3D rendering glossary
Real-time rendering: what it is, engines and applications
Real-time rendering is the technique that calculates the images of a 3D scene instantly, usually between 30 and 60 times per second, so that the user can move through and interact with it without waiting. It is the basis of video games, virtual tours, interactive models and virtual reality, and today it is also used in architecture and property development.
How real-time rendering works
Traditional (offline) rendering can take minutes or hours to calculate a single image, because it follows the path of millions of light rays with great precision. In real time, the engine has around 16 to 33 milliseconds per frame. To achieve that speed it uses the graphics card (GPU) and a number of shortcuts:
- Rasterisation: converts the triangles of the 3D mesh into pixels very quickly.
- Pre-calculated or dynamic lighting: some of the light is calculated in advance (lightmaps) and some on each frame.
- Levels of detail (LOD): distant objects are displayed with fewer polygons.
- Hardware ray tracing: current GPUs trace some rays in real time for more realistic reflections and shadows.
- AI upscaling (DLSS, FSR, XeSS): the engine draws at a lower resolution and reconstructs it, gaining smoothness.
Real time vs offline rendering
| Aspect | Real time | Offline |
|---|---|---|
| Time per image | Milliseconds | Minutes to hours |
| Interaction | The user moves freely | Fixed image or video |
| Realism | Very high, with some limits in indirect light and glass | Maximum physical control of light |
| Common engines | Unreal Engine, Unity, Twinmotion, Lumion, D5 Render, Enscape | V-Ray, Corona, Arnold, Cycles |
| Typical uses | Interactive models, tours, VR, configurators | Catalogue images, billboards, film |
The boundary is becoming increasingly blurred. Many studios use real-time engines also to produce images and videos, because they allow you to adjust the scene while seeing the final result immediately.
In practice: Render Fabrik is a 3D architectural rendering studio working with clients in Brazil and Europe, with a quote within 24 hours.
Applications in architecture and property development
- Interactive digital models: the buyer chooses the property, floor and orientation on a touch screen or on the web.
- Virtual tours: free visits through the show unit before it exists.
- Virtual reality: headsets such as Meta Quest allow you to walk through the spaces at true scale in the sales office.
- Finishes configurators: change flooring, kitchens or colours and see the effect instantly.
- Project review: architects and developers review volumes, views and sunlight in meetings, without waiting for new renders.
Other applications
- Video games, the industry that drove the technology.
- Virtual production in film and television, with LED backgrounds rendered live.
- Industry and training: digital twins, simulators and interactive manuals.
- E-commerce: 3D viewers and augmented reality to see a product from every angle.
How to prepare a project for real time
- Clean model: start from the architect's file (Revit, Archicad, SketchUp, Rhino) and remove layers, hidden objects and duplicate geometry.
- Optimisation: reduce polygons where they are not seen, group repeated objects (instances) and create levels of detail.
- PBR materials: flooring, facades, glass and metals are configured to respond well to light from any angle.
- Lighting: define the real sunlight according to location and orientation, and the interior artificial lighting.
- Interaction: program the menus, property selection, visit points or finish changes.
- Publication: export as an application for touch screen, for virtual reality headsets, for browser or for streaming from the cloud.
Delivery formats
| Format | Where it is viewed | Advantage |
|---|---|---|
| Desktop application | Computer or sales office screen | Maximum visual quality |
| Virtual reality | Standalone headsets or connected to a PC | Sense of true scale |
| Web | Browser, on mobile or computer | Shareable with a link |
| Pixel streaming | Browser, with the scene running in the cloud | High quality on any device |
| Pre-generated 360° tour | Any device | Lightweight and fast to load |
Requirements and limitations
- Scene optimisation: models with too many polygons or huge textures cause the frames per second to drop.
- User hardware: a browser or mobile experience needs to be lighter than one on a sales office computer.
- PBR materials: they are essential for the scene to look good in changing light.
- Glass, water and indirect light remain the areas where offline wins in quality.
Real time at Render Fabrik
At Render Fabrik we use real time for property virtual tours and interactive models of developments, and we combine it with offline rendering when a catalogue image requires maximum realism. We do it for developers throughout Spain and in cities such as Madrid and Barcelona. To choose a tool, also see our guide to rendering software.
Frequently asked questions
What does real-time rendering mean?
It means that the computer generates each image of the scene at the same time it is shown, dozens of times per second, so that the camera and objects can move according to what the user does.
Is it as realistic as a traditional render?
It comes very close, especially with hardware ray tracing. Offline rendering still offers more control over indirect light, glass and fine details, which is why it is preferred for large-format images.
What computer do you need?
To produce, a workstation with a powerful dedicated GPU. To view the result it depends on the format: a video or a 360° tour works on any mobile; a high-quality interactive model may require a sales office computer or cloud streaming.
What software is used in architecture?
The most common are Unreal Engine and Twinmotion, Lumion, D5 Render and Enscape. Unity is used above all in interactive applications and augmented reality.
Is real time useful for selling off-plan flats?
Yes, and it is one of its most impactful uses. The buyer can walk through the property, see the views from their floor and compare orientations before reserving. In the sales office it is used on touch screens or with virtual reality headsets; outside it, as a web tour that the sales agent sends by link to buyers who live in another city or country.
How long does it take to prepare a real-time experience?
It depends on the size of the development, the number of typologies and the interaction required. If the studio already has the 3D scene from the sales images, much of the work is done: the scene is optimised and navigation is added.