Is it possible to render a fairly graphical movie on a decent gaming-computer, with a GTX graphics-card, 4 2 GHz core CPU and 8 GB of RAM, or do you need to have a gigantic rendering-farm like Disney?
I've always wondered why Disney use rendering-farms when there are mainstream programs that seem to be able to do the trick on just one pc. Also is it possible to use some simple level of raytracing, for light reflections, and simple hair-physics?
It is possible to render a movie on a single computer. It depends on what movie it is. If you choose a style that renders extremely fast, it is possible. Nothing like the ones Disney make though. Not even remotely close.
Let's say you are rendering a movie that is 1 hour and 30 minutes. Let's say 1 frame of that movie renders extremely fast - 2 minutes. You are rendering 90 minutes of video, that is 5400 seconds and you probably need 30 frames for each second so that's 162000 frames. Each takes 2 minutes, so that comes to 324000 minutes that is 5400 hours and that is 225 days. So if you run your computer for 225 days, you will render your movie.
Now try having a simple scene that is inside some room and needs light that comes from a window(so it needs light that bounces around) and render it in 4k resolution in 2 minutes... That is a very hard thing to do. Chances are you will need a few hours at least for a single frame of any of the Disney movies on a single PC. That's why it is impossible to render on a single PC.
It is possible, but you must not compare apples and oranges.
I've rendered movies on a single computer (which was worth about as much as a middle-class car at that time) in the mid-1990s. No problem there. Leave your computer run all afternoon and over night, then in the morning watch your 3-minute 320x200 movie, and discover that something isn't quite right. So... change that, and repeat. Eventually you would repeat it with antialiasing enabled, which would take all week long. Mind you, some rather simple, reflective stuff at 320x200 resolution was really huge, awesome CGI at that time. Even moreso if the clip was longer than 15 seconds.
At that time, and even decades later, the big studios were using huge renderfarms. Why? Well, first of all because it makes getting things right a lot easier since near-production previews are minutes rather than days.
And second, because apples and oranges. Rather than a more or less hardwired renderer, studios used RenderMan which was already able to do approximately what GLSL provides today, plus quite a bit more (... in the 1990s!). Needless to say that it was millions of times slower.
OK, your GPU is just about as powerful as a render farm back then. Why do they still use renderfarms?
Professional movies, even when NPR, typically use very complex lighting models with literally hundreds of bounces, indirect lighting, volumetric lighting/shadowing, area lights, and literally dozens of shadow map samples, and several dozens of input fragments per pixel. And, of course, large scenes with very complex, detailled-to-the-hair models, and shadow maps so large that they'll hardly fit in your GPU's memory. Plus, motion blur and whatnot (real motion blur, not the fake alpha-blended-last-frame one).
Professional CGI (even when NPR) doesn't look like CGI, or it is bad CGI. That doesn't come for free.
For production, a single frame will easily take several minutes, and often hours. So, for a movie with roughly 150,000 frames... you had better have some kind of parallel processing, or it will take forever!
One GPU may be good enough for Eevee but hardly when using Cycles. Eevee does not support real time ray-tracing yet.
Disney renders in 4k or higher, a single computer is currently not good enough to handle their scenes (technically, it is, but you would have to wait years for the movie to be released).
With some upgrades, you can render a SHORT (path-traced) movie ideally in 1080p. I would recommend 3-4 GPUs connected to one PC (something like 2080s or better). If you have complicated scenes (volumetrics, transparencies, etc.) and want a decent quality, one frame can take up to 45 minutes (my experience with 3x 1080ti). So reserve a couple of months for your rendering.
Also 8 GB of ram is not enough. Go 32 or 64 GB at least.
If you want to render a Pixar quality movie, the answer is that it can't be done on an ordinary PC. The reason, as mentioned in Larry Gritz' answer to this question . .
https://stackoverflow.com/questions/38029698/why-do-we-use-cpus-for-ray-tracing-instead-of-gpus
. . is that asset loads for a single frame can be in the terabyte range, requiring roughly two orders of magnitude more RAM than your PC has.
Then there is the fact that you would die of old age long before it finished rendering anyway.
You can of course buy a RTX graphics card and render the sort of detail you get in a video game. This would be fine for an amateur/student project. It wouldn't fly at Pixar though.
It's a trade-off. It depends on the level of quality that you want.
You can easily render "movies" on one computer, even a laptop. I personally haven't delved very deeply into Blender, but I haven't created anything that took more than, say, 5 seconds per frame to render (using the default Blender Internal engine). At that speed, at 24 FPS, it will take you 2 minutes to render one frame of video. If you decrease the resolution, or render at 12 FPS, you could get it down to 30 seconds per second (but the quality will certainly not be as good).
In tools other than Blender, you can render movies in real time (1 second per second), or even faster. That is what a 3D video game does, after all. But it will not be professional movie quality.
Huge movie studios have huge teams of artists and programmers trying every trick they can think of to make their movies look professional. For them, realism is more important than cost and rendering time. Therefore, they end up with movies that look very real, but are really really really slow to render. Then, they buy tons of hardware so they can render it anyway.
If you're rendering on your PC, you would probably choose to make a movie that renders much faster, but doesn't look as good. You might not have the time to make it perfect, anyway - you're only one person.
Note that rendering is quite flexible. To get very quick feedback, you might render individual frames at a low resolution (like 320x200). You could preview sections of your movie at 12 FPS, by skipping 4 out of every 5 frames if it's meant for 60 FPS.
Then when you're absolutely finished, you can crank the knobs to 11, render in 4k 60FPS and let your computer chug away for two months. Or choose 1080p 30FPS instead, and have it done in two weeks. Of course, "two months" and "two weeks" are just examples - I don't know how long your movie will take to fully render.
If you find a small mistake in this final render, you can fix it and re-render those specific frames. If you find a big mistake when it's only halfway done, you can stop it, fix the mistake and render the second half. You don't need to wait for it to finish - you can let the computer work around your schedule. It's not like you have to start it going and then leave your computer on 24/7, and start all over again if there's a power cut. If your computer fan is too noisy to sleep with, you could do a chunk of rendering every day when you're at work, and stop it when you go to bed, and so on. (Note: this depends on the output format. For maximum flexibility, you want to save every frame as a separate picture, and then put them together into a video file once all the pictures are done)
