wayland: Introduce SurfaceInterface::bufferSourceBox()

The bufferSourceBox provides a way to get the source region of the
attached buffer. It can be used to compute the effective scale factor
when using wp_viewport.

src/core/output.cpp

@@ -60,6 +60,81 @@ OutputMode::Flags OutputMode::flags() const
     return m_flags;
 }
 
+Output::Transform invertOutputTransform(Output::Transform transform)
+{
+    switch (transform) {
+    case Output::Transform::Normal:
+        return Output::Transform::Normal;
+    case Output::Transform::Rotated90:
+        return Output::Transform::Rotated270;
+    case Output::Transform::Rotated180:
+        return Output::Transform::Rotated180;
+    case Output::Transform::Rotated270:
+        return Output::Transform::Rotated90;
+    case Output::Transform::Flipped:
+    case Output::Transform::Flipped90:
+    case Output::Transform::Flipped180:
+    case Output::Transform::Flipped270:
+        return transform; // inverse transform of a flip transform is itself
+    }
+}
+
+QRectF applyOutputTransform(const QRectF &rect, const QSizeF &bounds, Output::Transform transform)
+{
+    QRectF dest;
+
+    switch (transform) {
+    case Output::Transform::Normal:
+    case Output::Transform::Rotated180:
+    case Output::Transform::Flipped:
+    case Output::Transform::Flipped180:
+        dest.setWidth(rect.width());
+        dest.setHeight(rect.height());
+        break;
+    default:
+        dest.setWidth(rect.height());
+        dest.setHeight(rect.width());
+        break;
+    }
+
+    switch (transform) {
+    case Output::Transform::Normal:
+        dest.setX(rect.x());
+        dest.setY(rect.y());
+        break;
+    case Output::Transform::Rotated90:
+        dest.setX(bounds.height() - (rect.y() + rect.height()));
+        dest.setY(rect.x());
+        break;
+    case Output::Transform::Rotated180:
+        dest.setX(bounds.width() - (rect.x() + rect.width()));
+        dest.setY(bounds.height() - (rect.y() + rect.height()));
+        break;
+    case Output::Transform::Rotated270:
+        dest.setX(rect.y());
+        dest.setY(bounds.width() - (rect.x() + rect.width()));
+        break;
+    case Output::Transform::Flipped:
+        dest.setX(bounds.width() - (rect.x() + rect.width()));
+        dest.setY(rect.y());
+        break;
+    case Output::Transform::Flipped90:
+        dest.setX(rect.y());
+        dest.setY(rect.x());
+        break;
+    case Output::Transform::Flipped180:
+        dest.setX(rect.x());
+        dest.setY(bounds.height() - (rect.y() + rect.height()));
+        break;
+    case Output::Transform::Flipped270:
+        dest.setX(bounds.height() - (rect.y() + rect.height()));
+        dest.setY(bounds.width() - (rect.x() + rect.width()));
+        break;
+    }
+
+    return dest;
+}
+
 Output::Output(QObject *parent)
     : QObject(parent)
 {

src/core/output.h

@@ -371,6 +371,10 @@ protected:
     friend class EffectScreenImpl; // to access m_effectScreen
 };
 
+// TODO: Introduce an OutputTransform type with two methods: invert + apply?
+KWIN_EXPORT Output::Transform invertOutputTransform(Output::Transform transform);
+KWIN_EXPORT QRectF applyOutputTransform(const QRectF &rect, const QSizeF &bounds, Output::Transform transform);
+
 inline QRect Output::rect() const
 {
     return QRect(QPoint(0, 0), geometry().size());

src/wayland/surface_interface.cpp

@@ -785,6 +785,20 @@ QRegion SurfaceInterface::input() const
     return d->inputRegion;
 }
 
+QRectF SurfaceInterface::bufferSourceBox() const
+{
+    if (!d->current.viewport.sourceGeometryIsSet) {
+        return QRectF(0, 0, d->bufferSize.width(), d->bufferSize.height());
+    }
+
+    const QRectF box(d->current.viewport.sourceGeometry.x() * d->current.bufferScale,
+                     d->current.viewport.sourceGeometry.y() * d->current.bufferScale,
+                     d->current.viewport.sourceGeometry.width() * d->current.bufferScale,
+                     d->current.viewport.sourceGeometry.height() * d->current.bufferScale);
+
+    return KWin::applyOutputTransform(box, d->bufferSize, KWin::invertOutputTransform(d->current.bufferTransform));
+}
+
 KWin::Output::Transform SurfaceInterface::bufferTransform() const
 {
     return d->current.bufferTransform;

src/wayland/surface_interface.h

@@ -145,6 +145,7 @@ public:
     QRegion opaque() const;
     QRegion input() const;
     QRegion bufferDamage() const;
+    QRectF bufferSourceBox() const;
     /**
      * Returns the buffer transform that had been applied to the buffer to compensate for
      * output rotation.