Support for "Customized key mapping" in Linux

Should work in "typical" X11 environments. Tested in Debian Buster /
GNOME 3. Hi-DPI code copied from Windows-related parts and untested.
Wayland is not supported and considered currently.

QtScrcpy/device/ui/videoform.cpp

@@ -104,8 +104,11 @@ QRect VideoForm::getGrabCursorRect()
     rc.setY(rc.y() + 30);
     rc.setWidth(rc.width() - 180);
     rc.setHeight(rc.height() - 60);
-#else
-
+#elif defined(Q_OS_LINUX)
+    rc = QRect(ui->keepRadioWidget->mapToGlobal(m_videoWidget->pos()), m_videoWidget->size());
+    // high dpi support -- taken from the WIN32 section and untested
+    rc.setTopLeft(rc.topLeft() * m_videoWidget->devicePixelRatio());
+    rc.setBottomRight(rc.bottomRight() * m_videoWidget->devicePixelRatio());
 #endif
     return rc;
 }

QtScrcpy/util/mousetap/mousetap.cpp

@@ -7,6 +7,9 @@
 #ifdef Q_OS_OSX
 #include "cocoamousetap.h"
 #endif
+#ifdef Q_OS_LINUX
+#include "xmousetap.h"
+#endif
 
 MouseTap *MouseTap::s_instance = Q_NULLPTR;
 MouseTap *MouseTap::getInstance()
@@ -19,7 +22,7 @@ MouseTap *MouseTap::getInstance()
         s_instance = new CocoaMouseTap();
 #endif
 #ifdef Q_OS_LINUX
-        Q_ASSERT(false);
+        s_instance = new XMouseTap();
 #endif
     }
     return s_instance;

QtScrcpy/util/mousetap/mousetap.pri

@@ -16,3 +16,11 @@ mac {
     LIBS += -framework Appkit
     QMAKE_CFLAGS += -mmacosx-version-min=10.6
 }
+
+linux {
+    HEADERS += $$PWD/xmousetap.h
+    SOURCES += $$PWD/xmousetap.cpp
+    LIBS    += -lxcb
+    QT      += x11extras
+}
+

QtScrcpy/util/mousetap/xmousetap.cpp

@@ -0,0 +1,84 @@
+#include <QX11Info>
+
+#include <xcb/xproto.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+#include "xmousetap.h"
+
+XMouseTap::XMouseTap() {}
+
+XMouseTap::~XMouseTap() {}
+
+void XMouseTap::initMouseEventTap() {}
+
+void XMouseTap::quitMouseEventTap() {}
+
+static void find_grab_window_recursive(xcb_connection_t *dpy, xcb_window_t window,
+        QRect rc, int16_t offset_x, int16_t offset_y,
+        xcb_window_t *grab_window, uint32_t *grab_window_size) {
+    xcb_query_tree_cookie_t tree_cookie;
+    xcb_query_tree_reply_t *tree;
+    tree_cookie = xcb_query_tree(dpy, window);
+    tree = xcb_query_tree_reply(dpy, tree_cookie, NULL);
+
+    xcb_window_t *children = xcb_query_tree_children(tree);
+    for (int i = 0; i < xcb_query_tree_children_length(tree); i++) {
+        xcb_get_geometry_cookie_t gg_cookie;
+        xcb_get_geometry_reply_t *gg;
+        gg_cookie = xcb_get_geometry(dpy, children[i]);
+        gg = xcb_get_geometry_reply(dpy, gg_cookie, NULL);
+
+        if (gg->x + offset_x <= rc.left() && gg->x + offset_x + gg->width >= rc.right() &&
+                gg->y + offset_y <= rc.top() && gg->y + offset_y + gg->height >= rc.bottom()) {
+            if (!*grab_window || gg->width * gg->height <= *grab_window_size) {
+                *grab_window = children[i];
+                *grab_window_size = gg->width * gg->height;
+            }
+        }
+
+        find_grab_window_recursive(dpy, children[i], rc,
+                gg->x + offset_x, gg->y + offset_y,
+                grab_window, grab_window_size);
+
+        free(gg);
+    }
+
+    free(tree);
+}
+
+void XMouseTap::enableMouseEventTap(QRect rc, bool enabled) {
+    if (enabled && rc.isEmpty()) {
+        return;
+    }
+
+    xcb_connection_t *dpy = QX11Info::connection();
+
+    if (enabled) {
+        // We grab the top-most smallest window
+        xcb_window_t grab_window = 0;
+        uint32_t grab_window_size = 0;
+
+        find_grab_window_recursive(dpy, QX11Info::appRootWindow(QX11Info::appScreen()),
+                rc, 0, 0, &grab_window, &grab_window_size);
+
+        if (grab_window) {
+            xcb_grab_pointer_cookie_t grab_cookie;
+            xcb_grab_pointer_reply_t *grab;
+            grab_cookie = xcb_grab_pointer(dpy, /* owner_events = */ 1,
+                    grab_window, /* event_mask = */ 0,
+                    XCB_GRAB_MODE_ASYNC, XCB_GRAB_MODE_ASYNC,
+                    grab_window, XCB_NONE, XCB_CURRENT_TIME);
+            grab = xcb_grab_pointer_reply(dpy, grab_cookie, NULL);
+
+            free(grab);
+        }
+    } else {
+        xcb_void_cookie_t ungrab_cookie;
+        xcb_generic_error_t *error;
+        ungrab_cookie = xcb_ungrab_pointer_checked(dpy, XCB_CURRENT_TIME);
+        error = xcb_request_check(dpy, ungrab_cookie);
+
+        free(error);
+    }
+}

QtScrcpy/util/mousetap/xmousetap.h

@@ -0,0 +1,19 @@
+#ifndef XMOUSETAP_H
+#define XMOUSETAP_H
+
+#include <xcb/xproto.h>
+
+#include "mousetap.h"
+
+class XMouseTap : public MouseTap
+{
+public:
+    XMouseTap();
+    virtual ~XMouseTap();
+
+    void initMouseEventTap() override;
+    void quitMouseEventTap() override;
+    void enableMouseEventTap(QRect rc, bool enabled) override;
+};
+
+#endif // XMOUSETAP_H