[platforms/drm] Fix cursor hotspot for inverted landscape rotation

Summary:
This change fixes the hotspot calculation by introducing a dedicated
matrix to map the hotspot.

To better test the hotspot a small test application is added. The app
renders a red point at the cursor position and uses a cross for cursor
with the hotspot position being transparent. So if KWin renders the
cursor at the correct position a red point is visible in the center of
the cross. The test app supports several cursor hotspot positions:
 * center (default)
 * top left
 * top right
 * bottom right
 * bottom left

To switch between the variants press the space key.

Test Plan:
Rotated screen, used test app to verify the hotspot is
correct. Also scaled display, still correct

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D8668

plugins/platforms/drm/drm_output.cpp

@@ -140,14 +140,19 @@ void DrmOutput::updateCursor()
 void DrmOutput::moveCursor(const QPoint &globalPos)
 {
     QMatrix4x4 matrix;
+    QMatrix4x4 hotspotMatrix;
     if (m_orientation == Qt::InvertedLandscapeOrientation) {
-        matrix.translate(pixelSize().width() /2, pixelSize().height() / 2);
+        matrix.translate(pixelSize().width() /2.0, pixelSize().height() / 2.0);
         matrix.rotate(180.0f, 0.0f, 0.0f, 1.0f);
-        matrix.translate(-pixelSize().width() /2, -pixelSize().height() / 2);
+        matrix.translate(-pixelSize().width() /2.0, -pixelSize().height() / 2.0);
+        const auto cursorSize = m_backend->softwareCursor().size();
+        hotspotMatrix.translate(cursorSize.width()/2.0, cursorSize.height()/2.0);
+        hotspotMatrix.rotate(180.0f, 0.0f, 0.0f, 1.0f);
+        hotspotMatrix.translate(-cursorSize.width()/2.0, -cursorSize.height()/2.0);
     }
     matrix.scale(m_scale);
     matrix.translate(-m_globalPos.x(), -m_globalPos.y());
-    const QPoint p = matrix.map(globalPos) - m_backend->softwareCursorHotspot();
+    const QPoint p = matrix.map(globalPos) - hotspotMatrix.map(m_backend->softwareCursorHotspot());
     drmModeMoveCursor(m_backend->fd(), m_crtc->id(), p.x(), p.y());
 }
 

tests/CMakeLists.txt

@@ -40,3 +40,6 @@ target_link_libraries(x11shadowreader XCB::XCB Qt5::Widgets Qt5::X11Extras KF5::
 add_executable(pointergestures pointergesturestest.cpp)
 add_definitions(-DDIR="${CMAKE_CURRENT_SOURCE_DIR}")
 target_link_libraries(pointergestures Qt5::Gui Qt5::Quick KF5::WaylandClient)
+
+add_executable(cursorhotspottest cursorhotspottest.cpp)
+target_link_libraries(cursorhotspottest Qt5::Widgets)

tests/cursorhotspottest.cpp

@@ -0,0 +1,157 @@
+/*
+ * Copyright 2017  Martin Flöser <mgraesslin@kde.org>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License or (at your option) version 3 or any later version
+ * accepted by the membership of KDE e.V. (or its successor approved
+ * by the membership of KDE e.V.), which shall act as a proxy
+ * defined in Section 14 of version 3 of the license.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#include <QApplication>
+#include <QCursor>
+#include <QMouseEvent>
+#include <QPainter>
+#include <QWidget>
+
+class MouseCursorWidget : public QWidget
+{
+    Q_OBJECT
+public:
+    explicit MouseCursorWidget();
+    ~MouseCursorWidget();
+
+protected:
+    void paintEvent(QPaintEvent * event) override;
+    void mouseMoveEvent(QMouseEvent * event) override;
+    void keyPressEvent(QKeyEvent * event) override;
+
+private:
+    QPoint m_cursorPos;
+    QCursor m_cursors[5];
+    int m_cursorIndex = 0;
+};
+
+namespace {
+QCursor createCenterHotspotCursor()
+{
+    QPixmap cursor(64, 64);
+    cursor.fill(Qt::transparent);
+    QPainter p(&cursor);
+    p.setPen(Qt::black);
+    const QPoint center = cursor.rect().center();
+    p.drawLine(0, center.y(), center.x()-1, center.y());
+    p.drawLine(center.x() + 1, center.y(), cursor.width(), center.y());
+    p.drawLine(center.x(), 0, center.x(), center.y() -1);
+    p.drawLine(center.x(), center.y() + 1, center.x(), cursor.height());
+    return QCursor(cursor, 31, 31);
+}
+
+QCursor createTopLeftHotspotCursor()
+{
+    QPixmap cursor(64, 64);
+    cursor.fill(Qt::transparent);
+    QPainter p(&cursor);
+    p.setPen(Qt::black);
+    p.drawLine(0, 1, 0, cursor.height());
+    p.drawLine(1, 0, cursor.width(), 0);
+    return QCursor(cursor, 0, 0);
+}
+
+QCursor createTopRightHotspotCursor()
+{
+    QPixmap cursor(64, 64);
+    cursor.fill(Qt::transparent);
+    QPainter p(&cursor);
+    p.setPen(Qt::black);
+    p.drawLine(cursor.width() -1, 1, cursor.width() -1, cursor.height());
+    p.drawLine(0, 0, cursor.width() -2, 0);
+    return QCursor(cursor, 63, 0);
+}
+
+QCursor createButtomRightHotspotCursor()
+{
+    QPixmap cursor(64, 64);
+    cursor.fill(Qt::transparent);
+    QPainter p(&cursor);
+    p.setPen(Qt::black);
+    p.drawLine(cursor.width() -1, 0, cursor.width() -1, cursor.height() - 2);
+    p.drawLine(0, cursor.height()-1, cursor.width() -2, cursor.height()-1);
+    return QCursor(cursor, 63, 63);
+}
+
+QCursor createButtomLeftHotspotCursor()
+{
+    QPixmap cursor(64, 64);
+    cursor.fill(Qt::transparent);
+    QPainter p(&cursor);
+    p.setPen(Qt::black);
+    p.drawLine(0, 0, 0, cursor.height() - 2);
+    p.drawLine(1, cursor.height()-1, cursor.width(), cursor.height()-1);
+    return QCursor(cursor, 0, 63);
+}
+
+}
+
+MouseCursorWidget::MouseCursorWidget()
+    : QWidget()
+{
+    setMouseTracking(true);
+    // create cursors
+    m_cursors[0] = createCenterHotspotCursor();
+    m_cursors[1] = createTopLeftHotspotCursor();
+    m_cursors[2] = createTopRightHotspotCursor();
+    m_cursors[3] = createButtomRightHotspotCursor();
+    m_cursors[4] = createButtomLeftHotspotCursor();
+
+    setCursor(m_cursors[m_cursorIndex]);
+}
+
+MouseCursorWidget::~MouseCursorWidget() = default;
+
+void MouseCursorWidget::paintEvent(QPaintEvent *event)
+{
+    Q_UNUSED(event)
+
+    QPainter p(this);
+    p.fillRect(0, 0, width(), height(), Qt::white);
+    if (geometry().contains(m_cursorPos)) {
+        p.setPen(Qt::red);
+        p.drawPoint(m_cursorPos);
+    }
+}
+
+void MouseCursorWidget::mouseMoveEvent(QMouseEvent *event)
+{
+    m_cursorPos = event->pos();
+    update();
+}
+
+void MouseCursorWidget::keyPressEvent(QKeyEvent* event)
+{
+    if (event->key() == Qt::Key_Space) {
+        m_cursorIndex = (m_cursorIndex + 1) % 5;
+        setCursor(m_cursors[m_cursorIndex]);
+    }
+}
+
+int main(int argc, char *argv[])
+{
+    QApplication app(argc, argv);
+
+    MouseCursorWidget widget;
+    widget.show();
+
+    return app.exec();
+}
+
+#include "cursorhotspottest.moc"