Path Tracing¶
In Path Traced mode the viewport calculates light, shadows, reflections and refraction by tracing rays through the scene. Each new frame starts as a noisy estimate. A denoiser cleans it up for interactive work, or progressive refinement combines frames while the view stays still, for a reference-quality image.
This page covers the path-tracing controls in the viewport toolbar and on the Rendering page of the Scene Renderer panel. They set up the Scene tabs only: recordings have their own path-tracing settings per camera, described in Video Encoding and FFmpeg.
In short
Click Path Traced in a Scene tab's toolbar, then pick a denoiser from the toolbar's Path Tracing menu. Use NVIDIA DLSS Ray Reconstruction on an NVIDIA RTX GPU and ReBLUR or ReLAX elsewhere. For a clean still image, set the denoiser to None and keep the camera still while progressive refinement converges. The denoiser, sampling and the environment multiplier are project settings, shared by every Scene tab; the render mode and view mode belong to each Scene tab.
Turning on path tracing¶
Click the Path Traced button near the right end of the Scene tab's toolbar, or set Render mode on the Scene Renderer's Rendering page. The mode belongs to that Scene tab, which remembers it. Path tracing needs a GPU with hardware ray tracing on Windows or Linux; see Rendering for the requirements and fallbacks.
The render-mode controls sit together near the right end of the toolbar:
| Control | Purpose |
|---|---|
| Rasterized and Path Traced buttons | Choose this Scene tab's render mode. The highlighted button is the mode in use, after any hardware fallback. |
| The arrow joined to them (Path tracing options) | Opens the Path Tracing menu. |
The Path Tracing menu has two rows:
| Row | The button shows | Purpose |
|---|---|---|
| View | The current view mode, for example Lit | Switch between the lit image and diagnostic views. Greyed out in Rasterized mode. See View modes. |
| Denoiser | No Denoiser, ReBLUR, ReLAX or DLSS RR | Choose the denoiser and its options. See Choosing a denoiser. |
The menu also opens in Rasterized mode, so you can choose the denoiser before you switch. The Denoiser button always shows the denoiser actually in use, after any hardware fallback.
Choosing a denoiser¶
Choose the denoiser from Denoiser in the toolbar's Path Tracing menu, or from Denoiser in the Denoising section of the Scene Renderer's Rendering page.
| Denoiser | Shown on the button as | Needs | Use it for |
|---|---|---|---|
| None | No Denoiser | Reference still images. The live image is noisy while anything moves; progressive refinement cleans it up while the camera and scene stay still. | |
| ReBLUR | ReBLUR | Any GPU that can path trace | Interactive work without an NVIDIA RTX GPU. Reduces noise using nearby pixels and earlier frames. |
| ReLAX | ReLAX | Any GPU that can path trace | An alternative real-time denoiser. Compare it with ReBLUR for your scene. |
| NVIDIA DLSS Ray Reconstruction | DLSS RR | An NVIDIA RTX GPU with DLSS support | Interactive work on NVIDIA RTX. AI denoising and upscaling, with a choice of DLSS mode. |
The denoiser is a project setting: it applies to every Scene tab and is saved with the project. Projects start with NVIDIA DLSS Ray Reconstruction. On a GPU without DLSS, the NVIDIA DLSS Ray Reconstruction entry is greyed out and the viewport uses ReBLUR instead; the project's choice is kept.
The denoisers that reuse earlier frames can leave faint trails behind moving objects. If you see them, compare the other denoisers, or switch to None for still images.
Path-traced recordings choose their denoiser separately, on each camera binding. They offer the same denoisers plus OIDN, a CPU denoiser available only for recording, and default to None (reference). Unlike the viewport, a recording never falls back to another denoiser: if the chosen one cannot run, recording fails. See Video Encoding and FFmpeg.
DLSS mode¶
With NVIDIA DLSS Ray Reconstruction selected, choose a mode from the DLSS Mode submenu of the toolbar's Denoiser menu, or from DLSS Mode on the Rendering page. Hover over DLSS Mode on the Rendering page for NVIDIA's description of each mode.
| Mode | What it does |
|---|---|
| Quality | Renders fewer pixels than the viewport and upscales the result, with the best image of the upscaling modes. The default. |
| Balanced | Renders fewer pixels than Quality, balancing speed and image quality. |
| Performance | Renders fewer pixels again, for faster frames. |
| Ultra Performance | Renders the fewest pixels. The fastest mode, with the least detail. |
| DLAA | Renders at the full viewport resolution. The most detail, the highest cost. |
The DLSS mode is a project setting, like the denoiser. While DLSS is active, the Scene Renderer shows the Internal resolution the viewport is rendered at before upscaling. A recorded camera has its own DLSS Mode, which defaults to DLAA.
Temporal anti-aliasing¶
With ReBLUR or ReLAX selected, a temporal anti-aliasing toggle appears: Temporal AA in the toolbar's Denoiser menu, and Temporal anti-aliasing in the Denoising section of the Rendering page. It is on by default.
Temporal anti-aliasing uses samples from earlier frames to smooth jagged edges and shimmer after denoising. It can soften fine detail during motion. It is a project setting, saved with the project.
With ReBLUR or ReLAX, the Denoising section also shows how much GPU memory the denoiser uses.
Progressive refinement and sampling¶
The Sampling section of the Scene Renderer's Rendering page controls how the viewport traces and combines samples. It appears only in Path Traced mode. Despite the note at the top of the section, its settings are project settings: they apply to every Scene tab and are saved with the project. They do not change recordings.
| Field | Default | Range | Description |
|---|---|---|---|
| Indirect bounces | 4 |
0 to 8 | How many times light bounces off diffuse (matte) surfaces after the first hit. 0 gives direct lighting only. Mirror and glossy reflections and glass do not count against this limit. More bounces can improve indirect lighting, at a higher cost. |
| Bright sample limit | 20 |
0 to 1000 | Limits unusually bright bounced samples to reduce bright speckles. Direct lighting, emission and the sky are never limited. 0 turns the limit off. |
| Progressive refinement | on | Combines samples while the camera and scene stay still. Any camera or scene change restarts refinement. | |
| Accumulation history limit | 16384 |
1 to 16384 | The most frames progressive refinement combines. When it is reached, refinement stops and the image holds until the camera or scene changes. |
| Adaptive sampling | off | Stops sampling pixels once their estimated noise is low enough. Requires progressive refinement. | |
| Minimum adaptive samples | 8 |
1 to 1024 | Shown with adaptive sampling. Samples per pixel before adaptive sampling may stop a pixel. |
| Noise target | 0.02 |
0.001 to 0.5 | Shown with adaptive sampling. Lower values refine longer; higher values finish sooner but may leave more noise. |
| Accumulated frames | Read-only. The number of frames combined so far. |
Progressive refinement and adaptive sampling need Denoiser set to None and the Lit view. With any other combination their fields are greyed out, and the section shows the message Progressive refinement and adaptive sampling require Denoiser: None and a lit view.
Rendering a clean still image¶
- In the toolbar's Path Tracing menu, set Denoiser to None and View to Lit.
- Open View → Scene Renderer, select the Rendering page and find the Sampling section.
- Make sure Progressive refinement is on.
- Frame the shot, then leave the camera and the scene still. Accumulated frames counts up as the image clears.
- Optionally turn on Adaptive sampling so that pixels that are already clean stop early.
The denoiser is a project setting, so step 1 changes every Scene tab. Set it back when you return to interactive work.
If bright speckles remain, lower Bright sample limit, but keep it above 0, which turns
the limit off. Lower values remove more speckles but can also dim bounced light that is meant
to be bright.
Live simulation
While a simulation plays, moving objects restart progressive refinement every frame. A denoiser gives a cleaner live image.
Environment multiplier¶
Environment multiplier on the Rendering page scales the light from the scene's
environment (the sky) in path-traced Scene tabs, on top of the environment intensity set in
the scene. The default is 1 and the range is 0 to 100.
It is a project setting that applies to every Scene tab, not part of the scene, and it does not change recordings. To change the environment in the scene itself, set the intensity on the scene's Sky Light; see Lights and Materials.
View modes¶
View in the toolbar's Path Tracing menu, and View mode on the Rendering page, switch between the lit image and diagnostic views that show what the path tracer sees. Lit is at the top of the toolbar menu; the other views are grouped in submenus.
| Group | View mode | Shows |
|---|---|---|
| Lit | The normal, lit image. | |
| Geometry | Instance ID | Each object instance in its own flat colour. |
| Barycentrics | A colour gradient across each triangle, showing how meshes are triangulated. | |
| Normals | The surface direction in world space, as colour. | |
| UVs | Texture coordinates in red and green, repeating across each texture tile. | |
| View Z | Distance from the camera in grey. Closer surfaces are brighter. | |
| Material | Albedo | The base colour of each surface, without lighting. |
| Transmission | The glass settings of each surface as colour. Transparent materials show blue; more Attenuation adds red and a higher IOR adds green. | |
| Diffuse Transmission Weight | In red, how much rough (frosted) glass scatters light softly rather than refracting it sharply. Green marks transparent materials. | |
| Motion Vectors | Surface Motion | How far each surface moves on screen between frames. Static objects stay black while the camera is still. |
| Specular Motion | How reflections move on screen between frames. |
Only the Lit view is denoised. The diagnostic views also skip bloom, exposure and depth of field, so they show the raw values. The view mode belongs to the Scene tab, which remembers it, like the render mode.
Performance statistics¶
The Scene Renderer's Statistics page shows what the active Scene tab costs.
- Mode shows the render mode and the viewport resolution.
- Viewport GPU shows the viewport's GPU time per frame, in milliseconds.
- VSync turns vertical sync on or off for the editor window.
In Path Traced mode the page adds two sections:
- Path tracing GPU timings is a table of GPU times with a Last (ms) column, the latest measurement, and a Smoothed (ms) column, a running average. The first row, Path tracing total, is the overall cost; it includes denoising but not bloom, compositing or editor overlays. The values arrive a few frames late, and a dash means that nothing was measured. These are viewport costs, not recording speed.
- Path tracing workload summarises the work: the trace resolution and the output resolution (they differ when DLSS upscales), the indirect bounce limit, the progressive history in frames, whether adaptive sampling is on, the number of ray-tracing instances, how many static meshes are ready or still being prepared, and the number of light entries. Light entries count the lights and the emissive triangles, but not the environment.
Tips¶
- Moving the camera, or changing anything in the scene, restarts progressive refinement.
- When a scene is first path traced, or a large scene is still loading, objects can appear one by one over the first moments while their geometry is prepared.
- In the toolbar's Camera menu, Near Clip works in both modes, but Far Clip is hidden in Path Traced mode: path tracing does not clip surfaces at the far plane.
- Selection outlines, the grid, gizmos and icons work as usual, and animated meshes are path traced.
- Aperture depth of field, lens models and vignetting work only in Path Traced mode. See Cameras and Exposure.
- Area lights cast soft shadows and emissive materials light the scene only in Path Traced mode. See Lights and Materials.
- You can change the render mode, the view mode and the denoiser during Play; the change shows straight away.
Where to go next¶
- Scene Renderer Panel for every field on the Rendering page and the other pages.
- Cameras and Exposure for exposure, focus and physical cameras.
- Lights and Materials for area lights, emissive materials and glass.
- Video Encoding and FFmpeg to record path-traced video.