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

1 files changed, 13 insertions, 0 deletions

diff --git a/source/blender/imbuf/IMB_colormanagement.h b/source/blender/imbuf/IMB_colormanagement.h
index 620f8984d9f..e683d38a0aa 100644
--- a/source/blender/imbuf/IMB_colormanagement.h
+++ b/source/blender/imbuf/IMB_colormanagement.h
@@ -58,6 +58,10 @@ void IMB_colormanagement_assign_rect_colorspace(struct ImBuf *ibuf, const char *
 const char *IMB_colormanagement_get_float_colorspace(struct ImBuf *ibuf);
 const char *IMB_colormanagement_get_rect_colorspace(struct ImBuf *ibuf);
 
+bool IMB_colormanagement_space_is_data(struct ColorSpace *colorspace);
+bool IMB_colormanagement_space_is_scene_linear(struct ColorSpace *colorspace);
+bool IMB_colormanagement_space_is_srgb(struct ColorSpace *colorspace);
+
 BLI_INLINE float IMB_colormanagement_get_luminance(const float rgb[3]);
 BLI_INLINE unsigned char IMB_colormanagement_get_luminance_byte(const unsigned char[3]);
 BLI_INLINE void IMB_colormangement_xyz_to_rgb(float rgb[3], const float xyz[3]);
@@ -124,6 +128,14 @@ void IMB_colormanagement_colorspace_to_scene_linear(float *buffer,
                                                     struct ColorSpace *colorspace,
                                                     bool predivide);
 
+void IMB_colormanagement_imbuf_to_srgb_texture(unsigned char *rect,
+                                               const int x,
+                                               const int y,
+                                               const int width,
+                                               const int height,
+                                               const struct ImBuf *ibuf,
+                                               const bool compress_as_srgb);
+
 void IMB_colormanagement_scene_linear_to_color_picking_v3(float pixel[3]);
 void IMB_colormanagement_color_picking_to_scene_linear_v3(float pixel[3]);
 
@@ -340,6 +352,7 @@ enum {
   COLOR_ROLE_DEFAULT_SEQUENCER,
   COLOR_ROLE_DEFAULT_BYTE,
   COLOR_ROLE_DEFAULT_FLOAT,
+  COLOR_ROLE_DATA,
 };
 
 #include "intern/colormanagement_inline.c"