Maths question: proximity to centre of ellipse

Tim Lloyd

I've done some forum and google searching, and found some info that I couldn't quite wrap my head around.

If I have an ellipse drawn into [lcd ], how do I go about calculating its centre point, and the mouse proximity to this point, and test for a mouse-over of just the ellipse, not including its "surrounding rectangle".

All the calculations I found made vague sense, but it's been such a long time since I had to do any that the solution is escaping me! Is this a situation where [cartopol ] might help?

Max Patch

Copy patch and select New From Clipboard in Max.

Cheers, I know this isn't going to be remotely complex for many people :P

jvkr

The equation for a circle is x*x+y*y=1 y=√(1-x*x). In the case of an oval this becomes y=√(1-ax*ax). If you work on a mac, there's the beautiful application Grapher part of the utilities to get a visual representation. What you need to do is to find the solution of where the equation of your oval and a line through it's centre point and the mouse meet and to divided the distance of the one by the other. Does this help?

Tim Lloyd

I'm not 100% sure I'm following you, but I'll give it a go in a couple days when I have some more time.

I need to get myself an A-level maths book to jog my memory, then I'll be ok!

Thanks for the help and the tip about grapher, I'll check that out as well!

Tim Lloyd

Thanks for the replies.

Still not following the maths behind how this works....

@ pizza_olives, how do you calculate the values (175 and 125) that are in the [offset ] subpatch?

It's probably because I'm really mathematically dense, but I can't work out how those numbers relate to the co-ordinates used to draw the oval into lcd in the first place.

cheers

-Tim

Tim Lloyd

Ok, I've got that mostly working. There are a couple issues though, probably to do with how I've hooked it all up. I'll go back through your patch and check it.

Max Patch

Copy patch and select New From Clipboard in Max.

Here is a patch to demonstrate the issues:

Thanks for the maths help!

Tim Lloyd

Haha don't worry, my uni course only involves max/msp for learning about audio synthesis, not exploring the intriguing world of creating interfaces :( This is just something I've been messing with the past few days when I should have been doing my other work!

I had tried swapping long/large but without adding 2/pi to the angle, so it didn't help............I really do need to get back into maths........Your A

Thanks loads for clearing up how this works. It's going to be fun to play around with!