iOS的石英繪圖應用

Question

更新我已經按以下步驟進行的建議，添加路徑，以一個陣列並拉到一個CGLayer。但是，當繪製大量路徑時，性能確實很慢。我犯過什麼錯誤嗎？

- (void)pan:(UIPanGestureRecognizer *)pan 
{ 
    CGPoint velocity = [pan velocityInView:self]; 

    previousPoint2 = previousPoint1; 
    previousPoint1 = currentPoint; 
    currentPoint = [pan locationInView:self]; 

    float velocityMagnitude = sqrtf(velocity.x * velocity.x + velocity.y * velocity.y); 

    float clampedVelocityMagnitude = clamp(VELOCITY_CLAMP_MIN, VELOCITY_CLAMP_MAX, velocityMagnitude); 
    float normalizedVelocity = (clampedVelocityMagnitude - VELOCITY_CLAMP_MIN)/(VELOCITY_CLAMP_MAX - VELOCITY_CLAMP_MIN); 

    float lowPassFilterAlpha = STROKE_WIDTH_SMOOTHING; 
    float newThickness = (STROKE_WIDTH_MAX - STROKE_WIDTH_MIN) * normalizedVelocity + STROKE_WIDTH_MIN; 
    self.lineWidth = self.lineWidth * lowPassFilterAlpha + newThickness * (1 - lowPassFilterAlpha); 

    CGPoint mid1 = midPoint(previousPoint1, previousPoint2); 
    CGPoint mid2 = midPoint(currentPoint, previousPoint1); 
    CGMutablePathRef subpath = CGPathCreateMutable(); 
    CGPathMoveToPoint(subpath, NULL, mid1.x, mid1.y); 
    CGPathAddQuadCurveToPoint(subpath, NULL, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y); 
    CGRect bounds = CGPathGetBoundingBox(subpath); 

    Path *path = [[Path alloc] init]; 
    path.width = self.lineWidth; 
    path.color = [UIColor redColor]; 
    path.bezierPath = [UIBezierPath bezierPathWithCGPath:subpath]; 
    [pathArray addObject:path]; 
    CGPathRelease(subpath); 

    CGRect drawBox = bounds; 
    drawBox.origin.x -= self.lineWidth * 2.0; 
    drawBox.origin.y -= self.lineWidth * 2.0; 
    drawBox.size.width += self.lineWidth * 4.0; 
    drawBox.size.height += self.lineWidth * 4.0; 

    [self setNeedsDisplayInRect:drawBox]; 

    if (pan.state == UIGestureRecognizerStateEnded | pan.state == UIGestureRecognizerStateCancelled) 
    { 
     self.lineWidth = STROKE_WIDTH_MIN; 
    } 
} 

- (void)drawRect:(CGRect)rect { 
    [self.backgroundColor set]; 
    UIRectFill(rect); 

    CGContextRef context = UIGraphicsGetCurrentContext(); 

    if(layer == nil) 
    { 
     float scale = [UIScreen mainScreen].scale; 
     CGRect bounds = CGRectMake(0, 0, rect.size.width * scale, rect.size.height * scale); 
     layer = CGLayerCreateWithContext(context, bounds.size, NULL); 
     layerContext = CGLayerGetContext(layer); 
    } 

    for(int i = 0; i < [pathArray count]; i++) 
    { 
     Path *path = [pathArray objectAtIndex:i]; 
     UIBezierPath *bezierPath = path.bezierPath; 
     CGContextAddPath(layerContext, bezierPath.CGPath); 
     CGContextSetLineWidth(layerContext, path.width); 
     CGContextSetStrokeColorWithColor(layerContext, path.color.CGColor); 
     CGContextSetLineCap(layerContext, kCGLineCapRound); 
     CGContextStrokePath(layerContext); 
    } 

    CGContextDrawLayerAtPoint(context, CGPointZero, layer); 

    self.empty = NO; 
} 

我正在使用下面的代碼根據用戶的平移手勢的速度繪製可變寬度的線條。它工作正常，但是當我在前面繪製的線附近或之上繪製時，其線寬將更改爲與當前手勢和線的速度相匹配。我怎樣才能確保畫出的線條保持原來繪製的厚度？

- (void)pan:(UIPanGestureRecognizer *)pan 
{ 
    CGPoint velocity = [pan velocityInView:self]; 

    previousPoint2 = previousPoint1; 
    previousPoint1 = currentPoint; 
    currentPoint = [pan locationInView:self]; 

    float velocityMagnitude = sqrtf(velocity.x * velocity.x + velocity.y * velocity.y); 

    float clampedVelocityMagnitude = clamp(VELOCITY_CLAMP_MIN, VELOCITY_CLAMP_MAX, velocityMagnitude); 
    float normalizedVelocity = (clampedVelocityMagnitude - VELOCITY_CLAMP_MIN)/(VELOCITY_CLAMP_MAX - VELOCITY_CLAMP_MIN); 

    float lowPassFilterAlpha = STROKE_WIDTH_SMOOTHING; 
    float newThickness = (STROKE_WIDTH_MAX - STROKE_WIDTH_MIN) * normalizedVelocity + STROKE_WIDTH_MIN; 
    self.lineWidth = self.lineWidth * lowPassFilterAlpha + newThickness * (1 - lowPassFilterAlpha); 

    CGPoint mid1 = midPoint(previousPoint1, previousPoint2); 
    CGPoint mid2 = midPoint(currentPoint, previousPoint1); 
    CGMutablePathRef subpath = CGPathCreateMutable(); 
    CGPathMoveToPoint(subpath, NULL, mid1.x, mid1.y); 
    CGPathAddQuadCurveToPoint(subpath, NULL, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y); 
    CGRect bounds = CGPathGetBoundingBox(subpath); 

    CGPathAddPath(path, NULL, subpath); 
    CGPathRelease(subpath); 

    CGRect drawBox = bounds; 
    drawBox.origin.x -= self.lineWidth * 2.0; 
    drawBox.origin.y -= self.lineWidth * 2.0; 
    drawBox.size.width += self.lineWidth * 4.0; 
    drawBox.size.height += self.lineWidth * 4.0; 

    if (pan.state == UIGestureRecognizerStateEnded | pan.state == UIGestureRecognizerStateCancelled) 
    { 
     self.lineWidth = STROKE_WIDTH_MIN; 
    } 
    else 
    { 
     [self setNeedsDisplayInRect:drawBox]; 
    } 
} 

- (void)drawRect:(CGRect)rect { 
    [self.backgroundColor set]; 
    UIRectFill(rect); 

    CGContextRef context = UIGraphicsGetCurrentContext(); 

    CGContextAddPath(context, path); 
    CGContextSetLineCap(context, kCGLineCapRound); 

    CGContextSetLineWidth(context, self.lineWidth); 
    CGContextSetStrokeColorWithColor(context, self.lineColor.CGColor); 

    CGContextStrokePath(context); 

    self.empty = NO; 
} 

Answer 1

每當線寬發生變化，您需要開始一個新的路徑。您需要將所有這些路徑存儲到數組（或類似）中，並在調用drawRect:時繪製它們中的每一個。這將保持繪製時的線寬。

目前發生的情況是，您總是繪製單個路徑，因此您總是重置整個路徑的線寬。這只是爲了刷新drawBox，這是您實際看到更新的唯一一點。

表現會不好當您添加更多行，所以你可能會想開始尋找使用CGLayer緩存以前繪製的路徑和渲染層到上下文drawRect:，而不是迭代的路徑。