Why does rendering nothing take 45 seconds?

Question

I've disabled all objects except the camera and hit F12 to do a quick render.

Blender takes 45 seconds just to draw a blue screen.

In my user preferences my 2011 GeForce card is enabled.

Why so long? How do I improve this please?

If this information helps, maybe some other setting is wrong, because my Cycles Renderer looks fine in the 3D window:

but my Blender Renderer looks completely wrong, turning my green hairy plane orange. And when trying to F12 with it it just draws a grey screen instantly with no world background color.

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UPDATE:

I've done all these tips to bring down render speed:

• in render options - light paths set bounces from 0 to 4
• change dimension - resolution - to 50%
• performance - change tile size to 256
• shading - disable ray tracing
• world - disable ambient occlusion
• light paths - disable shadows
• render - sampling - reduce to 8 from 128

That takes rendering nothing from 45 seconds to 5 seconds. But I want it to be almost instant. I have to render an animation that's thousands of frames long and it's just a simple cube moving across the screen.

I tried making a similar animation in three.js and it draws things pretty much instantly in real time in my web browser. I don't understand why Blender is being so slow :(

Answer 1

It is not a big surprise.

This is the time it takes to render nothing on an old i7 2600K processor:

And this is the time it takes to render the same nothing on the same old i7 2600K processor 2048 times(2048 samples):

Cycles is not very adaptive. It does not care much that it is the same plain color you ask to be sampled 128 times. It will do precisely that. This is pretty normal. The GPU you are using might not be a very powerfull solution for rendering. You could try CPU rendering as well see if that is any better with the CPU you have.

If you need simple results, you could also look into OpenGL rendering. That will render whatever you see in the viewport. It has a few settings so you could use better antialiasing as well.

Answer 2

The Cycles renderer does ray tracing and thus takes ages to calculate every frame. See here: https://gamedev.stackexchange.com/questions/136757/how-do-modern-game-engines-achieve-real-time-rendering-vs-blenders-slow-rende#answer-136776

If you're using Blender before 2.8 then use the Internal Render engine, it's MUCH faster than the Cycles Render engine.

If you're using Blender 2.8 or after then use the EEVEE Render engine.

This alone should fix the problem, reducing your renders to near instant.

You're getting funny colors on your objects because when you switch between Cycles and Internal you have to reassign all your materials - each engine has different materials that aren't compatible with the other renderer.

If you want to use Cycles for some reason then you can improve render times a bit by trying:

• in render options - light paths set bounces from 0 to 4
• change dimension - resolution - to 50%
• performance - change tile size to 256 (16 for cpu only with no gpu)
• shading - disable ray tracing
• world - disable ambient occlusion
• scene - simplify
• light paths - disable shadows
• render - sampling - reduce to 8 from 128