OpenColorIO: upgrade to version 2.0.0

Ref T84819

Build System
============

This is an API breaking new version, and the updated code only builds with
OpenColorIO 2.0 and later. Adding backwards compatibility was too complicated.

* Tinyxml was replaced with Expat, adding a new dependency.
* Yaml-cpp is now built as a dependency on Unix, as was already done on Windows.
* Removed currently unused LCMS code.
* Pystring remains built as part of OCIO itself, since it has no good build system.
* Linux and macOS check for the OpenColorIO verison, and disable it if too old.

Ref D10270

Processors and Transforms
=========================

CPU processors now need to be created to do CPU processing. These are cached
internally, but the cache lookup is not fast enough to execute per pixel or
texture sample, so for performance these are now also exposed in the C API.

The C API for transforms will no longer be needed afer all changes, so remove
it to simplify the API and fallback implementation.

Ref D10271

Display Transforms
==================

Needs a bit more manual work constructing the transform. LegacyViewingPipeline
could also have been used, but isn't really any simpler and since it's legacy
we better not rely on it.

We moved more logic into the opencolorio module, to simplify the API. There is
no need to wrap a dozen functions just to be able to do this in C rather than C++.
It's also tightly coupled to the GPU shader logic, and so should be in the same
module.

Ref D10271

GPU Display Shader
==================

To avoid baking exposure and gamma into the GLSL shader and requiring slow
recompiles when tweaking, we manually apply them in the shader. This leads
to some logic duplicaton between the CPU and GPU display processor, but it
seems unavoidable.

Caching was also changed. Previously this was done both on the imbuf and
opencolorio module levels. Now it's all done in the opencolorio module by
simply matching color space names. We no longer use cacheIDs from OpenColorIO
since computing them is expensive, and they are unlikely to match now that
more is baked into the shader code.

Shaders can now use multiple 2D textures, 3D textures and uniforms, rather
than a single 3D texture. So allocating and binding those adds some code.

Color space conversions for blending with overlays is now hardcoded in the
shader. This was using harcoded numbers anyway, if this every becomes a
general OpenColorIO transform it can be changed, but for now there is no
point to add code complexity.

Ref D10273

CIE XYZ
=======

We need standard CIE XYZ values for rendering effects like blackbody emission.
The relation to the scene linear role is based on OpenColorIO configuration.

In OpenColorIO 2.0 configs roles can no longer have the same name as color
spaces, which means our XYZ role and colorspace in the configuration give an
error.

Instead use the new standard aces_interchange role, which relates scene linear
to a known scene referred color space. Compatibility with the old XYZ role is
preserved, if the configuration file has no conflicting names.

Also includes a non-functional change to the configuraton file to use an
XYZ-to-ACES matrix instead of REC709-to-ACES, makes debugging a little easier
since the matrix is the same one we have in the code now and that is also
found easily in the ACES specs.

Ref D10274

1 files changed, 30 insertions, 12 deletions

diff --git a/intern/opencolorio/gpu_shader_display_transform.glsl b/intern/opencolorio/gpu_shader_display_transform.glsl
index 61da755f02f..ca0d2566ed1 100644
--- a/intern/opencolorio/gpu_shader_display_transform.glsl
+++ b/intern/opencolorio/gpu_shader_display_transform.glsl
@@ -1,17 +1,18 @@
 /* Blender OpenColorIO implementation */
 
-uniform sampler1D curve_mapping_texture;
 uniform sampler2D image_texture;
 uniform sampler2D overlay_texture;
-uniform sampler3D lut3d_texture;
-uniform sampler3D lut3d_display_texture;
 
 uniform float dither;
+uniform float scale;
+uniform float exponent;
 uniform bool predivide;
-uniform bool curve_mapping;
 uniform bool overlay;
 
-layout(std140) uniform OCIO_GLSLCurveMappingParameters
+#ifdef USE_CURVE_MAPPING
+uniform sampler1D curve_mapping_texture;
+
+layout(std140) uniform OCIO_GPUCurveMappingParameters
 {
   /* Curve mapping parameters
    *
@@ -114,6 +115,7 @@ vec4 curvemapping_evaluate_premulRGBF(vec4 col)
   result.a = col.a;
   return result;
 }
+#endif /* USE_CURVE_MAPPING */
 
 /* Using a triangle distribution which gives a more final uniform noise.
  * See Banding in Games:A Noisy Rant(revision 5) Mikkel Gjøl, Playdead (slide 27) */
@@ -145,9 +147,9 @@ vec4 apply_dither(vec4 col, vec2 uv)
 
 vec4 OCIO_ProcessColor(vec4 col, vec4 col_overlay, vec2 noise_uv)
 {
-  if (curve_mapping) {
-    col = curvemapping_evaluate_premulRGBF(col);
-  }
+#ifdef USE_CURVE_MAPPING
+  col = curvemapping_evaluate_premulRGBF(col);
+#endif
 
   if (predivide) {
     if (col.a > 0.0 && col.a < 1.0) {
@@ -160,15 +162,31 @@ vec4 OCIO_ProcessColor(vec4 col, vec4 col_overlay, vec2 noise_uv)
    *       for straight alpha at this moment
    */
 
-  col = OCIO_to_display_linear_with_look(col, lut3d_texture);
+  /* Convert to scene linear (usually a no-op). */
+  col = OCIO_to_scene_linear(col);
+
+  /* Apply exposure in scene linear. */
+  col.rgb *= scale;
+
+  /* Convert to display space. */
+  col = OCIO_to_display(col);
 
+  /* Blend with overlay in UI colorspace.
+   *
+   * UI colorspace here refers to the display linear color space,
+   * i.e: The linear color space w.r.t. display chromaticity and radiometry.
+   * We separate the colormanagement process into two steps to be able to
+   * merge UI using alpha blending in the correct color space. */
   if (overlay) {
+    col.rgb = pow(col.rgb, vec3(exponent * 2.2));
     col = clamp(col, 0.0, 1.0);
     col *= 1.0 - col_overlay.a;
     col += col_overlay; /* Assumed unassociated alpha. */
+    col.rgb = pow(col.rgb, vec3(1.0 / 2.2));
+  }
+  else {
+    col.rgb = pow(col.rgb, vec3(exponent));
   }
-
-  col = OCIO_to_display_encoded(col, lut3d_display_texture);
 
   if (dither > 0.0) {
     col = apply_dither(col, noise_uv);
@@ -189,4 +207,4 @@ void main()
   vec2 noise_uv = round_to_pixel(image_texture, texCoord_interp.st);
 
   fragColor = OCIO_ProcessColor(col, col_overlay, noise_uv);
-}
\ No newline at end of file
+}