Text Tool gets Insert Mode in addition to Overwrite Mode

[porg]

Feature Proposal

Use Cases

• Ofc overall overwrite mode is the right mode for an ASCII Art software in general
  • But sometimes you may want to correct text by normal text insertion
• Doing that with an overwrite mode can be quite tedious:
  • Move text with the move tool
  • Then type in text in newly free blank postion
  • Notice you have a few blanks to few or too many
  • Move text with the move tool
  • … until you finally got it.
• Or export, paste into other text editor, perform insertions there, then clear all and paste back.
  • … also an interrupted not so smooth workflow.

So having an insert mode, would definitely pay off for some situations.

[porg]

• Or as all other tool shortcuts are bound to the alt key, feel free to bind alt-i to toggling "insert mode" on/off.
• alt-o is already proposed by me for an upcoming "oval" tool,
  see section "Tool shortcuts" in #238