Alpha premul pipeline cleanup

This assumptions are now made:
- Internally float buffers are always linear alpha-premul colors
- Readers should worry about delivering float buffers with that
  assumptions.
- There's an input image setting to say whether it's stored with
  straight/premul alpha on the disk.
- Byte buffers are now assumed have straight alpha, readers should
  deliver straight alpha.

Some implementation details:

- Removed scene's color unpremultiply setting, which was very
  much confusing and was wrong for default settings.
  Now all renderers assumes to deliver premultiplied alpha.

- IMB_buffer_byte_from_float will now linearize alpha when
  converting from buffer.

- Sequencer's effects were changed to assume bytes have got
  straight alpha. Most of effects will work with bytes still,
  however for glow it was more tricky to avoid data loss, so
  there's a commented out glow implementation which converts
  byte buffer to floats first, operates on floats and returns
  bytes back. It's slower and not sure if it should actually
  be used -- who're using glow on alpha anyway?

- Sequencer modifiers should also be working nice with straight
  bytes now.

- GLSL preview will predivide float textures to make nice shading,
  shading with byte textures worked nice (GLSL was assuming straight
  alpha).

- Blender Internal will set alpha=1 to the whole sky. The same
  happens in Cycles and there's no way to avoid this -- sky is
  neither straight nor premul and doesn't fit color pipeline well.

- Straight alpha mode for render result was also eliminated.

- Conversion to correct alpha need to be done before linearizing
  float buffer.

- TIFF will now load and save files with proper alpha mode setting
  in file meta data header.

- Remove Use Alpha from texture mapping and replaced with image
  datablock setting.

  Behaves much more predictable and clear from code point of view
  and solves possible regressions when non-premultiplied images were
  used as textures with ignoring alpha channel.

1 files changed, 12 insertions, 2 deletions

diff --git a/source/blender/makesdna/DNA_image_types.h b/source/blender/makesdna/DNA_image_types.h
index fe3550327f7..0f47ee224ae 100644
--- a/source/blender/makesdna/DNA_image_types.h
+++ b/source/blender/makesdna/DNA_image_types.h
@@ -111,6 +111,9 @@ typedef struct Image {
 
 	/* color management */
 	ColorManagedColorspaceSettings colorspace_settings;
+	char alpha_mode;
+
+	char pad[7];
 } Image;
 
 
@@ -119,15 +122,16 @@ typedef struct Image {
 /* Image.flag */
 #define IMA_FIELDS			1
 #define IMA_STD_FIELD		2
-#define IMA_DO_PREMUL		4
+#define IMA_DO_PREMUL		4    /* deprecated, should not be used */
 #define IMA_REFLECT			16
 #define IMA_NOCOLLECT   	32
 #define IMA_DEPRECATED		64
 #define IMA_OLD_PREMUL		128
-#define IMA_CM_PREDIVIDE	256
+/*#define IMA_CM_PREDIVIDE	256*/  /* deprecated, should not be used */
 #define IMA_USED_FOR_RENDER	512
 #define IMA_USER_FRAME_IN_RANGE	1024 /* for image user, but these flags are mixed */
 #define IMA_VIEW_AS_RENDER	2048
+#define IMA_IGNORE_ALPHA	4096
 
 /* Image.tpageflag */
 #define IMA_TILES			1
@@ -148,4 +152,10 @@ typedef struct Image {
 /* gen_flag */
 #define IMA_GEN_FLOAT		1
 
+/* alpha_mode */
+enum {
+	IMA_ALPHA_STRAIGHT = 0,
+	IMA_ALPHA_PREMUL = 1,
+};
+
 #endif