New feature request: Low resolution collision test flag

**AndyH** · 27th February 2012, 12:55 PM

I wonder if it would be possible to add a new flag to MMF specifically for iOS, Android etc called 'Low resolution collisions' along with a resolution factor setting?

In my game I tried placing in a rotating active object that was a specific shape that the player had to avoid. This works fine in Windows but on iOS, including iPad2/iTouch 4th Gen devices, the frame rate dropped to around 30FPS when the player and the rotated object were in proximity of each other. The rotating object is quite large, 256x256 but even making it smaller or breaking up into several active objects didn't help. I also tried after the recent optimisations but it was more or less the same.

I understand why performance takes this hit and I now have lots of smaller active objects that don't rotate themselves, but move in a rotating path around the centre point to make the same shapes I wanted. This method is nice and quick and achieves what I want but at the expense of how it looks.

I was wondering if some performance can be clawed back at the expense of accuracy by offering a low resolution collision option?

My thinking is if you choose to tick this option on an active object, any collision tests that involve this object would be done with a smaller collision mask resolution. For example, if I have a 256x256 object that is rotating, MMF by default has to create a mask in memory that is a minimum of 256x256 in size but most of the time will be bigger as the object rotates before testing if a collision has occurred. With the flag on and the resolution set to 1/2, the size comes down to upwards from 128x128 and the collision accuracy is still good. Even if the resolution factor is set to 1/4 the collision accuracy would still be pretty good but the size of the object for collision testing goes down to around the 64x64 size. It would mean that all objects that are affected by the low resolution test would need to be scaled down do the performance boost could be significant with an acceptable trade off on accuracy.

This would of course be an optional setting if it could be implemented.

**DistantJ** · 27th February 2012, 02:51 PM

Great idea. I'll second this.

**colej_uk** · 27th February 2012, 05:09 PM

Good idea, I've noticed that the collision masks can take up a lot of performance. I'm using the 'fine collision detection' disabled option in my more complex projects to compensate, but this would be a great middle option.

Even better, a customisable collision mask would be really cool. As in the ability to edit the collision mask in the same way as an alpha channel for example. At the moment, if you want an element in your game to only collide with a portion of an active object, you have to create multiple active objects- and then making multiple instances behave as one can be a bit of a nightmare. A customisable collision mask would help a lot with this. Maybe a mmf3 feature? I imagine this would be really useful in all runtimes.

**Olivier** · 27th February 2012, 05:56 PM

The custom collision mask is in the wishlist for MMF3. Let's hope that it will be implemented.

**Anders** · 28th February 2012, 07:34 AM

I am working on a further improvement to the collision system that should take far less CPU than now.
I don't think it will be in the next release, but it should hopefully be in the next