include: Added category docs for SDL_mouse.h

Reference Issue #11847.

Author: icculus

include/SDL3/SDL_mouse.h

@@ -22,7 +22,36 @@
 /**
  * # CategoryMouse
  *
- * SDL mouse handling.
+ * Any GUI application has to deal with the mouse, and SDL provides functions
+ * to manage mouse input and the displayed cursor.
+ *
+ * Most interactions with the mouse will come through the event subsystem.
+ * Moving a mouse generates an SDL_EVENT_MOUSE_MOTION event, pushing a button
+ * generates SDL_EVENT_MOUSE_BUTTON_DOWN, etc, but one can also query the
+ * current state of the mouse at any time with SDL_GetMouseState().
+ *
+ * For certain games, it's useful to disassociate the mouse cursor from mouse
+ * input. An FPS, for example, would not want the player's motion to stop as
+ * the mouse hits the edge of the window. For these scenarios, use
+ * SDL_SetWindowRelativeMouseMode(), which hides the cursor, grabs mouse input
+ * to the window, and reads mouse input no matter how far it moves.
+ *
+ * Games that want the system to track the mouse but want to draw their own
+ * cursor can use SDL_HideCursor() and SDL_ShowCursor(). It might be more
+ * efficient to let the system manage the cursor, if possible, using
+ * SDL_SetCursor() with a custom image made through SDL_CreateColorCursor(),
+ * or perhaps just a specific system cursor from SDL_CreateSystemCursor().
+ *
+ * SDL can, on many platforms, differentiate between multiple connected mice,
+ * allowing for interesting input scenarios and multiplayer games. They can
+ * be enumerated with SDL_GetMice(), and SDL will send SDL_EVENT_MOUSE_ADDED
+ * and SDL_EVENT_MOUSE_REMOVED events as they are connected and unplugged.
+ *
+ * Since many apps only care about basic mouse input, SDL offers a virtual
+ * mouse device for touch and pen input, which often can make a desktop
+ * application work on a touchscreen phone without any code changes. Apps that
+ * care about touch/pen separately from mouse input should filter out
+ * events with a `which` field of SDL_TOUCH_MOUSEID/SDL_PEN_MOUSEID.
  */
 
 #ifndef SDL_mouse_h_