[gtk/gamma-shenanigans: 1/2] memorytexture: Add a 16bpp format

[Matthias Clasen <matthiasc src gnome org>]

commit 2fdad1297b0061e1ebb0cc352c5357525ca726e7
Author: Matthias Clasen <mclasen redhat com>
Date:   Sun Sep 5 17:37:52 2021 -0400

    memorytexture: Add a 16bpp format
    
    Add GDK_MEMORY_R16G16B16A16_PREMULTIPLIED, which
    matches the libpng PNG_FORMAT_LINEAR_RGB_ALPHA
    format. Loading images in this format using the
    png_image api applies the gamma and provides
    linear data.

 gdk/gdkmemorytexture.c | 37 ++++++++++++++++++++++++++++++++++++-
 gdk/gdkmemorytexture.h |  3 +++
 2 files changed, 39 insertions(+), 1 deletion(-)
---
diff --git a/gdk/gdkmemorytexture.c b/gdk/gdkmemorytexture.c
index 06fa3d6619..fbb77851d9 100644
--- a/gdk/gdkmemorytexture.c
+++ b/gdk/gdkmemorytexture.c
@@ -62,6 +62,9 @@ gdk_memory_format_bytes_per_pixel (GdkMemoryFormat format)
     case GDK_MEMORY_B8G8R8:
       return 3;
 
+    case GDK_MEMORY_R16G16B16A16_PREMULTIPLIED:
+      return 8;
+
     case GDK_MEMORY_N_FORMATS:
     default:
       g_assert_not_reached ();
@@ -283,6 +286,37 @@ SWIZZLE_PREMULTIPLY (3,0,1,2, 0,1,2,3)
 SWIZZLE_PREMULTIPLY (3,0,1,2, 3,0,1,2)
 SWIZZLE_PREMULTIPLY (3,0,1,2, 0,3,2,1)
 
+#define SWIZZLE_16TO8(A,R,G,B) \
+static void \
+convert_16to8_swizzle_ ## A ## R ## G ## B (guchar       *dest_data, \
+                                            gsize         dest_stride, \
+                                            const guchar *src_data, \
+                                            gsize         src_stride, \
+                                            gsize         width, \
+                                            gsize         height) \
+{ \
+  gsize x, y; \
+\
+  for (y = 0; y < height; y++) \
+    { \
+      guint16 *src = (guint16 *)src_data; \
+      for (x = 0; x < width; x++) \
+        { \
+          dest_data[4 * x + A] = src[4 * x + 0] >> 8; \
+          dest_data[4 * x + R] = src[4 * x + 1] >> 8; \
+          dest_data[4 * x + G] = src[4 * x + 2] >> 8; \
+          dest_data[4 * x + B] = src[4 * x + 3] >> 8; \
+        } \
+\
+      dest_data += dest_stride; \
+      src_data += src_stride; \
+    } \
+}
+
+SWIZZLE_16TO8(0,1,2,3)
+SWIZZLE_16TO8(2,1,0,3)
+SWIZZLE_16TO8(1,2,3,0)
+
 typedef void (* ConversionFunc) (guchar       *dest_data,
                                  gsize         dest_stride,
                                  const guchar *src_data,
@@ -300,7 +334,8 @@ static ConversionFunc converters[GDK_MEMORY_N_FORMATS][3] =
   { convert_swizzle_premultiply_3210_3012, convert_swizzle_premultiply_0123_3012, 
convert_swizzle_premultiply_3012_3012 },
   { convert_swizzle_premultiply_3210_0321, convert_swizzle_premultiply_0123_0321, 
convert_swizzle_premultiply_3012_0321 },
   { convert_swizzle_opaque_3210, convert_swizzle_opaque_0123, convert_swizzle_opaque_3012 },
-  { convert_swizzle_opaque_3012, convert_swizzle_opaque_0321, convert_swizzle_opaque_3210 }
+  { convert_swizzle_opaque_3012, convert_swizzle_opaque_0321, convert_swizzle_opaque_3210 },
+  { convert_16to8_swizzle_2103, convert_16to8_swizzle_1230, convert_16to8_swizzle_0123 }
 };
 
 void
diff --git a/gdk/gdkmemorytexture.h b/gdk/gdkmemorytexture.h
index b9f1f21282..eeeb3ad4a7 100644
--- a/gdk/gdkmemorytexture.h
+++ b/gdk/gdkmemorytexture.h
@@ -42,6 +42,8 @@ G_BEGIN_DECLS
  * @GDK_MEMORY_A8B8G8R8: 4 bytes; for alpha, blue, green, red.
  * @GDK_MEMORY_R8G8B8: 3 bytes; for red, green, blue. The data is opaque.
  * @GDK_MEMORY_B8G8R8: 3 bytes; for blue, green, red. The data is opaque.
+ * @GDK_MEMORY_R16G16B16A16_PREMULTIPLIED: 4 guint16 values; for red, green, blue, alpha.
+ *   The color values are premultiplied with the alpha value.
  * @GDK_MEMORY_N_FORMATS: The number of formats. This value will change as
  *   more formats get added, so do not rely on its concrete integer.
  *
@@ -67,6 +69,7 @@ typedef enum {
   GDK_MEMORY_A8B8G8R8,
   GDK_MEMORY_R8G8B8,
   GDK_MEMORY_B8G8R8,
+  GDK_MEMORY_R16G16B16A16_PREMULTIPLIED,
 
   GDK_MEMORY_N_FORMATS
 } GdkMemoryFormat;