Optimize png files by reducing amount of colors to 255 + use oxipng m…

…ax compressions

Godot head have only 4 colors (counting transparent) but in non quantized form our
files use dozens of colors. Usually 500 and up to 1000 in one of them. All additional
colors are colors used to anti-alias the image. Lots of them are used in file only once
or twice. They are mostly indistingusahble between each other so they are safe to remove
When we reduce count of colors used by PNG file to 256, we can change it is mode to
"Indexed". In this mode palette is created (up to 256 colors) and all the pixels are
described not by using RGB(A) 3/4 bytes but by in index in palette 1 byte

Signed-off-by: Yevhen Babiichuk (DustDFG) <dfgdust@gmail.com>

misc/scripts/optimize_pngs.py

@@ -0,0 +1,52 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+# Requires ImageMagic 7+
+# Requires oxipng 9.1.3+
+
+import multiprocessing
+import subprocess
+import sys
+
+
+def quantize_image(filename, desired_colors):
+    """
+    Godot head have only 4 colors (counting transparent) but in non quantized form our
+    files use dozens of colors. Usually 500 and up to 1000 in one of them. All additional
+    colors are colors used to anti-alias the image. Lots of them are used in file only once
+    or twice. They are mostly indistingusahble between each other so they are safe to remove
+    When we reduce count of colors used by PNG file to 256, we can change it is mode to
+    "Indexed". In this mode palette is created (up to 256 colors) and all the pixels are
+    described not by using RGB(A) 3/4 bytes but by in index in palette 1 byte
+    """
+
+    # Retrieve amount of colors in the source image
+    command = ["magick", filename, "-format", "%k", "info:-"]
+    colors_count = int(subprocess.check_output(command))
+
+    # Reduce amount of colors in image 1 by 1 for each step
+    # It is much slower then reducing to desired amount of colors in one call
+    # and gives slightly worse results but produces output without any artifacts
+    for i in range(colors_count, desired_colors, -1):
+        command = ["magick", filename, "-dither", "None", "-colors", str(i), filename]
+        subprocess.run(command)
+
+
+def optimize_image(filename):
+    """
+    Uses `oxipng's` "max" compression to compress image even further
+    """
+    command = ["oxipng", "-t1", "-omax", "-q", "--zopfli", "--zi", "255", "--strip", "all", filename]
+    subprocess.run(command)
+
+
+def process_image(filename):
+    print(f"quantize_image: {filename}")
+    quantize_image(filename, 255)
+    print(f"optimize_image: {filename}")
+    optimize_image(filename)
+
+
+for i in range(1, len(sys.argv)):
+    process = multiprocessing.Process(target=process_image, args=[sys.argv[i]])
+    process.start()

tests/core/io/test_pck_packer.h

@@ -111,10 +111,10 @@ TEST_CASE("[PCKPacker] Pack a PCK file with some files and directories") {
 			err == OK,
 			"The generated non-empty PCK file should be opened successfully.");
 	CHECK_MESSAGE(
-			f->get_length() >= 18000,
+			f->get_length() >= 7000,
 			"The generated non-empty PCK file should be large enough to actually hold the contents specified above.");
 	CHECK_MESSAGE(
-			f->get_length() <= 27000,
+			f->get_length() <= 16000,
 			"The generated non-empty PCK file shouldn't be too large.");
 }
 } // namespace TestPCKPacker