cocoa - NSImage 变换后变得模糊

Question

我使用 NSAffineTransform 类在其中心旋转了 NSImage，它可以工作。代码在这里:

- (NSImage*)rotateImage: (NSImage*)myImage angle:(float)rotateAngle {

    NSRect imageBounds = {NSZeroPoint, [myImage size]};
    NSRect transformedImageBounds = imageBounds;
    NSBezierPath* boundsPath = [NSBezierPath bezierPathWithRect:imageBounds];
    NSAffineTransform* transform = [NSAffineTransform transform];

    // calculate the bounds for the rotated image
    if (rotateAngle != 0) {

        NSAffineTransform* temptransform = [NSAffineTransform transform];
        [temptransform rotateByDegrees:rotateAngle];
        [boundsPath transformUsingAffineTransform:temptransform];

        NSRect rotatedBounds = {NSZeroPoint, [boundsPath bounds].size};

        // center the image within the rotated bounds
        imageBounds.origin.x += (NSWidth(rotatedBounds) - NSWidth (imageBounds))/2;
        imageBounds.origin.y += (NSHeight(rotatedBounds) - NSHeight (imageBounds))/2;

        // set up the rotation transform
        [transform translateXBy:+(NSWidth(rotatedBounds) / 2) yBy:+ (NSHeight(rotatedBounds) / 2)];
        [transform rotateByDegrees:rotateAngle];
        [transform translateXBy:-(NSWidth(rotatedBounds) / 2) yBy:- (NSHeight(rotatedBounds) / 2)];

        transformedImageBounds = rotatedBounds;
    }

    // draw the original image into the new image
    NSImage* transformedImage = [[NSImage alloc] initWithSize:transformedImageBounds.size];;
    [transformedImage lockFocus];
    [transform concat];
    [myImage drawInRect:imageBounds fromRect:NSZeroRect operation:NSCompositeCopy fraction:1.0] ;

    [transformedImage unlockFocus];

    return transformedImage;
}

但是生成的图像质量非常差。怎么解决？

有人说“lockFocus”方法导致了这种情况，但我不知道如何在不使用该方法的情况下做到这一点。

Answer 1

我不确定它在这个管道中的位置，但是如果您可以获取NSGraphicsContext(这可能很简单:

NSGraphicsContext *myContext = [NSGraphicsContext currentContext];

在您lockFocus之后)，您可以尝试

[myContext setImageInterpolation:NSImageInterpolationHigh]

要求 Cocoa 使用其最好的算法来缩放图像。如果您改用 CGImageRef API，我知道您可以轻松地更好地控制插值设置。