册中saveImage:

// 保存图片到相册
- (void)saveImage:(UIImage *)image {
    //将图片通过PHPhotoLibrary保存到系统相册
    [[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{
        [PHAssetChangeRequest creationRequestForAssetFromImage:image];
    } completionHandler:^(BOOL success, NSError * _Nullable error) {
        NSLog(@"success = %d, error = %@ 图片已保存到相册", success, error);
    }];
}

Demo：
LongLegDemo