Text: prerender font using dedicated function, not in constructor.

The number of possible combinations would explode for no reason when
opening font from different locations will be implemented.

src/Text/Font.cpp

@@ -26,13 +26,27 @@
 namespace Magnum { namespace Text {
 
 Font::Font(FontRenderer& renderer, const std::string& fontFile, GLfloat size): _size(size) {
-    /** @todo Use delegating constructor when GCC 4.6 support is dropped */
-    create(renderer, fontFile);
+    #ifndef MAGNUM_TARGET_GLES
+    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::ARB::texture_rg);
+    #else
+    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::EXT::texture_rg);
+    #endif
+
+    /* Create FreeType font */
+    CORRADE_INTERNAL_ASSERT(FT_New_Face(renderer.library(), fontFile.c_str(), 0, &_ftFont) == 0);
+    CORRADE_INTERNAL_ASSERT(FT_Set_Char_Size(_ftFont, 0, _size*64, 100, 100) == 0);
+
+    /* Create Harfbuzz font */
+    _hbFont = hb_ft_font_create(_ftFont, nullptr);
+
+    /* Set up the texture */
+    _texture.setWrapping(Texture2D::Wrapping::ClampToEdge)
+        ->setMinificationFilter(Texture2D::Filter::LinearInterpolation)
+        ->setMagnificationFilter(Texture2D::Filter::LinearInterpolation);
 }
 
-Font::Font(FontRenderer& renderer, const std::string& fontFile, GLfloat size, const std::string& characters, const Vector2i& atlasSize): _size(size) {
-    /** @todo Use delegating constructor when GCC 4.6 support is dropped */
-    create(renderer, fontFile);
+void Font::prerender(const std::string& characters, const Vector2i& atlasSize) {
+    glyphs.clear();
 
     /** @bug Crash when atlas is too small */
     /** @todo Get rid of duplicate characters */
@@ -79,8 +93,8 @@ Font::Font(FontRenderer& renderer, const std::string& fontFile, GLfloat size, co
 
         /* Save character texture position and texture coordinates for given character index */
         glyphs.insert({charIndices[i], std::make_tuple(
-            Rectangle::fromSize(Vector2(glyph->bitmap_left, glyph->bitmap_top-charPositions[i].height())/size,
-                                Vector2(charPositions[i].size())/size),
+            Rectangle::fromSize(Vector2(glyph->bitmap_left, glyph->bitmap_top-charPositions[i].height())/_size,
+                                Vector2(charPositions[i].size())/_size),
             Rectangle(Vector2(charPositions[i].bottomLeft())/atlasSize,
                       Vector2(charPositions[i].topRight())/atlasSize)
         )});
@@ -94,26 +108,6 @@ Font::Font(FontRenderer& renderer, const std::string& fontFile, GLfloat size, co
     #endif
 }
 
-void Font::create(FontRenderer& renderer, const std::string& fontFile) {
-    #ifndef MAGNUM_TARGET_GLES
-    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::ARB::texture_rg);
-    #else
-    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::EXT::texture_rg);
-    #endif
-
-    /* Create FreeType font */
-    CORRADE_INTERNAL_ASSERT(FT_New_Face(renderer.library(), fontFile.c_str(), 0, &_ftFont) == 0);
-    CORRADE_INTERNAL_ASSERT(FT_Set_Char_Size(_ftFont, 0, _size*64, 100, 100) == 0);
-
-    /* Create Harfbuzz font */
-    _hbFont = hb_ft_font_create(_ftFont, nullptr);
-
-    /* Set up the texture */
-    _texture.setWrapping(Texture2D::Wrapping::ClampToEdge)
-        ->setMinificationFilter(Texture2D::Filter::LinearInterpolation)
-        ->setMagnificationFilter(Texture2D::Filter::LinearInterpolation);
-}
-
 void Font::destroy() {
     if(!_ftFont) return;
 

src/Text/Font.h

@@ -46,24 +46,25 @@ class MAGNUM_TEXT_EXPORT Font {
 
     public:
         /**
-         * @brief Empty font constructor
+         * @brief Create font from file
          * @param renderer      %Font renderer
          * @param fontFile      %Font file
          * @param size          %Font size
          *
-         * Creates font with no prerendered characters.
+         * Creates font with no prerendered characters. See prerender() for
+         * more information.
          */
         Font(FontRenderer& renderer, const std::string& fontFile, GLfloat size);
 
         /**
-         * @brief Create font for given character set
-         * @param renderer      %Font renderer
-         * @param fontFile      %Font file
-         * @param size          %Font size
+         * @brief Prerender given character set
          * @param characters    Characters to render
          * @param atlasSize     Size of resulting atlas
+         *
+         * Creates new atlas with prerendered characters, replacing the
+         * previous one (if any).
          */
-        Font(FontRenderer& renderer, const std::string& fontFile, GLfloat size, const std::string& characters, const Vector2i& atlasSize);
+        void prerender(const std::string& characters, const Vector2i& atlasSize);
 
         ~Font();
 
@@ -95,7 +96,6 @@ class MAGNUM_TEXT_EXPORT Font {
         inline hb_font_t* font() { return _hbFont; }
 
     private:
-        void MAGNUM_TEXT_LOCAL create(FontRenderer& renderer, const std::string& fontFile);
         void MAGNUM_TEXT_LOCAL destroy();
         void MAGNUM_TEXT_LOCAL move();