[gegl] buffer: force nearest neighbor scaling for CMYK buffers

[Øyvind "pippin" Kolås <ok src gnome org>]

commit da209085ec13de57d9120771c8704c0993dd8e2c
Author: Øyvind Kolås <pippin gimp org>
Date:   Fri Nov 23 04:30:27 2018 +0100

    buffer: force nearest neighbor scaling for CMYK buffers
    
    This makes it possible to work with CMYK based buffers in the ui of
    the standalone GEGL binary at zoom factors <100%. The problem this
    works around is RGB assumptions in the 2x2 downscale and boxfilter
    algorithms for GeglBuffer.

 gegl/buffer/gegl-buffer-access.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)
---
diff --git a/gegl/buffer/gegl-buffer-access.c b/gegl/buffer/gegl-buffer-access.c
index 5d4599e37..e89007353 100644
--- a/gegl/buffer/gegl-buffer-access.c
+++ b/gegl/buffer/gegl-buffer-access.c
@@ -2015,6 +2015,7 @@ _gegl_buffer_get_unlocked (GeglBuffer          *buffer,
 
   g_return_if_fail (scale > 0.0f);
 
+
   if (format == NULL)
     format = buffer->soft_format;
 
@@ -2090,6 +2091,17 @@ _gegl_buffer_get_unlocked (GeglBuffer          *buffer,
     gint interpolation = (flags & GEGL_BUFFER_FILTER_ALL);
     gint    factor = 1;
 
+    /* XXX: temporary, force nearest neighbor filter for blit saling of
+       CMYK based buffers
+     */
+    const Babl *bfmt = gegl_buffer_get_format (buffer);
+    const char *babl_name = babl_get_name (bfmt);
+    if (babl_name[0] == 'c' ||
+        babl_name[0] == 'C')
+    {
+      interpolation = GEGL_BUFFER_FILTER_NEAREST;
+    }
+
     while (scale <= 0.5)
       {
         x1 = 0 < x1 ? x1 / 2 : (x1 - 1) / 2;