Preliminary OCIO Code Generation Support

[bernardkwok]

Update #815.

Preliminary setup for OCIO support

Basic Build Setup

• MATERIALX_BUILD_OCIO cmake option to enable OCIO building
• MATERIALX_OCIO_DIR cmake option to incidate root directory of OCIO install
  • New OCIO color management system with corresponding custom OCIO source code generator node logic
  • New OCIO config option (_options.mtlx) on unit tests. Only GenGLSL and RenderGLSL unit tests take this into account.
  • (To look at added an external project dependency if desired later)

Basic Support

• Can generate code for LUT and non-LUT based transforms.
• LUT (texture based) transforms have no mechanism to prase and pass back image data for introspection. Delayed as config for base MTLX will most likely not have LUTs.
• Support for color3 inputs and outputs using color3->color4 conversion and color4->color3 conversion nodes connected to each OCIO shader node. This basically brackets the main function call.

Test Results

• Example generated GLSL code:

  vec4 c3_to_color3_acescg_value_cm_out = vec4(c3_to_color3_acescg_value_cm_in.x, c3_to_color3_acescg_value_cm_in.y, c3_to_color3_acescg_value_cm_in.z, 1);
  vec4 c3_to_color3_acescg2_value_cm_out = vec4(c3_to_color3_acescg2_value_cm_in.x, c3_to_color3_acescg2_value_cm_in.y, c3_to_color3_acescg2_value_cm_in.z, 1);
  vec4 color3_acescg_value_cm_out = IM_acescg_to_lin_rec709_color3_ocio(c3_to_color3_acescg_value_cm_out);
  vec4 color3_acescg2_value_cm_out = IM_acescg_to_lin_rec709_color3_ocio(c3_to_color3_acescg2_value_cm_out);
  vec3 color3_acescg_value_cm_to_c3_out = vec3(color3_acescg_value_cm_out.x, color3_acescg_value_cm_out.y, color3_acescg_value_cm_out.z);
  vec3 color3_acescg2_value_cm_to_c3_out = vec3(color3_acescg2_value_cm_out.x, color3_acescg2_value_cm_out.y, color3_acescg2_value_cm_out.z);
  vec3 color3_acescg_out = color3_acescg_value_cm_to_c3_out;
  vec3 color3_acescg2_out = color3_acescg2_value_cm_to_c3_out;
  vec3 add_acescg_out = color3_acescg_out + color3_acescg2_out;

  where 2 transforms are bracketed and then routed to a add function to combine for final result.

  Single copy of translform (in this case acescg to lin_rec709) looks like this (generated by OCIO code gen):

  // Declaration of the OCIO shader function
  vec4 IM_acescg_to_lin_rec709_color3_ocio(in vec4 inPixel)
  {
    vec4 outColor = inPixel;
  
     // Add a Matrix processing
  
    outColor = mat4(1.7049986809609248, -0.13025866763271018, -0.024007514741958086, 0., -0.62174765641381313, 1.1408020008115505, -0.12898266957287285, 0., -0.083251260888346112, -0.010544731974266384, 1.1529906045288774, 0., 0., 0., 0., 1.) * outColor;
  
   return outColor;
  } 

  • Test renders (GLSL) for new unit test look as follows.
• Includes:
  • Test of color4
  • Test of color3 where no conversion from color3->color4->color3 is required
    • Test reuse single update node with a given color transform (above add, and of transformed color3(0.5, 0,0, 0.0) and color3(0.0, 0.5, 0.0) -- resulting in yellow render)
    • Test use of multiple upstream nodes using the same color transform code but different inputs / outputs

[niklasharrysson]

Very cool to have OCIO support in the works!