如何用渐变填充UIBezierPath？ [英] How to fill a UIBezierPath with a gradient?

问题描述

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。但是我不确定如何使渐变仅适用于图形而不是整个视图，我已经阅读了几个问题，但没有找到适用的任何问题。

I've drawn a graph using a UIBezierPath. I can fill the area under the graph with a solid color but I want to fill the area under the graph with a gradient rather than with a solid color. But I'm not sure how to make the gradient apply only to the graph and not to the whole view, I've read a few questions but not found anything applicable.

这是主要的图形绘制代码：

This is the main graph drawing code:

// 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如下代码来填充图表，但说实话尽管经过了各种教程和文档，但我不确定我在做什么：

I've been attempting to fill the graph by experimenting with code like the following, but to be honest am not %100 sure what I'm doing despite going through various tutorials and documentation:

[barGraph closePath];

CGFloat colors [] = {
    1.0, 0.0, 0.0, 1.0,
    1.0, 1.0, 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);

推荐答案

最简单的方法是使用原始图形bezier路径帮助您构建蒙版并将此蒙版强加于渐变图层。现在将图形图层放在渐变图层的顶部。

The easiest approach is to use the original graph bezier path to help you construct a mask and impose this mask on a gradient layer. Now impose the graph layer on top of the gradient layer.

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，填黑。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并使CAShapeLayer成为掩码。在此之前，放置实际图表。

So, for example, make a CAShapeLayer, close the graph bezier path, set its path as the shape layer's path, and fill it black. Now you have a mask that is the shape of the area under the graph. Now make a CAGradientLayer and make the CAShapeLayer its mask. In front of that, place the actual graph.

例如（ EDITED ）：

这是我用来创建该绘图的代码（我的bezier路径很简单，只有四个点由三行连接，但你可以清楚地看到它下面的区域是一个渐变）：

Here's the code I used to create that drawing (my bezier path is very simple, just four points joined by three lines, but you can see clearly that the area under it is a gradient):

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];

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