ios - 让用户在 View 上绘画的技术是什么？

Question

iOS 下让用户在交互模式下绘制矩形、线段或其他简单形状的最佳实践是什么？假设我在用户第一次按下时捕捉到，那么当移动手指时我该怎么办？我应该捕捉当前坐标，设置一些内部点并为 View 调用 setNeedsDisplay 并绘制这两个点之间的线吗？

如果我想在已经有一堆形状的表面上绘画怎么办？把它们全部检查一遍再重新粉刷会不会花太多时间？

在Windows下我是用异或运算只绘制用户移动鼠标时需要的东西，iOS有什么技巧？非常感谢任何文章。

谢谢

Answer 1

试试这个

-(void) drawSquareFrom:(CGPoint)from to:(CGPoint)to {
    CGContextRef context = [self offscreenContext];
    CGRect draw , full = [self offscreenContextBounds];

    draw.origin = from;
    draw.size.width = to.x - from.x;
    draw.size.height = to.y - from.y;
    draw = CGRectStandardize( draw );

    [[UIColor redColor] setStroke];
    [[UIColor clearColor] setFill];
    CGContextClearRect( context , full );
    CGContextFillRect( context , draw );
    CGContextStrokeRectWithWidth( context , draw , 10 );
    [_imageView setNeedsDisplay];
}

-(CGContextRef) offscreenContext {
    if ( nil == myContext ) {
        size_t width = 400;
        size_t height = 300;
        CFMutableDataRef data = CFDataCreateMutable( NULL , width * height * 4 ); // 4 is bytes per pixel
        CGDataProviderRef provider = CGDataProviderCreateWithCFData( data );
        CGImageRef image = CGImageCreate( width , height , ... , provider , ... );
        CGBitmapContextRef context = CGBitmapContextCreate( CFDataGetMutableBytePtr( data ) , width , height , ... );
        CFRelease( data ); // retained by provider I think
        CGDataProviderRelease( provider ); // retained by image

        myImage = image;
        myContext = context;
        myContextFrame.origin = CGPointZero;
        myContextFrame.size.width = width;
        myContextFrame.size.height = height;
        _imageView.image = [UIImage imageWithCGImage:image];
    }

    return myContext;
}
-(CGRect) offscreenContextBounds {
    return myContextFrame;
}

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