Provided by: libsdl3-doc_3.2.20+ds-2_all 

NAME
SDL_PEN_TOUCHID - The SDL_TouchID for touch events simulated with pen input.
SYNOPSIS
#include <SDL3/SDL_pen.h>
#define SDL_PEN_TOUCHID ((SDL_TouchID)-2)
AVAILABILITY
This macro is available since SDL 3.2.0.
Simple Directmedia Layer SDL 3.2.20 SDL_PEN_TOUCHID(3)