3D models are rendered onto live video feeds in augmented reality (AR) through a combination of real-time tracking, environment understanding, and compositing. The process begins by capturing the live video feed from a camera and analyzing it to determine the device’s position and orientation in 3D space. This is typically done using computer vision techniques like SLAM (Simultaneous Localization and Mapping), which identifies feature points in the environment and tracks their movement frame-to-frame. Once the device’s pose (position and rotation) is known relative to the physical world, a virtual camera in the AR system is aligned to match this pose, ensuring that 3D models appear anchored to real-world surfaces or coordinates.
The next step involves rendering the 3D model using a graphics pipeline. The model’s vertices are transformed into the virtual camera’s view space using matrices that account for the device’s pose. Lighting and shadows are calculated to match the real environment—for example, AR frameworks like ARKit or ARCore use ambient light estimation from the camera feed to adjust the virtual model’s brightness and color. Shaders then process the model’s textures and materials, blending them with the live video feed. A critical part of this stage is occlusion handling, where depth buffers or segmentation masks ensure the model appears behind or in front of real objects correctly. For instance, if a virtual cup is placed on a table, depth testing prevents it from rendering over a real object that passes in front of it.
Finally, the rendered 3D model is composited onto the live video feed. This involves alpha blending to combine the model’s pixels with the camera’s pixels while maintaining transparency effects. Performance optimizations, such as reducing polygon counts or using level-of-detail (LOD) techniques, are often applied to maintain a smooth frame rate. Developers working with tools like Unity or Unreal Engine can leverage built-in AR plugins to automate much of this process. For example, in Unity’s AR Foundation, a single shader might handle both environmental lighting and occlusion by sampling the camera’s depth texture. The result is a seamless integration of virtual and real elements, enabling applications like furniture previews or interactive gaming that feel grounded in the user’s physical space.