Ray-tracing Moveable Objects

Question

I am fond of creating graphics and animations using the frameworks on the iOS platform; lately, I discovered that, in order to create better visual designs, those higher-level of frameworks do not provide enough controls to satisfy the needs of creating more advanced-level designs. Hence, I decided to invest my time in studying OpenGL ES.

Whilst doing so, I came across the ray-tracing topic; I have spent quite a bit of time studying the mathematics and topics related to it. And, I have been able to render simple stationary objects (geometrically) using this technique.

In order to learn deeper, I started to toy around with the idea of allowing these objects to have movements based upon user-interactions (I.e., when the user moves the object on the screen with her finger, the corresponding object will spin around or simply move to the respective location based upon the user's touch (on mobile device)).

According to what I have studied thus far on ray-tracing, however, this operation of allowing the objects to move based on user-interactions could be very costly in ray-tracing. To me, for example, it would mean that, if a rendered sphere were to spin around based on user's touch on the screen, I would need to ray-trace the whole sphere for every frames as the sphere spins.

Is my understanding correct here?

My question is, is it possible to perform ray-tracing on objects that are movable; if so, is there another ray-tracing technique specialized especially for this purpose, which could be less costly? Or, is ray-tracing more suitable for rendering only architectural objects, which are usually stationary?

Thank you.

Answer 1

Ray tracing is great for many uses and very interesting but it is a very computationally heavy process. Most of the time when you move an object you are going to have to retrace it, but this is not always the case. If you are not changing the perspective or the camera or the orientation of the object and it's not in shadow then you could keep the already traced version as a display.

Alternatively, you could have a fallback method of rendering for when you are moving the object around if this is not an extremely dynamic scene. For example if it's an adventure game then moving objects around does not usually happen that often so you could fall back onto standard rendering. Then your ray tracing could be done offline ie in a multi-frame process instead of making your whole rendering wait. Then once it's ready you could pop the finished render into the scene.

I did something similar in a project a while back to create icons for a drag and drop inventory and it worked like a charm.