Generic raycasting through grid (Digital Differential Algorithm)

ray.lua

-- v1.0
local floor = math.floor

-- cell_width being the width of the cell along an axis e.g. x/y axis
local initRayData = function(cell_width,i,f)
	local d       = f-i
	local cell_i  = floor(i/cell_width)
	
	local dRatio,Delta,Step,Start
	if d > 0 then 
		Step   = 1 
		Start  = 1 
	else 
		Step   = -1 
		Start  = 0
	end
	-- zero hack for when 0/0
	if d == 0 then
		dRatio = math.huge
		Delta  = 0
	else
		dRatio  = (cell_width*(cell_i+Start)-i)/d
		Delta   = cell_width/d * Step
	end
	
	return dRatio,Delta,Step,cell_i
end

local getState = function(width,height,x,y,x2,y2)
	local s = {minRatio = 0}
	s.dxRatio,s.xDelta,s.xStep,s.gx = initRayData(width,x,x2)
	s.dyRatio,s.yDelta,s.yStep,s.gy = initRayData(height,y,y2)
	return s
end

local next = function(s)
	local gx,gy = s.gx,s.gy
	-- if the next voxel is within range then go to the next voxel
	if s.minRatio <= 1 then
		if s.dxRatio < s.dyRatio then
			s.minRatio= s.dxRatio
			s.dxRatio = s.dxRatio + s.xDelta
			s.gx      = s.gx + s.xStep
		else
			s.minRatio= s.dyRatio
			s.dyRatio = s.dyRatio + s.yDelta
			s.gy      = s.gy + s.yStep
		end
		return gx,gy
	end
end

local iterate = function(width,height,x,y,x2,y2)
	return next,getState(width,height,x,y,x2,y2)
end

return 
{
	next      = next,
	getState  = getState,
	iterate   = iterate,
}

Thread: https://love2d.org/forums/viewtopic.php?f=5&t=11730