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quad-quad interception

Started by cannonicus Jul 31, 2005 at 6:26 AM 2 replies 900+ views

Original Post

Jul 31, 2005 at 6:26 AM

Hello What is the fastest way of checking whether or not 2 quads are partially or completly overlapping each others in 2d? I guess one could check for line interception between all lines in the quads, but that would be 16 pretty costly computations. There should be a better way. Thanks in advance //Emil

oliii

270

oliii

Jul 31, 2005 at 9:28 AM

axis aligned? rotated?

cannonicus

Author

cannonicus

Jul 31, 2005 at 10:39 AM

one of them will always be axis aligned. the other one can be both rotated and scewed, but it will always be a quad.

I will use this to determin if a section of my 2d sidescroller terrain (the axis alined quad) is partially or completly inside the camera frustum (the skewed / rotated quad).

Zakwayda

1,120

Zakwayda

Jul 31, 2005 at 11:05 AM

Quote:
one of them will always be axis aligned. the other one can be both rotated and scewed, but it will always be a quad.

I will use this to determin if a section of my 2d sidescroller terrain (the axis alined quad) is partially or completly inside the camera frustum (the skewed / rotated quad).

As oliii will probably tell you as well, the separating axis theorem may be what you're looking for. In 2d, it can very quickly determine intersection or non-intersection between the shapes you mention.

However, for frustum culling of any sort, accuracy is often sacrificed for a slightly faster test. The standard AABB/frustum test culls the AABB against the planes of the frustum; this method can easily be adapted to 2d. It's basically the SAT, except that only the axes from the frustum planes are tested (resulting in the occasional false positive).

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