绘制图像、阴影和渐变

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@end

#import "AppDelegate.h"

#import "NewHypnosister.h"

@interface AppDelegate ()

@end

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

{

    self.window = [[UIWindow alloc]initWithFrame:[[UIScreen mainScreen]bounds]];

    self.window.rootViewController = [[UIViewController alloc]init];

    CGRect firstFrame = self.window.bounds;

    NewHypnosister *firstView = [[NewHypnosister alloc]initWithFrame:firstFrame];

    [self.window addSubview:firstView];

    self.window.backgroundColor = [UIColor whiteColor];

    [self.window makeKeyAndVisible];

    return YES;

}

 @end

#import <UIKit/UIKit.h>

@interface NewHypnosister : UIView

@end

#import "NewHypnosister.h"

@implementation NewHypnosister

- (instancetype)initWithFrame:(CGRect)frame

{

    self = [super initWithFrame:frame];

    if (self){

        self.backgroundColor = [UIColor clearColor];

    }

    return self;

}

- (void)drawRect:(CGRect)rect

{

    CGRect bounds = self.bounds;

    CGPoint center;

    center.x = (bounds.origin.x + bounds.size.width)/2.0;

    center.y = (bounds.origin.y + bounds.size.height)/2.0;

    float maxRadius = hypot(bounds.size.width, bounds.size.height)/2.0;

    UIBezierPath *path = [[UIBezierPath alloc]init];

    for (float currentRadius = maxRadius; currentRadius > 0; currentRadius -= 20.0) {

        [path moveToPoint:CGPointMake(center.x + currentRadius, center.y)];

        [path addArcWithCenter:center

                        radius:currentRadius

                    startAngle:0.0

                      endAngle:M_PI*2.0

                     clockwise:YES];

    }

    path.lineWidth = 10.0;

    [[UIColor lightGrayColor] setStroke];

    [path stroke];

    //设置阴影

    CGContextRef currentContext = UIGraphicsGetCurrentContext();

    void CGContextShadow(CGContextRef context, CGSize offSet, CGFloat blur);

    CGContextSetShadow(currentContext, CGSizeMake(4, 7), 3);

    //绘制三角形，顶点(bounds.origin.x + bounds.size.width/2.0, bounds.origin.y),底边为bounds底边

    UIBezierPath *myPath = [UIBezierPath bezierPath];

    CGPoint myPoint[3];

    myPoint[0] = CGPointMake(bounds.origin.x + bounds.size.width/2.0, bounds.origin.y);

    myPoint[1] = CGPointMake(bounds.origin.x, bounds.origin.y + bounds.size.height);

    myPoint[2] = CGPointMake(bounds.origin.x + bounds.size.width, bounds.origin.y + bounds.size.height);

    //绘制三角形

    [myPath moveToPoint:myPoint[0]];

    [myPath addLineToPoint:myPoint[1]];

    [myPath addLineToPoint:myPoint[2]];

    [myPath stroke];

    //保存剪切三角形及设置颜色渐变

    CGContextSaveGState(currentContext);

    [myPath addClip];

    CGFloat locations[2] = {0.0, 1.0};

    CGFloat components[8] = {0.0, 1.0, 0.0, 1.0,//起始颜色为黄色

                             1.0, 1.0, 0.0, 1.0};//终止颜色为绿色

    CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();

    CGGradientRef gradient = CGGradientCreateWithColorComponents(colorspace, components, locations, 2);

    CGPoint startPoint = myPoint[0];

    CGPoint endPoint = myPoint[2];

    CGContextDrawLinearGradient(currentContext, gradient, startPoint, endPoint, 0);

    CGGradientRelease(gradient);

    CGColorSpaceRelease(colorspace);

    CGContextRestoreGState(currentContext);

    UIImage *logoImage = [UIImage imageNamed:@"logo.png"];

    [logoImage drawInRect:rect];

}

@end

绘制图像、阴影和渐变

原文：http://www.cnblogs.com/zjxsd/p/5088059.html