move saving flxsprite to png to SpriteTools

src/kiss_flixel/SpriteTools.hx

@@ -6,6 +6,11 @@ import flixel.FlxSprite;
 import flixel.util.FlxColor;
 import flixel.text.FlxText;
 import flixel.math.FlxPoint;
+import flash.display.PNGEncoderOptions;
+import flash.utils.ByteArray;
+#if sys
+import sys.io.File;
+#end
 
 enum RelativeCoordinate {
     // Negative means to count back from the far edge

src/kiss_flixel/SpriteTools.kiss

@@ -50,4 +50,12 @@
             (let [text (new FlxText 0 0 0 text size)]
                 (when color
                     (set text.color color))
-                (drawOnSprite text canvas pos)))))
+                (drawOnSprite text canvas pos)))))
+
+// Source: https://gist.github.com/miltoncandelero/0c452f832fa924bfdd60fe9d507bc581
+(#when sys
+    (function :Void saveToPNG [:FlxSprite sprite :String file]
+        (let [bitmapData sprite.pixels
+                &mut bytes (new ByteArray)]
+            (set bytes (bitmapData.encode bitmapData.rect (new PNGEncoderOptions true) bytes))
+                (File.saveBytes file bytes))))