I touched on complex objects a bit in my previous collision detection post, and now I plan to talk more about them. Specifically, creating AABB‘s for complex objects, and drawing complex objects. You can find the example löve file here.
For the purposes of this post, I will define a complex object as a set of points that are connected in a specific order to create a shape. What do I mean by that? Something along the lines of this:
obj1 = {{10, 50},{20, 30},{30, 70},{70, 90},{20, 10},{70, 30}}
That would create this object:
Image broken, use link untill I fix it.
I have created 2 useful functions when dealing with complex objects. A function to draw a complex object, and a function to calculate the AABB of a complex object.
To draw a complex object, use this:
function drawcompobj(obj)
local ppx = obj[#obj][1]
local ppy = obj[#obj][2]
for i=1, #obj, 1 do
love.graphics.line(ppx, ppy, obj[i][1], obj[i][2])
ppx = obj[i][1]
ppy = obj[i][2]
end
end
Line by line, here’s what it does:
local ppx = obj[#obj][1]
local ppy = obj[#obj][2]
This sets ppx and ppy to the last coordinates in the array. these will be used as the starting point for each line it draws.
for i=1, #obj, 1 do
This loops through all of the coordinates in the array “obj.” We will draw a line for each one of these points.
love.graphics.line(ppx, ppy, obj[i][1], obj[i][2])
This draws a line from the previous point to the current point.
ppx = obj[i][1]
ppy = obj[i][2]
This sets the previous points to the current points.
I also have a way to get an AABB for a complex object. All this does is loops through all of the points, and gets the biggest and smallest X’s and Y’s. Here is the code:
function makeaabb(obj)
local minx, maxx, miny, maxy = obj[1][1], obj[1][1], obj[1][2], obj[1][2]
for i=1, #obj, 1 do
if obj[i][1] > maxx then maxx = obj[i][1] end
if obj[i][1] < minx then minx = obj[i][1] end
if obj[i][2] > maxy then maxy = obj[i][2] end
if obj[i][2] < miny then miny = obj[i][2] end
end
return {minx, miny, (maxx - minx), (maxy - miny)}
end
Here’s what it does, line by line:
local minx, maxx, miny, maxy = obj[1][1], obj[1][1], obj[1][2], obj[1][2]
This sets the default minimum and maximum values for X and Y.
for i=1, #obj, 1 do
This loops through all of the points in the complex object.
if obj[i][1] > maxx then maxx = obj[i][1] end
--Other similar stuff.
This sets the current highest x value to reflect it being compared to the previous highest x value. The other 3 lines do basically the same thing.
return {minx, miny, (maxx - minx), (maxy - miny)}
This returns the x, y, width and height of the complex object.
I hope you find these functions useful, or at least that you enjoyed reading about them.
Once again, you can find the example löve file here.
