Factor out text measurement from wxDC and wxWindow into wxTextMeasure.

Add a new private wxTextMeasure class implementing methods for measuring text
and move the often duplicated (but not always identically) code for doing the
same from wxDC and wxWindow into it.

Currently this class is only really implemented in wxMSW and wxGTK.

Also extend the test for text measuring functions and rename it to
MeasuringTextTestCase from MeasuringContextTestCase as it's not wxGC-specific
any more.

Closes #14705.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72699 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/private/textmeasure.h

@@ -0,0 +1,138 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/private/textmeasure.h
+// Purpose:     declaration of wxTextMeasure class
+// Author:      Manuel Martin
+// Created:     2012-10-05
+// Copyright:   (c) 1997-2012 wxWidgets team
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_PRIVATE_TEXTMEASURE_H_
+#define _WX_PRIVATE_TEXTMEASURE_H_
+
+#include "wx/vector.h"
+
+class WXDLLIMPEXP_FWD_CORE wxDC;
+class WXDLLIMPEXP_FWD_CORE wxFont;
+class WXDLLIMPEXP_FWD_CORE wxWindow;
+
+// ----------------------------------------------------------------------------
+// wxTextMeasure: class used to measure text extent.
+// ----------------------------------------------------------------------------
+
+class wxTextMeasureBase
+{
+public:
+    // The first ctor argument must be non-NULL, i.e. each object of this class
+    // is associated with either a valid wxDC or a valid wxWindow.
+    wxTextMeasureBase(const wxDC *dc, const wxFont *theFont);
+    wxTextMeasureBase(const wxWindow *win, const wxFont *theFont);
+
+    // Even though this class is not supposed to be used polymorphically, give
+    // it a virtual dtor to avoid compiler warnings.
+    virtual ~wxTextMeasureBase() { }
+
+
+    // Return the extent of a single line string.
+    void GetTextExtent(const wxString& string,
+                       wxCoord *width,
+                       wxCoord *height,
+                       wxCoord *descent = NULL,
+                       wxCoord *externalLeading = NULL);
+
+    // The same for a multiline (with '\n') string.
+    void GetMultiLineTextExtent(const wxString& text,
+                                wxCoord *width,
+                                wxCoord *height,
+                                wxCoord *heightOneLine = NULL);
+
+    // Find the dimensions of the largest string.
+    void GetLargestStringExtent(const wxVector<wxString>& strings,
+                                wxCoord *width,
+                                wxCoord *height);
+
+    // Fill the array with the widths for each "0..N" substrings for N from 1
+    // to text.length().
+    //
+    // The scaleX argument is the horizontal scale used by wxDC and is only
+    // used in the generic implementation.
+    bool GetPartialTextExtents(const wxString& text,
+                               wxArrayInt& widths,
+                               double scaleX);
+
+protected:
+    // These functions are called by our public methods before and after each
+    // call to DoGetTextExtent(). Derived classes may override them to prepare
+    // for -- possibly several -- subsequent calls to DoGetTextExtent().
+    //
+    // As these calls must be always paired, they're never called directly but
+    // only by our friend MeasuringGuard class.
+    virtual void BeginMeasuring() { }
+    virtual void EndMeasuring() { }
+
+    // RAII wrapper for the two methods above.
+    class MeasuringGuard
+    {
+    public:
+        MeasuringGuard(wxTextMeasureBase& tm) : m_tm(tm)
+        {
+            m_tm.BeginMeasuring();
+        }
+
+        ~MeasuringGuard()
+        {
+            m_tm.EndMeasuring();
+        }
+
+    private:
+        wxTextMeasureBase& m_tm;
+    };
+
+
+    // The main function of this class, to be implemented in platform-specific
+    // way used by all our public methods except GetLargestStringExtents().
+    //
+    // The width and height pointers here are never NULL and the input string
+    // is not empty.
+    virtual void DoGetTextExtent(const wxString& string,
+                                 wxCoord *width,
+                                 wxCoord *height,
+                                 wxCoord *descent = NULL,
+                                 wxCoord *externalLeading = NULL) = 0;
+
+    // The real implementation of GetPartialTextExtents().
+    //
+    // On input, widths array contains text.length() zero elements and the text
+    // is guaranteed to be non-empty.
+    virtual bool DoGetPartialTextExtents(const wxString& text,
+                                         wxArrayInt& widths,
+                                         double scaleX) = 0;
+
+
+    // Exactly one of m_dc and m_win is non-NULL for any given object of this
+    // class.
+    const wxDC* const m_dc;
+    const wxWindow* const m_win;
+
+    // This one can be NULL or not.
+    const wxFont* const m_font;
+
+    wxDECLARE_NO_COPY_CLASS(wxTextMeasureBase);
+};
+
+// Include the platform dependant class declaration, if any.
+#if defined(__WXGTK20__)
+    #include "wx/gtk/private/textmeasure.h"
+#elif defined(__WXMSW__)
+    #include "wx/msw/private/textmeasure.h"
+#else // no platform-specific implementation of wxTextMeasure yet
+    #include "wx/generic/private/textmeasure.h"
+
+    #define wxUSE_GENERIC_TEXTMEASURE 1
+#endif
+
+#ifndef wxUSE_GENERIC_TEXTMEASURE
+    #define wxUSE_GENERIC_TEXTMEASURE 0
+#endif
+
+#endif // _WX_PRIVATE_TEXTMEASURE_H_