[effects] Add interactive window selection mode to ScreenshotEffect

Summary:
EffectsHandler gains a new method to startInteractiveWindowSelection
which just delegates to the one in Platform. That way a window can be
selected and returned to an Effect.

The screenshot effect makes use of this new functionality and provides
an interactive window screenshot mode which saves to a temporary file.
Note that this is not yet the variant intended for use in spectacle.

Test Plan: Took a screenshot on Wayland

Reviewers: #kwin, #plasma_on_wayland

Subscribers: plasma-devel, kwin

Tags: #plasma_on_wayland, #kwin

Differential Revision: https://phabricator.kde.org/D3367

autotests/mock_effectshandler.h

@@ -245,6 +245,10 @@ public:
 
     void showCursor() override {}
 
+    void startInteractiveWindowSelection(std::function<void(KWin::EffectWindow*)> callback) override {
+        callback(nullptr);
+    }
+
 private:
     bool m_animationsSuported = true;
 };

effects.cpp

@@ -1572,6 +1572,19 @@ void EffectsHandlerImpl::showCursor()
     kwinApp()->platform()->showCursor();
 }
 
+void EffectsHandlerImpl::startInteractiveWindowSelection(std::function<void(KWin::EffectWindow*)> callback)
+{
+    kwinApp()->platform()->startInteractiveWindowSelection(
+        [callback] (KWin::Toplevel *t) {
+            if (t && t->effectWindow()) {
+                callback(t->effectWindow());
+            } else {
+                callback(nullptr);
+            }
+        }
+    );
+}
+
 //****************************************
 // EffectWindowImpl
 //****************************************

effects.h

@@ -231,6 +231,8 @@ public:
     void hideCursor() override;
     void showCursor() override;
 
+    void startInteractiveWindowSelection(std::function<void(KWin::EffectWindow*)> callback) override;
+
     Scene *scene() const {
         return m_scene;
     }

effects/screenshot/screenshot.cpp

@@ -168,17 +168,22 @@ void ScreenShotEffect::postPaintScreen()
                 grabPointerImage(img, m_scheduledScreenshot->x() + left, m_scheduledScreenshot->y() + top);
             }
 
-            const int depth = img.depth();
-            xcb_pixmap_t xpix = xcb_generate_id(xcbConnection());
-            xcb_create_pixmap(xcbConnection(), depth, xpix, x11RootWindow(), img.width(), img.height());
-
-            xcb_gcontext_t cid = xcb_generate_id(xcbConnection());
-            xcb_create_gc(xcbConnection(), cid, xpix, 0, NULL);
-            xcb_put_image(xcbConnection(), XCB_IMAGE_FORMAT_Z_PIXMAP, xpix, cid, img.width(), img.height(),
-                        0, 0, 0, depth, img.byteCount(), img.constBits());
-            xcb_free_gc(xcbConnection(), cid);
-            xcb_flush(xcbConnection());
-            emit screenshotCreated(xpix);
+            if (m_windowMode == WindowMode::Xpixmap) {
+                const int depth = img.depth();
+                xcb_pixmap_t xpix = xcb_generate_id(xcbConnection());
+                xcb_create_pixmap(xcbConnection(), depth, xpix, x11RootWindow(), img.width(), img.height());
+
+                xcb_gcontext_t cid = xcb_generate_id(xcbConnection());
+                xcb_create_gc(xcbConnection(), cid, xpix, 0, NULL);
+                xcb_put_image(xcbConnection(), XCB_IMAGE_FORMAT_Z_PIXMAP, xpix, cid, img.width(), img.height(),
+                            0, 0, 0, depth, img.byteCount(), img.constBits());
+                xcb_free_gc(xcbConnection(), cid);
+                xcb_flush(xcbConnection());
+                emit screenshotCreated(xpix);
+                m_windowMode = WindowMode::NoCapture;
+            } else if (m_windowMode == WindowMode::File) {
+                sendReplyImage(img);
+            }
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
             if (xImage) {
                 xcb_image_destroy(xImage);
@@ -229,6 +234,7 @@ void ScreenShotEffect::sendReplyImage(const QImage &img)
     m_multipleOutputsImage = QImage();
     m_multipleOutputsRendered = QRegion();
     m_captureCursor = false;
+    m_windowMode = WindowMode::NoCapture;
 }
 
 QString ScreenShotEffect::saveTempImage(const QImage &img)
@@ -274,11 +280,40 @@ void ScreenShotEffect::screenshotForWindow(qulonglong winid, int mask)
     m_type = (ScreenShotType) mask;
     EffectWindow* w = effects->findWindow(winid);
     if(w && !w->isMinimized() && !w->isDeleted()) {
+        m_windowMode = WindowMode::Xpixmap;
         m_scheduledScreenshot = w;
         m_scheduledScreenshot->addRepaintFull();
     }
 }
 
+QString ScreenShotEffect::interactive(int mask)
+{
+    if (!calledFromDBus()) {
+        return QString();
+    }
+    if (!m_scheduledGeometry.isNull() || m_windowMode != WindowMode::NoCapture) {
+        sendErrorReply(QDBusError::Failed, "A screenshot is already been taken");
+        return QString();
+    }
+    m_type = (ScreenShotType) mask;
+    m_windowMode = WindowMode::File;
+    m_replyConnection = connection();
+    m_replyMessage = message();
+    setDelayedReply(true);
+    effects->startInteractiveWindowSelection(
+        [this] (EffectWindow *w) {
+            if (!w) {
+                m_replyConnection.send(m_replyMessage.createErrorReply(QDBusError::Failed, "Screenshot got cancelled"));
+                m_windowMode = WindowMode::NoCapture;
+                return;
+            } else {
+                m_scheduledScreenshot = w;
+                m_scheduledScreenshot->addRepaintFull();
+            }
+    });
+    return QString();
+}
+
 QString ScreenShotEffect::screenshotFullscreen(bool captureCursor)
 {
     if (!calledFromDBus()) {

effects/screenshot/screenshot.h

@@ -54,6 +54,16 @@ public:
     static void convertFromGLImage(QImage &img, int w, int h);
 public Q_SLOTS:
     Q_SCRIPTABLE void screenshotForWindow(qulonglong winid, int mask = 0);
+    /**
+     * Starts an interactive window screenshot session. The user can select a window to
+     * screenshot.
+     *
+     * Once the window is selected the screenshot is saved into a file and the path gets
+     * returned to the DBus peer.
+     *
+     * @param mask The mask for what to include in the screenshot
+     **/
+    Q_SCRIPTABLE QString interactive(int mask = 0);
     Q_SCRIPTABLE void screenshotWindowUnderCursor(int mask = 0);
     /**
      * Saves a screenshot of all screen into a file and returns the path to the file.
@@ -102,6 +112,12 @@ private:
     QImage m_multipleOutputsImage;
     QRegion m_multipleOutputsRendered;
     bool m_captureCursor = false;
+    enum class WindowMode {
+        NoCapture,
+        Xpixmap,
+        File
+    };
+    WindowMode m_windowMode = WindowMode::NoCapture;
 };
 
 } // namespace

libkwineffects/kwineffects.h

@@ -48,6 +48,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <limits.h>
 #include <netwm.h>
 
+#include <functional>
+
 class KConfigGroup;
 class QFont;
 class QGraphicsScale;
@@ -1198,6 +1200,20 @@ public:
      **/
     virtual void showCursor() = 0;
 
+    /**
+     * Starts an interactive window selection process.
+     *
+     * Once the user selected a window the @p callback is invoked with the selected EffectWindow as
+     * argument. In case the user cancels the interactive window selection or selecting a window is currently
+     * not possible (e.g. screen locked) the @p callback is invoked with a @c nullptr argument.
+     *
+     * During the interactive window selection the cursor is turned into a crosshair cursor.
+     *
+     * @param callback The function to invoke once the interactive window selection ends
+     * @since 5.9
+     **/
+    virtual void startInteractiveWindowSelection(std::function<void(KWin::EffectWindow*)> callback) = 0;
+
 Q_SIGNALS:
     /**
      * Signal emitted when the current desktop changed.