geometry.lua

local geometry = {}

-- http://en.wikipedia.org/wiki/Bresenham's_line_algorithm
-- rasterize a line and calls fun(x,y) for each point
function geometry.raster_line(x0,y0, x1,y1, fun)
	local dx = math.abs(x1-x0)
	local dy = math.abs(y1-y0) 
	if x0 < x1 then sx = 1 else sx = -1 end
	if y0 < y1 then sy = 1 else sy = -1 end
	local err = dx-dy

	while true do
		fun(x0,y0)
		if x0 == x1 and y0 == y1 then return end
		local e2 = 2*err
		if e2 > -dy then 
			err = err - dy
			x0 = x0 + sx
		end
		if x0 == x1 and y0 == y1 then 
			fun(x0,y0)
			return
		end
		if e2 < dx then 
			err = err + dx
			y0 = y0 + sy 
		end
	end
end


-- result = {x,y,numInLine,x,y,numLine,...} using table.insert
function geometry.raster_line_it(x0,y0, x1,y1, result)
	local numInLine = 0
	local dx = math.abs(x1-x0)
	local dy = math.abs(y1-y0) 
	if x0 < x1 then sx = 1 else sx = -1 end
	if y0 < y1 then sy = 1 else sy = -1 end
	local err = dx-dy

	while true do
		table.insert(result, x0)
		table.insert(result, y0)
		table.insert(result, numInLine)
		numInLine = numInLine + 1
		
		if x0 == x1 and y0 == y1 then return end
		local e2 = 2*err
		if e2 > -dy then 
			err = err - dy
			x0 = x0 + sx
		end
		if x0 == x1 and y0 == y1 then 
			table.insert(result, x0)
			table.insert(result, y0)
			table.insert(result, numInLine)
			numInLine = numInLine + 1
			return
		end
		if e2 < dx then 
			err = err + dx
			y0 = y0 + sy 
		end
	end
end
    
--~ geometry.raster_line(0,0, 10,0, function(x,y) print(x,y) end)
--~ print("---")
--~ for x,y in geometry.raster_line_it(0,0, 10,0) do print(x,y) end

return geometry