File 0569-scale-mirror-pixmap.patch of Package OpenBoard

From d835e5ef719356c3840c11aade9e671a26d5c6ce Mon Sep 17 00:00:00 2001
From: letsfindaway <me@letsfindaway.de>
Date: Sun, 9 Jan 2022 10:40:12 +0100
Subject: [PATCH] fix: scaling of mirror pixmap

- when scaling the pixmap take the devicePixelRatio into account
- do not scale the already scaled pixmap when drawing in UBScreenMirror
- use device independent coordinates when positioning the pixmap
---
 src/gui/UBScreenMirror.cpp | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/gui/UBScreenMirror.cpp b/src/gui/UBScreenMirror.cpp
index db5b65116..ff9810862 100644
--- a/src/gui/UBScreenMirror.cpp
+++ b/src/gui/UBScreenMirror.cpp
@@ -66,10 +66,12 @@ void UBScreenMirror::paintEvent(QPaintEvent *event)
 
     if (!mLastPixmap.isNull())
     {
-        int x = (width() - mLastPixmap.width()) / 2;
-        int y = (height() - mLastPixmap.height()) / 2;
+        // compute size and offset in device independent coordinates
+        QSizeF pixmapSize = mLastPixmap.size() / mLastPixmap.devicePixelRatioF();
+        int x = (width() - pixmapSize.width()) / 2;
+        int y = (height() - pixmapSize.height()) / 2;
 
-        painter.drawPixmap(x, y, width(), height(), mLastPixmap);
+        painter.drawPixmap(x, y, mLastPixmap);
     }
 }
 
@@ -95,7 +97,7 @@ void UBScreenMirror::grabPixmap()
     }
 
     if (!mLastPixmap.isNull())
-        mLastPixmap = mLastPixmap.scaled(width(), height(), Qt::KeepAspectRatio, Qt::SmoothTransformation);
+        mLastPixmap = mLastPixmap.scaled(size() * mLastPixmap.devicePixelRatioF(), Qt::KeepAspectRatio, Qt::SmoothTransformation);
 }