Interior Rendering with Unreal Engine Path Tracer: MRQ Settings

As described in Unreal Engine’s official documentation, Path Tracer can be used to achieve physically based lighting, reflections, and refractions in architectural visualization scenes. It runs on a hardware ray tracing pipeline and can be combined with Movie Render Queue (MRQ) to output stills or animations. Epic’s documentation does not specify a particular Unreal Engine version, so the steps below are limited to the settings and menu paths listed in the documentation.

1. Prepare the project for ray tracing

1. Before using Path Tracer, check that your project meets the hardware requirements. The documentation lists Windows 10 1809 or later, DirectX 12, and NVIDIA RTX or GTX-series graphics cards with DXR drivers enabled. The Movie Render Queue guide to high-quality frames is also aimed at Windows 10 64-bit users.

2. In Unreal Editor, follow Edit > Project Settings > Platforms > Windows > Targeted RHIs > Default RHI and set the default RHI to DirectX 12.

3. In Edit > Project Settings > Engine > Rendering > Hardware Ray Tracing, enable Support Hardware Ray Tracing. Path Tracer support must also be enabled in the same section.

4. When you enable hardware ray tracing, Unreal Engine may prompt you to turn on Support Compute Skin Cache if it is disabled. This feature is required, so follow the prompt and restart the engine for the settings changes to take effect.

2. Check Path Tracer in the viewport

1. In the Level Viewport, open the View Modes menu and select Path Tracing. As long as the camera remains still, the image gradually sharpens as samples accumulate.

2. Once the sample count reaches its target, noise in the final image is reduced if a denoiser is enabled in the Post Process settings. The relevant plugin must be enabled for the denoiser option to work; the documentation notes that the NNE Denoiser plugin is used by default.

3. Moving the camera, changing a material, or adding or moving an object invalidates the samples and starts accumulation from the beginning. Give the image time to settle again when testing lighting and materials.

Interiors can take longer to render than exteriors. According to Epic, light paths can involve more bounces indoors; materials with an albedo close to 1.0 can also lengthen those paths. Complex scenes and materials can further affect render times.

3. Configure frames in Movie Render Queue

1. To access MRQ, enable the Movie Render Pipeline plugin under Edit > Plugins. Then open Window > Cinematics > Movie Render Queue and add the Level Sequence you want to render to the queue.

2. Click Unsaved Config* in the queue. Add the required settings via + Setting. Along with the Path Tracer module, select Anti-aliasing for output type and sampling.

3. Path Tracer’s Post Process Volume settings include Samples Per Pixel; increasing this value can reduce noise, but also increases render time per frame. When using MRQ, the samples-per-pixel setting in the Post Process Volume is ignored; sampling is determined by Spatial Sample Count and Temporal Sample Count in MRQ.

4. The total samples per pixel equal the spatial sample count multiplied by the temporal sample count. For example, 16 samples can be achieved with 4 spatial and 4 temporal samples, 16 spatial and 1 temporal sample, or 1 spatial and 16 temporal samples. The right distribution depends in particular on whether motion blur is needed. For stills, increasing spatial samples while keeping temporal samples at 1 is recommended; for animation, use 1 spatial sample and more temporal samples with Reference Motion Blur enabled.

4. Choose the output format and resolution

MRQ’s Output settings let you specify the file type, naming, resolution, and frame range to render. PNG and EXR can output an alpha channel; to do so, enable Edit > Project Settings > Engine > Rendering > Postprocessing > Enable alpha channel support in post processing (experimental) > Linear color space only and restart the engine. For a transparent background, visibility must also be disabled for opaque objects such as Sky and Atmospheric Fog.

PNG is lossless and supports an alpha channel; JPG is lossy and suited to smaller preview files. EXR is a high-dynamic-range format that supports alpha channels. For high-resolution frames, MRQ’s High Resolution module can render the image as separate tiles and combine them. The maximum supported tile size depends on the graphics card.

What changes in architectural and visualization workflows?

Path Tracer can be useful for interior frames where reflections, refractions, and indirect lighting details are important. Sequencer and MRQ integration makes it possible to output high-quality frame sequences from the same scene. However, real-time navigation speed should not be treated as a fixed benchmark: while Path Tracer accumulates samples, render times are affected by scene complexity, materials, and hardware.

For render workstations, the priority is to verify compatibility with DirectX 12 and hardware ray tracing, as specified in the documentation. Temporal sampling should be planned for motion blur and animation; spatial sampling is preferable for stills. The sources do not provide license or pricing information for Path Tracer, nor do they specify the cost of the required hardware or performance times for any particular card.

Common mistakes

• Trying to use Path Tracer while hardware ray tracing or Support Compute Skin Cache is disabled.

• Overlooking that accumulated samples are discarded and recalculated after camera or scene changes.

• Adjusting sampling in MRQ through Samples Per Pixel in the Post Process Volume; MRQ ignores this value.

• Automatically using the same sample distribution for animations and stills. Motion blur requirements affect the choice of temporal sample count.