Fan speed for solid infill showing erratic behaviour

[kb-elmo]

Describe the bug
Solid infill areas seem to ignore all fan speed settings and get a value that is outside of the defined fan speed parameters

To Reproduce
Steps to reproduce the behavior:

1. Slice any model with three bottom layers (layer 2 and 3 as solid infill)
2. Set fan settings as shown in the screenshot
3. Layer 2 will have way slower fan speed than defined in the settings

>> Project File <<
BugBenchy.zip

Expected behavior
The solid infill shouln't get apparently random fan settings that are outside of the defined parameters.

Screenshots (click the images to show the full size)
Fan speed settings

Fan speed result of the second solid infill layer

Desktop (please complete the following information):

• OS: Windows 10
• Version 2.3.56.9

Additional context
Add any other context about the problem here.

[supermerill]

seems like /2 for the second layer

[kb-elmo]

seems like /2 for the second layer

I just noticed the same behaviour in PrusaSlicer.

I don't really understand why it's doing that?
There's no good reason why the second layer should get less cooling than the first one.

[supermerill]

that's because of the "Full fan speed at layer"
I found that if the disable is at 0, this thing set it to1 after the first the first layer.
I'll try to understand the thing and fix it.

[supermerill]

Ok, now if Full fan speed at layer > 1 and dsiable_fan_first_layers is 0:

• the fan is never shut down
• the ramp-up happens as if the layer '0' (which don't exist) was at 0 fan speed

So with 'full fan' at layer 3, and default fan at 100%, you should have:

• fan at 100% at layer 3
• fan at 66% at layer 2
• fan at 33% at layer 1