iOS从背景图中取色的代码

void *bitmapData; //内存空间的指针，该内存空间的大小等于图像使用RGB通道所占用的字节数。    static CGContextRef CreateRGBABitmapContext (CGImageRef inImage)  {      CGContextRef context = NULL;      CGColorSpaceRef colorSpace;      int bitmapByteCount;      int bitmapBytesPerRow;        size_t pixelsWide = CGImageGetWidth(inImage); //获取横向的像素点的个数      size_t pixelsHigh = CGImageGetHeight(inImage);        bitmapBytesPerRow   = (pixelsWide * 4); //每一行的像素点占用的字节数，每个像素点的ARGB四个通道各占8个bit(0-255)的空间      bitmapByteCount = (bitmapBytesPerRow * pixelsHigh); //计算整张图占用的字节数        colorSpace = CGColorSpaceCreateDeviceRGB();//创建依赖于设备的RGB通道      //分配足够容纳图片字节数的内存空间      bitmapData = malloc( bitmapByteCount );      //创建CoreGraphic的图形上下文，该上下文描述了bitmaData指向的内存空间需要绘制的图像的一些绘制参数      context = CGBitmapContextCreate (bitmapData,                                       pixelsWide,                                       pixelsHigh,                                       8,                                       bitmapBytesPerRow,                                       colorSpace,                                       kCGImageAlphaPremultipliedLast);      //Core Foundation中通过含有Create、Alloc的方法名字创建的指针，需要使用CFRelease()函数释放      CGColorSpaceRelease( colorSpace );      return context;  }    // 返回一个指针，该指针指向一个数组，数组中的每四个元素都是图像上的一个像素点的RGBA的数值(0-255)，用无符号的char是因为它正好的取值范围就是0-255  static unsigned char *RequestImagePixelData(UIImage *inImage)  {      CGImageRef img = [inImage CGImage];      CGSize size = [inImage size];      //使用上面的函数创建上下文      CGContextRef cgctx = CreateRGBABitmapContext(img);      CGRect rect = {{0,0},{size.width, size.height}};      //将目标图像绘制到指定的上下文，实际为上下文内的bitmapData。      CGContextDrawImage(cgctx, rect, img);      unsigned char *data = CGBitmapContextGetData (cgctx);      //释放上面的函数创建的上下文      CGContextRelease(cgctx);      return data;  }    //设置背景原图片,即取色所用的图片  - (void)setSourceImage:(NSString *)sourceImage ImageWidth:(int)_width ImageHeight:(int)_height {      //生成指定大小的背景图      UIImage *im = [UIImage imageNamed:sourceImage];      UIImage *newImage;      UIImageView *view = [[UIImageView alloc] initWithImage:im];      view.frame = CGRectMake(0, 0, _width, _height);      UIGraphicsBeginImageContext(CGSizeMake(_width, _height)); //size 为CGSize类型，即你所需要的图片尺寸      [im drawInRect:CGRectMake(0, 0, _width, _height)]; //newImageRect指定了图片绘制区域      newImage = UIGraphicsGetImageFromCurrentImageContext();      UIGraphicsEndImageContext();        width = newImage.size.width;      height = newImage.size.height;      //将解析背景图为像素，供取色用      imgPixel = RequestImagePixelData(newImage);  }    //计算颜色  -(UIColor*)calColor:(CGPoint)aPoint {      int i = 4 * width * round(aPoint.y+imageView.frame.size.height/2) + 4 * round(aPoint.x+imageView.frame.size.width/2);      int _r = (unsigned char)imgPixel[i];      int _g = (unsigned char)imgPixel[i+1];      int _b = (unsigned char)imgPixel[i+2];      NSLog(@"(%f,%f)",aPoint.x,aPoint.y);      NSLog(@"Red : %f   Green: %f   Blue: %f",_r/255.0,_g/255.0,_b/255.0);      return [UIColor colorWithRed:_r/255.0f green:_g/255.0f blue:_b/255.0f alpha:1.0];  }       - (void)changColor:(UIColor *)color{      int width_;      if (![Util isIpad]) {          width_ = 30;      } else {          width_ = 70;      }        UIGraphicsBeginImageContext(CGSizeMake(width_, width_));      CGContextRef ctx = UIGraphicsGetCurrentContext();      CGContextMoveToPoint(ctx, 20, 20);      CGContextSetFillColorWithColor(ctx, color.CGColor);      if (![Util isIpad]) {          CGContextAddArc(ctx, width_/2, width_/2, 14.5, 0, 6.3, 0);      } else {          CGContextAddArc(ctx, width_/2+0.5, width_/2, 31.3, 0, 6.3, 0);      }      CGContextFillPath(ctx);      self->pickedColorImageView.image = UIGraphicsGetImageFromCurrentImageContext();      UIGraphicsEndImageContext();  }  //该片段来自于http://outofmemory.cn
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iOS从背景图中取色的代码
