drawRect優化

Question

我正在研究允許用戶選擇圖像（相機或圖庫）的應用程序，然後用他們的手指在該圖像上繪圖。他們畫的區域變成了面具的透明部分。然後在第一個圖像下繪製第二個圖像。

我一直在努力提高性能，特別是在iPad 3上，我似乎碰到了一堵牆。我是iOS和Objective-C的新手。

所以我的問題是：我能做些什麼來提高我的應用程序的繪圖性能？

我用this tutorial作爲我的代碼的起點。

首先，我要畫一個緩存方面：

- (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)]; 
    } 
} 

而且我的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); 
} 

我昨天花了研究這些問題：

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

任何幫助表示讚賞！

感謝， 凱文

Answer 1

我可以給你一些提示，但你將需要進行試驗，看看問題出在哪裏（使用儀器）：

• 不要以爲你需要繪製整個視圖 - 當需要骯髒某個區域時，使用setNeedsDisplayInRect。然後在drawRect中只更新髒區域。

• 上述意味着你maskRef要小得多，更容易構建

• ，而不是「[self.original CGImage]」，創建使用CGImageCreateWithImageInRect（）更小的子區域的圖像，它可以讓你選擇的第一個圖像，然後與該蒙版一起使用該較小的圖像。