Huge improvement of apk file size thanks to Alayan.

The apk is now 20 MB smaller.

It may need some testing to see if there are no artifacts, but as far as I see there is no difference in quality.

android/generate_assets.sh

@@ -14,8 +14,8 @@
 # value greater than 0.
 # The CONVERT_TO_JPG variable enables converting all images that are safe to 
 # convert and keeps other images untouched.
-# The script needs imagemagick and ogg utils installed to use DECREASE_QUALITY
-# feature
+# The script needs imagemagick, pngquant and ogg utils installed in order to 
+# use DECREASE_QUALITY feature
 
 ################################################################################
 
@@ -203,7 +203,7 @@ convert_image()
     fi
 
     convert $SCALE_CMD $QUALITY_CMD "$FILE" "tmp.$FILE_TYPE"
-
+    
     if [ -s "tmp.$FILE_TYPE" ]; then
         SIZE_OLD=`du -k "$FILE" | cut -f1`
         SIZE_NEW=`du -k "tmp.$FILE_TYPE" | cut -f1`
@@ -259,6 +259,19 @@ convert_sound()
     rm -f tmp.wav tmp.ogg
 }
 
+optimize_png()
+{
+    FILE="$1"
+    echo "Optimize file: $FILE"
+
+    if [ ! -f "$FILE" ]; then
+        echo "  File doesn't exist."
+        return
+    fi
+    
+    pngquant --force --skip-if-larger --output "$FILE" -- "$FILE"
+}
+
 convert_to_jpg()
 {
     FILE="$1"
@@ -347,7 +360,7 @@ convert_to_jpg()
 convert_to_jpg_extract_b3dz()
 {
     FILE="$1"
-    echo "Convert file: $FILE"
+    echo "Convert file to jpg: $FILE"
 
     if [ ! -f "$FILE" ]; then
         echo "  File doesn't exist."
@@ -368,7 +381,7 @@ convert_to_jpg_extract_b3dz()
 convert_to_jpg_update_b3d()
 {
     FILE="$1"
-    echo "Convert file: $FILE"
+    echo "Update b3d file: $FILE"
 
     if [ ! -f "$1" ]; then
         echo "  File doesn't exist."
@@ -448,7 +461,7 @@ convert_to_jpg_update_b3d()
 convert_to_jpg_update_spm()
 {
     FILE="$1"
-    echo "Convert file: $FILE"
+    echo "Update spm file: $FILE"
 
     if [ ! -f "$1" ]; then
         echo "  File doesn't exist."
@@ -520,7 +533,7 @@ convert_to_jpg_update_spm()
 convert_to_jpg_update_xml()
 {
     FILE="$1"
-    echo "Convert file: $FILE"
+    echo "Update xml file: $FILE"
 
     if [ ! -f "$FILE" ]; then
         echo "  File doesn't exist."
@@ -568,6 +581,10 @@ if [ $CONVERT_TO_JPG -gt 0 ]; then
     fi
 fi
 
+if [ $DECREASE_QUALITY -gt 0 ]; then
+    find assets/data -iname "*.png" | while read f; do optimize_png "$f" "png"; done
+fi
+
 
 # Copy data directory
 echo "Copy data directory"