Remove GUI dependency from fonts (#2273)

* Remove GUI dependency from fonts

* use #ifndef

* Updated docs more
Co-authored-by: Davis King <davis@dlib.net>

dlib/CMakeLists.txt

@@ -269,6 +269,7 @@ if (NOT TARGET dlib)
       entropy_decoder/entropy_decoder_kernel_2.cpp
       entropy_encoder/entropy_encoder_kernel_1.cpp
       entropy_encoder/entropy_encoder_kernel_2.cpp
+      gui_widgets/fonts.cpp
       md5/md5_kernel_1.cpp
       tokenizer/tokenizer_kernel_1.cpp
       unicode/unicode.cpp
@@ -406,7 +407,6 @@ if (NOT TARGET dlib)
 
       if (NOT DLIB_NO_GUI_SUPPORT)
          set(source_files ${source_files}
-            gui_widgets/fonts.cpp
             gui_widgets/widgets.cpp
             gui_widgets/drawable.cpp
             gui_widgets/canvas_drawing.cpp

dlib/gui_widgets/fonts.cpp

@@ -657,6 +657,7 @@ namespace dlib
         return true;
     }
 
+#ifndef DLIB_NO_GUI_SUPPORT
 // ----------------------------------------------------------------------------------------
 
     const std::shared_ptr<font> get_native_font (
@@ -666,6 +667,7 @@ namespace dlib
     }
 
 // ----------------------------------------------------------------------------------------
+#endif
 
 }
 

dlib/gui_widgets/fonts.h

@@ -8,7 +8,6 @@
 #include <string>
 
 #include "fonts_abstract.h"
-#include "../gui_core.h"
 #include "../algs.h"
 #include "../serialize.h"
 #include "../unicode.h"
@@ -224,9 +223,9 @@ namespace dlib
 
     // ------------------------------------------------------------------------------------
 
-        template <typename T, typename traits, typename alloc, typename pixel_type>
+        template <typename C, typename T, typename traits, typename alloc, typename pixel_type>
         void draw_string (
-            const canvas& c,
+            const C& c,
             const rectangle& rect,
             const std::basic_string<T,traits,alloc>& str,
             const pixel_type& color,
@@ -316,9 +315,9 @@ namespace dlib
                 pos += l.width();
             }
         }
-        template <typename T, typename traits, typename alloc>
+        template <typename C, typename T, typename traits, typename alloc>
         void draw_string (
-            const canvas& c,
+            const C& c,
             const rectangle& rect,
             const std::basic_string<T,traits,alloc>& str
         ) const 

dlib/gui_widgets/fonts_abstract.h

@@ -3,7 +3,6 @@
 #undef DLIB_FONTs_ABSTRACT_
 #ifdef DLIB_FONTs_ABSTRACT_
 
-#include "../gui_core.h"
 #include <string>
 #include "../serialize.h"
 #include "../unicode.h"
@@ -275,9 +274,9 @@ namespace dlib
                     - #height == (count(str.begin(),str.end(),'\n')+1)*height()
         !*/
 
-        template <typename T, typename traits, typename alloc, typename pixel_type>
+        template <typename C, typename T, typename traits, typename alloc, typename pixel_type>
         void draw_string (
-            const canvas& c,
+            const C& c,
             const rectangle& rect,
             const std::basic_string<T,traits,alloc>& str,
             const pixel_type& color = rgb_pixel(0,0,0),
@@ -287,6 +286,7 @@ namespace dlib
         ) const;
         /*!
             requires
+                - C is a dlib::canvas or an object with a compatible interface.
                 - if (last != std::basic_string<T,traits,alloc>::npos) then
                     - first <= last
                     - last < str.size()
@@ -480,6 +480,8 @@ namespace dlib
     const shared_ptr_thread_safe<font> get_native_font(
     );
     /*!
+        requires
+            - DLIB_NO_GUI_SUPPORT is not defined
         ensures
             - returns a font object that uses the local font
     !*/

dlib/gui_widgets/nativefont.h

@@ -2,10 +2,12 @@
 // License: Boost Software License   See LICENSE.txt for the full license.
 #ifndef DLIB_IGG_FONT_RENDERER_H_
 #define DLIB_IGG_FONT_RENDERER_H_
+#ifndef DLIB_NO_GUI_SUPPORT
+
 #include "../platform.h"
 
 
-#include "../gui_widgets.h"
+#include "../gui_widgets/fonts.h"
 #include "../unicode.h"
 #include "../uintn.h"
 
@@ -608,5 +610,6 @@ namespace nativefont
 
 }
 
+#endif // DLIB_NO_GUI_SUPPORT
 #endif // DLIB_IGG_FONT_RENDERER_H_
 

dlib/image_transforms/draw.h

@@ -7,7 +7,7 @@
 #include "../algs.h"
 #include "../pixel.h"
 #include "../matrix.h"
-#include "../gui_widgets.h"
+#include "../gui_widgets/fonts.h"
 #include <cmath>
 
 namespace dlib