Implement multiplier-based scaling with residual accumulation for
fine-grained mouse wheel and pan sensitivity control in report mode.

Applies divisor based scaling (1, 4, 8, 16) based on negotiated
multiplier values.
Then uses residual based approach to prevent precision loss:

  residual += delta
  output = residual / divisor
  residual -= output * divisor

Residual state preserved across VM migrations via VMState.

Signed-off-by: Soumyajyotii Ssarkar <soumyajyotisarkar23@gmail.com>
---
 hw/input/hid.c         | 60 ++++++++++++++++++++++++++++++++++++++++++
 include/hw/input/hid.h |  2 ++
 2 files changed, 62 insertions(+)

diff --git a/hw/input/hid.c b/hw/input/hid.c
index d0b7af7c13..9b800faeb0 100644
--- a/hw/input/hid.c
+++ b/hw/input/hid.c
@@ -365,6 +365,7 @@ void hid_pointer_activate(HIDState *hs)
 int hid_pointer_poll(HIDState *hs, uint8_t *buf, int len)
 {
     int dx, dy, dz, pan, l;
+    int wheel_divisor, pan_divisor;
     int index;
     HIDPointerEvent *e;

@@ -392,6 +393,54 @@ int hid_pointer_poll(HIDState *hs, uint8_t *buf, int len)
     e->pan -= pan;


+    if (hs->kind == HID_MOUSE && hs->protocol != 0) {
+        switch (hs->ptr.wheel_multiplier & 0x03) {
+        case 0:
+            wheel_divisor = 1;
+            break;
+        case 1:
+            wheel_divisor = 4;
+            break;
+        case 2:
+            wheel_divisor = 8;
+            break;
+        default:
+            wheel_divisor = 16;
+            break;
+        }
+
+        switch (hs->ptr.pan_multiplier & 0x03) {
+        case 0:
+            pan_divisor = 1;
+            break;
+        case 1:
+            pan_divisor = 4;
+            break;
+        case 2:
+            pan_divisor = 8;
+            break;
+        default:
+            pan_divisor = 16;
+            break;
+        }
+
+        if (wheel_divisor > 1) {
+            hs->ptr.wheel_residual += dz;
+            dz = hs->ptr.wheel_residual / wheel_divisor;
+            hs->ptr.wheel_residual -= dz * wheel_divisor;
+        } else {
+            hs->ptr.wheel_residual = 0;
+        }
+
+        if (pan_divisor > 1) {
+            hs->ptr.pan_residual += pan;
+            pan = hs->ptr.pan_residual / pan_divisor;
+            hs->ptr.pan_residual -= pan * pan_divisor;
+        } else {
+            hs->ptr.pan_residual = 0;
+        }
+    }
+
     if (hs->n &&
         !e->dz &&
         !e->pan &&
@@ -405,6 +454,7 @@ int hid_pointer_poll(HIDState *hs, uint8_t *buf, int len)
     dz = 0 - dz;
     pan = 0 - pan;
     l = 0;
+
     switch (hs->kind) {
     case HID_MOUSE:
         if (hs->protocol == 0) {
@@ -528,6 +578,11 @@ void hid_reset(HIDState *hs)
     case HID_MOUSE:
     case HID_TABLET:
         memset(hs->ptr.queue, 0, sizeof(hs->ptr.queue));
+        hs->ptr.mouse_grabbed = 0;
+        hs->ptr.wheel_multiplier = 0;
+        hs->ptr.pan_multiplier = 0;
+        hs->ptr.wheel_residual = 0;
+        hs->ptr.pan_residual = 0;
         break;
     }
     hs->head = 0;
@@ -619,6 +674,7 @@ static const VMStateDescription vmstate_hid_ptr_queue = {
         VMSTATE_INT32(xdx, HIDPointerEvent),
         VMSTATE_INT32(ydy, HIDPointerEvent),
         VMSTATE_INT32(dz, HIDPointerEvent),
+        VMSTATE_INT32(pan, HIDPointerEvent),
         VMSTATE_INT32(buttons_state, HIDPointerEvent),
         VMSTATE_END_OF_LIST()
     }
@@ -636,6 +692,10 @@ const VMStateDescription vmstate_hid_ptr_device = {
         VMSTATE_UINT32(n, HIDState),
         VMSTATE_INT32(protocol, HIDState),
         VMSTATE_UINT8(idle, HIDState),
+        VMSTATE_UINT8(ptr.wheel_multiplier, HIDState),
+        VMSTATE_UINT8(ptr.pan_multiplier, HIDState),
+        VMSTATE_INT32(ptr.wheel_residual, HIDState),
+        VMSTATE_INT32(ptr.pan_residual, HIDState),
         VMSTATE_END_OF_LIST(),
     }
 };
diff --git a/include/hw/input/hid.h b/include/hw/input/hid.h
index 1a1941d371..db902fa023 100644
--- a/include/hw/input/hid.h
+++ b/include/hw/input/hid.h
@@ -25,6 +25,8 @@ typedef struct HIDMouseState {
     int mouse_grabbed;
     uint8_t wheel_multiplier;
     uint8_t pan_multiplier;
+    int32_t wheel_residual;
+    int32_t pan_residual;
 } HIDMouseState;

 typedef struct HIDKeyboardState {
--
2.53.0