Gradient Color To CGContextRef

问题

I am drawing 4 arcs using CGContextRef.I can fill colour but now i want to set gradient color to that arcs.I did it.it is working fine.Now i want to set different color to each arc.Is there any way to do it?please help me.I am attaching my code and screenshot of that arc.Code :

CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB();

CGFloat comps[] = {1.0,1.0,1.0,1.0,0.0,1.0,1.0,1.0};
CGFloat locs[] = {0,1};
CGGradientRef g = CGGradientCreateWithColorComponents(space, comps, locs, 2);

CGContextRef context = UIGraphicsGetCurrentContext();
CGFloat startAngle = 0;
CGFloat endAngle = 90;
CGFloat radius = 100.0;
CGFloat levelWidth = 50;
for (int i = 0; i < 4; i++) {
    CGContextMoveToPoint(context, self.bounds.size.width/2, self.bounds.size.height/2);
    CGContextAddArc(context, self.bounds.size.width/2, self.bounds.size.height/2, radius, DEGREES_RADIANS(startAngle), DEGREES_RADIANS(endAngle), NO);
    CGContextAddArc(context, self.bounds.size.width/2, self.bounds.size.height/2, radius - levelWidth, DEGREES_RADIANS(endAngle),DEGREES_RADIANS(startAngle), YES);
    startAngle = endAngle;
    endAngle = endAngle + 90;
    CGContextClosePath(context);

}


//CGContextClosePath(context);
CGContextClip(context);
CGContextDrawRadialGradient(context, g, CGPointMake(self.bounds.size.width/2, self.bounds.size.height/2), 1.0f, CGPointMake(self.bounds.size.width/2, self.bounds.size.height/2), 150, 0);

And screen shot :

回答1:

You want to save the context with CGContextSaveGState before you clip, clip and draw the arc, and then restore the context with CGContextRestoreGState before drawing the next arc. And you obviously want an array of CGGradientRef. Thus:

CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB();

CGGradientRef g[4];

CGFloat comps0[] = {1.0,1.0,1.0,1.0,0.0,1.0,1.0,1.0};
CGFloat locs[] = {0,1};
g[0] = CGGradientCreateWithColorComponents(space, comps0, locs, 2);

CGFloat comps1[] = {1.0,1.0,1.0,1.0,1.0,0.0,1.0,1.0};
g[1] = CGGradientCreateWithColorComponents(space, comps1, locs, 2);

CGFloat comps2[] = {1.0,1.0,1.0,1.0,1.0,1.0,0.0,1.0};
g[2] = CGGradientCreateWithColorComponents(space, comps2, locs, 2);

CGFloat comps3[] = {1.0,1.0,1.0,1.0,0.5,0.0,0.5,1.0};
g[3] = CGGradientCreateWithColorComponents(space, comps3, locs, 2);

CGContextRef context = UIGraphicsGetCurrentContext();
CGFloat startAngle = 0;
CGFloat endAngle = 90;
CGFloat radius = 100.0;
CGFloat levelWidth = 50;
for (int i = 0; i < 4; i++) {
    CGContextSaveGState(context);
    CGContextMoveToPoint(context, self.bounds.size.width/2, self.bounds.size.height/2);
    CGContextAddArc(context, self.bounds.size.width/2, self.bounds.size.height/2, radius, DEGREES_RADIANS(startAngle), DEGREES_RADIANS(endAngle), NO);
    CGContextAddArc(context, self.bounds.size.width/2, self.bounds.size.height/2, radius - levelWidth, DEGREES_RADIANS(endAngle),DEGREES_RADIANS(startAngle), YES);
    startAngle = endAngle;
    endAngle = endAngle + 90;
    CGContextClosePath(context);
    CGContextClip(context);
    CGContextDrawRadialGradient(context, g[i], CGPointMake(self.bounds.size.width/2, self.bounds.size.height/2), 1.0f, CGPointMake(self.bounds.size.width/2, self.bounds.size.height/2), 150, 0);
    CGContextRestoreGState(context);
    CGGradientRelease(g[i]);         // don't forget to release the gradient
}

来源：https://stackoverflow.com/questions/18756056/gradient-color-to-cgcontextref

标签

ios

core-graphics