我有一个 PNG (52x52) 图像文件，如果我在 UIImageView (16x16) 中显示它，它显示良好。

但是如果我尝试使用 CGContextDrawImage 来绘制，质量很差。

请看下面的详细代码:

resizeImage 用于调整图像大小(从苹果网站复制)。 drawStonesPng 用于绘制图像并调用表单 CALayer::drawInContext

- (UIImage*)resizeImage:(UIImage*)image toWidth:(NSInteger)width height:(NSInteger)height
{
    // Create a graphics context with the target size
    // On iOS 4 and later, use UIGraphicsBeginImageContextWithOptions to take the scale into consideration
    // On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
    CGSize size = CGSizeMake(width, height);
    if (NULL != UIGraphicsBeginImageContextWithOptions)
        UIGraphicsBeginImageContextWithOptions(size, NO, 0);
    else
        UIGraphicsBeginImageContext(size);

    CGContextRef context = UIGraphicsGetCurrentContext();

    // Flip the context because UIKit coordinate system is upside down to Quartz coordinate system
    CGContextTranslateCTM(context, 0.0, height);
    CGContextScaleCTM(context, 1.0, -1.0);

    // Draw the original image to the context
    CGContextSetBlendMode(context, kCGBlendModeCopy);
    CGContextDrawImage(context, CGRectMake(0.0, 0.0, width, height), image.CGImage);

    // Retrieve the UIImage from the current context
    UIImage *imageOut = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return imageOut;
}



-(void)drawStonesPng:(CGContextRef)ctx{

    _cellWidth=16;
    float x1,y1;
    float f1=0.48;

   // self.contentsScale = [UIScreen mainScreen].scale;

    UIImage* resizedImageBlack = [self resizeImage:[UIImage imageNamed:@"blackstone52"] toWidth:_cellWidth*f1*2 height:_cellWidth*f1*2];
    UIImage* resizedImageBlackShadow = [self resizeImage:[UIImage imageNamed:@"blackshadow"] toWidth:_cellWidth*f1*2 height:_cellWidth*f1*2];
    CGImageRef imgBlack = [resizedImageBlack CGImage];
    CGImageRef imgBlackShadow = [resizedImageBlackShadow CGImage];
    CGFloat width = CGImageGetWidth(imgBlack), height = CGImageGetHeight(imgBlack);


//    CGContextSetInterpolationQuality(ctx, kCGInterpolationHigh);
//    CGContextSetShouldAntialias(ctx, true);
    for(int y=0; y<_boardSize; y++) {
        for(int x=0; x<_boardSize; x++) {

            STONE_T stone = [MyGoController getStoneType:x y:y];
            if(STONE_INVALID==stone){
                CGContextClosePath(ctx);
                return;
            }

            if(stone==STONE_BLACK){

                x1=(x+1)*_cellWidth-_cellWidth*f1;
                y1=(y+1)*_cellWidth-_cellWidth*f1;



//                CGFloat scale = _cellWidth*0.9/width;
//                NSLog(@"Scale: %f\nWidth: %f\nHeight: %f", scale, width, height);
//                CGContextTranslateCTM(ctx, 0, height / scale);
//                CGContextScaleCTM(ctx, 1.0, -1.0);


                CGFloat scale = [[UIScreen mainScreen] scale];

                self.contentsScale =[[UIScreen mainScreen] scale];

                NSLog(@"Scale: %f\nWidth: %f\nHeight: %f", scale, width, height);
                CGContextTranslateCTM(ctx, 0, width / scale);
                CGContextScaleCTM(ctx, 1.0, -1.0);


                CGContextDrawImage(ctx, CGRectMake(x1+1, y1+1, width/scale,width/scale), imgBlackShadow);
                CGContextDrawImage(ctx, CGRectMake(x1, y1, width/scale,width/scale), imgBlack);



            }

        }
    }

    resizedImageBlack = [self resizeImage:[UIImage imageNamed:@"whitestone52"] toWidth:_cellWidth*f1*2 height:_cellWidth*f1*2];
    resizedImageBlackShadow = [self resizeImage:[UIImage imageNamed:@"whiteshadow"] toWidth:_cellWidth*f1*2 height:_cellWidth*f1*2];
    imgBlack = [resizedImageBlack CGImage];
    imgBlackShadow = [resizedImageBlackShadow CGImage];

    //draw white stones

    for(int y=0; y<_boardSize; y++) {
        for(int x=0; x<_boardSize; x++) {
            STONE_T stone = [MyGoController getStoneType:x y:y];

            if(stone==STONE_WHITE){

                x1=(x+1)*_cellWidth-_cellWidth*f1;
                y1=(y+1)*_cellWidth-_cellWidth*f1;



                //                CGFloat scale = _cellWidth*0.9/width;
                //                NSLog(@"Scale: %f\nWidth: %f\nHeight: %f", scale, width, height);
                //                CGContextTranslateCTM(ctx, 0, height / scale);
                //                CGContextScaleCTM(ctx, 1.0, -1.0);


                CGContextDrawImage(ctx, CGRectMake(x1+1, y1+1, _cellWidth*f1*2,_cellWidth*f1*2), imgBlackShadow);
                CGContextDrawImage(ctx, CGRectMake(x1, y1, _cellWidth*f1*2,_cellWidth*f1*2), imgBlack);





            }

        }
    }

}

最佳答案

您需要设置您正在使用的图层的内容比例:

CALayer theLayer = ....;
theLayer.contentsScale = [UIScreen mainScreen].scale

关于ios - 为什么 PNG 图像在 UIImageView 中调整大小并显示得很好，但当我用 CGContextDrawImage 绘制时质量不佳，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22857117/