Question

我不知道从哪里开始。显然CGRectIntersectsRect在这种情况下不起作用，你会明白为什么。

我有一个UIView的子类，里面有一个UIImageView，放在UIView的确切中心：

UIView before rotation

然后我旋转自定义UIView来维护内部UIImageView的框架，同时仍然能够执行CGAffineRotation。结果框架看起来像这样：

UIView after rotation

我需要阻止用户将这些UIImageViews交叉，但我不知道如何检查两个UIImageViews之间的交集，因为它们的框架不仅不适用于父UIView，而且它们在不影响它们的情况下旋转他们的框架。

我尝试的唯一结果是不成功的。

有什么想法吗？

Answer 1

以下算法可用于检查两个（旋转或其他转换）视图是否重叠：

使用[view convertPoint:point toView:nil]转换两个视图的4个边界点到公共坐标系（窗口坐标）。
转换后的点形成两个凸四边形。
使用SAT (Separating Axis Theorem)检查四边形是否相交。

这个：http://www.geometrictools.com/Documentation/MethodOfSeparatingAxes.pdf是包含伪代码的算法的另一种描述，可以通过谷歌搜索“分离轴定理”找到更多。

更新：我试图为“分离轴定理”创建一个Objective-C方法，这就是我得到的。到目前为止，我只进行了一些测试，所以我希望没有太多错误。

- (BOOL)convexPolygon:(CGPoint *)poly1 count:(int)count1 intersectsWith:(CGPoint *)poly2 count:(int)count2;

测试2个凸多边形是否相交。两个多边形都作为顶点的CGPoint数组给出。

- (BOOL)view:(UIView *)view1 intersectsWith:(UIView *)view2

如果两个任意视图相交，则进行测试（如上所述）。

实现：

- (void)projectionOfPolygon:(CGPoint *)poly count:(int)count onto:(CGPoint)perp min:(CGFloat *)minp max:(CGFloat *)maxp
{
    CGFloat minproj = MAXFLOAT;
    CGFloat maxproj = -MAXFLOAT;
    for (int j = 0; j < count; j++) {
        CGFloat proj = poly[j].x * perp.x + poly[j].y * perp.y;
        if (proj > maxproj)
            maxproj = proj;
        if (proj < minproj)
            minproj = proj;
    }
    *minp = minproj;
    *maxp = maxproj;
}

-(BOOL)convexPolygon:(CGPoint *)poly1 count:(int)count1 intersectsWith:(CGPoint *)poly2 count:(int)count2
{
    for (int i = 0; i < count1; i++) {
        // Perpendicular vector for one edge of poly1:
        CGPoint p1 = poly1[i];
        CGPoint p2 = poly1[(i+1) % count1];
        CGPoint perp = CGPointMake(- (p2.y - p1.y), p2.x - p1.x);

        // Projection intervals of poly1, poly2 onto perpendicular vector:
        CGFloat minp1, maxp1, minp2, maxp2;
        [self projectionOfPolygon:poly1 count:count1 onto:perp min:&minp1 max:&maxp1];
        [self projectionOfPolygon:poly2 count:count1 onto:perp min:&minp2 max:&maxp2];

        // If projections do not overlap then we have a "separating axis"
        // which means that the polygons do not intersect:
        if (maxp1 < minp2 || maxp2 < minp1)
            return NO;
    }

    // And now the other way around with edges from poly2:
    for (int i = 0; i < count2; i++) {
        CGPoint p1 = poly2[i];
        CGPoint p2 = poly2[(i+1) % count2];
        CGPoint perp = CGPointMake(- (p2.y - p1.y), p2.x - p1.x);

        CGFloat minp1, maxp1, minp2, maxp2;
        [self projectionOfPolygon:poly1 count:count1 onto:perp min:&minp1 max:&maxp1];
        [self projectionOfPolygon:poly2 count:count1 onto:perp min:&minp2 max:&maxp2];

        if (maxp1 < minp2 || maxp2 < minp1)
            return NO;
    }

    // No separating axis found, then the polygons must intersect:
    return YES;
}

- (BOOL)view:(UIView *)view1 intersectsWith:(UIView *)view2
{
    CGPoint poly1[4];
    CGRect bounds1 = view1.bounds;
    poly1[0] = [view1 convertPoint:bounds1.origin toView:nil];
    poly1[1] = [view1 convertPoint:CGPointMake(bounds1.origin.x + bounds1.size.width, bounds1.origin.y) toView:nil];
    poly1[2] = [view1 convertPoint:CGPointMake(bounds1.origin.x + bounds1.size.width, bounds1.origin.y + bounds1.size.height) toView:nil];
    poly1[3] = [view1 convertPoint:CGPointMake(bounds1.origin.x, bounds1.origin.y + bounds1.size.height) toView:nil];

    CGPoint poly2[4];
    CGRect bounds2 = view2.bounds;
    poly2[0] = [view2 convertPoint:bounds2.origin toView:nil];
    poly2[1] = [view2 convertPoint:CGPointMake(bounds2.origin.x + bounds2.size.width, bounds2.origin.y) toView:nil];
    poly2[2] = [view2 convertPoint:CGPointMake(bounds2.origin.x + bounds2.size.width, bounds2.origin.y + bounds2.size.height) toView:nil];
    poly2[3] = [view2 convertPoint:CGPointMake(bounds2.origin.x, bounds2.origin.y + bounds2.size.height) toView:nil];

    return [self convexPolygon:poly1 count:4 intersectsWith:poly2 count:4];
}

Objective-C检查旋转的UIViews的子视图是否相交？

1 个答案: