如何用特定的颜色绘制CGGradient？

我有这个我find的这个Objective-C代码。 老实说，我不明白在那里发生的一件事情。 我根本不熟悉Core Graphics。 下面的代码表示左边的图像。 我想要的是一个类似的颜色渐变到右边的图像（所需的颜色有12,138,255的RGB）。 我在哪里改变这个代码来获得所需的结果？

- (void)drawRect:(CGRect)rect { CGContextRef context = UIGraphicsGetCurrentContext(); CGSize titleSize = [croppedTitle sizeWithFont:kTokenTitleFont]; CGRect bounds = CGRectMake(0, 0, titleSize.width + 17, titleSize.height + 5); CGRect textBounds = bounds; textBounds.origin.x = (bounds.size.width - titleSize.width) / 2; textBounds.origin.y += 4; CGFloat arcValue = (bounds.size.height / 2) + 1; CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB(); CGPoint endPoint = CGPointMake(1, self.bounds.size.height + 10); // Draw the outline. CGContextSaveGState(context); CGContextBeginPath(context); CGContextAddArc(context, arcValue, arcValue, arcValue, (M_PI / 2), (3 * M_PI / 2), NO); CGContextAddArc(context, bounds.size.width - arcValue, arcValue, arcValue, 3 * M_PI / 2, M_PI / 2, NO); CGContextClosePath(context); CGFloat red = 1; CGFloat green = 1; CGFloat blue = 1; CGFloat alpha = 1; [tintColor ti_getRed:&red green:&green blue:&blue alpha:&alpha]; if (highlighted){ // highlighted outline color CGContextSetFillColor(context, (CGFloat[8]){red, green, blue, 1}); CGContextFillPath(context); CGContextRestoreGState(context); } else { CGContextClip(context); CGFloat locations[2] = {0, 0.95}; // unhighlighted outline color CGFloat components[8] = {red + .2, green +.2, blue +.2, alpha, red, green, blue, alpha}; CGGradientRef gradient = CGGradientCreateWithColorComponents(colorspace, components, locations, 2); CGContextDrawLinearGradient(context, gradient, CGPointZero, endPoint, 0); CGGradientRelease(gradient); CGContextRestoreGState(context); } // Draw a white background so we can use alpha to lighten the inner gradient CGContextSaveGState(context); CGContextBeginPath(context); CGContextAddArc(context, arcValue, arcValue, (bounds.size.height / 2), (M_PI / 2) , (3 * M_PI / 2), NO); CGContextAddArc(context, bounds.size.width - arcValue, arcValue, arcValue - 1, (3 * M_PI / 2), (M_PI / 2), NO); CGContextClosePath(context); CGContextSetFillColor(context, (CGFloat[8]){1, 1, 1, 1}); CGContextFillPath(context); CGContextRestoreGState(context); // Draw the inner gradient. CGContextSaveGState(context); CGContextBeginPath(context); CGContextAddArc(context, arcValue, arcValue, (bounds.size.height / 2), (M_PI / 2) , (3 * M_PI / 2), NO); CGContextAddArc(context, bounds.size.width - arcValue, arcValue, arcValue - 1, (3 * M_PI / 2), (M_PI / 2), NO); CGContextClosePath(context); CGContextClip(context); CGFloat locations[2] = {0, highlighted ? 0.8 : 0.4}; CGFloat highlightedComp[8] = {red, green, blue, .6, red, green, blue, 1}; CGFloat nonHighlightedComp[8] = {red, green, blue, .2, red, green, blue, .4}; CGGradientRef gradient = CGGradientCreateWithColorComponents (colorspace, highlighted ? highlightedComp : nonHighlightedComp, locations, 2); CGContextDrawLinearGradient(context, gradient, CGPointZero, endPoint, 0); CGGradientRelease(gradient); CGColorSpaceRelease(colorspace); [(highlighted ? [UIColor whiteColor] : [UIColor blackColor]) set]; [croppedTitle drawInRect:textBounds withFont:kTokenTitleFont]; CGContextRestoreGState(context); } - (BOOL)ti_getRed:(CGFloat *)red green:(CGFloat *)green blue:(CGFloat *)blue alpha:(CGFloat *)alpha { CGColorSpaceModel colorSpaceModel = CGColorSpaceGetModel(CGColorGetColorSpace(self.CGColor)); const CGFloat * components = CGColorGetComponents(self.CGColor); if (colorSpaceModel == kCGColorSpaceModelMonochrome){ if (red) *red = components[0]; if (green) *green = components[0]; if (blue) *blue = components[0]; if (alpha) *alpha = components[1]; return YES; } if (colorSpaceModel == kCGColorSpaceModelRGB){ if (red) *red = components[0]; if (green) *green = components[1]; if (blue) *blue = components[2]; if (alpha) *alpha = components[3]; return YES; } return NO; } 

Answer 1

您可以使用以下代码绘制渐变。 把它放在你的drawRect：函数中。

 CGContextRef ref = UIGraphicsGetCurrentContext(); UIColor *lightGradientColor = [UIColor colorWithRed:0.8 green:0.8 blue:0.8 alpha:1.0]; UIColor *darkGradientColor = [UIColor colorWithRed:0.1 green:0.1 blue:0.1 alpha:1.0]; CGFloat locations[2] = {0.0, 1.0}; CFArrayRef colors = (CFArrayRef) [NSArray arrayWithObjects:(id)lightGradientColor.CGColor, (id)darkGradientColor.CGColor, nil]; CGColorSpaceRef colorSpc = CGColorSpaceCreateDeviceRGB(); CGGradientRef gradient = CGGradientCreateWithColors(colorSpc, colors, locations); CGContextDrawLinearGradient(ref, gradient, CGPointMake(0.5, 0.0), CGPointMake(0.5, 100.0), kCGGradientDrawsAfterEndLocation); //Adjust second point according to your view height CGColorSpaceRelease(colorSpc); CGGradientRelease(gradient);