如何从两个重叠的形状之间的差异边界找到CGPath

Question

它已很长时间我正在问一个关于SO的问题。请随意建议任何编辑或澄清

我想编写一个方法，它采用两个rects（主要和次要），如果他们rects相交，它会给我一个CGPath是在（Primary MINUS Secondary）

事情是这样的psudo代码： （假设rectTWO将永远非空，rectONE和wurectONE）

-(CGPathRef)clippedPathfromRect:(CGRect)rectONE clippingRect:(CGRect)rectTWO{   
     1. find -> rectFinal = rectONE MINUS rectTWO 
     2. create a path along the boundary of rectFinal (say finalPATH) 
     3. return rectFinal 
} 

Q2：如何将我在渲染这个形状之前或之后计算此文本的高度？

Answer 1

查看本答案https://stackoverflow.com/a/15228510/1717391。 您可以将rects添加到CGMutablePathRef，而不是将它们添加到NSMutableArray。

// helper function, returns the area between rect1 and rect2 along the edge 
static CGRect rectBetween(CGRect rect1, CGRect rect2, CGRect* remainder, CGRectEdge edge) 
{ 
    CGRect intersectedRect = CGRectIntersection(rect1, rect2); 
    if (CGRectIsEmpty(intersectedRect)) { 
     return CGRectNull; 
    } 

    CGRect rect3; 
    float chopAmount = 0; 
    switch (edge) { 
     case CGRectMaxYEdge: 
      chopAmount = rect1.size.height - (intersectedRect.origin.y - rect1.origin.y); 
      if (chopAmount > rect1.size.height) { chopAmount = rect1.size.height; } 
      break; 
     case CGRectMinYEdge: 
      chopAmount = rect1.size.height - (CGRectGetMaxY(rect1) - CGRectGetMaxY(intersectedRect)); 
      if (chopAmount > rect1.size.height) { chopAmount = rect1.size.height; } 
      break; 
     case CGRectMaxXEdge: 
      chopAmount = rect1.size.width - (intersectedRect.origin.x - rect1.origin.x); 
      if (chopAmount > rect1.size.width) { chopAmount = rect1.size.width; } 
      break; 
     case CGRectMinXEdge: 
      chopAmount = rect1.size.width - (CGRectGetMaxX(rect1) - CGRectGetMaxX(intersectedRect)); 
      if (chopAmount > rect1.size.width) { chopAmount = rect1.size.width; } 
      break; 
     default: 
      break; 
    } 
    CGRectDivide(rect1, remainder, &rect3, chopAmount, edge); 

    return rect3; 
} 

/** 
* create a path by substracting rect2 from rect1. 
* return NULL if rect1 is empty. 
* Caller have to released the resulting path 
*/ 
-(CGPathRef)createPathFromRect:(CGRect)rect1 clippingRect:(CGRect)rect2 
{ 
    if (CGRectIsEmpty(rect1)) { 
     return NULL; 
    } 
    CGMutablePathRef path = CGPathCreateMutable(); 

    CGRect intersectedRect = CGRectIntersection(rect1, rect2); 

    // No intersection 
    if (CGRectIsEmpty(intersectedRect)) { 
     CGPathAddRect(path, NULL, rect1); 
     return path; 
    } 

    CGRect remainder; 
    CGRect subtractedArea; 
    subtractedArea = rectBetween(rect1, intersectedRect, &remainder, CGRectMaxYEdge); 

    if (!CGRectIsEmpty(subtractedArea)) { 
     CGPathAddRect(path, NULL, subtractedArea); 
    } 

    subtractedArea = rectBetween(remainder, intersectedRect, &remainder, CGRectMinYEdge); 
    if (!CGRectIsEmpty(subtractedArea)) { 
     CGPathAddRect(path, NULL, subtractedArea); 
    } 

    subtractedArea = rectBetween(remainder, intersectedRect, &remainder, CGRectMaxXEdge); 
    if (!CGRectIsEmpty(subtractedArea)) { 
     CGPathAddRect(path, NULL, subtractedArea); 
    } 

    subtractedArea = rectBetween(remainder, intersectedRect, &remainder, CGRectMinXEdge); 
    if (!CGRectIsEmpty(subtractedArea)) { 
     CGPathAddRect(path, NULL, subtractedArea); 
    } 
    return path; 
} 

- (void)drawRect:(CGRect)rect 
{ 
    CGPathRef path = [self createPathFromRect:CGRectMake(10, 10, 200, 200) clippingRect:CGRectMake(210-40, 10, 40, 40)]; 
    if (path) 
    { 
     CGContextRef ctx = UIGraphicsGetCurrentContext(); 

     CGContextAddPath(ctx, path); 
     CGContextFillPath(ctx); 
     CFRelease(path); 
    } 
}