Merge pull request #936 from Kumataro:freetype2.927

* Support getTextSize() to resolve issue #927

This getTextSize() funtion helps to print more text,
either on the same line or on another line.
To add getTextSize() function, some member variables are removed
which are corresponding at putText() function's arguments.
And a negative fontHeight must be asserted.

* Fix to remove whitespace

modules/freetype/include/opencv2/freetype.hpp

@@ -115,7 +115,67 @@ The function putText renders the specified text string in the image. Symbols tha
         int thickness, int line_type, bool bottomLeftOrigin
     ) = 0;
 
+/** @brief Calculates the width and height of a text string.
+
+The function getTextSize calculates and returns the approximate size of a box that contains the specified text.
+That is, the following code renders some text, the tight box surrounding it, and the baseline: :
+@code
+    String text = "Funny text inside the box";
+    int fontHeight = 60;
+    int thickness = -1;
+    int linestyle = 8;
+
+    Mat img(600, 800, CV_8UC3, Scalar::all(0));
+
+    int baseline=0;
+
+    cv::Ptr<cv::freetype::FreeType2> ft2;
+    ft2 = cv::freetype::createFreeType2();
+    ft2->loadFontData( "./mplus-1p-regular.ttf", 0 );
+
+    Size textSize = ft2->getTextSize(text,
+                                     fontHeight,
+                                     thickness,
+                                     &baseline);
+
+    if(thickness > 0){
+        baseline += thickness;
+    }
+
+    // center the text
+    Point textOrg((img.cols - textSize.width) / 2,
+                  (img.rows + textSize.height) / 2);
+
+    // draw the box
+    rectangle(img, textOrg + Point(0, baseline),
+              textOrg + Point(textSize.width, -textSize.height),
+              Scalar(0,255,0),1,8);
+
+    // ... and the baseline first
+    line(img, textOrg + Point(0, thickness),
+         textOrg + Point(textSize.width, thickness),
+         Scalar(0, 0, 255),1,8);
+
+    // then put the text itself
+    ft2->putText(img, text, textOrg, fontHeight,
+                 Scalar::all(255), thickness, linestyle, true );
+@endcode
+
+@param text Input text string.
+@param fontHeight Drawing font size by pixel unit.
+@param thickness Thickness of lines used to render the text. See putText for details.
+@param[out] baseLine y-coordinate of the baseline relative to the bottom-most text
+point.
+@return The size of a box that contains the specified text.
+
+@see cv::putText
+ */
+CV_WRAP virtual Size getTextSize(const String& text,
+                            int fontHeight, int thickness,
+                            CV_OUT int* baseLine) = 0;
+
 };
+
 /** @brief Create FreeType2 Instance
 
 The function createFreeType2 create instance to draw UTF-8 strings.