From db3eb121df6f89a3e4e77c2b8d031adb08b5b11f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jonas=20=C3=85dahl?= <jadahl@gmail.com>
Date: Wed, 17 Feb 2016 13:51:08 +0800
Subject: [PATCH 1/2] wayland: Pre-multiply alpha of custom cursor images

Since the Wayland SHM buffer format is implicitly premultiplied and the
GLFWimage pixels are defined to be non-premultiplied, we need to
convert the non-premultiplied pixels to premultiplied when filling the
buffer.
---
 src/internal.h  |  7 +++++++
 src/wl_window.c | 10 ++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/internal.h b/src/internal.h
index 2fe2aee47..2fc47b77f 100644
--- a/src/internal.h
+++ b/src/internal.h
@@ -233,6 +233,13 @@ typedef VkResult (APIENTRY * PFN_vkEnumerateInstanceExtensionProperties)(const c
         y = t;                    \
     }
 
+// Helper for non-premultiplied alpha to premultiplied alpha conversion
+static inline unsigned char _glfwMultiplyAlpha(unsigned char alpha,
+					       unsigned char value)
+{
+    return (unsigned char) ((value * (unsigned int) alpha) / 255);
+}
+
 
 //========================================================================
 // Platform-independent structures
diff --git a/src/wl_window.c b/src/wl_window.c
index 75aa912e4..db0752ecb 100644
--- a/src/wl_window.c
+++ b/src/wl_window.c
@@ -571,10 +571,12 @@ int _glfwPlatformCreateCursor(_GLFWcursor* cursor,
     unsigned char* target = data;
     for (i = 0;  i < image->width * image->height;  i++, source += 4)
     {
-        *target++ = source[2];
-        *target++ = source[1];
-        *target++ = source[0];
-        *target++ = source[3];
+        unsigned char alpha = source[3];
+
+        *target++ = _glfwMultiplyAlpha(alpha, source[2]);
+        *target++ = _glfwMultiplyAlpha(alpha, source[1]);
+        *target++ = _glfwMultiplyAlpha(alpha, source[0]);
+        *target++ = alpha;
     }
 
     cursor->wl.buffer =

From 0556601a29d6332ab27b9236ed84f4f9a8cd84f4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jonas=20=C3=85dahl?= <jadahl@gmail.com>
Date: Wed, 17 Feb 2016 13:53:57 +0800
Subject: [PATCH 2/2] x11: Premultiply alpha of custom cursor pixel

As with Wayland, X11 expects cursor pixels to have the alpha
premultiplied, so lets convert the non-premultiplied pixels to
premultiplied pixels.

Fixes issue 353.
---
 src/x11_init.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/x11_init.c b/src/x11_init.c
index e17a7170c..a521c993a 100644
--- a/src/x11_init.c
+++ b/src/x11_init.c
@@ -705,10 +705,12 @@ Cursor _glfwCreateCursorX11(const GLFWimage* image, int xhot, int yhot)
 
     for (i = 0;  i < image->width * image->height;  i++, target++, source += 4)
     {
-        *target = (source[3] << 24) |
-                  (source[0] << 16) |
-                  (source[1] <<  8) |
-                   source[2];
+        unsigned char alpha = source[3];
+
+        *target = (alpha << 24) |
+                  (_glfwMultiplyAlpha(alpha, source[0]) << 16) |
+                  (_glfwMultiplyAlpha(alpha, source[1]) <<  8) |
+                  _glfwMultiplyAlpha(alpha, source[2]);
     }
 
     cursor = XcursorImageLoadCursor(_glfw.x11.display, native);