add function to load font from buffer

Author: razaqq

modules/freetype/include/opencv2/freetype.hpp

@@ -84,6 +84,19 @@ The function loadFontData loads font data.
 
     CV_WRAP virtual void loadFontData(String fontFileName, int idx) = 0;
 
+/** @brief Load font data.
+
+The function loadFontData loads font data.
+The data is not copied, the user needs to make sure the data lives at least as long as FreeType2.
+After the FreeType2 object is destroyed, the buffer can be safely deallocated.
+
+@param pBuf pointer to buffer containing font data
+@param bufSize size of buffer
+@param idx face_index to select a font faces in a single file.
+*/
+
+    CV_WRAP virtual void loadFontData(uchar* pBuf, size_t bufSize, int idx) = 0;
+
 /** @brief Set Split Number from Bezier-curve to line
 
 The function setSplitNumber set the number of split points from bezier-curve to line.

modules/freetype/src/freetype.cpp

@@ -67,6 +67,7 @@ class CV_EXPORTS_W FreeType2Impl CV_FINAL : public FreeType2
     FreeType2Impl();
     ~FreeType2Impl();
     void loadFontData(String fontFileName, int idx) CV_OVERRIDE;
+    void loadFontData(uchar* pBuf, size_t bufSize, int idx) CV_OVERRIDE;
     void setSplitNumber( int num ) CV_OVERRIDE;
     void putText(
         InputOutputArray img, const String& text, Point org,
@@ -181,16 +182,39 @@ FreeType2Impl::~FreeType2Impl()
 void FreeType2Impl::loadFontData(String fontFileName, int idx)
 {
     CV_Assert( idx >= 0 );
-    if( mIsFaceAvailable  == true )
+    if ( mIsFaceAvailable  == true )
     {
-        hb_font_destroy (mHb_font);
+        hb_font_destroy(mHb_font);
+        CV_Assert(!FT_Done_Face(mFace));
+    }
+
+    mIsFaceAvailable = false;
+    CV_Assert( !FT_New_Face( mLibrary, fontFileName.c_str(), static_cast<FT_Long>(idx), &mFace ) );
+
+    mHb_font = hb_ft_font_create(mFace, NULL);
+    if ( mHb_font == NULL )
+    {
+        CV_Assert(!FT_Done_Face(mFace));
+        return;
+    }
+    CV_Assert( mHb_font != NULL );
+    mIsFaceAvailable = true;
+}
+
+void FreeType2Impl::loadFontData(uchar* pBuf, size_t bufSize, int idx)
+{
+    CV_Assert( idx >= 0 );
+    if ( mIsFaceAvailable  == true )
+    {
+        hb_font_destroy(mHb_font);
         CV_Assert(!FT_Done_Face(mFace));
     }
 
     mIsFaceAvailable = false;
-    CV_Assert( !FT_New_Face( mLibrary, fontFileName.c_str(), static_cast<FT_Long>(idx), &(mFace) ) );
+    FT_Open_Args args{ FT_OPEN_MEMORY, (FT_Byte*)pBuf, static_cast<FT_Long>(bufSize), nullptr, nullptr, nullptr, 0, nullptr };
+    CV_Assert( !FT_Open_Face(mLibrary, &args, idx, &mFace) );
 
-    mHb_font = hb_ft_font_create (mFace, NULL);
+    mHb_font = hb_ft_font_create(mFace, NULL);
     if ( mHb_font == NULL )
     {
         CV_Assert(!FT_Done_Face(mFace));