iphone - iPhone中折线图的渐变效果

Question

我正在尝试生成具有渐变/阴影效果的图表。现在我可以绘制折线图并对该图应用渐变效果。它适用于整个 View 而不是图表。现在我得到像 这样的图像这。但我想要像 这。我想要图表下方的渐变效果。

请帮助我。提前致谢。

我正在使用的代码是:

UIGraphicsBeginImageContext(self.graphView.frame.size);
[graphView.image drawInRect:CGRectMake(0, 0, self.graphView.frame.size.width, self.graphView.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineJoin(UIGraphicsGetCurrentContext(), kCGLineJoinRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 2.0);
CGContextSetRGBFillColor(UIGraphicsGetCurrentContext(), 225, 48, 48, 1.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 225, 225, 0.0, 1.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());

float xCordinate, yCordinate;

for (int i = 0; i < [graphValues count]; i++) {
    int val = [[graphValues objectAtIndex: i] intValue] / 5;
    float diff = [[graphValues objectAtIndex: i] floatValue] / 5 - val;
    yCordinate = val * 120 + 120 * diff;
    xCordinate = graphWidth * i / [graphValues count] + 60;
    if (i == 0) 
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), xCordinate, graphHeight + 60 - yCordinate);
    else 
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), xCordinate, graphHeight + 60 - yCordinate);
}
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), xCordinate, graphHeight + 60);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), 60, graphHeight + 60);
CGContextClosePath(UIGraphicsGetCurrentContext()); 
CGContextSaveGState(UIGraphicsGetCurrentContext());
CGContextDrawPath(UIGraphicsGetCurrentContext(), kCGPathStroke);

//CGContextFillPath(UIGraphicsGetCurrentContext());

CGContextClip(UIGraphicsGetCurrentContext());


//Draw Gradient
UIColor *topColor = [UIColor colorWithRed: 1.0 green:1.0 blue:1.0 alpha:1.0];
UIColor *bottomColor = [UIColor colorWithRed:1.0 green:1.0 blue:1.0 alpha:0.0];
CGColorRef colorRef[] = { [topColor CGColor], [bottomColor CGColor] };
CFArrayRef colors = CFArrayCreate(NULL, (const void**)colorRef, sizeof(colorRef) / sizeof(CGColorRef), &kCFTypeArrayCallBacks);

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, colors, NULL);
CFRelease(colorSpace);
CFRelease(colors);

//  Draw a linear gradient from top to bottom
CGPoint gradStartPoint = CGPointMake(50.0, graphView.bounds.size.height);
CGPoint gradEndPoint = CGPointMake(50.0, 0.0);
CGContextDrawLinearGradient(UIGraphicsGetCurrentContext(), gradient, gradStartPoint, gradEndPoint, 0);

CFRelease(gradient);

// Cleanup
CGColorSpaceRelease(colorSpace);

CGContextRestoreGState(UIGraphicsGetCurrentContext());

graphView.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

Answer 1

诀窍是在绘制渐变之前设置剪切路径。有关详细信息，请参阅 CGContextRef 文档。