Support high-resolution scroll

VirtualMouse currently supports -1f to 1f float scroll values,
but it worked for integer values only as input framework supported
only REL_HWHEEL and REL_WHEEL events. With the introduction of
high-res scroll event support (REL_HWHEEL_HI_RES and REL_WHEEL_HI_RES),
granular mouse scrolling can be done, and VirtualMouse scroll API
would work for all float values.

Flag: android.companion.virtualdevice.flags.high_resolution_scroll
Test: atest VirtualMouseTest
Bug: 335160780
Change-Id: I7b13ac1722b6fd31736fe1c0117d4de6e838261a

1 files changed, 44 insertions, 4 deletions

diff --git a/libs/input/VirtualInputDevice.cpp b/libs/input/VirtualInputDevice.cpp
index b73ee65504..2e3e1a09b8 100644
--- a/libs/input/VirtualInputDevice.cpp
+++ b/libs/input/VirtualInputDevice.cpp
@@ -18,6 +18,7 @@
 
 #include <android/input.h>
 #include <android/keycodes.h>
+#include <android_companion_virtualdevice_flags.h>
 #include <fcntl.h>
 #include <input/Input.h>
 #include <input/VirtualInputDevice.h>
@@ -40,6 +41,8 @@ static bool isDebug() {
 
 namespace android {
 
+namespace vd_flags = android::companion::virtualdevice::flags;
+
 VirtualInputDevice::VirtualInputDevice(unique_fd fd) : mFd(std::move(fd)) {}
 
 VirtualInputDevice::~VirtualInputDevice() {
@@ -253,7 +256,10 @@ const std::map<int, int> VirtualMouse::BUTTON_CODE_MAPPING = {
         // clang-format on
 };
 
-VirtualMouse::VirtualMouse(unique_fd fd) : VirtualInputDevice(std::move(fd)) {}
+VirtualMouse::VirtualMouse(unique_fd fd)
+      : VirtualInputDevice(std::move(fd)),
+        mAccumulatedHighResScrollX(0),
+        mAccumulatedHighResScrollY(0) {}
 
 VirtualMouse::~VirtualMouse() {}
 
@@ -272,9 +278,43 @@ bool VirtualMouse::writeRelativeEvent(float relativeX, float relativeY,
 
 bool VirtualMouse::writeScrollEvent(float xAxisMovement, float yAxisMovement,
                                     std::chrono::nanoseconds eventTime) {
-    return writeInputEvent(EV_REL, REL_HWHEEL, xAxisMovement, eventTime) &&
-            writeInputEvent(EV_REL, REL_WHEEL, yAxisMovement, eventTime) &&
-            writeInputEvent(EV_SYN, SYN_REPORT, 0, eventTime);
+    if (!vd_flags::high_resolution_scroll()) {
+        return writeInputEvent(EV_REL, REL_HWHEEL, xAxisMovement, eventTime) &&
+                writeInputEvent(EV_REL, REL_WHEEL, yAxisMovement, eventTime) &&
+                writeInputEvent(EV_SYN, SYN_REPORT, 0, eventTime);
+    }
+
+    const int32_t highResScrollX = xAxisMovement * kEvdevMouseHighResScrollUnitsPerDetent;
+    const int32_t highResScrollY = yAxisMovement * kEvdevMouseHighResScrollUnitsPerDetent;
+    bool highResScrollResult =
+            writeInputEvent(EV_REL, REL_HWHEEL_HI_RES, highResScrollX, eventTime) &&
+            writeInputEvent(EV_REL, REL_WHEEL_HI_RES, highResScrollY, eventTime);
+    if (!highResScrollResult) {
+        return false;
+    }
+
+    // According to evdev spec, a high-resolution mouse needs to emit REL_WHEEL / REL_HWHEEL events
+    // in addition to high-res scroll events. Regular scroll events can approximate high-res scroll
+    // events, so we send a regular scroll event when the accumulated scroll motion reaches a detent
+    // (single mouse wheel click).
+    mAccumulatedHighResScrollX += highResScrollX;
+    mAccumulatedHighResScrollY += highResScrollY;
+    const int32_t scrollX = mAccumulatedHighResScrollX / kEvdevMouseHighResScrollUnitsPerDetent;
+    const int32_t scrollY = mAccumulatedHighResScrollY / kEvdevMouseHighResScrollUnitsPerDetent;
+    if (scrollX != 0) {
+        if (!writeInputEvent(EV_REL, REL_HWHEEL, scrollX, eventTime)) {
+            return false;
+        }
+        mAccumulatedHighResScrollX %= kEvdevMouseHighResScrollUnitsPerDetent;
+    }
+    if (scrollY != 0) {
+        if (!writeInputEvent(EV_REL, REL_WHEEL, scrollY, eventTime)) {
+            return false;
+        }
+        mAccumulatedHighResScrollY %= kEvdevMouseHighResScrollUnitsPerDetent;
+    }
+
+    return writeInputEvent(EV_SYN, SYN_REPORT, 0, eventTime);
 }
 
 // --- VirtualTouchscreen ---