iOS quartz 绘图应用程序

Question

更新:正确的绘制矩形方法如下所示

- (void)drawRect:(CGRect)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);
        CGContextScaleCTM(layerContext, scale, scale);
        viewRect = CGRectMake(0, 0, self.bounds.size.width, self.bounds.size.height);
    }

    UIBezierPath *bezierPath = path.bezierPath;
    CGContextAddPath(layerContext, bezierPath.CGPath);
    CGContextSetLineWidth(layerContext, path.width);
    CGContextSetStrokeColorWithColor(layerContext, path.color.CGColor);
    CGContextSetLineCap(layerContext, kCGLineCapRound);
    CGContextStrokePath(layerContext);

    CGContextDrawLayerInRect(context, viewRect, layer);
    self.empty = NO;
}

更新:我已按照建议完成，将路径添加到数组并绘制到 CGLayer，如下所示。但是，当绘制大量路径时，性能确实会降低。我犯了什么错误吗？

    - (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;
}

我使用下面的代码根据用户平移手势的速度绘制宽度可变的线条。它工作正常，但是当我靠近或越过之前绘制的线条时，它的线条宽度会发生变化以匹配当前手势和线条的速度。请问如何确保绘制的线条保持最初绘制时的粗细？

- (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

每次线宽变化时，您都需要开始一条新路径。您需要将所有这些路径存储到一个数组(或类似数组)中，并在 drawRect: 时绘制它们中的每一个。叫做。这将在绘制时保持线宽。

当前发生的情况是您始终绘制一条路径，因此您始终要为整条路径重置线宽。只是你的view只能刷新drawBox所以这是您实际看到更新的唯一一点。

添加更多行时性能会变差，因此您可能希望开始考虑使用 CGLayer缓存先前绘制的路径并将图层渲染到 drawRect: 中的上下文中而不是迭代路径。