drawRect优化

Question

我正在开发一个允许用户选择图像（相机或画廊），然后用手指在该图像上绘图的应用程序。他们绘制的区域成为蒙版的透明部分。然后在第一幅图像下方绘制第二幅图像。

我一直在努力提高性能，尤其是在 iPad 3 上，但我似乎碰壁了。我是 iOS 和 Objective-C 的新手。

所以我的问题是：我可以做些什么来提高我的应用程序的绘图性能？

我使用this tutorial 作为我的代码的起点。

首先我绘制到一个缓存上下文：

- (void) drawToCache {
    CGRect dirtyPoint1;
    CGRect dirtyPoint2;
    UIColor *color;

    if (point1.x > -1){
        hasDrawn = YES;

        maskContext = CGLayerGetContext(maskLayer);
        blackBackgroundContext = CGLayerGetContext(blackBackgroundLayer);

        if (!doUndo){
            color = [UIColor whiteColor];
            CGContextSetBlendMode(maskContext, kCGBlendModeColor);
        }
        else{
            color = [UIColor clearColor];
            CGContextSetBlendMode(maskContext, kCGBlendModeClear);
        }

        CGContextSetShouldAntialias(maskContext, YES);

        CGContextSetRGBFillColor(blackBackgroundContext, 0.0, 0.0, 0.0, 1.0);
        CGContextFillRect(blackBackgroundContext, self.bounds);

        CGContextSetStrokeColorWithColor(maskContext, [color CGColor]);
        CGContextSetLineCap(maskContext, kCGLineCapRound);
        CGContextSetLineWidth(maskContext, brushSize);

        double x0 = (point0.x > -1) ? point0.x : point1.x; //after 4 touches we should have a back anchor point, if not, use the current anchor point
        double y0 = (point0.y > -1) ? point0.y : point1.y; //after 4 touches we should have a back anchor point, if not, use the current anchor point
        double x1 = point1.x;
        double y1 = point1.y;
        double x2 = point2.x;
        double y2 = point2.y;
        double x3 = point3.x;
        double y3 = point3.y;

        double xc1 = (x0 + x1) / 2.0;
        double yc1 = (y0 + y1) / 2.0;
        double xc2 = (x1 + x2) / 2.0;
        double yc2 = (y1 + y2) / 2.0;
        double xc3 = (x2 + x3) / 2.0;
        double yc3 = (y2 + y3) / 2.0;

        double len1 = sqrt((x1-x0) * (x1-x0) + (y1-y0) * (y1-y0));
        double len2 = sqrt((x2-x1) * (x2-x1) + (y2-y1) * (y2-y1));
        double len3 = sqrt((x3-x2) * (x3-x2) + (y3-y2) * (y3-y2));

        double k1 = len1 / (len1 + len2);
        double k2 = len2 / (len2 + len3);

        double xm1 = xc1 + (xc2 - xc1) * k1;
        double ym1 = yc1 + (yc2 - yc1) * k1;
        double xm2 = xc2 + (xc3 - xc2) * k2;
        double ym2 = yc2 + (yc3 - yc2) * k2;

        double smooth_value = 0.5;
        float ctrl1_x = xm1 + (xc2 - xm1) * smooth_value + x1 - xm1;
        float ctrl1_y = ym1 + (yc2 - ym1) * smooth_value + y1 - ym1;
        float ctrl2_x = xm2 + (xc2 - xm2) * smooth_value + x2 - xm2;
        float ctrl2_y = ym2 + (yc2 - ym2) * smooth_value + y2 - ym2;

        CGContextMoveToPoint(maskContext, point1.x, point1.y);
        CGContextAddCurveToPoint(maskContext, ctrl1_x, ctrl1_y, ctrl2_x, ctrl2_y, point2.x, point2.y);
        CGContextStrokePath(maskContext);

        dirtyPoint1 = CGRectMake(point1.x-(brushSize/2), point1.y-(brushSize/2), brushSize, brushSize);
        dirtyPoint2 = CGRectMake(point2.x-(brushSize/2), point2.y-(brushSize/2), brushSize, brushSize);
        [self setNeedsDisplayInRect:CGRectUnion(dirtyPoint1, dirtyPoint2)];
    }
}

还有我的drawRect：

- (void)drawRect:(CGRect)rect {
    CGRect imageRect = CGRectMake(0, 0, 1024, 668);
    CGSize size =  CGSizeMake(1024, 668);

    //Draw the user touches to the context, this creates a black and white image to convert into a mask
    UIGraphicsBeginImageContext(size);
    CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(), YES);
    CGContextDrawLayerInRect(UIGraphicsGetCurrentContext(), imageRect, blackBackgroundLayer);
    CGContextDrawLayerInRect(UIGraphicsGetCurrentContext(), imageRect, maskLayer);
    CGImageRef maskRef = CGBitmapContextCreateImage(UIGraphicsGetCurrentContext());
    UIGraphicsEndImageContext();

    //Make the mask
    CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef), CGImageGetHeight(maskRef), CGImageGetBitsPerComponent(maskRef), CGImageGetBitsPerPixel(maskRef), CGImageGetBytesPerRow(maskRef), CGImageGetDataProvider(maskRef), NULL, false);
    //Mask the user image
    CGImageRef masked = CGImageCreateWithMask([self.original CGImage], mask);

    UIGraphicsBeginImageContext(size);
    CGContextDrawLayerInRect(UIGraphicsGetCurrentContext(), imageRect, backgroundTextureLayer);
    CGImageRef background = CGBitmapContextCreateImage(UIGraphicsGetCurrentContext());
    UIGraphicsEndImageContext();

    //Flip the context so everything is right side up
    CGContextTranslateCTM(UIGraphicsGetCurrentContext(), 0, 668);
    CGContextScaleCTM(UIGraphicsGetCurrentContext(), 1.0, -1.0);

    //Draw the background on the context
    CGContextDrawImage(UIGraphicsGetCurrentContext(), imageRect, background);

    //Draws the mask on the context
    CGContextDrawImage(UIGraphicsGetCurrentContext(), imageRect, masked);

    //Release everything to prevent memory leaks
    CGImageRelease(background);
    CGImageRelease(maskRef);
    CGImageRelease(mask);
    CGImageRelease(masked);
}

我昨天研究了这些问题：

How can I improve CGContextFillRect and CGContextDrawImage performance

CGContextDrawImage very slow on iPhone 4

Drawing in CATiledLayer with CoreGraphics CGContextDrawImage

iPhone: How do I add layers to UIView's root layer to display an image with the content property?

iPhone CGContextDrawImage and UIImageJPEGRepresentation drastically slowing down application

感谢任何帮助！

谢谢， 凯文

Answer 1

我可以给你一些提示，但你需要尝试看看问题出在哪里（使用仪器）：

• 不要假设您需要绘制整个视图 - 当您需要弄脏某些区域时，请使用 setNeedsDisplayInRect。然后在drawRect中只更新脏区。

• 以上意味着你的 maskRef 更小更容易构建

• 不要使用“[self.original CGImage]”，而是使用 CGImageCreateWithImageInRect() 创建一个较小的子区域图像，它允许您选择图像的一个子部分，然后将该较小的图像与蒙版结合使用。