在多个UIView中绘图会导致滞后。 为什么？
Drawing in multiple UIViews causes lag. Why?

我正在制作涉及绘图线的多人游戏。 我有10种不同的自定义UIView，其中使用Core Graphics以独特的颜色绘制了一条线。 所有视图彼此堆叠，并且是半透明的。 之所以在相应的UIView中绘制每种颜色而不是一种颜色，是因为我想让用户能够清除特定的视图。 但是，如果我同时绘制所有这些视图，则会发生大量的滞后。 如果我检查时间分析器，则大部分时间都花在绘图上。 但这并没有那么糟糕，也不会造成太大的滞后。 因此，有什么方法可以让我绘制多个UIView（或其他），而不会引起这种滞后。 是我的代码导致了这种滞后，还是UIView？

- (void)drawRect:(CGRect)rect {
//create a image reference from the bitmap and then draw it in the context of the UIView. 

CGContextRef context = UIGraphicsGetCurrentContext();

CGImageRef cacheImage = CGBitmapContextCreateImage(cacheContext);

  CGContextDrawImage(context, self.bounds, cacheImage);
   CGImageRelease(cacheImage);
}

-(void)draw{
 //drawing code. Could ignore the Beizer curve algorithm here.

 CGContextSetStrokeColorWithColor(cacheContext, [color CGColor]);
 CGContextSetFillColorWithColor(cacheContext, [[UIColor blueColor] CGColor]);

 CGContextSetLineCap(cacheContext, kCGLineCapButt);
 CGContextSetLineWidth(cacheContext, 6+thickness);

        point0 = point1;
        point1 = point2; // previous previous point
        point2 = pos; // previous touch point
        point3 = currentpos;

        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;



    // Assume we need to calculate the control
    // points between (x1,y1) and (x2,y2).
    // Then x0,y0 - the previous vertex,
    //      x3,y3 - the next one.

    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 = 0.8;
    // Resulting control points. Here smooth_value is mentioned
    // above coefficient K whose value should be in range [0...1].
    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(cacheContext, point1.x, point1.y);
        CGContextAddCurveToPoint(cacheContext, ctrl1_x, ctrl1_y, ctrl2_x, ctrl2_y, point2.x, point2.y);
        CGContextStrokePath(cacheContext);




    CGRect dirtyPoint1 = CGRectMake(point1.x-(8+thickness)/2, point1.y-(8+thickness)/2, (8+thickness), (8+thickness));
    CGRect dirtyPoint2 = CGRectMake(point2.x-(8+thickness)/2, point2.y-(8+thickness)/2, (8+thickness), (8+thickness));

    [self setNeedsDisplayInRect:CGRectUnion(dirtyPoint1, dirtyPoint2)];

}