[gimp] plug-ins: compute DDS variables earlier and support 16-bit masks

[Jacob Boerema <jboerema src gnome org>]

commit 868a6f1d4af92b60b285922973fc536d77197e31
Author: Jacob Boerema <jgboerema gmail com>
Date:   Mon May 2 14:42:43 2022 -0400

    plug-ins: compute DDS variables earlier and support 16-bit masks
    
    To be able to use certain variables we use in our DDS loader earlier,
    we move the computation of these variables up.
    We also add checks to see if the mask needs to be for 8 or 16-bit, since
    there are DDS images with 16 bits per sample.

 plug-ins/file-dds/ddsread.c | 38 +++++++++++++++++++++++++-------------
 1 file changed, 25 insertions(+), 13 deletions(-)
---
diff --git a/plug-ins/file-dds/ddsread.c b/plug-ins/file-dds/ddsread.c
index 1820856704..a7c7e0fabe 100644
--- a/plug-ins/file-dds/ddsread.c
+++ b/plug-ins/file-dds/ddsread.c
@@ -214,6 +214,31 @@ read_dds (GFile          *file,
         hdr.pixelfmt.flags |= DDPF_ALPHAPIXELS;
     }
 
+  d.rshift = color_shift (hdr.pixelfmt.rmask);
+  d.gshift = color_shift (hdr.pixelfmt.gmask);
+  d.bshift = color_shift (hdr.pixelfmt.bmask);
+  d.ashift = color_shift (hdr.pixelfmt.amask);
+  d.rbits  = color_bits (hdr.pixelfmt.rmask);
+  d.gbits  = color_bits (hdr.pixelfmt.gmask);
+  d.bbits  = color_bits (hdr.pixelfmt.bmask);
+  d.abits  = color_bits (hdr.pixelfmt.amask);
+  if (d.rbits <= 8)
+    d.rmask  = (hdr.pixelfmt.rmask >> d.rshift) << (8 - d.rbits);
+  else
+    d.rmask  = (hdr.pixelfmt.rmask >> d.rshift) << (16 - d.rbits);
+  if (d.gbits <= 8)
+    d.gmask  = (hdr.pixelfmt.gmask >> d.gshift) << (8 - d.gbits);
+  else
+    d.gmask  = (hdr.pixelfmt.gmask >> d.gshift) << (16 - d.gbits);
+  if (d.bbits <= 8)
+    d.bmask  = (hdr.pixelfmt.bmask >> d.bshift) << (8 - d.bbits);
+  else
+    d.bmask  = (hdr.pixelfmt.bmask >> d.bshift) << (16 - d.bbits);
+  if (d.abits <= 8)
+    d.amask  = (hdr.pixelfmt.amask >> d.ashift) << (8 - d.abits);
+  else
+    d.amask  = (hdr.pixelfmt.amask >> d.ashift) << (16 - d.abits);
+
   d.gimp_bps = 1; /* Most formats will be converted to 1 byte per sample */
   if (hdr.pixelfmt.flags & DDPF_FOURCC)
     {
@@ -354,19 +379,6 @@ read_dds (GFile          *file,
   pixels = g_new (guchar, d.tile_height * hdr.width * d.gimp_bpp);
   buf = g_malloc (hdr.pitch_or_linsize);
 
-  d.rshift = color_shift (hdr.pixelfmt.rmask);
-  d.gshift = color_shift (hdr.pixelfmt.gmask);
-  d.bshift = color_shift (hdr.pixelfmt.bmask);
-  d.ashift = color_shift (hdr.pixelfmt.amask);
-  d.rbits  = color_bits (hdr.pixelfmt.rmask);
-  d.gbits  = color_bits (hdr.pixelfmt.gmask);
-  d.bbits  = color_bits (hdr.pixelfmt.bmask);
-  d.abits  = color_bits (hdr.pixelfmt.amask);
-  d.rmask  = (hdr.pixelfmt.rmask >> d.rshift) << (8 - d.rbits);
-  d.gmask  = (hdr.pixelfmt.gmask >> d.gshift) << (8 - d.gbits);
-  d.bmask  = (hdr.pixelfmt.bmask >> d.bshift) << (8 - d.bbits);
-  d.amask  = (hdr.pixelfmt.amask >> d.ashift) << (8 - d.abits);
-
   if (! (hdr.caps.caps2 & DDSCAPS2_CUBEMAP) &&
       ! (hdr.caps.caps2 & DDSCAPS2_VOLUME) &&
       dx10hdr.arraySize == 0)