Use precise scrolling values

Since SDL 2.0.18, the amount scrolled horizontally or vertically is
exposed as a float (between 0 and 1). Forward a precise value to the
Android device when possible.

Refs <https://wiki.libsdl.org/SDL_MouseWheelEvent>
Fixes #3363 <https://github.com/Genymobile/scrcpy/issues/3363>
PR #3369 <https://github.com/Genymobile/scrcpy/pull/3369>

Signed-off-by: Romain Vimont <rom@rom1v.com>

app/src/control_msg.c

@@ -115,12 +115,15 @@ sc_control_msg_serialize(const struct sc_control_msg *msg, unsigned char *buf) {
             return 28;
         case SC_CONTROL_MSG_TYPE_INJECT_SCROLL_EVENT:
             write_position(&buf[1], &msg->inject_scroll_event.position);
-            sc_write32be(&buf[13],
+            // map [-1, 1] to [0, 1], then to uint16
-                             (uint32_t) msg->inject_scroll_event.hscroll);
+            uint16_t hscroll =
-            sc_write32be(&buf[17],
+                to_fixed_point_16((msg->inject_scroll_event.hscroll + 1) / 2);
-                             (uint32_t) msg->inject_scroll_event.vscroll);
+            uint16_t vscroll =
-            sc_write32be(&buf[21], msg->inject_scroll_event.buttons);
+                to_fixed_point_16((msg->inject_scroll_event.vscroll + 1) / 2);
-            return 25;
+            sc_write16be(&buf[13], hscroll);
+            sc_write16be(&buf[15], vscroll);
+            sc_write32be(&buf[17], msg->inject_scroll_event.buttons);
+            return 21;
         case SC_CONTROL_MSG_TYPE_BACK_OR_SCREEN_ON:
             buf[1] = msg->inject_keycode.action;
             return 2;
@@ -191,8 +194,8 @@ sc_control_msg_log(const struct sc_control_msg *msg) {
             break;
         }
         case SC_CONTROL_MSG_TYPE_INJECT_SCROLL_EVENT:
-            LOG_CMSG("scroll position=%" PRIi32 ",%" PRIi32 " hscroll=%" PRIi32
+            LOG_CMSG("scroll position=%" PRIi32 ",%" PRIi32 " hscroll=%g"
-                         " vscroll=%" PRIi32 " buttons=%06lx",
+                         " vscroll=%g buttons=%06lx",
                      msg->inject_scroll_event.position.point.x,
                      msg->inject_scroll_event.position.point.y,
                      msg->inject_scroll_event.hscroll,

app/src/control_msg.h

@@ -68,8 +68,8 @@ struct sc_control_msg {
         } inject_touch_event;
         struct {
             struct sc_position position;
-            int32_t hscroll;
+            float hscroll;
-            int32_t vscroll;
+            float vscroll;
             enum android_motionevent_buttons buttons;
         } inject_scroll_event;
         struct {

app/src/input_events.h

@@ -358,8 +358,8 @@ struct sc_mouse_click_event {
 
 struct sc_mouse_scroll_event {
     struct sc_position position;
-    int32_t hscroll;
+    float hscroll;
-    int32_t vscroll;
+    float vscroll;
     uint8_t buttons_state; // bitwise-OR of sc_mouse_button values
 };
 

app/src/input_manager.c

@@ -747,8 +747,13 @@ sc_input_manager_process_mouse_wheel(struct sc_input_manager *im,
             .point = sc_screen_convert_window_to_frame_coords(im->screen,
                                                               mouse_x, mouse_y),
         },
-        .hscroll = event->x,
+#if SDL_VERSION_ATLEAST(2, 0, 18)
-        .vscroll = event->y,
+        .hscroll = CLAMP(event->preciseX, -1.0f, 1.0f),
+        .vscroll = CLAMP(event->preciseY, -1.0f, 1.0f),
+#else
+        .hscroll = CLAMP(event->x, -1, 1),
+        .vscroll = CLAMP(event->y, -1, 1),
+#endif
         .buttons_state =
             sc_mouse_buttons_state_from_sdl(buttons, im->forward_all_clicks),
     };

server/src/main/java/com/genymobile/scrcpy/ControlMessage.java

@@ -33,8 +33,8 @@ public final class ControlMessage {
     private long pointerId;
     private float pressure;
     private Position position;
-    private int hScroll;
+    private float hScroll;
-    private int vScroll;
+    private float vScroll;
     private int copyKey;
     private boolean paste;
     private int repeat;
@@ -71,7 +71,7 @@ public final class ControlMessage {
         return msg;
     }
 
-    public static ControlMessage createInjectScrollEvent(Position position, int hScroll, int vScroll, int buttons) {
+    public static ControlMessage createInjectScrollEvent(Position position, float hScroll, float vScroll, int buttons) {
         ControlMessage msg = new ControlMessage();
         msg.type = TYPE_INJECT_SCROLL_EVENT;
         msg.position = position;
@@ -156,11 +156,11 @@ public final class ControlMessage {
         return position;
     }
 
-    public int getHScroll() {
+    public float getHScroll() {
         return hScroll;
     }
 
-    public int getVScroll() {
+    public float getVScroll() {
         return vScroll;
     }
 

server/src/main/java/com/genymobile/scrcpy/ControlMessageReader.java

@@ -10,7 +10,7 @@ public class ControlMessageReader {
 
     static final int INJECT_KEYCODE_PAYLOAD_LENGTH = 13;
     static final int INJECT_TOUCH_EVENT_PAYLOAD_LENGTH = 27;
-    static final int INJECT_SCROLL_EVENT_PAYLOAD_LENGTH = 24;
+    static final int INJECT_SCROLL_EVENT_PAYLOAD_LENGTH = 20;
     static final int BACK_OR_SCREEN_ON_LENGTH = 1;
     static final int SET_SCREEN_POWER_MODE_PAYLOAD_LENGTH = 1;
     static final int GET_CLIPBOARD_LENGTH = 1;
@@ -139,10 +139,7 @@ public class ControlMessageReader {
         int action = toUnsigned(buffer.get());
         long pointerId = buffer.getLong();
         Position position = readPosition(buffer);
-        // 16 bits fixed-point
+        float pressure = fixedPointToFloat(buffer.getShort());
-        int pressureInt = toUnsigned(buffer.getShort());
-        // convert it to a float between 0 and 1 (0x1p16f is 2^16 as float)
-        float pressure = pressureInt == 0xffff ? 1f : (pressureInt / 0x1p16f);
         int buttons = buffer.getInt();
         return ControlMessage.createInjectTouchEvent(action, pointerId, position, pressure, buttons);
     }
@@ -152,8 +149,9 @@ public class ControlMessageReader {
             return null;
         }
         Position position = readPosition(buffer);
-        int hScroll = buffer.getInt();
+        // map from [0; 1] to [-1; 1]
-        int vScroll = buffer.getInt();
+        float hScroll = fixedPointToFloat(buffer.getShort());
+        float vScroll = fixedPointToFloat(buffer.getShort());
         int buttons = buffer.getInt();
         return ControlMessage.createInjectScrollEvent(position, hScroll, vScroll, buttons);
     }
@@ -210,4 +208,10 @@ public class ControlMessageReader {
     private static int toUnsigned(byte value) {
         return value & 0xff;
     }
+
+    private static float fixedPointToFloat(short value) {
+        int unsignedShort = toUnsigned(value);
+        // convert 16 bits fixed-point to a float between 0 and 1 (0x1p16f is 2^16 as float)
+        return unsignedShort == 0xffff ? 1f : (unsignedShort / 0x1p16f);
+    }
 }

server/src/main/java/com/genymobile/scrcpy/Controller.java

@@ -223,7 +223,7 @@ public class Controller {
         return device.injectEvent(event, Device.INJECT_MODE_ASYNC);
     }
 
-    private boolean injectScroll(Position position, int hScroll, int vScroll, int buttons) {
+    private boolean injectScroll(Position position, float hScroll, float vScroll, int buttons) {
         long now = SystemClock.uptimeMillis();
         Point point = device.getPhysicalPoint(position);
         if (point == null) {

server/src/test/java/com/genymobile/scrcpy/ControlMessageReaderTest.java

@@ -126,8 +126,8 @@ public class ControlMessageReaderTest {
         dos.writeInt(1026);
         dos.writeShort(1080);
         dos.writeShort(1920);
-        dos.writeInt(1);
+        dos.writeShort(0x8000);
-        dos.writeInt(-1);
+        dos.writeShort(0);
         dos.writeInt(1);
 
         byte[] packet = bos.toByteArray();
@@ -143,8 +143,8 @@ public class ControlMessageReaderTest {
         Assert.assertEquals(1026, event.getPosition().getPoint().getY());
         Assert.assertEquals(1080, event.getPosition().getScreenSize().getWidth());
         Assert.assertEquals(1920, event.getPosition().getScreenSize().getHeight());
-        Assert.assertEquals(1, event.getHScroll());
+        Assert.assertEquals(0f, event.getHScroll(), 0f);
-        Assert.assertEquals(-1, event.getVScroll());
+        Assert.assertEquals(-1f, event.getVScroll(), 0f);
         Assert.assertEquals(1, event.getButtons());
     }