Existing OCCT path tracing engine used very simple additive material (BSDF) model, so it was possible to reproduce
behavior only of very basic materials such as metal, glass, or plastic. However, some important in CAD industry
materials like car paint or ceramic could not be modeled well. In this patch, OCCT BSDF was significantly improved
by replacing additive model with two-layered scattering model. Therefore, we have base diffuse, glossy, or transmissive
layer, covered by one glossy/specular coat. The layers themselves have no thickness; they can simply reflect light or
transmits it to the layer under it. Balancing different combinations of layer properties can produce a wide range of
different effects. At the same time, disabling the first (coat) layer allows to keep full compatibility with previously
supported scattering model. All new parameters are available via 'vbsdf' command.
Location of new sample for few material examples:
samples\tcl\pathtrace_materials.tcl
Fix shader compilation issue.
Fix test case sample_ball_alpha.
Shaders_PathtraceBase_fs.pxx - regenerate resource from origin
This commit provides useful functionality for path tracing rendering core.
1) Graphic3d_RenderingParams class was extended with additional AdaptiveScreenSampling option (disabled by default).
If this option is enabled, path tracing tries to adjust the number of samples for different screen areas.
In this way, the more complex areas (from the point of light conditions) are sampled more intensively,
while the simple areas are sampled very rarely.
For example, caustics and glossy reflections are typical candidates for more precise sampling.
In general, this allows to equalize image convergence and not to waste resources for already converged areas.
It is also possible to visualize sampling densities by enabling ShowSamplingTiles option
(activating and deactivating this option does not affect on the accumulated image).
2) Mixing OpenGL and ray-tracing output has been changed.
Now blending is performed using OpenGL functionality, while ray-tracing shaders only output correct Z-value.
Test case bugs vis bug27083 has been updated,
since the alpha value is now correctly set by Ray-Tracing to 1, opaque.
View-projection matrix was added to raytrace shaders (as uniform) in order to compute correct depth values for OpenGL.
For path tracing the additional depth buffer sampler was added to Display.fs program. It allows propagation of depth values from internal FBO to resulting FBO.
The old approach of mixing of OpenGL and ray-tracing graphics was kept in order to keep correct blending of transparent ray-traced objects with non-transparent OpenGL objects.
Replace 64-bit handles of bindless textures by uvec2 type in GLSL code for compatibility with AMD drivers.
OpenGl_View::initProgram() - fix NULL-dereference.
