feat: Implement S-Pen virtual barrel pointer system

- Add virtual pointer system for S-Pen barrel button detection
- Index 0: tip pointer (when tip pressed)
- Index 1: virtual barrel pointer (when barrel pressed, mirrors tip XY)
- pointer_count: 0 (hover), 1 (tip or barrel only), 2 (both)
- Maintains libretro semantics and backwards compatibility
- Allows cores to detect barrel via pointer_count > 1 or checking index 1
- Preserves existing multi-touch functionality

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: f4mrfaux

input/drivers/android_input.c

@@ -1116,25 +1116,37 @@ static INLINE void android_input_poll_event_type_motion(
                android->mouse_x_viewport = android->pointer[motion_ptr].x;
                android->mouse_y_viewport = android->pointer[motion_ptr].y;
 
-               if (stylus_pressed)  /* Only set pressed state and pointer count when contact detected */
-               {
-                  /* Ensure pointer_count covers this motion_ptr */
-                  if (android->pointer_count < (int)motion_ptr + 1)
-                     android->pointer_count = (int)motion_ptr + 1;
-                  
-                  /* Update mouse button states for menu interaction */
-                  android->mouse_l = tip_down;  /* Left click when tip touches */
-                  android->mouse_r = side_primary;  /* Right click on barrel button */
-                  
+               /* S-Pen Virtual Pointer System for libretro cores:
+                * Index 0 = tip pointer (when tip pressed)
+                * Index 1 = virtual barrel pointer (when barrel pressed, mirrors tip XY) 
+                * This allows cores to detect barrel via pointer_count > 1 or checking index 1 */
+               
+               android->pointer_count = 0; /* Reset count, will increment based on active states */
+               
+               if (tip_down) {
+                  /* Set up tip pointer at index 0 */
+                  android->pointer[0] = android->pointer[motion_ptr]; /* Copy translated coordinates */
+                  android->pointer_count = 1;
+               }
+               
+               if (side_primary) {
+                  /* Set up virtual barrel pointer at index 1, mirroring tip coordinates */
+                  android->pointer[1] = android->pointer[motion_ptr]; /* Same coordinates as tip */
+                  android->pointer_count = tip_down ? 2 : 1; /* Increment if tip also active */
+               }
+               
+               /* Update mouse button states for menu interaction */
+               android->mouse_l = tip_down;     /* Left click when tip touches */
+               android->mouse_r = side_primary; /* Right click on barrel button */
+               
 #ifdef DEBUG_ANDROID_INPUT
-                  if (action == AMOTION_EVENT_ACTION_DOWN)
-                     RARCH_LOG("[Stylus] POINTER DOWN @ (%.1f, %.1f) idx=%zu cnt=%d\n",
-                               x, y, motion_ptr, android->pointer_count);
+               if (action == AMOTION_EVENT_ACTION_DOWN)
+                  RARCH_LOG("[Stylus] POINTER DOWN @ (%.1f, %.1f) tip=%d barrel=%d cnt=%d\n",
+                            x, y, tip_down, side_primary, android->pointer_count);
 #endif
-               }
-               else
-               {
-                  /* Hovering: clear button states but maintain cursor position */
+               if (!tip_down && !side_primary) {
+                  /* Hovering: no active pointers, clear button states but maintain cursor position */
+                  android->pointer_count = 0;
                   android->mouse_l = false;
                   android->mouse_r = false;
 
@@ -1148,18 +1160,13 @@ static INLINE void android_input_poll_event_type_motion(
 
             if (action == AMOTION_EVENT_ACTION_UP)
             {
-               /* Compact/release pointer array like the touch path */
-               if (motion_ptr < MAX_TOUCH - 1)
-               {
-                  memmove(android->pointer + motion_ptr,
-                          android->pointer + motion_ptr + 1,
-                          (MAX_TOUCH - motion_ptr - 1) * sizeof(android->pointer[0]));
-               }
-               if (android->pointer_count > 0)
-                  android->pointer_count--;
+               /* S-Pen UP: Clear all virtual pointers and button states */
+               android->pointer_count = 0;
+               android->mouse_l = false;
+               android->mouse_r = false;
 
 #ifdef DEBUG_ANDROID_INPUT
-               RARCH_LOG("[Stylus] POINTER UP   idx=%zu cnt=%d\n", motion_ptr, android->pointer_count);
+               RARCH_LOG("[Stylus] POINTER UP - cleared all virtual pointers\n");
 #endif
                return;  /* Early return - no shared processing */
             }