Cycles/Eevee: unified and improved texture image color space handling

Cycles now uses the color space on the image datablock, and uses OpenColorIO
to convert to scene linear as needed. Byte images do not take extra memory,
they are compressed in scene linear + sRGB transfer function which in common
cases is a no-op.

Eevee and workbench were changed to work similar. Float images are stored as
scene linear. Byte images are compressed as scene linear + sRGB and stored in
a GL_SRGB8_ALPHA8 texture. From the GLSL shader side this means they are read
as scene linear, simplifying the code and taking advantage of hardware support.

Further, OpenGL image textures are now all stored with premultiplied alpha.
Eevee texture sampling looks a little different now because interpolation
happens premultiplied and in scene linear space.

Overlays and grease pencil work in sRGB space so those now have an extra
conversion to sRGB after reading from image textures. This is not particularly
elegant but as long as engines use different conventions, one or the other
needs to do conversion.

This change breaks compatibility for cases where multiple image texture nodes
were using the same image with different color space node settings. However it
gives more predictable behavior for baking and texture painting if save, load
and image editing operations have a single color space to handle.

Differential Revision: https://developer.blender.org/D4807

2 files changed, 2 insertions, 8 deletions

diff --git a/source/blender/makesdna/DNA_image_types.h b/source/blender/makesdna/DNA_image_types.h
index fec5f96b4f3..0aceeda20d5 100644
--- a/source/blender/makesdna/DNA_image_types.h
+++ b/source/blender/makesdna/DNA_image_types.h
@@ -191,8 +191,6 @@ enum {
   IMA_GPU_REFRESH = (1 << 0),
   /** All mipmap levels in OpenGL texture set? */
   IMA_GPU_MIPMAP_COMPLETE = (1 << 1),
-  /** OpenGL image texture bound as non-color data. */
-  IMA_GPU_IS_DATA = (1 << 2),
 };
 
 /* ima->type and ima->source moved to BKE_image.h, for API */
diff --git a/source/blender/makesdna/DNA_node_types.h b/source/blender/makesdna/DNA_node_types.h
index 226e1d2f841..3890fc63f3f 100644
--- a/source/blender/makesdna/DNA_node_types.h
+++ b/source/blender/makesdna/DNA_node_types.h
@@ -832,7 +832,7 @@ typedef struct NodeTexSky {
 typedef struct NodeTexImage {
   NodeTexBase base;
   ImageUser iuser;
-  int color_space;
+  int color_space DNA_DEPRECATED;
   int projection;
   float projection_blend;
   int interpolation;
@@ -853,7 +853,7 @@ typedef struct NodeTexBrick {
 typedef struct NodeTexEnvironment {
   NodeTexBase base;
   ImageUser iuser;
-  int color_space;
+  int color_space DNA_DEPRECATED;
   int projection;
   int interpolation;
   char _pad[4];
@@ -1121,10 +1121,6 @@ typedef struct NodeCryptomatte {
 #define SHD_SKY_OLD 0
 #define SHD_SKY_NEW 1
 
-/* image/environment texture */
-#define SHD_COLORSPACE_NONE 0
-#define SHD_COLORSPACE_COLOR 1
-
 /* environment texture */
 #define SHD_PROJ_EQUIRECTANGULAR 0
 #define SHD_PROJ_MIRROR_BALL 1