This page provides information on the Visual Debugger tool in V-Ray for Maya. (and 3ds Max?)
Overview
The Visual Debugger tool records and displays exact information about the traced rays for each pixel. The traced rays are visualized in the VFB and each can be selected for more data, found in the Visual Debugger tab of the VFB.
Workflow
First, select the pixel or area of pixels that need troubleshooting by using the Region render option of the VFB. It is recommended for the render to have small amount of Max subdivs, e.g. 1 and the AA filter turned off. Both options reside in the Image sampler rollout of the V-Ray render settings.
Enable the Visual Debugger option from Render Settings > Settings > System > System - advanced > Visual Debugger (Experimental).
Start the render.
In the completed render, hover with the mouse over a pixel or ray, and left-click to select it. Click on an empty space to deselect it.
The Visual Debugger tab offers information for each traced ray within the selected region. Exact hit point, type and distance, as well as the ray's direction, direction length, origin, type and probability are available as text data.
Different types of rays have different color. Dashed lines represent environment or background hits.
The blue dots represent camera ray hits (primary hits of the camera ray).
If you get camera (primary) rays outside the selected region, check if the AA filter is disabled as recommended.
When the limit for maximum stored camera rays (64) of the debugger tool is hit, the traced rays have odd patterns and/or some pixels are missing. The limit is easily achievable with bigger render regions or many samples per pixel, so keep these at the recommended values.
The debug render does a full render including export.
At the top of the Visual Debugger tab in the VFB, there is an Inactive ray alpha slider, which controls the transparency of the unselected traced rays.
Known Issues and Limitations
A maximum of 64 camera rays are stored. This means that the first 64 rays that finish shading are written, the rest are discarded. This is highly non-deterministic but the limitation is needed in order to maintain good performance during both rendering and debugging.
A debug render does a full render including export.
The debug information is displayed in the VFB after the end of the render process, so it's not useful in IPR.
When the debug tool and Light Cache GI are both enabled, Light Cache is built at full resolution overriding the current render region.
The ray contribution for secondary rays is incorrect.
The debug tool is available with V-Ray CPU only.
Only physical and pinhole cameras are supported.
Incorrect ray clipping in physical camera may occur. Some environment hits are fully clipped incorrectly.
Camera rays may have unknown ray and hit type.
Unknown volume rays may occur.