Issue Summary

As the name implies, having a discrete constraint (i.e variable degree from initial click placement) to create straight lines is a very widespread and useful feature that Pencil2D has been missing ever since it was created.

Even the polyline tool could benefit from this behavior as creating straight lines at odd angles doesn't look really nice when you need precision drawing for creating certain shapes.

Expected Results

To be able to create a straight line at regular or odd intervals depending on a modifier key (normally SHIFT). This would however have to be validated against the Quick-sizing behavior which already uses the hard coded SHIFT key to change the brush size when enabled

Angle based on initial mouse / stylus direction
H: Horizontal Angle (0°, 180°)
V: Vertical Angle (90°, 270°)
D: Discreet Angle (Depends on degree setting, initially 45° steps)

• Pencil Tool: H & V
• Pen Tool: H & V
• Brush Tool: H & V
• Eraser Tool: H & V
• Polyline Tool: H, V, D

Video or Image Reference

Red: odd angle straight lines (current)
Blue: discrete angle straight lines