From f72c2196c7b735d863a8f0f23bf1cf87c768afb2 Mon Sep 17 00:00:00 2001
From: Vlad Zahorodnii <vlad.zahorodnii@kde.org>
Date: Fri, 12 Nov 2021 17:11:07 +0200
Subject: [PATCH] Calculate correct surface-to-buffer matrix with only upscaled
 viewport

Currently, if a wp_viewport upscales the surface but doesn't set the
source rectangle, the surface-to-buffer matrix will be calculated
incorrectly.

If the source rect is not set, we need to calculate the source size
based on the buffer size and compare it with the destination size. If
the two are not the same, add a scale transform.

BUG: 445346
---
 src/wayland/surface_interface.cpp | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/wayland/surface_interface.cpp b/src/wayland/surface_interface.cpp
index 74a6929a68..c8fdfb8601 100644
--- a/src/wayland/surface_interface.cpp
+++ b/src/wayland/surface_interface.cpp
@@ -434,8 +434,17 @@ QMatrix4x4 SurfaceInterfacePrivate::buildSurfaceToBufferMatrix()
 
     if (current.viewport.sourceGeometry.isValid()) {
         surfaceToBufferMatrix.translate(current.viewport.sourceGeometry.x(), current.viewport.sourceGeometry.y());
-        surfaceToBufferMatrix.scale(current.viewport.sourceGeometry.width() / surfaceSize.width(),
-                                    current.viewport.sourceGeometry.height() / surfaceSize.height());
+    }
+
+    QSizeF sourceSize;
+    if (current.viewport.sourceGeometry.isValid()) {
+        sourceSize = current.viewport.sourceGeometry.size();
+    } else {
+        sourceSize = bufferSize / current.bufferScale;
+    }
+
+    if (sourceSize != surfaceSize) {
+        surfaceToBufferMatrix.scale(sourceSize.width() / surfaceSize.width(), sourceSize.height() / surfaceSize.height());
     }
 
     return surfaceToBufferMatrix;