consolidate single color sprites into one master file

_helpers.lua

@@ -160,11 +160,12 @@ function cellShapeFromBox(box)
 	return cells
 end
 
--- Which 16x16 cells of an image are non-empty, for multi-cell collision
--- shapes. LÖVE 11 no longer exposes Image:getData(), so inspect ImageData
--- directly instead of creating a GPU Image first.
-function getCellsFromSprite(spritePath)
-	local img = love.image.newImageData(spritePath)
+-- Which 16x16 cells of an ImageData are non-empty, for multi-cell collision
+-- shapes. `channel` ("red"/"green"/"blue") restricts the test to one colour
+-- gun: a single full-colour master now feeds all three copies, so each copy's
+-- collision shape comes from its own channel of the master (a cell with only
+-- red pixels blocks the red copy but not blue). nil = "any channel lit".
+local function cellsFromImageData(img, channel)
 	local w, h = img:getWidth(), img:getHeight()
 	local box = {w = w / 16, h = h / 16}
 	local boxCells = cellShapeFromBox(box)
@@ -182,7 +183,12 @@ function getCellsFromSprite(spritePath)
 		for i = startPixel.x, endPixel.x do
 			for j = startPixel.y, endPixel.y do
 				local r, g, b, a = img:getPixel(i, j)
-				if a > 0 and (r > 0 or g > 0 or b > 0) then
+				local lit
+				if channel == "red" then lit = r > 0
+				elseif channel == "green" then lit = g > 0
+				elseif channel == "blue" then lit = b > 0
+				else lit = r > 0 or g > 0 or b > 0 end
+				if a > 0 and lit then
 					empty = false
 				end
 			end
@@ -204,3 +210,20 @@ function getCellsFromSprite(spritePath)
 
 	return boxCells
 end
+
+-- LÖVE 11 no longer exposes Image:getData(), so inspect ImageData directly
+-- instead of creating a GPU Image first.
+function getCellsFromSprite(spritePath, channel)
+	return cellsFromImageData(love.image.newImageData(spritePath), channel)
+end
+
+-- Per-channel collision cell shapes for one full-colour master, loaded once.
+-- Returns { red = cells, green = cells, blue = cells }.
+function getChannelCells(spritePath)
+	local img = love.image.newImageData(spritePath)
+	return {
+		red   = cellsFromImageData(img, "red"),
+		green = cellsFromImageData(img, "green"),
+		blue  = cellsFromImageData(img, "blue"),
+	}
+end