[adwaita-icon-theme] anicursorgen: change the PNG compression use logic

[Jakub Steiner <jimmac src gnome org>]

commit a6275c6cb201eae72a8839777a3ee5d0113738b9
Author: Руслан Ижбулатов <lrn1986 gmail com>
Date:   Mon Aug 22 15:23:29 2016 +0000

    anicursorgen: change the PNG compression use logic
    
    Previously anicursorgen used PNG compression for any
    cursor frames larger than 48x48, for no immediately
    apparent reason, even to me (the author of anicursorgen).
    
    Tests on Windows 10 revealed that this logic is faulty:
    Windows 10 does not recognize PNG-compressed frames as valid, thus
    all Adwaita cursors are effectively 32x32 and 48x48 (all larger
    frames are ignored by the OS). This becomes obvious in HiDPI mode,
    where the OS will try to use larger cursor sizes.
    
    Windows 10 loads up uncompressed cursors just fine, and
    stock Windows 10 cursors are uncompressed. However, animated
    cursors with large numbers of frames, when stored without
    compression, are also ignored by the OS (probably due to their
    massive size).
    
    My hypothesis is that the correct way of using PNG compression
    is to compress or not compress *all* frames, not just the large ones.
    However, verifying that requires more tests (or asking MS developers).
    
    In the end i've settled enabling PNG compression for all frames
    in animated cursors and disabling PNG compression for all frames
    in non-animated cursors. This works for Adwaita, and that's all we
    really need.

 src/cursors/anicursorgen.py |   16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)
---
diff --git a/src/cursors/anicursorgen.py b/src/cursors/anicursorgen.py
index 425eb73..ad4b7c0 100755
--- a/src/cursors/anicursorgen.py
+++ b/src/cursors/anicursorgen.py
@@ -128,7 +128,7 @@ def frames_have_animation (frames):
 
   return False
 
-def make_cur (frames, args):
+def make_cur (frames, args, animated=False):
   buf = io.BytesIO ()
   buf.write (p ('<HHH', 0, 2, len (frames)))
   frame_offsets = []
@@ -165,7 +165,17 @@ def make_cur (frames, args):
         frame_png.close ()
         frame_png = shadowed
 
-    compressed = frame[0] > 48
+#   Windows 10 fails to read PNG-compressed cursors for some reason
+#   and the information about storing PNG-compressed cursors is
+#   sparse. This is why PNG compression is not used.
+#   Previously this was conditional on cursor size (<= 48 to be uncompressed).
+    compressed = False
+
+#   On the other hand, Windows 10 refuses to read very large
+#   uncompressed animated cursor files, but does accept
+#   PNG-compressed animated cursors for some reason. Go figure.
+    if animated:
+      compressed = True
 
     if compressed:
       write_png (buf, frame, frame_png)
@@ -264,7 +274,7 @@ def make_ani (frames, out, args):
 
   for frameset in framesets:
     buf.write (b'icon')
-    cur = make_cur (frameset, args)
+    cur = make_cur (frameset, args, animated=True)
     cur_size = cur.seek (0, io.SEEK_END)
     aligned_cur_size = cur_size
     #if cur_size % 4 != 0: