Pixel-perfect collider-free picking of objects in Unity. Picking here meaning getting an object reference for an arbitrary screen location. More of a proof-of-concept for future reference than anything else.

• If your models use multiple materials contributing to the pickable area you may also want to adjust Pickable to adjust all materials, not just the primary one.
• If your camera uses some sort of postprocessing effects, you'll want to use a separate camera which doesn't (to avoid altering the pickable ids rendered as colors).

A script attached to a camera (PickingProvider) renders pickable objects' ids into a RenderTexture using a replacement shader which gets the id via a shader property named _PickableId, set by a component that has to be present on each pickable object, Pickable. The RenderTexture is then read back into a NativeArray<Color32> to allow reading pickable ids at any screen coordinate in constant time.

The following components are needed:

• Pickable, adds override render tag PickableType=Pickable to the primary material of all renderers on its GameObject and all child GameObjects and adds the pickable's id as a shader property named _PickableId to the MaterialPropertyBlock of these renderers (adds one if necessary).
• PickingProvider, must be attached to a camera, manages GPU and CPU side data (RenderTexture and NativeArray<Color32>) and renders pickable ids into the texture then reads it back using an asynchronous GPU read request. Provides lookup of screen position to pickable object reference.
• PickingManager, a singleton, i.e. only one can exist at a time. Tracks all adjusted material instances for their original materials, so Pickables can re-use already adjusted materials (avoids Pickable components creating new materials all over the place to add the override tag). The adjusted materials get destroyed when the PickingManager gets destroyed. Also provides lookup of pickable ids to pickable objects.