Extract pclx to a random generated folder name to avoid name conflicts

[chchwy]

Related issues #932 #752

The issue described by @scribblemaniac :
If a user opens the same project twice in a row, Penci2D will:

1. Create data folder for file to load
2. Load everything into the data folder
3. Stop if there is an error
4. Switch to using the new data folder
5. Delete the old data folder

However, if the old data folder and new data folder are the same, then step 5 ends up deleting all the data from our project!

In order to resolve the name conflicts, the data folder will include an 8 character long random string.

For example:

• YourProject_Y2xD_6xseyd51
• Default_Y2xD_5zy4hsui

[scribblemaniac]

For my peace of mind, could we change the following few lines to this:

QString strWorkingDir;
QDir dir(QDir::tempPath());
do {
    strWorkingDir =
        QString("%1/Pencil2D/%2_%3_%4/").arg(QDir::tempPath()).arg(strFolderName).arg(PFF_TMP_DECOMPRESS_EXT).arg(uniqueString(8));
} while(dir.exists(strWorkingDir));

The chance of generating the same string is almost impossible, but I would feel better if we checked for it anyway.

[chchwy]

Done. thanks for reminding.

[scribblemaniac]

The default folders are not getting deleted. This is because the Object destructor only calls deleteWorkingDir if filePath() is empty. Instead I think we should always call deleteWorkingDir, and just add a check in that function to make sure that mWorkingDirPath is not empty.

On a slightly unrelated note, is there any reason why we don't just call init in the Object constructor? That way we can be sure that it is called at least once.

[chchwy]

The behaviours were introduced in a PR #591, I don't really remember why it's working in this way. So the working directory will be deleted anyway now.

For my understanding, Object::init() is for a new Object. In Pencil2D it's the starting default project and the project when you click from the menu File->New. It's no harm to call init() on an Object from a pclx file but all data will be overwritten immediately.

[J5lx]

Seems good to me except for what scribblemaniac noted. Also, not directly related to the PR, but what does Y2xC and Y2xD stand for? It seems the last letter distinguishes between (de)compression, but what about the rest? Just curious.

[chchwy]

Y2xC is legacy and not used anymore. I deleted it. Preserved Y2xD for the sake of debugging. I can quickly check all pencil2d working directories on my computer by a keyword.