Rect的intersect 方法坑

￡神魔★判官ぃ 2022-01-11 10:29 342阅读 0赞

在使用android 做一些小游戏的时候，可能需要用到碰撞检测，而矩形的  
Rect.intersect(Rect a)方法可能被用到  
但是需要注意的是：这个方法是用来取两个矩形的相交部分，并设置给Rect

/** * If the rectangle specified by left,top,right,bottom intersects this * rectangle, return true and set this rectangle to that intersection, * otherwise return false and do not change this rectangle. No check is * performed to see if either rectangle is empty. Note: To just test for * intersection, use {@link #intersects(Rect, Rect)}. * * @param left The left side of the rectangle being intersected with this * rectangle * @param top The top of the rectangle being intersected with this rectangle * @param right The right side of the rectangle being intersected with this * rectangle. * @param bottom The bottom of the rectangle being intersected with this * rectangle. * @return true if the specified rectangle and this rectangle intersect * (and this rectangle is then set to that intersection) else * return false and do not change this rectangle. */
        @CheckResult
        public boolean intersect(int left, int top, int right, int bottom) { 
            if (this.left < right && left < this.right && this.top < bottom && top < this.bottom) { 
                if (this.left < left) this.left = left;
                if (this.top < top) this.top = top;
                if (this.right > right) this.right = right;
                if (this.bottom > bottom) this.bottom = bottom;
                return true;
            }
            return false;
        }

如果不知道这一点，在写游戏时会发现有时候碰撞检测没有作用，很是恼火。  
正确的应该使用这一个方式：

/** * Returns true if this rectangle intersects the specified rectangle. * In no event is this rectangle modified. No check is performed to see * if either rectangle is empty. To record the intersection, use intersect() * or setIntersect(). * * @param left The left side of the rectangle being tested for intersection * @param top The top of the rectangle being tested for intersection * @param right The right side of the rectangle being tested for * intersection * @param bottom The bottom of the rectangle being tested for intersection * @return true iff the specified rectangle intersects this rectangle. In * no event is this rectangle modified. */
        public boolean intersects(int left, int top, int right, int bottom) { 
            return this.left < right && left < this.right && this.top < bottom && top < this.bottom;
        }

**在调试时，可以将Rect 以红色画出来，方便观察。**