[gimp/gimp-2-10] Issue #189 - Store channel colors when saving as PSD

[Ell <ell src gnome org>]

commit 3424a0844c871494b90e4b4d0601988cf8bedef6
Author: Ell <ell_se yahoo com>
Date:   Sun Apr 26 22:56:11 2020 +0300

    Issue #189 - Store channel colors when saving as PSD
    
    In file-psd, write a DisplayInfo image resource with the color/
    opacity of all channels.

 plug-ins/file-psd/psd-save.c | 62 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)
---
diff --git a/plug-ins/file-psd/psd-save.c b/plug-ins/file-psd/psd-save.c
index ce92977bef..f418c22d59 100644
--- a/plug-ins/file-psd/psd-save.c
+++ b/plug-ins/file-psd/psd-save.c
@@ -699,6 +699,68 @@ save_resources (FILE   *fd,
         write_gchar (fd, 0, "pad byte");
     }
 
+  /* --------------- Write Channel properties --------------- */
+
+  if (PSDImageData.nChannels > 0 ||
+      gimp_drawable_has_alpha (PSDImageData.merged_layer))
+    {
+      xfwrite (fd, "8BIM", 4, "imageresources signature");
+      write_gint16 (fd, 0x0435, "0x0435 Id"); /* 1077 */
+      /* write_pascalstring (fd, Name, "Id name"); */
+      write_gint16 (fd, 0, "Id name"); /* Set to null string (two zeros) */
+      write_gint32 (fd,
+                    4  +
+                    13 * (gimp_drawable_has_alpha (PSDImageData.merged_layer) +
+                          PSDImageData.nChannels),
+                    "0x0435 resource size");
+
+      /* The function of the first 4 bytes is unclear. As per
+       * load_resource_1077() in psd-image-res-load.c, it seems to be a version
+       * number that is always one.
+       */
+      write_gint32 (fd, 1, "0x0435 version");
+
+      /* Write all channel properties */
+
+      #define DOUBLE_TO_INT16(x) ROUND (SAFE_CLAMP (x, 0.0, 1.0) * 0xffff)
+
+      /* if the merged_image contains transparency, write its properties first */
+      if (gimp_drawable_has_alpha (PSDImageData.merged_layer))
+        {
+          write_gint16 (fd, PSD_CS_RGB, "channel color space");
+          write_gint16 (fd, DOUBLE_TO_INT16 (1.0), "channel color r");
+          write_gint16 (fd, DOUBLE_TO_INT16 (0.0), "channel color g");
+          write_gint16 (fd, DOUBLE_TO_INT16 (0.0), "channel color b");
+          write_gint16 (fd, 0,                     "channel color padding");
+          write_gint16 (fd, 100,                   "channel opacity");
+          write_gchar  (fd, 1,                     "channel mode");
+        }
+
+      for (i = PSDImageData.nChannels - 1; i >= 0; i--)
+        {
+          GimpRGB color;
+          gdouble opacity;
+
+          gimp_channel_get_color (PSDImageData.lChannels[i], &color);
+          opacity = gimp_channel_get_opacity (PSDImageData.lChannels[i]);
+
+          write_gint16 (fd, PSD_CS_RGB,                "channel color space");
+          write_gint16 (fd, DOUBLE_TO_INT16 (color.r), "channel color r");
+          write_gint16 (fd, DOUBLE_TO_INT16 (color.g), "channel color g");
+          write_gint16 (fd, DOUBLE_TO_INT16 (color.b), "channel color b");
+          write_gint16 (fd, 0,                         "channel color padding");
+          write_gint16 (fd, ROUND (opacity),           "channel opacity");
+          write_gchar  (fd, 1,                         "channel mode");
+        }
+
+      #undef DOUBLE_TO_INT16
+
+      /* Pad if length is odd */
+
+      if (ftell (fd) & 1)
+        write_gchar (fd, 0, "pad byte");
+    }
+
   /* --------------- Write Guides --------------- */
   if (gimp_image_find_next_guide(image_id, 0))
     {