Premultiply alpha when converting to Xcursor

requirements.txt

@@ -1 +1,2 @@
+numpy
 Wand

setup.py

@@ -9,7 +9,7 @@ setup(
     name='win2xcur',
     version='0.0.3',
     packages=find_packages(),
-    install_requires=['Wand'],
+    install_requires=['numpy', 'Wand'],
 
     entry_points={
         'console_scripts': [

win2xcur/utils.py

@@ -0,0 +1,10 @@
+import numpy
+
+
+def premultiply_alpha(source: bytes) -> bytes:
+    buffer = numpy.frombuffer(source, dtype=numpy.uint8).astype(numpy.double)
+    alpha = buffer[3::4] / 255.0
+    buffer[0::4] *= alpha
+    buffer[1::4] *= alpha
+    buffer[2::4] *= alpha
+    return buffer.astype(numpy.uint8).tobytes()

win2xcur/writer/x11.py

@@ -4,6 +4,7 @@ from typing import List
 
 from win2xcur.cursor import CursorFrame
 from win2xcur.parser import XCursorParser
+from win2xcur.utils import premultiply_alpha
 
 
 def to_x11(frames: List[CursorFrame]) -> bytes:
@@ -15,7 +16,7 @@ def to_x11(frames: List[CursorFrame]) -> bytes:
             header = XCursorParser.IMAGE_HEADER.pack(
                 XCursorParser.IMAGE_HEADER.size,
                 XCursorParser.CHUNK_IMAGE,
-                cursor.image.width,
+                cursor.nominal,
                 1,
                 cursor.image.width,
                 cursor.image.height,
@@ -25,8 +26,8 @@ def to_x11(frames: List[CursorFrame]) -> bytes:
             )
             chunks.append((
                 XCursorParser.CHUNK_IMAGE,
-                cursor.image.width,
-                header + bytes(cursor.image.export_pixels(channel_map='BGRA'))
+                cursor.nominal,
+                header + premultiply_alpha(bytes(cursor.image.export_pixels(channel_map='BGRA')))
             ))
 
     header = XCursorParser.FILE_HEADER.pack(