From 2e508c73e95ef50947e3ed6e941b67b1f6b5bed4 Mon Sep 17 00:00:00 2001
From: falkTX <falktx@falktx.com>
Date: Sat, 14 Aug 2021 13:34:33 +0100
Subject: [PATCH] Fix fullviewport-drawing auto-scaling for Cairo

Signed-off-by: falkTX <falktx@falktx.com>
---
 dgl/src/Cairo.cpp  | 23 ++++++++++++++++++++---
 dgl/src/OpenGL.cpp |  6 +++---
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/dgl/src/Cairo.cpp b/dgl/src/Cairo.cpp
index 66ccf86e..ebefaa56 100644
--- a/dgl/src/Cairo.cpp
+++ b/dgl/src/Cairo.cpp
@@ -735,9 +735,7 @@ void SubWidget::PrivateData::display(const uint width, const uint height, const
     {
         // full viewport size
         cairo_translate(handle, 0, 0);
-
-        // no scaling
-        cairo_scale(handle, 1.0, 1.0);
+        cairo_scale(handle, autoScaleFactor, autoScaleFactor);
     }
     else
     {
@@ -776,15 +774,34 @@ void TopLevelWidget::PrivateData::display()
     if (! selfw->pData->visible)
         return;
 
+    cairo_t* const handle = static_cast<const CairoGraphicsContext&>(self->getGraphicsContext()).handle;
+
     const Size<uint> size(window.getSize());
     const uint width  = size.getWidth();
     const uint height = size.getHeight();
 
     const double autoScaleFactor = window.pData->autoScaleFactor;
 
+    cairo_matrix_t matrix;
+    cairo_get_matrix(handle, &matrix);
+
+    // full viewport size
+    if (window.pData->autoScaling)
+    {
+        cairo_translate(handle, 0, 0);
+        cairo_scale(handle, autoScaleFactor, autoScaleFactor);
+    }
+    else
+    {
+        cairo_translate(handle, 0, 0);
+        cairo_scale(handle, 1.0, 1.0);
+    }
+
     // main widget drawing
     self->onDisplay();
 
+    cairo_set_matrix(handle, &matrix);
+
     // now draw subwidgets if there are any
     selfw->pData->displaySubWidgets(width, height, autoScaleFactor);
 }
diff --git a/dgl/src/OpenGL.cpp b/dgl/src/OpenGL.cpp
index 8cc6d889..098c33e6 100644
--- a/dgl/src/OpenGL.cpp
+++ b/dgl/src/OpenGL.cpp
@@ -649,9 +649,9 @@ void TopLevelWidget::PrivateData::display()
     if (window.pData->autoScaling)
     {
         glViewport(0,
-                   -static_cast<int>(height * autoScaleFactor - height),
-                   static_cast<int>(width * autoScaleFactor),
-                   static_cast<int>(height * autoScaleFactor));
+                   -static_cast<int>(height * autoScaleFactor - height + 0.5),
+                   static_cast<int>(width * autoScaleFactor + 0.5),
+                   static_cast<int>(height * autoScaleFactor + 0.5));
     }
     else
     {