{"id":56,"date":"2012-08-03T11:59:48","date_gmt":"2012-08-03T16:59:48","guid":{"rendered":"http:\/\/www.playwithlua.com\/?p=56"},"modified":"2012-08-03T11:59:48","modified_gmt":"2012-08-03T16:59:48","slug":"points","status":"publish","type":"post","link":"http:\/\/www.playwithlua.com\/?p=56","title":{"rendered":"Points"},"content":{"rendered":"

I’ve been doing a lot of writing games in Löve. Writing games usually involves a lot of code that deals with positions and directions and velocities. To make this easier to write, I made a little library to represent a point in a two-dimensional coordinate space.<\/p>\n

This is a little different for posts here because I’m not going to go into the code too much; I’m just going to show some examples of how to use it. Really, the motivation here is that I want to make other posts with code examples that use this, and so I should document it. Next up, my “map” class.<\/p>\n

If you just want the code, the canonical repository is here<\/a>.<\/p>\n

<\/p>\n

Basic stuff<\/h2>\n

First, the library is in one file, that I call point.lua<\/code>. You can require it like any other module:<\/p>\n\n

local<\/span> point =<\/span> require<\/span>(<\/span>'point'<\/span>)<\/span><\/pre><\/div><\/div><\/div>\n\n
To create a point, you can call point.new<\/code>:<\/p>\n\n
p =<\/span> point.<\/span>new(<\/span>2<\/span>,<\/span> 3<\/span>)<\/span><\/pre><\/div><\/div><\/div>\n\n
Or use the shorthand of just calling the module:<\/p>\n\n
p =<\/span> point(<\/span>2<\/span>,<\/span> 3<\/span>)<\/span><\/pre><\/div><\/div><\/div>\n\n
Getting the components of the point is easy enough:<\/p>\n\n
p =<\/span> point(<\/span>2<\/span>,<\/span> 3<\/span>)<\/span>\n \nassert<\/span>(<\/span>p.<\/span>x ==<\/span> 2<\/span>)<\/span>\nassert<\/span>(<\/span>p.<\/span>y ==<\/span> 3<\/span>)<\/span><\/pre><\/div><\/div><\/div>\n\n
It also intelligently handles equality:<\/p>\n\n
p =<\/span> point(<\/span>2<\/span>,<\/span> 3<\/span>)<\/span>\np2 =<\/span> point(<\/span>2<\/span>,<\/span> 3<\/span>)<\/span>\n \nassert<\/span>(<\/span>p ==<\/span> p2)<\/span><\/pre><\/div><\/div><\/div>\n\n
And can be converted to a string:<\/p>\n\n
p =<\/span> point(<\/span>2<\/span>,<\/span> 3<\/span>)<\/span>\n \nassert<\/span>(<\/span> tostring<\/span>(<\/span>p)<\/span> ==<\/span> "(2, 3)"<\/span> )<\/span>\nprint<\/span>(<\/span>p)<\/span> -- prints (2, 3)<\/span><\/pre><\/div><\/div><\/div>\n\n
Arithmetic<\/h2>\n
Points can be added and subtracted:<\/p>\n\n
p =<\/span> point(<\/span>2<\/span>,<\/span> 3<\/span>)<\/span>\np2 =<\/span> point(<\/span>1<\/span>,<\/span> 1<\/span>)<\/span>\n \nassert<\/span>(<\/span> p +<\/span> p2 ==<\/span> point(<\/span>3<\/span>,<\/span> 4<\/span>)<\/span> )<\/span>\nassert<\/span>(<\/span> p2 -<\/span> p ==<\/span> point(<\/span>-<\/span>1<\/span>,<\/span> -<\/span>2<\/span>)<\/span> )<\/span><\/pre><\/div><\/div><\/div>\n\n
They can also be multiplied, by points or numbers:<\/p>\n\n
p =<\/span> point(<\/span>2<\/span>,<\/span> 3<\/span>)<\/span>\n \nassert<\/span>(<\/span> p *<\/span> point(<\/span>-<\/span>1<\/span>,<\/span> 0<\/span>)<\/span> ==<\/span> point(<\/span>-<\/span>2<\/span>,<\/span> 0<\/span>)<\/span> )<\/span>\nassert<\/span>(<\/span> p *<\/span> 2<\/span> ==<\/span> point(<\/span>4<\/span>,<\/span> 6<\/span>)<\/span> )<\/span><\/pre><\/div><\/div><\/div>\n\n
Features for tile maps<\/h2>\n
Points whose components are both integers, like coordinates on a tile map, have some useful methods:<\/p>\n
adjacent<\/h3>\n
Returns whether two points are next to each other, not counting diagonals:<\/p>\n\n
p =<\/span> point(<\/span>2<\/span>,<\/span> 3<\/span>)<\/span>\nassert<\/span>(<\/span> p:<\/span>adjacent(<\/span>point(<\/span>2<\/span>,<\/span> 2<\/span>)<\/span>)<\/span> )<\/span>\nassert<\/span>(<\/span> not<\/span> p:<\/span>adjacent(<\/span>p)<\/span> )<\/span><\/pre><\/div><\/div><\/div>\n\n
ortho<\/h3>\n
Returns whether two points are on the same row or column:<\/p>\n\n
p =<\/span> point(<\/span>2<\/span>,<\/span> 3<\/span>)<\/span>\nassert<\/span>(<\/span> p:<\/span>ortho(<\/span>point(<\/span>2<\/span>,<\/span> 2<\/span>)<\/span>)<\/span> )<\/span>\nassert<\/span>(<\/span> not<\/span> p:<\/span>ortho(<\/span>point(<\/span>0<\/span>,<\/span> 0<\/span>)<\/span>)<\/span> )<\/span><\/pre><\/div><\/div><\/div>\n\n
toward<\/h3>\n
If two points are on the same row or column, returns a new point representing the direction you have to move to get closer to the second one. For example, for these three points:<\/p>\n
\r\n..........\r\n..........\r\n...A...B..\r\n..........\r\n..........\r\n..........\r\n...C......\r\n..........\r\n..........\r\n\r\n<\/pre>\n\n
a:<\/span>toward(<\/span>b)<\/span> -- returns point(1, 0)<\/span>\nb:<\/span>toward(<\/span>a)<\/span> -- returns point(-1, 0)<\/span>\n \na:<\/span>toward(<\/span>c)<\/span> -- returns point(0, 1) assuming +y is downward<\/span>\n \nb:<\/span>toward(<\/span>c)<\/span> -- raises an error!<\/span><\/pre><\/div><\/div><\/div>\n\n
Comparisons<\/h2>\n
Comparing two points means comparing both components:<\/p>\n\n
p =<\/span> point(<\/span>2<\/span>,<\/span> 3<\/span>)<\/span>\np2 =<\/span> point(<\/span>5<\/span>,<\/span> 6<\/span>)<\/span>\np3 =<\/span> point(<\/span>2<\/span>,<\/span> 4<\/span>)<\/span>\n \nassert<\/span>(<\/span> p <<\/span> p2 )<\/span>\nassert<\/span>(<\/span> p <=<\/span> p3 )<\/span>\nassert<\/span>(<\/span> p2 ><\/span> p3 )<\/span><\/pre><\/div><\/div><\/div>\n\n
Other things<\/h2>\n
There are a few constants defined:<\/p>\n\n
assert<\/span>(<\/span> point.<\/span>up ==<\/span> point(<\/span>0<\/span>,<\/span> -<\/span>1<\/span>)<\/span> )<\/span>\nassert<\/span>(<\/span> point.<\/span>east ==<\/span> point(<\/span>1<\/span>,<\/span> 0<\/span>)<\/span> )<\/span><\/pre><\/div><\/div><\/div>\n\n
Up, down, left, right, north, south, east, and west are all there, and they assume that going downward means an increase in Y (which is how Löve coordinates work).<\/p>\n
I’ll probably be making changes and additions to the class periodically as I need things. The canonical repository is here<\/a> and I’ll try to update this post when I add stuff.<\/p>\n","protected":false},"excerpt":{"rendered":"
I’ve been doing a lot of writing games in Löve. Writing games usually involves a lot of code that deals with positions and directions and velocities. To make this easier to write, I made a little library to represent a point in a two-dimensional coordinate space. This is a little different for posts here because […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"_links":{"self":[{"href":"http:\/\/www.playwithlua.com\/index.php?rest_route=\/wp\/v2\/posts\/56"}],"collection":[{"href":"http:\/\/www.playwithlua.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.playwithlua.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.playwithlua.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.playwithlua.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=56"}],"version-history":[{"count":0,"href":"http:\/\/www.playwithlua.com\/index.php?rest_route=\/wp\/v2\/posts\/56\/revisions"}],"wp:attachment":[{"href":"http:\/\/www.playwithlua.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=56"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.playwithlua.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=56"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.playwithlua.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=56"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}