Embarrassed...but here goes: Hopefully the render dialog can be demystified

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12 is the bounding total. So if a ray hits 4 diffuse surfaces, 4 glossy surfaces and 8 transparency surfaces it will stop after 12 bounces. The reason is that you can have more bounces for surfaces that take longer to converge without wasting time computing unneccessary diffuse and specular bounces.

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are you sure? I also never understood this:
imagine you hit 5 diffuse and the 6th bounce would be glossy. What then?
Does it terminate after 4 diffuse? Cant just skip one…

edit: and even more - the only way a ray contributes is when the last hit is the sky or a light / emissive shader - how does this correlate with the diffuse vs. total?

As far as I understand, the integrator keeps track of bounces by type and terminates the ray when it reaches the limit (either the total or one of the bounce types). After 4 bounces the contribution to the overall radiance is quite small (maybe even negligible).

How the integrator connects the ray to a light source is beyond my understanding. However, I do see that lights have their own max boucnes setting (1024 by default).

So, if a single surface has both, diffuse and glossy, is it counted as two total bounces?

Nope, they raise the count by 1 both for diffuse and for glossy.
And even more confusing: unless you are using branched path tracing, only 1 component at time will be choosed (randomly) for each single path camera-to-lightsource(or end of bounces).

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Which means the 12 we typed here inside transmission (which happened to be the default setting by the way) will not be ultilize/executed at all ?
WHY THEN does the user be allowed to change a setting that WILL NOT BE RESPECTED then ?

This is all so very confusing, I never understood this.
It’s almost like the dialog is saying “Set your numbers but F you anyway, I will just do my own shit.”

I know you are not the creator of the engine and you are trying your best to help, I want you to know WE ALL APPRECIATE your attempt, you are trying and we know and appreciate it.
But it seems in your attempt to help, even you realize just how much you are confused by this too.

BIG HUG and love to you @WombleMonster.

Hi Bracer,

This might help, pay particular attention to the pathtracing part of the video.


@Grimm, I have seen that video before.
Thank you for your attempt, I do believe most of us understand the basics of ray bounce here which is basically what that video is about, 10 minutes of generic ray bounce explanation.

The issue here is not about “I don’t understand path tracing” or “I don’t know what ray-tracing is”, the issue here is “I can’t make heads or tail about the non-coherent Blender light integrator dialog settings, the numbers doesn’t even add up”, look at my first post and look at the picture that speaks a thousand words ;p

Ah, sorry, no problem. The settings are there so you can have some control over your rendering. You don’t know ahead of time how many bounces will happen for any pixel being traced. In a pathtracer (Cycles) every bounce is randomly chosen by type (diffuse, reflection, refraction, specular, etc.) Like was said before the integrator adds these up and terminates the ray when the total threshold is reached. It has the total bounce number so the tracer doesn’t go off and keep tracing rays that don’t change the pixel color very much. It just sets a max bounce limit. The other bounces happen until their limits are reached, then they are excluded from the random choice.


Total is just a cap. It’s not the total mathematically of the things listed beneath it. It’s the total maximum number of bounces. Imagine you set all the bounces below to 128. You could then use Total at 4 or 8 for initial renders and then change it to a higher number for final renders.


You can use the bounding limit for test renderings while working on a project. I.e, you have figured out you need so and so many of different bounces for a certain part of the scene, you can limit it down while working on scene objects and test rendering those.

The transparency is Independant from all other. It can be as high has it goes and not be affecting the others. Because the transparency is for the alpha textures. In 2.7 it had its own category, I wonder why they merged the visuals.

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It is also useful to animate it so you can fade to less bounces in animations when the camera passes an area where less bounces are needed.

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To be nitpcky, it is for transparent shaders.

Hello John, are you saying that the total is nothing but a proportional scale ?
To make it easier for me to understand does that mean that if I set total to 2 but I set EVERYTHING to 20 and now I set total to 1 EVERYTHING will now be rendered as though they are 10 ?

No. It’s a cap. If you set everything to 20 and Total to 10 you would get a maximum of 10 bounces. If you then set it to 20 you would get 20 bounces.

The tooltip for Total reads “Max bounces: Total maximum number of bounces”. The tooltip for Diffuse reads “Diffuse Bounces: Maximum number of diffuse reflection bounces, bounded by total maximum”. Same for the rest apart from Transparency which isn’t bounded by Total.

:angry" but there is not diamond icon next to that! I had never even thought it might be animatable!

You can animate most things in Blender. Even drop down menus such as the the “view transform” from “filmic” to “standard” or “raw”. Or the render device from “gpu” to “cpu” or the feature set from “supported” to “experimental”.

Ok, then I have decided to down from 20 to 7 but the ray count bounce for different slot diffuse/transmission/whatever are ALL DIFFERENT, how is the cut off/redistribution done ?