iOS实现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0-255static 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();}