13.2 矢量圖形

矢量圖形

????我們用Core Graphics來繪圖的一個通常原因就是只是用圖片或是圖層效果不能輕易地繪制出矢量圖形。矢量繪圖包含一下這些：

• 任意多邊形（不僅僅是一個矩形）
• 斜線或曲線
• 文本
• 漸變

????舉個例子，清單13.1 展示了一個基本的畫線應(yīng)用。這個應(yīng)用將用戶的觸摸手勢轉(zhuǎn)換成一個UIBezierPath上的點(diǎn)，然后繪制成視圖。我們在一個UIView子類DrawingView中實(shí)現(xiàn)了所有的繪制邏輯，這個情況下我們沒有用上view controller。但是如果你喜歡你可以在view controller中實(shí)現(xiàn)觸摸事件處理。圖13.1是代碼運(yùn)行結(jié)果。

清單13.1 用Core Graphics實(shí)現(xiàn)一個簡單的繪圖應(yīng)用

#import "DrawingView.h"

@interface DrawingView ()

@property (nonatomic, strong) UIBezierPath *path;

@end

@implementation DrawingView

- (void)awakeFromNib
{
    //create a mutable path
    self.path = [[UIBezierPath alloc] init];
    self.path.lineJoinStyle = kCGLineJoinRound;
    self.path.lineCapStyle = kCGLineCapRound;
    ?
    self.path.lineWidth = 5;
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    //get the starting point
    CGPoint point = [[touches anyObject] locationInView:self];

    //move the path drawing cursor to the starting point
    [self.path moveToPoint:point];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    //get the current point
    CGPoint point = [[touches anyObject] locationInView:self];

    //add a new line segment to our path
    [self.path addLineToPoint:point];

    //redraw the view
    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect
{
    //draw path
    [[UIColor clearColor] setFill];
    [[UIColor redColor] setStroke];
    [self.path stroke];
}
@end