eglfs: Fix the logical dpi calculation for some devices

KMS and backends using the default logicalDpi() implementation
(EGLDevice for instance) did not correctly check if the physical width
and height are greater than zero. The result is a NaN dpi on systems
where the drivers report a zero size. This in turn breaks font
rendering and various other things.

isValid() is changed to !isEmpty(). This way we check for width and
height > 0 instead of >= 0.

Change-Id: I8cdcf93a116379ae33c65599ad792a3b712518a3
Reviewed-by: Louai Al-Khanji <louai.al-khanji@theqtcompany.com>

3 files changed, 23 insertions, 8 deletions

diff --git a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsscreen.cpp b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsscreen.cpp
index 60586f98a7..048f5433dc 100644
--- a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsscreen.cpp
+++ b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsscreen.cpp
@@ -160,10 +160,10 @@ QSizeF QEglFSKmsScreen::physicalSize() const
 
 QDpi QEglFSKmsScreen::logicalDpi() const
 {
-    QSizeF ps = physicalSize();
-    QSize s = geometry().size();
+    const QSizeF ps = physicalSize();
+    const QSize s = geometry().size();
 
-    if (ps.isValid() && s.isValid())
+    if (!ps.isEmpty() && !s.isEmpty())
         return QDpi(25.4 * s.width() / ps.width(),
                     25.4 * s.height() / ps.height());
     else
diff --git a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_egldevice/qeglfskmsegldeviceintegration.cpp b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_egldevice/qeglfskmsegldeviceintegration.cpp
index 1ddcb3b862..f7450708ab 100644
--- a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_egldevice/qeglfskmsegldeviceintegration.cpp
+++ b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_egldevice/qeglfskmsegldeviceintegration.cpp
@@ -33,6 +33,7 @@
 
 #include "qeglfskmsegldeviceintegration.h"
 #include <QLoggingCategory>
+#include <private/qmath_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -115,7 +116,18 @@ EGLDisplay QEglFSKmsEglDeviceIntegration::createDisplay(EGLNativeDisplayType nat
 
 QSizeF QEglFSKmsEglDeviceIntegration::physicalScreenSize() const
 {
-    return QSizeF(m_drm_connector->mmWidth, m_drm_connector->mmHeight);
+    const int defaultPhysicalDpi = 100;
+    static const int width = qEnvironmentVariableIntValue("QT_QPA_EGLFS_PHYSICAL_WIDTH");
+    static const int height = qEnvironmentVariableIntValue("QT_QPA_EGLFS_PHYSICAL_HEIGHT");
+    QSizeF size(width, height);
+    if (size.isEmpty()) {
+        size = QSizeF(m_drm_connector->mmWidth, m_drm_connector->mmHeight);
+        if (size.isEmpty()) {
+            const float pixelsPerMm = Q_MM_PER_INCH / defaultPhysicalDpi;
+            size = QSizeF(screenSize().width() * pixelsPerMm, screenSize().height() * pixelsPerMm);
+        }
+    }
+    return size;
 }
 
 QSize QEglFSKmsEglDeviceIntegration::screenSize() const
diff --git a/src/plugins/platforms/eglfs/qeglfsdeviceintegration.cpp b/src/plugins/platforms/eglfs/qeglfsdeviceintegration.cpp
index 064b9f6306..8af48a893b 100644
--- a/src/plugins/platforms/eglfs/qeglfsdeviceintegration.cpp
+++ b/src/plugins/platforms/eglfs/qeglfsdeviceintegration.cpp
@@ -212,11 +212,14 @@ QSize QEGLDeviceIntegration::screenSize() const
 
 QDpi QEGLDeviceIntegration::logicalDpi() const
 {
-    QSizeF ps = physicalScreenSize();
-    QSize s = screenSize();
+    const QSizeF ps = physicalScreenSize();
+    const QSize s = screenSize();
 
-    return QDpi(25.4 * s.width() / ps.width(),
-                25.4 * s.height() / ps.height());
+    if (!ps.isEmpty() && !s.isEmpty())
+        return QDpi(25.4 * s.width() / ps.width(),
+                    25.4 * s.height() / ps.height());
+    else
+        return QDpi(100, 100);
 }
 
 qreal QEGLDeviceIntegration::pixelDensity() const