Request: Allow drawing with a custom keyboard key instead of mouse button

Summary
Currently, all major raster drawing programs require a mouse click (or pen press) to trigger brush strokes. This can be uncomfortable or imprecise for users working with a touchpad, small mouse, or on the go. I propose adding support for customizable keyboard keys to act as the drawing trigger — e.g., pressing and holding Space, A, Caps Lock, or any other key to simulate “left mouse button held”.

Motivation
Clicking with a mouse or pressing a touchpad introduces physical tension that reduces accuracy, especially during slow or precise strokes. A keyboard key does not affect pointer position — resulting in smoother, more controlled drawing.
Microsoft Paint (on Windows 10+) incidentally demonstrates this: it treats Space as LMB (though inconsistently). This accidental feature makes it surprisingly good for drawing with a touchpad or weak grip. However, it’s buggy and unintentional.

Request

  • Add an option to set a keyboard key as the brush activation trigger.
  • While this key is held, brush strokes should be drawn as if the left mouse button is held.
  • This key should be user-assignable and not interfere with existing shortcuts.
  • Ideally works with all brush-based tools.

Use Cases

  • Artists on laptops without drawing tablets.
  • Touchpad-only workflows (e.g., mobile work, minimal setups).
  • People with motor issues, hand tremor, or fatigue from mouse clicking.
  • Anyone who prefers decoupling position from pressure.

Hum, doesn’t most OSs have accessibility options to do just that? Specially for keyboard with a numpad?
Not sure about the mobile people tho, but still…