我使用UIBezierPath绘制了一个图形.我可以使用纯色填充图表下方的区域,但我想用渐变而不是纯色填充图表下方的区域.但我不知道如何使渐变仅适用于图形而不是整个视图,我已经阅读了一些问题,但没有找到任何适用的问题.
这是主要的图形绘制代码：
// Draw the graph
UIBezierPath *barGraph = [UIBezierPath bezierPath];
barGraph.lineWidth = 1.0f;
[blueColor setStroke];
TCDataPoint *dataPoint = self.testData[0];
CGFloat x = [self convertTimeToXPoint:dataPoint.time];
CGFloat y = [self convertDataToYPoint:dataPoint.dataUsage];
CGPoint plotPoint = CGPointMake(x,y);
[barGraph moveToPoint:plotPoint];
for (int ii = 1; ii < [self.testData count]; ++ii)
{
dataPoint = self.testData[ii];
x = [self convertTimeToXPoint:dataPoint.time];
y = [self convertDataToYPoint:dataPoint.dataUsage];
plotPoint = CGPointMake(x,y);
[barGraph addLineToPoint:plotPoint];
}
[barGraph stroke];
我一直试图通过试验下面的代码来填充图表,但说实话,不是吗？0确定我正在做什么,尽管经历了各种教程和文档：
[barGraph closePath];
CGFloat colors [] = {
1.0,0.0,1.0,1.0
};
CGColorSpaceRef baseSpace = CGColorSpaceCreateDeviceRGB();
CGGradientRef gradient = CGGradientCreateWithColorComponents(baseSpace,colors,NULL,2);
CGColorSpaceRelease(baseSpace);
CGPoint startPoint = CGPointMake(CGRectGetMidX(self.bounds),self.topY);
CGPoint endPoint = CGPointMake(CGRectGetMidX(self.bounds),self.bottomY);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextClip(context);
CGContextDrawLinearGradient(context,gradient,startPoint,endPoint,0);
CGGradientRelease(gradient);
解决方法
最简单的方法是使用原始图形贝塞尔曲线路径来帮助您构建蒙版并将此蒙版强加于渐变图层.现在将图层施加在渐变图层的顶部.
因此,例如,创建一个CAShapeLayer,关闭图形bezier路径,将其路径设置为形状图层的路径,并将其填充为黑色.现在你有一个掩码,它是图形下面积的形状.现在制作一个CAGradientLayer并将CAShapeLayer作为掩码.在此之前,放置实际图表.
例如(EDITED)：
这是我用来创建绘图的代码(我的bezier路径非常简单,只有四个点由三条线连接,但你可以清楚地看到它下面的区域是一个渐变)：
CAShapeLayer* shape = [[CAShapeLayer alloc] init];
shape.frame = self.graph.bounds;
CGFloat h = shape.frame.size.height;
CGFloat w = shape.frame.size.width;
NSArray* points = @[
[NSValue valueWithCGPoint:CGPointMake(0,h-50)],[NSValue valueWithCGPoint:CGPointMake(70,h-100)],[NSValue valueWithCGPoint:CGPointMake(140,h-75)],[NSValue valueWithCGPoint:CGPointMake(w,h-150)],];
UIBezierPath* p = [UIBezierPath new];
[p moveToPoint:[points[0] CGPointValue]];
for (NSInteger i = 1; i < points.count; i++)
[p addLineToPoint:[points[i] CGPointValue]];
shape.path = p.CGPath;
shape.strokeColor = [UIColor blackColor].CGColor;
shape.lineWidth = 2;
shape.fillColor = nil;
CAGradientLayer* grad = [[CAGradientLayer alloc] init];
grad.frame = self.graph.bounds;
grad.colors = @[(id)[UIColor blueColor].CGColor,(id)[UIColor yellowColor].CGColor];
CAShapeLayer* mask = [[CAShapeLayer alloc] init];
mask.frame = self.graph.bounds;
[p addLineToPoint:CGPointMake(w,h)];
[p addLineToPoint:CGPointMake(0,h)];
[p closePath];
mask.path = p.CGPath;
mask.fillColor = [UIColor blackColor].CGColor;
grad.mask = mask;
[self.graph.layer addSublayer:grad];
[self.graph.layer addSublayer:shape];
