Print Page - Grabbing Index with Coordinates?

Title: Grabbing Index with Coordinates?
Post by: G_G on April 09, 2011, 01:09:16 pm

Alright so heres this icon set.

Spoiler: Show

The index to grab icons starts at 0 and in the upper left corner and goes to the right adding one to the index. Now I'm trying to make it so when the user clicks on the icon set it'll grab that icon. I'm just having troubles getting an index using the x and y locations of the mouse.

So x is 24 and y is 24. The icon that should be selected would be the 2nd icon on the second row. The index would turn out to be 17. How do I accomplish this? I know its just a simple equation but I can't seem to figure it out.

Title: Re: Grabbing Index with Coordinates?
Post by: winkio on April 09, 2011, 01:12:33 pm


int index
x = (index % 16) * 24
y = (index / 16) * 24

EDIT: oh, you want to do it backwards too:


int x, y
index = (y / 24) * 16 + x / 24

Title: Re: Grabbing Index with Coordinates?
Post by: G_G on April 09, 2011, 01:29:55 pm

Thanks winkio. I knew how to get the x and y from an index, just wasn't sure how to reverse it. Thanks :3

Title: Re: Grabbing Index with Coordinates?
Post by: winkio on April 09, 2011, 01:34:47 pm

I mean, if you have the first one, it's easy to solve for the second one, it's just algebra.
Also, since x and y are ints, you don't have to round them to the nearest 24x24 index, so the position (28, 35) would still return index 17. Pretty useful.

Title: Re: Grabbing Index with Coordinates?
Post by: Blizzard on April 09, 2011, 01:42:05 pm

This is one of the great things about integer arithmetic.

Chaos Project

Game Development => General Discussion => Topic started by: G_G on April 09, 2011, 01:09:16 pm