From b4ffe734c1e078231bcfdb02d5d961bacef78e38 Mon Sep 17 00:00:00 2001
From: Artur Wieczorek <artwik@wp.pl>
Date: Tue, 5 Apr 2016 23:46:33 +0200
Subject: [PATCH] Fixed inheriting wxMemoryDC transformation settings by
 wxGraphicsContext with Cairo renderer (wxMSW).

When wxGraphicsContext is created from wxMemoryDC with selected 32bppp wxBitmap then transformation settings applied to the source wxMemoryDC are not passed directly to the Cairo context through underlying HDC and therefore they need to be passed to the context explicitly.
These inherited transformations settings should be used only internally by wxGraphicsContext object and shouldn't be exposed through e.g. GetTransform() function and hence they are stored separately (in a dedicated variable) and "subtracted" from actual transformation settings for reporting purposes.

See #17482.
---
 src/common/cairo.cpp     |  2 ++
 src/generic/graphicc.cpp | 58 +++++++++++++++++++++++++++++++---------
 2 files changed, 47 insertions(+), 13 deletions(-)

diff --git a/src/common/cairo.cpp b/src/common/cairo.cpp
index fc8c7b7d14..1f8b6f92cb 100644
--- a/src/common/cairo.cpp
+++ b/src/common/cairo.cpp
@@ -170,6 +170,8 @@
        (cairo_surface_t *surface), (surface) ) \
     m( cairo_set_source_surface, \
        (cairo_t *cr, cairo_surface_t *surface, double x, double y), (cr, surface, x, y) ) \
+    m( cairo_matrix_init_identity, \
+       (cairo_matrix_t *matrix), (matrix) ) \
 
 #ifdef __WXMAC__
 #define wxCAIRO_PLATFORM_METHODS(m) \
diff --git a/src/generic/graphicc.cpp b/src/generic/graphicc.cpp
index 797f4fbbe9..419252ce5f 100644
--- a/src/generic/graphicc.cpp
+++ b/src/generic/graphicc.cpp
@@ -442,10 +442,6 @@ public:
     }
 
     virtual void Clip( const wxRegion &region ) wxOVERRIDE;
-#ifdef __WXMSW__
-    cairo_surface_t* m_mswSurface;
-    WindowHDC m_mswWindowHDC;
-#endif
 
     // clips drawings to the rect
     virtual void Clip( wxDouble x, wxDouble y, wxDouble w, wxDouble h ) wxOVERRIDE;
@@ -501,9 +497,14 @@ protected:
     QImage* m_qtImage;
     cairo_surface_t* m_qtSurface;
 #endif
+#ifdef __WXMSW__
+    cairo_surface_t* m_mswSurface;
+    WindowHDC m_mswWindowHDC;
+#endif
 
 private:
     cairo_t* m_context;
+    cairo_matrix_t m_internalTransform;
 
     wxVector<float> m_layerOpacities;
 
@@ -1915,14 +1916,36 @@ wxCairoContext::wxCairoContext( wxGraphicsRenderer* renderer, const wxMemoryDC&
     }
 
     Init( cairo_create(m_mswSurface) );
-    // If we've created a image surface, we need to flip the Y axis so that 
-    // all drawing will appear right side up.
-    if (hasBitmap) {
-        cairo_matrix_t matrix;
-        cairo_matrix_init(&matrix, 1.0, 0.0, 0.0, -1.0, 0.0, height);
-        cairo_set_matrix(m_context, &matrix);
+    // If we've created a image surface, we need:
+    //   1. To flip the Y axis so that all drawing will appear right side up.
+    //   2. To explicitly transfer transformations settings from source DC
+    //      to Cairo context because they are not inherited implicitly.
+    // We have to remember these operations as an internal transformation
+    // which is not going to be exposed through e.g. GetTransform().
+    if (hasBitmap)
+    {
+        // Flip the Y axis.
+        cairo_matrix_init(&m_internalTransform, 1.0, 0.0, 0.0, -1.0, 0.0, height);
+
+        // Transfer transformation settings from source DC to Cairo context on our own.
+        wxPoint org = dc.GetDeviceOrigin();
+        cairo_matrix_translate(&m_internalTransform, org.x, org.y);
+
+        double sx, sy;
+        dc.GetUserScale(&sx, &sy);
+        double lsx, lsy;
+        dc.GetLogicalScale(&lsx, &lsy);
+        sx *= lsx;
+        sy *= lsy;
+        cairo_matrix_scale(&m_internalTransform, sx, sy);
+
+        org = dc.GetLogicalOrigin();
+        cairo_matrix_translate(&m_internalTransform, -org.x, -org.y);
+
+        // Apply all above transformations.
+        cairo_set_matrix(m_context, &m_internalTransform);
     }
-#endif
+#endif // __WXMSW__
     
 #ifdef __WXGTK3__
     cairo_t* cr = static_cast<cairo_t*>(dc.GetImpl()->GetCairoContext());
@@ -2102,7 +2125,9 @@ wxCairoContext::~wxCairoContext()
 
 void wxCairoContext::Init(cairo_t *context)
 {
-    m_context = context ;
+    m_context = context;
+    cairo_matrix_init_identity(&m_internalTransform);
+
     PushState();
     PushState();
 }
@@ -2207,7 +2232,14 @@ void wxCairoContext::SetTransform( const wxGraphicsMatrix& matrix )
 wxGraphicsMatrix wxCairoContext::GetTransform() const
 {
     wxGraphicsMatrix matrix = CreateMatrix();
-    cairo_get_matrix(m_context,(cairo_matrix_t*) matrix.GetNativeMatrix());
+    cairo_matrix_t* transformMatrix = (cairo_matrix_t*)matrix.GetNativeMatrix();
+    cairo_get_matrix(m_context, transformMatrix);
+
+    // Don't expose internal transformations.
+    cairo_matrix_t intTransformMatrixRev = m_internalTransform;
+    if ( cairo_matrix_invert(&intTransformMatrixRev) == CAIRO_STATUS_SUCCESS )
+        cairo_matrix_multiply(transformMatrix, transformMatrix, &intTransformMatrixRev);
+
     return matrix;
 }