From b4fc7812e43d6b3e745cad5981cdabb8e3ac2aa0 Mon Sep 17 00:00:00 2001
From: Quantum <quantum2048@gmail.com>
Date: Sun, 4 Oct 2020 03:57:39 -0400
Subject: [PATCH] Premultiply alpha when converting to Xcursor

---
 requirements.txt       |  1 +
 setup.py               |  2 +-
 win2xcur/utils.py      | 10 ++++++++++
 win2xcur/writer/x11.py |  7 ++++---
 4 files changed, 16 insertions(+), 4 deletions(-)
 create mode 100644 win2xcur/utils.py

diff --git a/requirements.txt b/requirements.txt
index c7d00f5..c81de1e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1 +1,2 @@
+numpy
 Wand
diff --git a/setup.py b/setup.py
index 0d68d49..71c79c2 100644
--- a/setup.py
+++ b/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': [
diff --git a/win2xcur/utils.py b/win2xcur/utils.py
new file mode 100644
index 0000000..771288d
--- /dev/null
+++ b/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()
diff --git a/win2xcur/writer/x11.py b/win2xcur/writer/x11.py
index 3e68fb1..377fd9f 100644
--- a/win2xcur/writer/x11.py
+++ b/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(