[platforms/hwcomposer] Add scaling support

Summary:
Despite plasma frameworks doing it's own scaling with fonts, it's been
requested to use kwin/wayland scaling.

Like DRM, when kscreen is not used, scale value is loaded from a config
file.

Config format is
[HWComposerOutputs][0]
Scale=N

The 0 is to map similarly to DRM and support multi-screen, but with a
screen index
rather than a UUID based on EDID.

Because we don't support multi screen this is always 0 for now.

Test Plan: Ran with the config value unset and with the config value at
Scale=3.

Reviewers: #kwin, romangg

Reviewed By: #kwin, romangg

Subscribers: bshah, romangg, nicolasfella, zzag, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D18810

plugins/platforms/hwcomposer/egl_hwcomposer_backend.cpp

@@ -130,6 +130,10 @@ bool EglHwcomposerBackend::makeContextCurrent()
         qCWarning(KWIN_HWCOMPOSER) << "Error occurred while creating context " << error;
         return false;
     }
+
+    const QSize overall = m_backend->size();
+    glViewport(0, 0, overall.width(), overall.height());
+
     return true;
 }
 

plugins/platforms/hwcomposer/hwcomposer_backend.cpp

@@ -27,6 +27,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "wayland_server.h"
 // KWayland
 #include <KWayland/Server/output_interface.h>
+// KDE
+#include <KConfigGroup>
 // Qt
 #include <QKeyEvent>
 #include <QDBusConnection>
@@ -253,7 +255,7 @@ void HwcomposerBackend::init()
     setReady(true);
 }
 
-QSize HwcomposerBackend::screenSize() const
+QSize HwcomposerBackend::size() const
 {
     if (m_output) {
         return m_output->pixelSize();
@@ -261,6 +263,22 @@ QSize HwcomposerBackend::screenSize() const
     return QSize();
 }
 
+QSize HwcomposerBackend::screenSize() const
+{
+    if (m_output) {
+        return m_output->pixelSize() / m_output->scale();
+    }
+    return QSize();
+}
+
+int HwcomposerBackend::scale() const
+ {
+    if (m_output) {
+        return m_output->scale();
+    }
+    return 1;
+}
+
 void HwcomposerBackend::initLights()
 {
     hw_module_t *lightsModule = nullptr;
@@ -510,6 +528,9 @@ HwcomposerOutput::HwcomposerOutput(hwc_composer_device_1_t *device)
     setInternal(true);
     setEnabled(true);
     setDpmsSupported(true);
+
+    const auto outputGroup = kwinApp()->config()->group("HWComposerOutputs").group("0");
+    setScale(outputGroup.readEntry("Scale", 1));
     setWaylandMode(m_pixelSize, mode.refreshRate);
 }
 

plugins/platforms/hwcomposer/hwcomposer_backend.h

@@ -80,11 +80,11 @@ public:
     Outputs outputs() const override;
     Outputs enabledOutputs() const override;
 
-    QSize size() const {
-        return screenSize();
-    }
+    QSize size() const;
     QSize screenSize() const override;
 
+    int scale() const;
+
     HwcomposerWindow *createSurface();
 
     hwc_composer_device_1_t *device() const {