Merge branch 'dc-clear-white-default'

Fix regression in wxDC::Clear() and make wxGCDC::Clear() consistent with
it by using white if the background brush hadn't been explicitly set.

See https://github.com/wxWidgets/wxWidgets/pull/1582

interface/wx/dc.h

@@ -261,6 +261,9 @@ public:
         Note that SetBackground() method must be used to set the brush used by
         Clear(), the brush used for filling the shapes set by SetBrush() is
         ignored by it.
+
+        If no background brush was set, solid white brush is used to clear the
+        device context.
     */
     void Clear();
 

src/common/dcgraph.cpp

@@ -543,8 +543,6 @@ void wxGCDCImpl::SetBrush( const wxBrush &brush )
 void wxGCDCImpl::SetBackground( const wxBrush &brush )
 {
     m_backgroundBrush = brush;
-    if (!m_backgroundBrush.IsOk())
-        return;
 }
 
 void wxGCDCImpl::SetLogicalFunction( wxRasterOperationMode function )
@@ -1286,9 +1284,11 @@ void wxGCDCImpl::Clear()
 {
     wxCHECK_RET( IsOk(), wxT("wxGCDC(cg)::Clear - invalid DC") );
 
-    if ( m_backgroundBrush.IsOk() )
+    if ( m_backgroundBrush.IsTransparent() )
-    {
+        return;
-        m_graphicContext->SetBrush( m_backgroundBrush );
+
+    m_graphicContext->SetBrush( m_backgroundBrush.IsOk() ? m_backgroundBrush
+                                                         : *wxWHITE_BRUSH );
     wxPen p = *wxTRANSPARENT_PEN;
     m_graphicContext->SetPen( p );
     wxCompositionMode formerMode = m_graphicContext->GetCompositionMode();
@@ -1301,13 +1301,6 @@ void wxGCDCImpl::Clear()
     m_graphicContext->SetCompositionMode(formerMode);
     m_graphicContext->SetPen( m_pen );
     m_graphicContext->SetBrush( m_brush );
-    }
-    else
-    {
-        double x, y, w, h;
-        m_graphicContext->GetClipBox(&x, &y, &w, &h);
-        m_graphicContext->ClearRectangle(x, y, w, h);
-    }
 }
 
 void wxGCDCImpl::DoGetSize(int *width, int *height) const

src/common/prntbase.cpp

@@ -2054,7 +2054,6 @@ bool wxPrintPreviewBase::RenderPageIntoBitmap(wxBitmap& bmp, int pageNum)
 {
     wxMemoryDC memoryDC;
     memoryDC.SelectObject(bmp);
-    memoryDC.SetBackground(*wxWHITE_BRUSH);
     memoryDC.Clear();
 
     return RenderPageIntoDC(memoryDC, pageNum);

src/gtk/dcclient.cpp

@@ -1508,7 +1508,7 @@ void wxWindowDCImpl::Clear()
 
     if (!m_gdkwindow) return;
 
-    if (!m_backgroundBrush.IsOk() || m_backgroundBrush.GetStyle() == wxBRUSHSTYLE_TRANSPARENT)
+    if (m_backgroundBrush.IsTransparent())
         return;
 
     int width,height;
@@ -1738,7 +1738,8 @@ void wxWindowDCImpl::SetBackground( const wxBrush &brush )
 
     m_backgroundBrush = brush;
 
-    if (!m_backgroundBrush.IsOk()) return;
+    if (!m_backgroundBrush.IsOk())
+        m_backgroundBrush = *wxWHITE_BRUSH;
 
     if (!m_gdkwindow) return;
 

src/msw/dc.cpp

@@ -729,8 +729,23 @@ void wxMSWDCImpl::Clear()
             return;
     }
 
+    HBRUSH hbr;
     if ( !m_backgroundBrush.IsOk() )
+    {
+        // By default, use the stock white brush for compatibility with the
+        // previous wx versions.
+        hbr = WHITE_BRUSH;
+    }
+    else if ( !m_backgroundBrush.IsTransparent() )
+    {
+        hbr = GetHbrushOf(m_backgroundBrush);
+    }
+    else // Using transparent background brush.
+    {
+        // Clearing with transparent brush doesn't do anything, just as drawing
+        // with transparent pen doesn't.
         return;
+    }
 
     RECT rect;
     ::GetClipBox(GetHdc(), &rect);
@@ -738,7 +753,7 @@ void wxMSWDCImpl::Clear()
     // to compensate rounding errors if DC is the subject
     // of complex transformation (is e.g. rotated).
     ::InflateRect(&rect, 1, 1);
-    ::FillRect(GetHdc(), &rect, GetHbrushOf(m_backgroundBrush));
+    ::FillRect(GetHdc(), &rect, hbr);
 
     RealizeScaleAndOrigin();
 }

tests/graphics/bitmap.cpp

@@ -25,6 +25,8 @@
 #include "wx/graphics.h"
 #endif // wxUSE_GRAPHICS_CONTEXT
 
+#include "testimage.h"
+
 #define ASSERT_EQUAL_RGB(c, r, g, b) \
     CHECK( (int)r == (int)c.Red() ); \
     CHECK( (int)g == (int)c.Green() ); \
@@ -915,4 +917,118 @@ TEST_CASE("BitmapTestCase::SubBitmapAlphaWithMask", "[bitmap][subbitmap][alpha][
         ASSERT_EQUAL_RGB(p, maskClrBottomRight.Red(), maskClrBottomRight.Green(), maskClrBottomRight.Blue());
     }
 }
+
+namespace Catch
+{
+    template <>
+    struct StringMaker<wxBitmap>
+    {
+        static std::string convert(const wxBitmap& bmp)
+        {
+            return wxString::Format("bitmap of size %d*%d",
+                                    bmp.GetWidth(),
+                                    bmp.GetHeight()).ToStdString();
+        }
+    };
+}
+
+class BitmapColourMatcher : public Catch::MatcherBase<wxBitmap>
+{
+public:
+    explicit BitmapColourMatcher(const wxColour& col)
+        : m_col(col)
+    {
+    }
+
+    bool match(const wxBitmap& bmp) const wxOVERRIDE
+    {
+        const wxImage img(bmp.ConvertToImage());
+
+        const unsigned char* data = img.GetData();
+        for ( int y = 0; y < img.GetHeight(); ++y )
+        {
+            for ( int x = 0; x < img.GetWidth(); ++x, data += 3 )
+            {
+                if ( wxColour(data[0], data[1], data[2]) != m_col )
+                    return false;
+            }
+        }
+
+        return true;
+    }
+
+    std::string describe() const wxOVERRIDE
+    {
+        return wxString::Format("doesn't have all %s pixels",
+                                m_col.GetAsString()).ToStdString();
+    }
+
+private:
+    const wxColour m_col;
+};
+
+inline BitmapColourMatcher AllPixelsAre(const wxColour& col)
+{
+    return BitmapColourMatcher(col);
+}
+
+TEST_CASE("DC::Clear", "[bitmap][dc]")
+{
+    // Just some arbitrary pixel data.
+    static unsigned char data[] =
+    {
+        0xff, 0, 0,
+        0, 0xff, 0,
+        0, 0, 0xff,
+        0x7f, 0, 0x7f
+    };
+
+    const wxImage img(2, 2, data, true /* don't take ownership of data */);
+
+    wxBitmap bmp(img);
+
+    SECTION("Clearing uses white by default")
+    {
+        {
+            wxMemoryDC dc(bmp);
+            dc.Clear();
+        }
+
+        CHECK_THAT(bmp, AllPixelsAre(*wxWHITE));
+    }
+
+    SECTION("Clearing with specified brush works as expected")
+    {
+        {
+            wxMemoryDC dc(bmp);
+            dc.SetBackground(*wxRED_BRUSH);
+            dc.Clear();
+        }
+        CHECK_THAT(bmp, AllPixelsAre(*wxRED));
+    }
+
+    SECTION("Clearing with transparent brush does nothing")
+    {
+        {
+            wxMemoryDC dc(bmp);
+            dc.SetBackground(*wxTRANSPARENT_BRUSH);
+            dc.Clear();
+        }
+
+        CHECK_THAT(bmp.ConvertToImage(), RGBSameAs(img));
+    }
+
+    SECTION("Clearing with invalid brush uses white too")
+    {
+        {
+            wxMemoryDC dc(bmp);
+            dc.SetBackground(*wxBLACK_BRUSH);
+            dc.SetBackground(wxBrush());
+            dc.Clear();
+        }
+
+        CHECK_THAT(bmp, AllPixelsAre(*wxWHITE));
+    }
+}
+
 #endif //wxHAS_RAW_BITMAP