| Value | Meaning |
|---|---|
| SDL_PEN_AXIS_PRESSURE | Pen pressure. Unidirectional: 0 to 1.0 |
| SDL_PEN_AXIS_XTILT | Pen horizontal tilt angle. Bidirectional: -90.0 to 90.0 (left-to-right). |
| SDL_PEN_AXIS_YTILT | Pen vertical tilt angle. Bidirectional: -90.0 to 90.0 (top-to-down). |
| SDL_PEN_AXIS_DISTANCE | Pen distance to drawing surface. Unidirectional: 0.0 to 1.0 |
| SDL_PEN_AXIS_ROTATION | Pen barrel rotation. Bidirectional: -180 to 179.9 (clockwise, 0 is facing up, -180.0 is facing down). |
| SDL_PEN_AXIS_SLIDER | Pen finger wheel or slider (e.g., Airbrush Pen). Unidirectional: 0 to 1.0 |
| SDL_PEN_AXIS_TANGENTIAL_PRESSURE | Pressure from squeezing the pen ("barrel pressure"). |
| SDL_PEN_AXIS_COUNT | Total known pen axis types in this version of SDL. This number may grow in future releases! |
Pen axis indices.
These are the valid values for the axis field in SDL_PenAxisEvent. All axes are either normalised to 0..1 or report a (positive or negative) angle in degrees, with 0.0 representing the centre. Not all pens/backends support all axes: unsupported axes are always zero.
To convert angles for tilt and rotation into vector representation, use SDL_sinf on the XTILT, YTILT, or ROTATION component.