Allow passing already parsed HTML to wxHtmlDCRenderer

This is more efficient when the same HTML is reused multiple times, e.g.
for measuring it first and then rendering it.

The new function also makes it simpler to parse HTML and manipulate it
in some way before measuring and rendering it.

include/wx/html/htmprint.h

@@ -54,6 +54,11 @@ public:
     // (see wxFileSystem for detailed explanation)
     void SetHtmlText(const wxString& html, const wxString& basepath = wxEmptyString, bool isdir = true);
 
+    // Sets the HTML cell that will be rendered: this is more efficient than
+    // using text as it allows to parse it only once. Note that the cell will
+    // be modified by this call.
+    void SetHtmlCell(wxHtmlContainerCell& cell);
+
     // Sets fonts to be used when displaying HTML page. (if size null then default sizes used).
     void SetFonts(const wxString& normal_face, const wxString& fixed_face, const int *sizes = NULL);
 
@@ -79,11 +84,14 @@ public:
     int GetTotalHeight() const;
 
 private:
+    void DoSetHtmlCell(wxHtmlContainerCell* cell);
+
     wxDC *m_DC;
     wxHtmlWinParser *m_Parser;
     wxFileSystem *m_FS;
     wxHtmlContainerCell *m_Cells;
     int m_Width, m_Height;
+    bool m_ownsCells;
 
     wxDECLARE_NO_COPY_CLASS(wxHtmlDCRenderer);
 };

interface/wx/html/htmprint.h

@@ -168,6 +168,19 @@ public:
                      const wxString& basepath = wxEmptyString,
                      bool isdir = true);
 
+    /**
+        Associate the given HTML contents to the renderer.
+
+        This is similar to SetHtmlText(), but is more efficient as the text can
+        be parsed only once, using wxHtmlParser::Parse(), and then passed to
+        wxHtmlDCRenderer multiple times or already reused for other purposes.
+
+        Note that @a cell will be modified (e.g. laid out) by this function.
+
+        @since 3.1.2
+     */
+    void SetHtmlCell(wxHtmlContainerCell& cell);
+
     /**
         Set size of output rectangle, in pixels. Note that you @b can't change
         width of the rectangle between calls to Render() !

src/html/htmprint.cpp

@@ -70,6 +70,7 @@ wxHtmlDCRenderer::wxHtmlDCRenderer() : wxObject()
     m_DC = NULL;
     m_Width = m_Height = 0;
     m_Cells = NULL;
+    m_ownsCells = false;
     m_Parser = new wxHtmlWinParser();
     m_FS = new wxFileSystem();
     m_Parser->SetFS(m_FS);
@@ -80,7 +81,9 @@ wxHtmlDCRenderer::wxHtmlDCRenderer() : wxObject()
 
 wxHtmlDCRenderer::~wxHtmlDCRenderer()
 {
-    if (m_Cells) delete m_Cells;
+    if ( m_ownsCells )
+        delete m_Cells;
+
     if (m_Parser) delete m_Parser;
     if (m_FS) delete m_FS;
 }
@@ -110,14 +113,33 @@ void wxHtmlDCRenderer::SetHtmlText(const wxString& html, const wxString& basepat
     wxCHECK_RET( m_DC, "SetDC() must be called before SetHtmlText()" );
     wxCHECK_RET( m_Width, "SetSize() must be called before SetHtmlText()" );
 
-    wxDELETE(m_Cells);
-
     m_FS->ChangePathTo(basepath, isdir);
-    m_Cells = (wxHtmlContainerCell*) m_Parser->Parse(html);
+
+    wxHtmlContainerCell* const cell = (wxHtmlContainerCell*) m_Parser->Parse(html);
+    wxCHECK_RET( cell, "Failed to parse HTML" );
+
+    DoSetHtmlCell(cell);
+
+    m_ownsCells = true;
+}
+
+void wxHtmlDCRenderer::DoSetHtmlCell(wxHtmlContainerCell* cell)
+{
+    if ( m_ownsCells )
+        delete m_Cells;
+
+    m_Cells = cell;
     m_Cells->SetIndent(0, wxHTML_INDENT_ALL, wxHTML_UNITS_PIXELS);
     m_Cells->Layout(m_Width);
 }
 
+void wxHtmlDCRenderer::SetHtmlCell(wxHtmlContainerCell& cell)
+{
+    DoSetHtmlCell(&cell);
+
+    m_ownsCells = false;
+}
+
 
 void wxHtmlDCRenderer::SetFonts(const wxString& normal_face, const wxString& fixed_face,
                                 const int *sizes)