SCUMM: PUTTZOO Animation overlap bug with final iceberg in Putt-Putt Saves the Zoo

[Thunderforge]

During the puzzle to free the baby hippo, moving the final iceberg (the square one) results in an animation bug.

The iceberg moves past three penguins standing on ice. It correctly moves underneath the first penguin and his section of ice, but over the second penguin and his ice, before moving under the third penguin. After a moment, the ice then jumps underneath the second penguin and his ice. Instead, it should move underneath all three.

See the attached animated gif for a demonstration.

Reproduction

1. Either
   • Load the attached savegame
   • Open the debug console and type in room 17
2. Order the icebergs, finally clicking on the square iceberg
   • The savegame is set to right before this
3. Watch the animation as the square iceberg slides into place

Versions Tested

• ScummVM 2.5.1, Windows x64 and macOS x64
• Steam version of Putt-Putt Saves the Zoo

[AndywinXp]

In f216ee38:

SCUMM: HE: Fix TMSK ZPlanes handling

This closes ticket 13420:
"SCUMM: PUTTZOO Animation overlap bug
with final iceberg in Putt-Putt Saves the Zoo"

Not only this now works correctly, but now in updated versions
of the game the hair of the lower left penguin is not masked
anymore, so the iceberg piece will be drawn on top of said hair.
I have verified that this is 100% accurate, the code for TMSK
decompression is the same in every HE version, and the original
executable shows exactly the same behavior.

So refrain from filing a bug for that, thanks :P