From f8bc9abfc460255ca4a6a6885a25f29972fe2cf7 Mon Sep 17 00:00:00 2001
From: JulianSmart <julian@anthemion.co.uk>
Date: Sun, 29 Nov 2015 20:01:10 +0000
Subject: [PATCH] Work around poor image scaling on WIN32, especially on HiDPI
 displays where all images without size specification will be scaled

---
 src/html/m_image.cpp | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/src/html/m_image.cpp b/src/html/m_image.cpp
index 27e0f93977..c34042d109 100644
--- a/src/html/m_image.cpp
+++ b/src/html/m_image.cpp
@@ -465,17 +465,7 @@ void wxHtmlImageCell::SetImage(const wxImage& img)
         if ( m_bmpH == wxDefaultCoord)
             m_bmpH = hh;
 
-        // Only scale the bitmap at the rendering stage,
-        // so we don't lose quality twice
-/*
-        if ((m_bmpW != ww) || (m_bmpH != hh))
-        {
-            wxImage img2 = img.Scale(m_bmpW, m_bmpH);
-            m_bitmap = new wxBitmap(img2);
-        }
-        else
-*/
-            m_bitmap = new wxBitmap(img);
+        m_bitmap = new wxBitmap(img);
     }
 #endif
 }
@@ -605,6 +595,24 @@ void wxHtmlImageCell::Draw(wxDC& dc, int x, int y,
         // and height, so we only do the scaling once.
         double imageScaleX = 1.0;
         double imageScaleY = 1.0;
+
+        // Optimisation for Windows: WIN32 scaling for window DCs is very poor,
+        // so unless we're using a printer DC, do the scaling ourselves.
+#ifdef __WXMSW__
+        if (m_Width >= 0 && m_Width != m_bitmap->GetWidth() && !dc.IsKindOf(CLASSINFO(wxPrinterDC)))
+        {
+            wxImage image(m_bitmap->ConvertToImage());
+            if (image.HasMask())
+            {
+                // Convert the mask to an alpha channel or scaling won't work correctly
+                image.InitAlpha();
+            }
+            image.Rescale(m_Width, m_Height, wxIMAGE_QUALITY_HIGH);
+            delete m_bitmap;
+            m_bitmap = new wxBitmap(image);
+        }
+#endif 
+
         if (m_Width != m_bitmap->GetWidth())
             imageScaleX = (double) m_Width / (double) m_bitmap->GetWidth();
         if (m_Height != m_bitmap->GetHeight())