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嗨，我目前正在开发一个包含通过绘图记笔记的应用程序。我遵循了 ray wenderlich 教程，据我所知，我最终得到了以下代码：

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    mouseSwiped = NO;
    UITouch *touch = [touches anyObject];
    lastPoint = [touch locationInView:self];
} 

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    CGFloat red,green,blue,alpha;

    mouseSwiped = YES;
    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self];



    UIGraphicsBeginImageContext(self.mainImage.frame.size);
    [self.tempDrawImage.image drawInRect:CGRectMake(0, 0, self.mainImage.frame.size.width, self.mainImage.frame.size.height)];

    CGContextSetBlendMode(UIGraphicsGetCurrentContext(),[self getBlendMode]);

    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x , lastPoint.y  );
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x , currentPoint.y  );
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), [self getBrushSize] );

    [[self getPaintColor] getRed:&red green:&green blue:&blue alpha:&alpha];
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1);

    CGContextSetBlendMode(UIGraphicsGetCurrentContext(),[self getBlendMode]);

    CGContextStrokePath(UIGraphicsGetCurrentContext());
    self.tempDrawImage.image = UIGraphicsGetImageFromCurrentImageContext();
    [self.tempDrawImage setAlpha:[self getPaintAlpha]];
    UIGraphicsEndImageContext();

    lastPoint = currentPoint;
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    CGFloat red,green,blue;

    if(!mouseSwiped) {

        UIGraphicsBeginImageContext(self.mainImage.frame.size);
        [self.tempDrawImage.image drawInRect:CGRectMake(0, 0, self.mainImage.frame.size.width, self.mainImage.frame.size.height)];
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), [self getBrushSize]);

        [[self getPaintColor] getRed:&red green:&green blue:&blue alpha:nil];
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, [self getPaintAlpha]);
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y - self.mainImage.frame.origin.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y - self.mainImage.frame.origin.y );
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        CGContextFlush(UIGraphicsGetCurrentContext());
        self.tempDrawImage.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }

    UIGraphicsBeginImageContext(self.mainImage.frame.size);

    [self.mainImage.image drawInRect:CGRectMake(0, 0, self.mainImage.frame.size.width, self.mainImage.frame.size.height) blendMode:[self getBlendMode] alpha:1.0];
    [self.tempDrawImage.image drawInRect:CGRectMake(0, 0, self.mainImage.frame.size.width, self.mainImage.frame.size.height) blendMode:[self getBlendMode] alpha:[self getPaintAlpha]];
    if(self.drawMode != DrawEraser)
    {
        self.mainImage.image = UIGraphicsGetImageFromCurrentImageContext();
        self.tempDrawImage.image = nil;
    }
    UIGraphicsEndImageContext();
    mouseSwiped = NO;
}

这段代码在一个小框架上工作得很好，但是当我将框架增加到比以前大 2 倍时，不幸的是性能不是很好。所以我在考虑优化代码。我特别关注 touchesMoved 方法。据我了解，它在上下文中绘制整个图像并对其进行一些更改并将上下文分配给图像。绘制整个图像似乎超载。所以我想知道，是否可以将图像的某些部分绘制到上下文中并进行一些更改，然后将上下文的这一部分绘制到图像中。

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1 回答 1

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you're right - redrawing the whole image every time in touchesMoved is a bad idea. I think you should create and keep a reference to the context at the beginning. In touches moved, you should draw on to that and create an image from the context. You can use CGBitmapContextCreate() to create the context instead of UIGraphicsBeginImageContext() and CGBitmapContextCreateImage() to create an image from the context instead of UIGraphicsGetImageFromCurrentImageContext(). Here is the documentation on how to use those (https://developer.apple.com/library/mac/#documentation/graphicsimaging/reference/CGBitmapContext/Reference/reference.html).

于 2013-07-18T13:54:03.127 回答