Layer Opacity dialog: Fade in/out not working properly

[MrStevns]

• Fade in/out buttons would not be updated when changing the selection on the timeline

How to reproduce:
Open the layer opacity window, select a few frames on the timeline.

Result:
Fade in/out buttons are not enabled.

Expected:
Fade in/out buttons would be enabled when 3 or more keyframes had been selected

---

• Fade in would never make the last frame fully appear

How to reproduce:

• Create 3 keyframes and draw numbers on them, 1, 2, 3 respectively
• Select the 3 keyframes on the timeline and open the layer opacity window from Layer menu -> "Layer /Keyframe opacity"
• Select the "Fade in" button

Result:

• frame 1: 33% opacity
• frame 2: 66% opacity
• frame 3: 100% opacity

Expected:

• frame 1: 0%
• frame 2: 50%
• frame 3: 100%

---

• Fade out would never make the last frame fully disappear

How to reproduce:

• Create 3 keyframes and draw numbers on them, 1, 2, 3 respectively
• Select the 3 keyframes on the timeline and open the layer opacity window from Layer menu -> "Layer /Keyframe opacity"
• Select the "Fade Out" button

Result:

1. 100%
2. 66%
3. 33%

Expected:

1. 100%
2. 50%
3. 0%

---

• Fade functionality didn't take the initial keyframe opacity into account

How to reproduce:

• Create 3 keyframes and draw numbers on them, 1, 2, 3 respectively
• Select the 3 keyframes on the timeline and open the layer opacity window from Layer menu -> "Layer /Keyframe opacity"
• Scrub to keyframe 1 and set the opacity to 50%
• Select the "Fade Out" button

Result:

1. 50%
2. 33.2%
3. 16.6%

Expected:

1. 50%
2. 25%
3. 0%

Application details

Version: 0.7.0.911
commit: 7e83608
date: 2024-06-19_01:01:26

Operating System: macOS 12.7
CPU Architecture: x86_64
Qt Version: 5.15.13

[chchwy]

Fixed in #1854