In HitFilm you can composite in two dimensions, three dimensions, or a mixture of both.
Working in 3D is not necessarily better or more advanced, as 2D compositing will be faster and more appropriate for some projects. You can change layers from 2D to 3D and back again at any time, so you can experiment with different setups to see which best suit your project.
If all your layers are in 2D you will create composites by ordering your layers, with higher layers obscuring lower layers.
If you're new to 2D compositing, it is easiest to think of it like a stack of paper. Each piece of paper is a layer on your timeline. When you look down on the stack of paper you only see the top piece, which is exactly how HitFilm sees your 2D layers. If your top piece of paper is smaller than the rest, or if you cut a hole in it, you'll then be able to see the layers below.
Most special layers can exist in 2D or 3D. When in 2D they will behave like any other 2D layer.
When you're working only in 2D, light and camera layers do not have any effect.
You can switch layers to 3D at any point using the 2D/3D toggle.
Additional properties become available when a layer is switched to 3D.
If any 3D layers are present in a composite shot there must be at least one camera. If you try to create a 3D layer without any camera layers you will be given the option of creating one automatically or switching back to 2D.
Detailed information on working in 3D can be found in subsequent chapters, particularly the Viewer panel section.
3D Layer order
When layers are in 3D their visibility is usually determined by their location in 3D space. If more than one layer occupies the exact same space the timeline's layer order is then used to determine the compositing order.
For example, if two images share the same 3D position and angle, the image on the higher timeline layer will be the visible one.
All special layers can exist in 3D. Light and camera layers are always in 3D.
2D & 3D
You can mix 2D and 3D layers together in the same composite shot.
While timeline layer order is less important for 3D layers (although see the exception above), if you mix 2D and 3D in the same composite shot the layer order becomes very important.
Any 2D layer positioned on the timeline between 3D layers will split them into separate render groups. Any 3D layers above the 2D layer will not affect any 3D layers below the 2D layer.
This can make a big difference to the end result. For example, if you are using lights, a 2D layer between the light layer and your 3D layers will stop the light from affecting those layers. Similarly, 3D layers separated by a 2D layer will not be able to interact in 3D space.
RECAP 2D and 3D layers can co-exist in the same composite shot.