Pixel Perfect mode for brush, eraser and lighten/darken (#222)

* Add pixel perfect mode for pencil and eraser

* Add Pixel Perfect for left and right tools

Co-authored-by: Dávid Gábor Bodor <david.gabor.bodr@gmail.com>

Scripts/Drawers.gd

@@ -0,0 +1,37 @@
+class Drawer:
+	func reset() -> void:
+		pass
+
+	func set_pixel(sprite: Image, pos: Vector2, new_color: Color) -> void:
+		pass
+
+
+class SimpleDrawer extends Drawer:
+	func reset() -> void:
+		pass
+
+	func set_pixel(sprite: Image, pos: Vector2, new_color: Color) -> void:
+		sprite.set_pixel(pos.x, pos.y, new_color)
+
+
+class PixelPerfectDrawer extends Drawer:
+	const neighbours = [Vector2(0, 1), Vector2(1, 0), Vector2(-1, 0), Vector2(0, -1)]
+	const corners = [Vector2(1, 1), Vector2(-1, -1), Vector2(-1, 1), Vector2(1, -1)]
+	var last_pixels = [null, null]
+
+	func reset():
+		last_pixels = [null, null]
+
+	func set_pixel(sprite: Image, pos: Vector2, new_color: Color) -> void:
+		last_pixels.push_back([pos, sprite.get_pixel(pos.x, pos.y)])
+		sprite.set_pixel(pos.x, pos.y, new_color)
+
+		var corner = last_pixels.pop_front()
+		var neighbour = last_pixels[0]
+
+		if corner == null or neighbour == null:
+			return
+
+		if pos - corner[0] in corners and pos - neighbour[0] in neighbours:
+			sprite.set_pixel(neighbour[0].x, neighbour[0].y, neighbour[1])
+			last_pixels[0] = corner