iOS Core Graphics基础入门（3）

## 绘制阴影// 创建一块画布CGContextRef context = UIGraphicsGetCurrentContext();// 添加阴影颜色 CGContextSetShadowWithColor(context, CGSizeMake(1.2, 1.2), 0, [UIColor lightGrayColor].CGColor);// 绘制字符串   [@"Hello" drawAtPoint:CGPointMake(20, 100)       withAttributes:@{ NSFontAttributeName: [UIFont systemFontOfSize:20]}];

## 绘制图片UIImage* image = [UIImage imageNamed:@"02"];// 第一种方法[image drawAtPoint:CGPointMake(0, 0)];// 第二种方法[image drawInRect:CGRectMake(20.f, 20.0f, 320 / 2.f, 568 / 2.f)];

## 绘制屋顶- (void)drawRect:(CGRect)rect{    [self drawRooftopAtTopPointof:CGPointMake(160.0f, 40.0f) textToDisplay:@"Miter" lineJoin:kCGLineJoinMiter];    [self drawRooftopAtTopPointof:CGPointMake(160.0f, 180.0f) textToDisplay:@"Bevel" lineJoin:kCGLineJoinBevel];    [self drawRooftopAtTopPointof:CGPointMake(160.0f, 320.0f) textToDisplay:@"Round" lineJoin:kCGLineJoinRound];}- (void)drawRooftopAtTopPointof:(CGPoint)paramTopPoint textToDisplay:(NSString * )paramText lineJoin:(CGLineJoin)paramLineJoin{    [[UIColor brownColor] set];    CGContextRef currentContext = UIGraphicsGetCurrentContext();    CGContextSetLineJoin(currentContext,paramLineJoin);    CGContextSetLineWidth(currentContext, 20.0f);    CGContextMoveToPoint(currentContext, paramTopPoint.x - 140, paramTopPoint.y + 100);    CGContextAddLineToPoint(currentContext, paramTopPoint.x, paramTopPoint.y);    CGContextAddLineToPoint(currentContext, paramTopPoint.x + 140, paramTopPoint.y + 100);    CGContextStrokePath(currentContext);    [[UIColor blackColor] set];    [paramText drawAtPoint:CGPointMake(paramTopPoint.x - 40.0f, paramTopPoint.y + 60.0f) withFont:[UIFont boldSystemFontOfSize:30.0f]];}

## 绘制矩形CGContextRef context  = UIGraphicsGetCurrentContext();CGMutablePathRef path = CGPathCreateMutable();CGPathAddRect(path, NULL, CGRectMake(0, 0, 200, 300));CGContextAddPath(context, path);[[UIColor colorWithRed:1 green:0 blue:0 alpha:1] setFill];[[UIColor greenColor] setStroke];CGContextSetLineWidth(context, 5.0f);CGContextDrawPath(context, kCGPathFillStroke);CGPathRelease(path);

## 绘制多个矩形CGContextRef context  = UIGraphicsGetCurrentContext();CGMutablePathRef path = CGPathCreateMutable();CGRect rectangle1 = CGRectMake(20.0f, 20.0f, 200.0f, 300.0f);CGRect rectangle2 = CGRectMake(40.0f, 100.0f, 90.0f, 300.0f);CGRect rectangles[2] = {rectangle1, rectangle2};CGPathAddRects(path, NULL, (const CGRect *)&rectangles, 2);CGContextAddPath(context, path);[[UIColor colorWithRed:0 green:1 blue:0 alpha:1] setFill];[[UIColor blackColor] setStroke];CGContextDrawPath(context, kCGPathFillStroke);CGPathRelease(path);

## 绘制渐变效果CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();UIColor * startColor = [UIColor blueColor];CGFloat * startColorComponents = (CGFloat *)CGColorGetComponents([startColor CGColor]);UIColor * endColor = [UIColor greenColor];CGFloat * endColorComponents = (CGFloat *)CGColorGetComponents([endColor CGColor]);CGFloat colorComponents[8] = {    startColorComponents[0],    startColorComponents[1],    startColorComponents[2],    startColorComponents[3],    endColorComponents[0],    endColorComponents[1],    endColorComponents[2],    endColorComponents[3]};CGFloat colorIndices[2] = {0.0f,1.0f};CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace, (const CGFloat *)&colorComponents, (const CGFloat *)&colorIndices, 2);CGColorSpaceRelease(colorSpace);CGRect screenBounds = [[UIScreen mainScreen] bounds];CGPoint startPoint, endPoint;startPoint = CGPointMake(0.0f, screenBounds.size.height/2.0f);endPoint = CGPointMake(screenBounds.size.width, startPoint.y);CGContextRef currentContext = UIGraphicsGetCurrentContext();CGContextDrawLinearGradient(currentContext,gradient , startPoint, endPoint, 0);CGGradientRelease(gradient);