Hello, I've been advised to submit my patch adding support for drawing
coloured stipples on NS Emacs here:

From 87c143b1b77ae02a08b9e1bbe27da57859e28a8d Mon Sep 17 00:00:00 2001
From: Ben Simms <ben@bensimms.moe>
Date: Fri, 20 Sep 2024 09:50:47 +0200
Subject: [PATCH] Support drawing coloured stipples

This makes use of CoreGraphics, while this works fine on macos systems,
I'm unsure how to test this on a GNUStep or other supported NS
implementation.
---
 src/nsimage.m | 17 +++++++++++++---
 src/nsterm.h  |  4 ++--
 src/nsterm.m  | 56 +++++++++++++++++++++++++++++++++++++++++++++------
 3 files changed, 66 insertions(+), 11 deletions(-)

diff --git a/src/nsimage.m b/src/nsimage.m
index ee72d6e0ea..100af5c3e9 100644
--- a/src/nsimage.m
+++ b/src/nsimage.m
@@ -28,6 +28,7 @@ Updated by Christian Limpach (chris@nice.ch)
 /* This should be the first include, as it may set up #defines affecting
    interpretation of even the system includes.  */
 #include <config.h>
+#include <CoreGraphics/CoreGraphics.h>

 #include "lisp.h"
 #include "dispextern.h"
@@ -510,10 +511,20 @@ - (void) setAlphaAtX: (int) x Y: (int) y to:
(unsigned char) a
 }

 /* Returns a pattern color, which is cached here.  */
-- (NSColor *)stippleMask
+- (CGImageRef)stippleMask
 {
-  if (stippleMask == nil)
-      stippleMask = [[NSColor colorWithPatternImage: self] retain];
+  if (stippleMask == nil) {
+    CGDataProviderRef provider = CGDataProviderCreateWithData (NULL,
[bmRep bitmapData],
+                                                             [self
sizeInBytes], NULL);
+    id mask = (id)CGImageMaskCreate(
+                                          [self size].width,
+                                          [self size].height,
+                                          8, 8, [self size].width,
+                                          provider, NULL, 0);
+
+    CGDataProviderRelease(provider);
+    stippleMask = (CGImageRef)[mask retain];
+  }
   return stippleMask;
 }

diff --git a/src/nsterm.h b/src/nsterm.h
index 3a713f8e8c..7ec851966f 100644
--- a/src/nsterm.h
+++ b/src/nsterm.h
@@ -670,7 +670,7 @@ #define NSTRACE_UNSILENCE()
 {
   NSBitmapImageRep *bmRep; /* used for accessing pixel data */
   unsigned char *pixmapData[5]; /* shortcut to access pixel data */
-  NSColor *stippleMask;
+  CGImageRef stippleMask;
 @public
   NSAffineTransform *transform;
   BOOL smoothing;
@@ -687,7 +687,7 @@ #define NSTRACE_UNSILENCE()
                green: (unsigned char)g blue: (unsigned char)b
               alpha:(unsigned char)a;
 - (void)setAlphaAtX: (int)x Y: (int)y to: (unsigned char)a;
-- (NSColor *)stippleMask;
+- (CGImageRef)stippleMask;
 - (Lisp_Object)getMetadata;
 - (BOOL)setFrame: (unsigned int) index;
 - (void)setTransform: (double[3][3]) m;
diff --git a/src/nsterm.m b/src/nsterm.m
index 794630de1c..84084f12a4 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -3826,9 +3826,28 @@ Function modeled after x_draw_glyph_string_box ().

       if (s->stippled_p)
  {
+  [[NSColor colorWithUnsignedLong:face->background] set];
+  r = NSMakeRect (s->x, s->y + box_line_width,
+  s->background_width,
+  s->height - 2 * box_line_width);
+  NSRectFill (r);
+  s->background_filled_p = 1;
   struct ns_display_info *dpyinfo = FRAME_DISPLAY_INFO (s->f);
-  [[dpyinfo->bitmaps[face->stipple-1].img stippleMask] set];
-  goto fill;
+  CGImageRef mask =
+    [dpyinfo->bitmaps[face->stipple - 1].img stippleMask];
+  CGRect bounds = CGRectMake (s->x, s->y + box_line_width,
+      s->background_width,
+      s->height - 2 * box_line_width);
+  NSGraphicsContext *ctx = [NSGraphicsContext currentContext];
+  [ctx saveGraphicsState];
+  CGContextRef context = [ctx CGContext];
+  CGContextClipToRect (context, bounds);
+  CGContextScaleCTM (context, 1, -1);
+  [[NSColor colorWithUnsignedLong:face->foreground] set];
+  CGRect imageSize = CGRectMake (0, 0, CGImageGetWidth (mask),
+ CGImageGetHeight (mask));
+  CGContextDrawTiledImage (context, imageSize, mask);
+  [[NSGraphicsContext currentContext] restoreGraphicsState];
  }
       else if (FONT_HEIGHT (s->font) < s->height - 2 * box_line_width
        /* When xdisp.c ignores FONT_HEIGHT, we cannot trust font
@@ -3851,7 +3870,6 @@ Function modeled after x_draw_glyph_string_box ().
   else
     [FRAME_CURSOR_COLOR (s->f) set];

- fill:
   r = NSMakeRect (s->x, s->y + box_line_width,
   s->background_width,
   s->height - 2 * box_line_width);
@@ -4175,10 +4193,36 @@ Function modeled after x_draw_glyph_string_box ().
   dpyinfo = FRAME_DISPLAY_INFO (s->f);
   if (s->hl == DRAW_CURSOR)
     [FRAME_CURSOR_COLOR (s->f) set];
-  else if (s->stippled_p)
-    [[dpyinfo->bitmaps[s->face->stipple - 1].img stippleMask] set];
-  else
+  else if (s->stippled_p) {
+      [[NSColor colorWithUnsignedLong:s->face->background]
+ set];
+      NSRectFill (
+ NSMakeRect (x, s->y, background_width, s->height));
+      CGImageRef mask =
+ [dpyinfo->bitmaps[s->face->stipple - 1]
+    .img stippleMask];
+      CGRect bounds
+ = CGRectMake (s->x, s->y, s->background_width,
+      s->height);
+      NSGraphicsContext *ctx =
+ [NSGraphicsContext currentContext];
+      [ctx saveGraphicsState];
+      CGContextRef context = [ctx CGContext];
+      CGContextClipToRect(context, bounds);
+      CGContextScaleCTM (context, 1, -1);
+      [[NSColor colorWithUnsignedLong:s->face->foreground]
+ set];
+      CGRect imageSize
+ = CGRectMake (0, 0, CGImageGetWidth (mask),
+      CGImageGetHeight (mask));
+      CGContextDrawTiledImage (context, imageSize, mask);
+      [[NSGraphicsContext currentContext]
+ restoreGraphicsState];
+    }
+  else {
     [[NSColor colorWithUnsignedLong: s->face->background] set];
+    NSRectFill (NSMakeRect (x, s->y, background_width, s->height));
+  }

   NSRectFill (NSMakeRect (x, s->y, background_width, s->height));
  }
-- 
2.45.2