Refactor: OpenColorIO integration

Briefly about this change:
- OpenColorIO C-API is removed.
- The information about color spaces in ImBuf module is removed.
  It was stored in global ListBase in colormanagement.cc.
- Both OpenColorIO and fallback implementation supports GPU drawing.
- Fallback implementation supports white point, RGB curves, etc.
- Removed check for support of GPU drawing in IMB.

Historically it was implemented in a separate library with C-API, this
is because way back C++ code needed to stay in intern. This causes all
sort of overheads, and even calls that are strictly considered bad
level.

This change moves OpenColorIO integration into a module within imbuf,
next to movie, and next to IMB_colormanagement which is the main user
of it. This allows to avoid copy of color spaces, displays, views etc
in the ImBuf: they were used to help quickly querying information to
be shown on the interface. With this change it can be stored in the
same data structures as what is used by the OpenColorIO integration.
While it might not be fully avoiding duplication it is now less, and
there is no need in the user code to maintain the copies.

In a lot of cases this change also avoids allocations done per access
to the OpenColorIO. For example, it is not needed anymore to allocate
image descriptor in a heap.

The bigger user-visible change is that the fallback implementation now
supports GLSL drawing, with the whole list of supported features, such
as curve mapping and white point. This should help simplifying code
which relies on color space conversion on GPU: there is no need to
figure out fallback solution in such cases. The only case when drawing
will not work is when there is some actual bug, or driver issue, and
shader has failed to compile.

The change avoids having an opaque type for color space, and instead
uses forward declaration. It is a bit verbose on declaration, but helps
avoiding unsafe type-casts. There are ways to solve this in the future,
like having a header for forward declaration, or to flatten the name
space a bit.

There should be no user-level changes under normal operation.
When building without OpenColorIO or the configuration has a typo or
is missing a fuller set of color management tools is applies (such as the
white point correction).

Pull Request: https://projects.blender.org/blender/blender/pulls/138433

source/blender/python/intern/CMakeLists.txt

@@ -8,7 +8,6 @@ set(INC
   ../../imbuf/intern/oiio
   ../../makesrna
   ../../../../intern/mantaflow/extern
-  ../../../../intern/opencolorio
   # RNA_prototypes.hh
   ${CMAKE_BINARY_DIR}/source/blender/makesrna
 )
@@ -130,6 +129,7 @@ set(LIB
   PRIVATE bf::intern::guardedalloc
   PRIVATE bf::animrig
   bf_python_gpu
+  PRIVATE bf::imbuf::opencolorio
 
   ${PYTHON_LINKFLAGS}
   ${PYTHON_LIBRARIES}
@@ -328,10 +328,6 @@ if(WITH_ALEMBIC)
   add_definitions(-DWITH_ALEMBIC)
 endif()
 
-if(WITH_OPENCOLORIO)
-  add_definitions(-DWITH_OCIO)
-endif()
-
 if(WITH_OPENVDB)
   add_definitions(-DWITH_OPENVDB)
   list(APPEND INC

source/blender/python/intern/bpy_app_build_options.cc

@@ -273,7 +273,7 @@ static PyObject *make_builtopts_info()
   SetObjIncref(Py_False);
 #endif
 
-#ifdef WITH_OCIO
+#ifdef WITH_OPENCOLORIO
   SetObjIncref(Py_True);
 #else
   SetObjIncref(Py_False);

source/blender/python/intern/bpy_app_ocio.cc

@@ -13,9 +13,9 @@
 
 #include "../generic/py_capi_utils.hh"
 
-#ifdef WITH_OCIO
-#  include "ocio_capi.h"
-#endif
+#include "OCIO_version.hh"
+
+namespace ocio = blender::ocio;
 
 static PyTypeObject BlenderAppOCIOType;
 
@@ -38,28 +38,23 @@ static PyObject *make_ocio_info()
   PyObject *ocio_info;
   int pos = 0;
 
-#ifdef WITH_OCIO
-  int curversion;
-#endif
-
   ocio_info = PyStructSequence_New(&BlenderAppOCIOType);
   if (ocio_info == nullptr) {
     return nullptr;
   }
 
-#ifndef WITH_OCIO
+#ifndef WITH_OPENCOLORIO
 #  define SetStrItem(str) PyStructSequence_SET_ITEM(ocio_info, pos++, PyUnicode_FromString(str))
 #endif
 
 #define SetObjItem(obj) PyStructSequence_SET_ITEM(ocio_info, pos++, obj)
 
-#ifdef WITH_OCIO
-  curversion = OCIO_getVersionHex();
+#ifdef WITH_OPENCOLORIO
+  const ocio::Version ocio_version = ocio::get_version();
   SetObjItem(PyBool_FromLong(1));
-  SetObjItem(
-      PyC_Tuple_Pack_I32({curversion >> 24, (curversion >> 16) % 256, (curversion >> 8) % 256}));
+  SetObjItem(PyC_Tuple_Pack_I32({ocio_version.major, ocio_version.minor, ocio_version.patch}));
   SetObjItem(PyUnicode_FromFormat(
-      "%2d, %2d, %2d", curversion >> 24, (curversion >> 16) % 256, (curversion >> 8) % 256));
+      "%2d, %2d, %2d", ocio_version.major, ocio_version.minor, ocio_version.patch));
 #else
   SetObjItem(PyBool_FromLong(0));
   SetObjItem(PyC_Tuple_Pack_I32({0, 0, 0}));