Why are games rendered with a GPU while Blender, Cinebench and other programs use the CPU to render high quality 3d imagery? Why do some start rendering in the center and go outwards (e.g. Cinebench, Blender) and others first make a crappy image and then refine it (vRay Benchmark)?

Question

Why are games rendered with a GPU while Blender, Cinebench and other programs use the CPU to render high quality 3d imagery? Why do some start rendering in the center and go outwards (e.g. Cinebench, Blender) and others first make a crappy image and then refine it (vRay Benchmark)?

In: Technology

Answer 1

These are all different programs each with a different way of rendering graphics.

GPUs tend to render the image as a series of triangles with textures on them. This is good enough for video games and more importantly with the GPU it can be done in real time so you can get 60-120 frames per second without too much issue. Lighting calculations must be done separately and you’ve likely seen video games produce crappy shadows for moving objects and maybe have a setting to control how good they look in exchange for CPU performance.

You CAN make GPUs do rendering differently, but you have to write the code to do it yourself rather than using Direct3D or OpenGL to do it for you. This can be difficult to do as it’s like a whole new language.

These other programs use different methods of rendering. What matters most though is they are doing it pixel by pixel and take the properties of light and reflection very seriously. The shadows produced will be as close to perfect as possible taking into account multiple light sources, point vs area light, and reflections. Consequently they look VERY good but take a lot longer to render.

Starting from the centre and working your way out is just a preference thing. Some renderers start from the top-left corner. But since the object in question tends to be at the centre of the camera shot and these renders take a while, starting from the centre makes sense in order to draw the thing in frame most quickly.

vRay renders the whole frame at once rather than starting in a small spot and working its way out. I don’t use it, but from seeing other benchmarks I suspect it works by firing light rays from the light sources (eg: the sun) which find their way to the camera rather than firing scanning rays from the camera to produce an image more consistently. This means the image is produced chaotically as photons from the sun find the camera rather than the camera discovering the scene lit by the sun.