Multilight can use the power of your graphics card to accelerate the slider adjustments, displaying your lighting changes instantly in the main render view (instead of in the small Preview window). Even the SimuLens features (Scattering and Dispersion) are updated instantly, giving you a high precision custom control.
GPU accelerated Multilight in action
The Fast Multilight Preview is disabled by default and has to be enabled manually in the Maxwell Preferences panel. To enable it, simply open Maxwell, and in the File>Preferences panel, enable the Fast Multilight Preview checkbox.
Enabling the GPU -accelerated Fast Multilight in the Maxwell Preferences panel
- Fast Multilight Preview: Enables the GPU to perform the slider adjustments interactively.
- Automatic Update After Editing: Enables the CPU (slower but more accurate) to update the image after you finish the adjustment (when you release any slider).
Although the GPU provides a quick and instant display, the final version of the image must be calculated by the CPU (which is slower but more accurate) to get the exact light result. You can force this update manually by hitting the "Preview" button in the small Preview window, or automatically by enabling the aforementioned Automatic Update After Editing option.
About graphic card specifications
The only specification required for the graphics card to properly run this feature is OpenCL support - almost all regular graphics cards today support OpenCL and have enough RAM memory to hold the MXI file you are rendering in memory.
GPU memory limitations
If you are working with a high resolution image that could overload the GPU memory size, Maxwell may not be able to run the Fast Multilight feature (Simulens can trigger a memory allocation failure at HD resolutions). In that case Maxwell Render will try to continue in two ways:
If the memory overload was made by activating Scattering or Diffraction (SimuLens), both will be deactivated automatically.
The Fast Multilight feature is not compatible with the Color Multilight mode and can get unexpected results.
If there is a general failure due to GPU memory overload (i.e. OpenCL can't recover from a memory allocation failure), Maxwell Render will deactivate the Fast Multilight Preview, so the user can continue editing the render using the older V2 way using CPU only, and the small preview window for interactive previews.