Handle mouse integer scrolling locally

Do not rely on SDL to expose integer scroll values, as they are not
available in all versions.

It was reimplemented in SDL 3.2.12 by this commit:
<0447c2f3c3>

Refs #6156 <https://github.com/Genymobile/scrcpy/issues/6156>

app/src/hid/hid_mouse.c

@@ -166,6 +166,12 @@ sc_hid_buttons_from_buttons_state(uint8_t buttons_state) {
     return c;
 }
 
+void
+sc_hid_mouse_init(struct sc_hid_mouse *hid) {
+    hid->residual_hscroll = 0;
+    hid->residual_vscroll = 0;
+}
+
 void
 sc_hid_mouse_generate_input_from_motion(struct sc_hid_input *hid_input,
                                     const struct sc_mouse_motion_event *event) {
@@ -192,22 +198,37 @@ sc_hid_mouse_generate_input_from_click(struct sc_hid_input *hid_input,
     data[4] = 0; // no horizontal scrolling
 }
 
+static int8_t
+consume_scroll_integer(float *scroll) {
+    float value = CLAMP(*scroll, -127, 127);
+    int8_t consume = value; // truncate towards 0
+    float residual = value - consume;
+    *scroll = residual;
+    return consume;
+}
+
 bool
-sc_hid_mouse_generate_input_from_scroll(struct sc_hid_input *hid_input,
+sc_hid_mouse_generate_input_from_scroll(struct sc_hid_mouse *hid,
+                                        struct sc_hid_input *hid_input,
                                     const struct sc_mouse_scroll_event *event) {
-    if (!event->vscroll_int && !event->hscroll_int) {
-        // Need a full integral value for HID
+    sc_hid_mouse_input_init(hid_input);
+
+    hid->residual_hscroll += event->hscroll;
+    hid->residual_vscroll += event->vscroll;
+    int8_t hscroll = consume_scroll_integer(&hid->residual_hscroll);
+    int8_t vscroll = consume_scroll_integer(&hid->residual_vscroll);
+
+    if (!hscroll && !vscroll) {
+        // Not enough scrolling to inject a scroll event
         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
-    data[3] = CLAMP(event->vscroll_int, -127, 127);
-    data[4] = CLAMP(event->hscroll_int, -127, 127);
+    data[3] = vscroll;
+    data[4] = hscroll;
     return true;
 }
 

app/src/hid/hid_mouse.h

@@ -8,6 +8,13 @@
 
 #define SC_HID_ID_MOUSE 2
 
+struct sc_hid_mouse {
+    float residual_hscroll;
+    float residual_vscroll;
+};
+
+void sc_hid_mouse_init(struct sc_hid_mouse *hid);
+
 void
 sc_hid_mouse_generate_open(struct sc_hid_open *hid_open);
 
@@ -23,7 +30,8 @@ sc_hid_mouse_generate_input_from_click(struct sc_hid_input *hid_input,
                                     const struct sc_mouse_click_event *event);
 
 bool
-sc_hid_mouse_generate_input_from_scroll(struct sc_hid_input *hid_input,
+sc_hid_mouse_generate_input_from_scroll(struct sc_hid_mouse *hid,
+                                        struct sc_hid_input *hid_input,
                                     const struct sc_mouse_scroll_event *event);
 
 #endif

app/src/input_events.h

@@ -393,8 +393,6 @@ 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

@@ -903,8 +903,6 @@ 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 +55,8 @@ sc_mouse_processor_process_mouse_scroll(struct sc_mouse_processor *mp,
     struct sc_mouse_uhid *mouse = DOWNCAST(mp);
 
     struct sc_hid_input hid_input;
-    if (!sc_hid_mouse_generate_input_from_scroll(&hid_input, event)) {
+    if (!sc_hid_mouse_generate_input_from_scroll(&mouse->hid, &hid_input,
+                                                 event)) {
         return;
     }
 
@@ -65,6 +66,8 @@ sc_mouse_processor_process_mouse_scroll(struct sc_mouse_processor *mp,
 bool
 sc_mouse_uhid_init(struct sc_mouse_uhid *mouse,
                    struct sc_controller *controller) {
+    sc_hid_mouse_init(&mouse->hid);
+
     mouse->controller = controller;
 
     static const struct sc_mouse_processor_ops ops = {

app/src/uhid/mouse_uhid.h

@@ -4,11 +4,13 @@
 #include <stdbool.h>
 
 #include "controller.h"
+#include "hid/hid_mouse.h"
 #include "trait/mouse_processor.h"
 
 struct sc_mouse_uhid {
     struct sc_mouse_processor mouse_processor; // mouse processor trait
 
+    struct sc_hid_mouse hid;
     struct sc_controller *controller;
 };
 

app/src/usb/mouse_aoa.c

@@ -42,7 +42,8 @@ sc_mouse_processor_process_mouse_scroll(struct sc_mouse_processor *mp,
     struct sc_mouse_aoa *mouse = DOWNCAST(mp);
 
     struct sc_hid_input hid_input;
-    if (!sc_hid_mouse_generate_input_from_scroll(&hid_input, event)) {
+    if (!sc_hid_mouse_generate_input_from_scroll(&mouse->hid, &hid_input,
+                                                 event)) {
         return;
     }
 
@@ -64,6 +65,8 @@ sc_mouse_aoa_init(struct sc_mouse_aoa *mouse, struct sc_aoa *aoa) {
         return false;
     }
 
+    sc_hid_mouse_init(&mouse->hid);
+
     static const struct sc_mouse_processor_ops ops = {
         .process_mouse_motion = sc_mouse_processor_process_mouse_motion,
         .process_mouse_click = sc_mouse_processor_process_mouse_click,

app/src/usb/mouse_aoa.h

@@ -6,11 +6,13 @@
 #include <stdbool.h>
 
 #include "usb/aoa_hid.h"
+#include "hid/hid_mouse.h"
 #include "trait/mouse_processor.h"
 
 struct sc_mouse_aoa {
     struct sc_mouse_processor mouse_processor; // mouse processor trait
 
+    struct sc_hid_mouse hid;
     struct sc_aoa *aoa;
 };
 

app/src/usb/screen_otg.c

@@ -171,8 +171,6 @@ sc_screen_otg_process_mouse_wheel(struct sc_screen_otg *screen,
         .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),
     };