Quartz2D简单绘制之渐变色

// 渐变色 gradient
    CGFloat colors [] = { 
        1.0, 1.0, 1.0, 1.0, 
        1.0, 0.0, 0.0, 1.0, 
        0.0, 0.0, 0.0, 1.0
    };
    CGFloat locations[] = {
        0.0f,0.5f,1.0f
    };
    CGColorSpaceRef baseSpace = CGColorSpaceCreateDeviceRGB();
    CGGradientRef gradient = CGGradientCreateWithColorComponents(baseSpace, colors, locations, sizeof(colors)/(sizeof(colors[0])*4));
    CGColorSpaceRelease(baseSpace), baseSpace = NULL;
    
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGRect aRect = CGRectInset(CGContextGetClipBoundingBox(context), 50.0f, 20.0f);
    CGContextSaveGState(context);                // SaveGState
    CGContextClipToRect(context, aRect);
    
    CGPoint startPoint = CGPointMake(CGRectGetMidX(aRect), CGRectGetMinY(aRect)); 
    CGPoint endPoint = CGPointMake(CGRectGetMidX(aRect), CGRectGetMaxY(aRect)); 
    
    // kCGGradientDrawsBeforeStartLocation    开始位置之外的也画
    // kCGGradientDrawsAfterEndLocation        结束位置之外的也画
    // 0                                    正常状态
    CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0);
    CGGradientRelease(gradient), gradient = NULL;
    
    CGContextRestoreGState(context);            // RestoreGState
    CGContextDrawPath(context, kCGPathStroke);