dlib C++ Library - fonts_abstract.h

    // Copyright (C) 2005  Davis E. King (davis@dlib.net), Nils Labugt, Keita Mochizuki
    // License: Boost Software License   See LICENSE.txt for the full license.
    #undef DLIB_FONTs_ABSTRACT_
    #ifdef DLIB_FONTs_ABSTRACT_

    #include <string>
    #include "../serialize.h"
    #include "../unicode.h"
    #include <iostream>

    namespace dlib
    {

    // ----------------------------------------------------------------------------------------

        class letter
        {
            /*!
                WHAT THIS OBJECT REPRESENTS
                    This object represents a letter in a font.  It tells you the nominal
                    width of the letter and which pixels form the letter.

                THREAD SAFETY
                    const versions of this object are thread safe but if you are going to
                    be modifying it then you must serialize access to it.
            !*/
        public:
            struct point
            {
                /*!
                    WHAT THIS OBJECT REPRESENTS
                        This object represents one of the pixels of a letter.

                        The origin (i.e. (0,0)) of the coordinate plane is at the left
                        side of the letter's baseline.  Also note that y is negative when
                        above the baseline and positive below (it is zero on the baseline
                        itself).

                        The x value is positive going to the right and negative to the left.
                        The meaning of a negative x value is that any points with a negative
                        x value will overlap with the preceding letter.
                !*/

                point (
                );
                /*!
                    ensures
                        - This constructor does nothing.  The value of x and y
                          are undefined after its execution.
                !*/

                point (
                    signed char x_,
                    signed char y_
                );
                /*!
                    ensures
                        - #x == x_
                        - #y == y_
                !*/

                signed char x;
                signed char y;
            };

            // ---------------------------------

            letter (
            );
            /*!
                ensures
                    - #width() == 0
                    - #num_of_points() == 0
            !*/

            letter (
                unsigned short width_,
                unsigned short point_count
            );
            /*!
                ensures
                    - #width() == width_
                    - #num_of_points() == point_count
            !*/

            ~letter(
            );
            /*!
                ensures
                    - any resources used by *this have been freed
            !*/

            const unsigned short width (
            ) const;
            /*!
                ensures
                    - returns the width reserved for this letter in pixels.  This is the
                      number of pixels that are reserved for this letter between adjoining
                      letters.  It isn't necessarily the width of the actual letter itself.
                      (for example, you can make a letter with a width less than how wide it
                      actually is so that it overlaps with its neighbor letters.)
            !*/

            const unsigned short num_of_points (
            ) const;
            /*!
                ensures
                    - returns the number of pixels that make up this letter.
            !*/

            point& operator[] (
                unsigned short i
            );
            /*!
                requires
                    - i < num_of_points()
                ensures
                    - returns a non-const reference to the ith point in this letter.
            !*/

            const point& operator[] (
                unsigned short i
            ) const;
            /*!
                requires
                    - i < num_of_points()
                ensures
                    - returns a const reference to the ith point in this letter.
            !*/

            void swap (
                letter& item
            );
            /*!
                ensures
                    - swaps *this with item
            !*/

            private:

            // restricted functions
            letter(letter&);        // copy constructor
            letter& operator=(letter&);    // assignment operator
        };

        inline void swap (
            letter& a,
            letter& b
        ) { a.swap(b); }
        /*!
            provides a global swap
        !*/

    // ----------------------------------------------------------------------------------------

        void serialize (
            const letter& item,
            std::ostream& out
        );
        /*!
            provides serialization support for letter objects
        !*/

        void deserialize (
            letter& item,
            std::istream& in
        );
        /*!
            provides deserialization support for letter objects
        !*/

    // ----------------------------------------------------------------------------------------

        class font
        {
            /*!
                WHAT THIS OBJECT REPRESENTS
                    This object defines an interface for a font type.  It provides metrics
                    for the font and functions to help you draw strings on a canvas object.

                THREAD SAFETY
                    All the functions in this class are thread safe.
            !*/

        public:

            virtual bool has_character (
                unichar ch
            )const=0;
            /*!
                ensures
                    - if (this font has a glyph for the given character) then
                        - returns true
                    - else
                        - returns false
            !*/
            bool has_character(char ch) const    { return this->has_character(zero_extend_cast<unichar>(ch)); }
            bool has_character(wchar_t ch) const { return this->has_character(zero_extend_cast<unichar>(ch)); }
            /* Cast char and wchar_t to unichar correctly when char or wchar_t is a signed type */

            virtual const letter& operator[] (
                unichar ch
            )const=0;
            /*!
                ensures
                    - if (has_character(ch) == true) then
                        - returns a letter object that tells you how to draw this character.
                    - else
                        - returns some default glyph for characters that aren't in this font.
            !*/
            const letter& operator[] (char ch)    const { return (*this)[zero_extend_cast<unichar>(ch)]; };
            const letter& operator[] (wchar_t ch) const { return (*this)[zero_extend_cast<unichar>(ch)]; };
            /* Cast char and wchar_t to unichar correctly when char or wchar_t is a signed type */

            virtual const unsigned long height (
            ) const = 0;
            /*!
                ensures
                    - returns the height in pixels of the tallest letter in the font
            !*/

            virtual const unsigned long ascender (
            ) const = 0;
            /*!
                ensures
                    - returns the height() minus the number of pixels below the baseline used
                      by the letter that hangs the lowest below the baseline.
            !*/

            virtual const unsigned long left_overflow (
            ) const = 0;
            /*!
                ensures
                    - returns how far outside and to the left of its width a letter
                      from this font may set pixels.  (i.e. how many extra pixels to its
                      left may a font use)
            !*/

            virtual const unsigned long right_overflow (
            ) const = 0;
            /*!
                ensures
                    - returns how far outside and to the right of its width a letter
                      from this font may set pixels.  (i.e. how many extra pixels to its
                      right may a font use)
            !*/

            template <typename T, typename traits, typename alloc>
            void compute_size (
                const std::basic_string<T,traits,alloc>& str,
                unsigned long& width,
                unsigned long& height,
                typename std::basic_string<T,traits,alloc>::size_type first = 0,
                typename std::basic_string<T,traits,alloc>::size_type last = std::basic_string<T,traits,alloc>::npos
            ) const;
            /*!
                requires
                    - if (last != std::basic_string<T,traits,alloc>::npos) then
                        - first <= last
                        - last < str.size()
                ensures
                    - all characters in str with an index < first are ignored by this
                      function.
                    - if (last != std::basic_string<T,traits,alloc>::npos) then
                        - all characters in str with an index > last are ignored by
                          this function.
                    - if (str.size() == 0) then
                        - #width == 0
                        - #height == 0
                    - else
                        - #width == sum of the widths of the characters in the widest
                          line in str + left_overflow() + right_overflow().
                        - #height == (count(str.begin(),str.end(),'\n')+1)*height()
            !*/

            template <typename C, typename T, typename traits, typename alloc, typename pixel_type>
            void draw_string (
                const C& c,
                const rectangle& rect,
                const std::basic_string<T,traits,alloc>& str,
                const pixel_type& color = rgb_pixel(0,0,0),
                typename std::basic_string<T,traits,alloc>::size_type first = 0,
                typename std::basic_string<T,traits,alloc>::size_type last = std::basic_string<T,traits,alloc>::npos,
                const rectangle area = rectangle(-infinity,-infinity,infinity,infinity)
            ) 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()
                ensures
                    - all characters in str with an index < first are ignored by this
                      function.
                    - if (last != std::basic_string<T,traits,alloc>::npos) then
                        - all characters in str with an index > last are ignored by
                          this function.
                    - if (str.size() == 0) then
                        - does nothing
                    - else
                        - draws str on the given canvas at the position defined by rect.
                          Also uses the given pixel colors for the font color.
                    - If the string is too big to fit in rect then the right and
                      bottom sides of it will be clipped to make it fit.
                    - only the part of the string that is contained inside the area
                      rectangle will be drawn
            !*/

            template <typename T, typename traits, typename alloc>
            const rectangle compute_cursor_rect (
                const rectangle& rect,
                const std::basic_string<T,traits,alloc>& str,
                unsigned long index,
                typename std::basic_string<T,traits,alloc>::size_type first = 0,
                typename std::basic_string<T,traits,alloc>::size_type last = std::basic_string<T,traits,alloc>::npos
            ) const;
            /*!
                requires
                    - if (last != std::basic_string<T,traits,alloc>::npos) then
                        - first <= last
                        - last < str.size()
                ensures
                    - the returned rectangle has a width of 1 and a
                      height of this->height().
                    - computes the location of the cursor that would sit just before
                      the character str[index] if str were drawn on the screen by
                      draw_string(rect,str,...,first,last).  The cursor location is
                      returned in the form of a rectangle.
                    - if (index < first) then
                        - the returned cursor will be just before the character str[first].
                    - if (last != std::basic_string<T,traits,alloc>::npos && index > last) then
                        - the returned cursor will be just after the character str[last]
                    - if (str.size() == 0) then
                        - the returned cursor will be just at the start of the rectangle where
                          str would be drawn if it wasn't empty.
                    - if (index > str.size()-1) then
                        - the returned cursor will be just after the character str[str.size()-1]
            !*/

            template <typename T, typename traits, typename alloc>
            const unsigned long compute_cursor_pos (
                const rectangle& rect,
                const std::basic_string<T,traits,alloc>& str,
                long x,
                long y,
                typename std::basic_string<T,traits,alloc>::size_type first = 0,
                typename std::basic_string<T,traits,alloc>::size_type last = std::basic_string<T,traits,alloc>::npos
            ) const;
            /*!
                requires
                    - if (last != std::basic_string<T,traits,alloc>::npos) then
                        - first <= last
                        - last < str.size()
                ensures
                    - returns a number idx that has the following properties:
                        - if (first < str.size()) then
                            - first <= idx
                        - else
                            - idx == str.size()
                        - if (last != std::basic_string<T,traits,alloc>::npos) then
                            - idx <= last + 1
                        - compute_cursor_rect(rect,str,idx,first,last) == the cursor
                          position that is closest to the pixel (x,y)
            !*/

        private:

            // restricted functions
            font(font&);        // copy constructor
            font& operator=(font&);    // assignment operator
        };

    // ----------------------------------------------------------------------------------------

        class default_font : public font
        {
            /*!
                WHAT THIS OBJECT REPRESENTS
                    This is an implementation of the Helvetica 12 point font.

                THREAD SAFETY
                    It is safe to call get_font() and access the returned font from any
                    thread and no synchronization is needed as long as it is called
                    after the main() function has been entered.
            !*/

        public:
            static const shared_ptr_thread_safe<font> get_font(
            );
            /*!
                ensures
                    - returns an instance of this font.
                throws
                    - std::bad_alloc
                        This exception is thrown if there is a problem gathering the needed
                        memory for the font object.
            !*/

        private:

            // restricted functions
            default_font();        // normal constructor
            default_font(default_font&);        // copy constructor
            default_font& operator=(default_font&);    // assignment operator
        };

    // ----------------------------------------------------------------------------------------

        class bdf_font : public font
        {

            /*!
                WHAT THIS OBJECT REPRESENTS
                    This is a font object that is capable of loading of loading BDF (Glyph
                    Bitmap Distribution Format) font files.

                THREAD SAFETY
                    If you only access this object via the functions in the parent class font
                    then this object is thread safe.  But if you need to call any of the
                    functions introduced in this derived class then you need to serialize
                    access to this object while you call these functions.
            !*/

        public:

            bdf_font(
                long default_char = -1
            );
            /*!
                ensures
                    - for all x:
                        - #has_character(x) == false
                          (i.e. this font starts out empty.  You have to call read_bdf_file()
                          to load it with data)
                    - if (default_char == -1) then
                        - the letter returned by (*this)[ch] for values of
                          ch where has_character(ch) == false will be the
                          default glyph defined in the bdf file.
                    - else
                        - the letter returned by (*this)[ch] for values of
                          ch where has_character(ch) == false will be the
                          letter (*this)[default_char].
            !*/

            long read_bdf_file(
                std::istream& in,
                unichar max_enc,
                unichar min_enc = 0
            );
            /*!
                ensures
                    - attempts to read the font data from the given input stream into
                      *this.  The input stream is expected to contain a valid BDF file.
                    - reads in characters with encodings in the range min_enc to max_enc
                      into this font.  All characters in the font file outside this range
                      are ignored.
                    - returns the number of characters loaded into this font from the
                      given input stream.
            !*/

            void adjust_metrics();
            /*!
                ensures
                    - Computes metrics based on actual glyphs loaded, instead of using
                      the values in the bdf file header. (May be useful if loading glyphs
                      from more than one file or a small part of a file.)
            !*/

        private:

            bdf_font( bdf_font& );      // copy constructor
            bdf_font& operator=( bdf_font& );  // assignment operator

        };

    // ----------------------------------------------------------------------------------------

        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
        !*/

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_FONTs_ABSTRACT_