Fix HID mouse support with SDL precise scrolling

Over HID, only integral scroll values can be sent. When SDL precise
scrolling is active, scroll events may include fractional values (e.g.,
0.05), which are truncated to 0 in the HID event.

To fix the problem, use the integral scroll value reported by SDL, which
internally accumulates fractional deltas.

Fixes #6156 <https://github.com/Genymobile/scrcpy/issues/6156>
PR #6172 <https://github.com/Genymobile/scrcpy/pull/6172>

app/src/hid/hid_mouse.c

@@ -175,19 +175,23 @@ sc_hid_mouse_generate_input_from_click(struct sc_hid_input *hid_input,
     data[3] = 0; // wheel coordinates only used for scrolling
 }
 
-void
+bool
 sc_hid_mouse_generate_input_from_scroll(struct sc_hid_input *hid_input,
                                     const struct sc_mouse_scroll_event *event) {
+    if (!event->vscroll_int) {
+        // Need a full integral value for HID
+        return false;
+    }
+
     sc_hid_mouse_input_init(hid_input);
 
     uint8_t *data = hid_input->data;
     data[0] = 0; // buttons state irrelevant (and unknown)
     data[1] = 0; // no x motion
     data[2] = 0; // no y motion
-    // In practice, vscroll is always -1, 0 or 1, but in theory other values
-    // are possible
-    data[3] = CLAMP(event->vscroll, -127, 127);
+    data[3] = CLAMP(event->vscroll_int, -127, 127);
     // Horizontal scrolling ignored
+    return true;
 }
 
 void sc_hid_mouse_generate_open(struct sc_hid_open *hid_open) {

app/src/hid/hid_mouse.h

@@ -22,7 +22,7 @@ void
 sc_hid_mouse_generate_input_from_click(struct sc_hid_input *hid_input,
                                     const struct sc_mouse_click_event *event);
 
-void
+bool
 sc_hid_mouse_generate_input_from_scroll(struct sc_hid_input *hid_input,
                                     const struct sc_mouse_scroll_event *event);
 

app/src/input_events.h

@@ -393,6 +393,8 @@ struct sc_mouse_scroll_event {
     struct sc_position position;
     float hscroll;
     float vscroll;
+    int32_t hscroll_int;
+    int32_t vscroll_int;
     uint8_t buttons_state; // bitwise-OR of sc_mouse_button values
 };
 

app/src/input_manager.c

@@ -903,6 +903,8 @@ sc_input_manager_process_mouse_wheel(struct sc_input_manager *im,
         .hscroll = event->x,
         .vscroll = event->y,
 #endif
+        .hscroll_int = event->x,
+        .vscroll_int = event->y,
         .buttons_state = im->mouse_buttons_state,
     };
 

app/src/uhid/mouse_uhid.c

@@ -55,7 +55,9 @@ sc_mouse_processor_process_mouse_scroll(struct sc_mouse_processor *mp,
     struct sc_mouse_uhid *mouse = DOWNCAST(mp);
 
     struct sc_hid_input hid_input;
-    sc_hid_mouse_generate_input_from_scroll(&hid_input, event);
+    if (!sc_hid_mouse_generate_input_from_scroll(&hid_input, event)) {
+        return;
+    }
 
     sc_mouse_uhid_send_input(mouse, &hid_input, "mouse scroll");
 }

app/src/usb/mouse_aoa.c

@@ -42,7 +42,9 @@ sc_mouse_processor_process_mouse_scroll(struct sc_mouse_processor *mp,
     struct sc_mouse_aoa *mouse = DOWNCAST(mp);
 
     struct sc_hid_input hid_input;
-    sc_hid_mouse_generate_input_from_scroll(&hid_input, event);
+    if (!sc_hid_mouse_generate_input_from_scroll(&hid_input, event)) {
+        return;
+    }
 
     if (!sc_aoa_push_input(mouse->aoa, &hid_input)) {
         LOGW("Could not push AOA HID input (mouse scroll)");

app/src/usb/screen_otg.c

@@ -164,8 +164,15 @@ sc_screen_otg_process_mouse_wheel(struct sc_screen_otg *screen,
 
     struct sc_mouse_scroll_event evt = {
         // .position not used for HID events
+#if SDL_VERSION_ATLEAST(2, 0, 18)
+        .hscroll = event->preciseX,
+        .vscroll = event->preciseY,
+#else
         .hscroll = event->x,
         .vscroll = event->y,
+#endif
+        .hscroll_int = event->x,
+        .vscroll_int = event->y,
         .buttons_state = sc_mouse_buttons_state_from_sdl(sdl_buttons_state),
     };