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+/**
+
+ \page	drawing	5 - Drawing Things in FLTK
+
+This chapter covers the drawing functions that are provided with FLTK.
+
+\section sect_WhenCanYouDraw When Can You Draw Things in FLTK?
+
+There are only certain places you can execute drawing code in FLTK.
+Calling these functions at other places will result in undefined behavior!
+
+\li The most common place is inside the virtual Fl_Widget::draw() method.
+    To write code here, you must subclass one of the existing Fl_Widget
+    classes and implement your own version of draw().
+
+\li The most common place is inside the virtual method
+    <A href="subclassing.html#draw"><tt>Fl_Widget::draw()</tt></A>. 
+    To write code here, you must subclass one of the existing Fl_Widget
+    classes and implement your own version of draw().
+
+\li You can also write <A href="common.html#boxtypes">boxtypes</A> and
+    <A href="common.html#labeltypes">labeltypes</A>. These are small
+    procedures that can be called by existing
+    <A HREF="subclassing.html#draw"><tt>Fl_Widget::draw()</tt></A>
+    methods. These "types" are identified by an 8-bit index that is stored
+    in the widget's box(), labeltype(), and possibly other properties.
+
+\li You can call Fl_Window::make_current() to do incremental update of a
+    widget. Use Fl_Widget::window() to find the window.
+
+
+\section sect_DrawingFunctions Drawing Functions
+
+To use the drawing functions you must first include the <FL/fl_draw.H>
+header file. FLTK provides the following types of drawing functions:
+
+\li \ref ssect_Boxes
+\li \ref ssect_Clipping
+\li \ref drawing_colors
+\li \ref ssect_Lines
+\li \ref ssect_Fast
+\li \ref ssect_Complex
+\li \ref ssect_Text
+\li \ref ssect_Fl_Image
+\li \ref ssect_Overlay
+\li \ref ssect_Offscreen
+
+<A name="boxdraw"></A> <!-- For old HTML links only ! -->
+\subsection ssect_Boxes Boxes
+
+FLTK provides three functions that can be used to draw boxes for buttons
+and other UI controls. Each function uses the supplied upper-lefthand corner
+and width and height to determine where to draw the box.
+
+<A NAME="fl_draw_box"> </A> <!-- For old HTML links only ! -->
+void fl_draw_box(Fl_Boxtype b, int x, int y, int w, int h, Fl_Color c);
+
+\par
+The first box drawing function is fl_draw_box()
+which draws a standard boxtype \a b in the specified color \a c .
+
+<A NAME="fl_frame"></A> <!-- For old HTML links only ! -->
+void fl_frame(const char *s, int x, int y, int w, int h)
+
+\par
+The fl_frame() function draws a series of line segments around the
+given box. The string \a s must contain groups of 4 letters which specify
+one of 24 standard grayscale values, where 'A' is black and 'X' is white.
+The order of each set of 4 characters is: top, left, bottom, right. The
+results of calling fl_frame() with a string that is not a multiple
+of 4 characters in length are undefined.
+
+\par
+The only difference between this function and fl_frame2() is the
+order of the line segments.
+
+\par
+See also: <A HREF="common.html#fl_frame">fl_frame boxtype</A>.
+
+<A NAME="fl_frame2"></A> <!-- For old HTML links only ! -->
+void fl_frame2(const char *s, int x, int y, int w, int h);
+
+\par
+The fl_frame2() function draws a series of line segments around
+the given box. The string \a s must contain groups of 4 letters which
+specify one of 24 standard grayscale values, where 'A' is black and 'X' is
+white. The order of each set of 4 characters is: bottom, right, top, left.
+The results of calling fl_frame2() with a string that is
+not a multiple of 4 characters in length are undefined.
+
+\par
+The only difference between this function and fl_frame()
+is the order of the line segments.
+
+<A name="clipping"></A> <!-- For old HTML links only ! -->
+\subsection ssect_Clipping Clipping
+
+You can limit all your drawing to a rectangular region by calling
+fl_push_clip(), and put the drawings back by using fl_pop_clip().
+This rectangle is measured in pixels and is unaffected by the current
+transformation matrix.
+
+In addition, the system may provide clipping when updating windows
+which may be more complex than a simple rectangle.
+
+<A name="fl_push_clip"></A> <!-- For old HTML links only ! -->
+void fl_clip(int x, int y, int w, int h) <br>
+void fl_push_clip(int x, int y, int w, int h)
+
+\par
+Intersect the current clip region with a rectangle and push this new
+region onto the stack. The fl_clip() name is deprecated and
+will be removed from future releases.
+
+<A NAME="fl_push_no_clip"></A> <!-- For old HTML links only ! -->
+void fl_push_no_clip()
+
+\par
+Pushes an empty clip region on the stack so nothing will be clipped.
+
+<A NAME="fl_pop_clip"></A> <!-- For old HTML links only ! -->
+void fl_pop_clip()
+
+\par
+Restore the previous clip region.
+
+\par
+\b Note:
+You must call fl_pop_clip() once for every time you call fl_push_clip().
+If you return to FLTK with the clip stack not empty unpredictable results
+occur.
+
+<A NAME="fl_not_clipped"></A> <!-- For old HTML links only ! -->
+int fl_not_clipped(int x, int y, int w, int h)
+
+\par
+Returns non-zero if any of the rectangle intersects the current clip
+region. If this returns 0 you don't have to draw the object.
+
+\par
+\b Note:
+Under X this returns 2 if the rectangle is partially clipped,
+and 1 if it is entirely inside the clip region.
+
+<A NAME="fl_clip_box"></A> <!-- For old HTML links only ! -->
+int fl_clip_box(int x, int y, int w, int h, int &X, int &Y, int &W, int &H)
+
+\par
+Intersect the rectangle <tt>x,y,w,h</tt> with the current
+clip region and returns the bounding box of the result in
+<tt>X,Y,W,H</tt>. Returns non-zero if the resulting rectangle is
+different than the original. This can be used to limit the
+necessary drawing to a rectangle. \c W and \c H are
+set to zero if the rectangle is completely outside the region.
+
+<A NAME="fl_clip_region"></A> <!-- For old HTML links only ! -->
+void fl_clip_region(Fl_Region r) <br>
+Fl_Region fl_clip_region()
+
+\par
+Replace the top of the clip stack with a clipping region of any shape.
+Fl_Region is an operating system specific type. The second form returns 
+the current clipping region.
+
+
+<A NAME="colors"></A> <!-- For old HTML links only ! -->
+\section drawing_colors Colors
+
+FLTK manages colors as 32-bit unsigned integers. Values from
+0 to 255 represent colors from the FLTK 1.0.x standard colormap
+and are allocated as needed on screens without TrueColor
+support. The Fl_Color enumeration type defines the
+standard colors and color cube for the first 256 colors. All of
+these are named with symbols in
+<A href="enumerations.html#colors"><tt><FL/Enumerations.H></tt></A>.
+
+Color values greater than 255 are treated as 24-bit RGB
+values. These are mapped to the closest color supported by the
+screen, either from one of the 256 colors in the FLTK 1.0.x
+colormap or a direct RGB value on TrueColor screens. You can
+generate 24-bit RGB color values using the
+<A HREF="functions.html#fl_rgb_color"><tt>fl_rgb_color()</tt></A>
+function.
+
+<A name="fl_color"></A> <!-- For old HTML links only ! -->
+void fl_color(Fl_Color)
+
+\par
+Sets the color for all subsequent drawing operations.
+
+\par
+For colormapped displays, a color cell will be allocated out
+of <tt>fl_colormap</tt> the first time you use a color. If the
+colormap fills up then a least-squares algorithm is used to find
+the closest color.
+
+Fl_Color fl_color()
+
+\par
+Returns the last fl_color() that was set. This can
+be used for state save/restore.
+
+void fl_color(uchar r, uchar g, uchar b)
+
+\par
+Set the color for all subsequent drawing operations. The
+closest possible match to the RGB color is used. The RGB color
+is used directly on TrueColor displays. For colormap visuals the
+nearest index in the gray ramp or color cube is used.
+
+<A name="lines"></A> <!-- For old HTML links only ! -->
+\subsection ssect_Lines Line Dashes and Thickness
+
+FLTK supports drawing of lines with different styles and
+widths. Full functionality is not available under Windows 95, 98,
+and Me due to the reduced drawing functionality these operating
+systems provide.
+
+<A NAME="fl_line_style"></A> <!-- For old HTML links only ! -->
+void fl_line_style(int style, int width=0, char* dashes=0)
+
+\par
+Set how to draw lines (the "pen").  If you change this it is your
+responsibility to set it back to the default with
+fl_line_style(0).
+
+\par
+\b Note:
+Because of how line styles are implemented on WIN32 systems, you <I>must</I>
+set the line style <I>after</I> setting the drawing color. If you set the
+color after the line style you will lose the line style settings!
+
+<i>style</i> is a bitmask which is a bitwise-OR of the following
+values. If you don't specify a dash type you will get a solid
+line. If you don't specify a cap or join type you will get a
+system-defined default of whatever value is fastest.
+
+\li <tt>FL_SOLID&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -------</tt>
+\li <tt>FL_DASH&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; - - - -</tt>
+\li <tt>FL_DOT&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; .......</tt>
+\li <tt>FL_DASHDOT&nbsp;&nbsp;&nbsp; - . - .</tt>
+\li <tt>FL_DASHDOTDOT - .. -</tt>
+\li <tt>FL_CAP_FLAT</tt>
+\li <tt>FL_CAP_ROUND</tt>
+\li <tt>FL_CAP_SQUARE</tt> (extends past end point 1/2 line width)
+\li <tt>FL_JOIN_MITER</tt> (pointed)
+\li <tt>FL_JOIN_ROUND</tt>
+\li <tt>FL_JOIN_BEVEL</tt> (flat)
+
+<i>width</i> is the number of pixels thick to draw the lines.
+Zero results in the system-defined default, which on both X and
+Windows is somewhat different and nicer than 1.
+
+<!-- NEED 4in -->
+
+<i>dashes</i> is a pointer to an array of dash lengths, measured in
+pixels.  The first location is how long to draw a solid portion, the
+next is how long to draw the gap, then the solid, etc.  It is
+terminated with a zero-length entry. A <tt>NULL</tt> pointer or a zero-length
+array results in a solid line. Odd array sizes are not supported and
+result in undefined behavior.
+
+\note
+The dashes array does not work under Windows 95, 98, or Me, since those
+operating systems do not support complex line styles.
+
+<A name="fast"></A> <!-- For old HTML links only ! -->
+\subsection ssect_Fast Drawing Fast Shapes
+
+These functions are used to draw almost all the FLTK widgets.
+They draw on exact pixel boundaries and are as fast as possible.
+Their behavior is duplicated exactly on all platforms FLTK is
+ported. It is undefined whether these are affected by the
+<A href="#complex">transformation matrix</A>,
+so you should only call these while the matrix is set to the
+identity matrix (the default).
+
+<A NAME="fl_point"></A> <!-- For old HTML links only ! -->
+void fl_point(int x, int y)
+
+\par
+Draw a single pixel at the given coordinates.
+
+<A NAME="fl_rectf"></A> <!-- For old HTML links only ! -->
+void fl_rectf(int x, int y, int w, int h) <br>
+void fl_rectf(int x, int y, int w, int h)
+
+\par
+Color a rectangle that exactly fills the given bounding box.
+
+void fl_rectf(int x, int y, int w, int h, uchar r, uchar g, uchar b)
+
+\par
+Color a rectangle with "exactly" the passed
+<tt>r,g,b</tt> color. On screens with less than 24 bits of
+color this is done by drawing a solid-colored block using
+<A href="#fl_draw_image"><tt>fl_draw_image()</tt></A>
+so that the correct color shade is produced.
+
+<A NAME="fl_rect"></A> <!-- For old HTML links only ! -->
+void fl_rect(int x, int y, int w, int h) <br>
+void fl_rect(int x, int y, int w, int h, Fl_Color c)
+
+\par
+Draw a 1-pixel border <I>inside</I> this bounding box.
+
+<A NAME="fl_line"></A> <!-- For old HTML links only ! -->
+void fl_line(int x, int y, int x1, int y1) <br>
+void fl_line(int x, int y, int x1, int y1, int x2, int y2)
+
+\par
+Draw one or two lines between the given points.
+
+<A NAME="fl_loop"></A> <!-- For old HTML links only ! -->
+void fl_loop(int x, int y, int x1, int y1, int x2, int y2) <br>
+void fl_loop(int x, int y, int x1, int y1, int x2, int y2, int x3, int y3)
+
+\par
+Outline a 3 or 4-sided polygon with lines.
+
+<A NAME="fl_polygon"></A> <!-- For old HTML links only ! -->
+void fl_polygon(int x, int y, int x1, int y1, int x2, int y2) <br>
+void fl_polygon(int x, int y, int x1, int y1, int x2, int y2, int x3, int y3)
+
+\par
+Fill a 3 or 4-sided polygon. The polygon must be convex.
+
+<A NAME="fl_xyline"></A> <!-- For old HTML links only ! -->
+void fl_xyline(int x, int y, int x1) <br>
+void fl_xyline(int x, int y, int x1, int y2) <br>
+void fl_xyline(int x, int y, int x1, int y2, int x3)
+
+\par
+Draw horizontal and vertical lines. A horizontal line is
+drawn first, then a vertical, then a horizontal.
+
+<A NAME="fl_yxline"></A> <!-- For old HTML links only ! -->
+void fl_yxline(int x, int y, int y1) <br>
+void fl_yxline(int x, int y, int y1, int x2) <br>
+void fl_yxline(int x, int y, int y1, int x2, int y3)
+
+\par
+Draw vertical and horizontal lines. A vertical line is drawn
+first, then a horizontal, then a vertical.
+
+<A NAME="fl_pie"></A> <!-- For old HTML links only ! -->
+void fl_arc(int x, int y, int w, int h, double a1, double a2) <br>
+void fl_pie(int x, int y, int w, int h, double a1, double a2)
+
+\par
+Draw ellipse sections using integer coordinates. These
+functions match the rather limited circle drawing code provided
+by X and WIN32. The advantage over using
+<A href="#fl_arc"><tt>fl_arc</tt></A>
+with floating point
+coordinates is that they are faster because they often use the
+hardware, and they draw much nicer small circles, since the
+small sizes are often hard-coded bitmaps.
+
+If a complete circle is drawn it will fit inside the passed bounding
+box. The two angles are measured in degrees counterclockwise from
+3'oclock and are the starting and ending angle of the arc, <tt>a2</tt>
+must be greater or equal to <tt>a1</tt>.
+
+fl_arc() draws a series of lines to approximate the arc.
+Notice that the integer version of fl_arc() has a different
+number of arguments than the
+<A href="#fl_arc"><tt>fl_arc()</tt></A>
+function described later in this chapter.
+
+fl_pie() draws a filled-in pie slice. This slice may
+extend outside the line drawn by fl_arc(); to avoid this
+use <tt>w - 1</tt> and <tt>h - 1</tt>.
+
+<A name="fl_scroll"></A> <!-- For old HTML links only ! -->
+void fl_scroll(int X, int Y, int W, int H, int dx, int dy,
+void (*draw_area)(void*, int,int,int,int), void* data)
+
+\par
+Scroll a rectangle and draw the newly exposed portions. The contents
+of the rectangular area is first shifted by <tt>dx</tt> and 
+<tt>dy</tt> pixels. The callback is then called for every newly 
+exposed rectangular area,
+
+<A name="complex"></A> <!-- For old HTML links only ! -->
+\subsection ssect_Complex Drawing Complex Shapes
+
+The complex drawing functions let you draw arbitrary shapes
+with 2-D linear transformations. The functionality matches that
+found in the Adobe&reg; PostScript&tm; language. The
+exact pixels that are filled are less defined than for the fast
+drawing functions so that FLTK can take advantage of drawing
+hardware. On both X and WIN32 the transformed vertices are
+rounded to integers before drawing the line segments: this
+severely limits the accuracy of these functions for complex
+graphics, so use OpenGL when greater accuracy and/or performance
+is required.
+
+<A NAME="fl_push_matrix"></A> <!-- For old HTML links only ! -->
+void fl_push_matrix() <br>
+void fl_pop_matrix()
+
+\par
+Save and restore the current transformation.  The maximum
+depth of the stack is 4.
+
+<A NAME="fl_scale"></A> <!-- For old HTML links only ! -->
+void fl_scale(float x, float y) <br>
+void fl_scale(float x) <br>
+void fl_translate(float x, float y) <br>
+void fl_rotate(float d) <br>
+void fl_mult_matrix(float a, float b, float c, float d, float x, float y)
+
+\par
+Concatenate another transformation onto the current one. The rotation
+angle is in degrees (not radians) and is counter-clockwise.
+
+<A NAME="fl_transform"></A> <!-- For old HTML links only ! -->
+double fl_transform_x(double x, double y) <br>
+double fl_transform_y(double x, double y) <br>
+double fl_transform_dx(double x, double y) <br>
+double fl_transform_dy(double x, double y) <br>
+void fl_transformed_vertex(double xf, double yf)
+
+\par
+Transform a coordinate or a distance trough the current transformation matrix.
+After transforming a coordinate pair, it can be added to the vertex
+list without any forther translations using <tt>fl_transformed_vertex</tt>.
+
+<A NAME="fl_begin_points"></A> <!-- For old HTML links only ! -->
+void fl_begin_points() <br>
+void fl_end_points()
+
+\par
+Start and end drawing a list of points. Points are added to
+the list with <tt>fl_vertex</tt>.
+
+<A NAME="fl_begin_line"></A> <!-- For old HTML links only ! -->
+void fl_begin_line() <br>
+void fl_end_line()
+
+\par
+Start and end drawing lines.
+
+<A NAME="fl_begin_loop"></A> <!-- For old HTML links only ! -->
+void fl_begin_loop() <br>
+void fl_end_loop()
+
+\par
+Start and end drawing a closed sequence of lines.
+
+<A NAME="fl_begin_polygon"></A> <!-- For old HTML links only ! -->
+void fl_begin_polygon() <br>
+void fl_end_polygon()
+
+\par
+Start and end drawing a convex filled polygon.
+
+<A NAME="fl_begin_complex_polygon"></A> <!-- For old HTML links only ! -->
+void fl_begin_complex_polygon() <br>
+void fl_gap() <br>
+void fl_end_complex_polygon()
+
+\par
+Start and end drawing a complex filled polygon. This polygon
+may be concave, may have holes in it, or may be several
+disconnected pieces. Call fl_gap() to separate loops of
+the path. It is unnecessary but harmless to call
+fl_gap() before the first vertex, after the last one,
+or several times in a row.
+
+\par
+\b Note:
+For portability, you should only draw polygons that appear the same whether
+"even/odd" or "non-zero" winding rules are used to fill them. Holes should
+be drawn in the opposite direction of the outside loop.
+
+\par
+fl_gap() should only be called between 
+fl_begin_complex_polygon() and
+fl_end_complex_polygon(). To outline the polygon, use
+fl_begin_loop() and replace each fl_gap() with
+fl_end_loop();fl_begin_loop().
+
+<A NAME="fl_vertex"></A> <!-- For old HTML links only ! -->
+void fl_vertex(float x, float y)
+
+\par
+Add a single vertex to the current path.
+
+<A NAME="fl_curve"></A> <!-- For old HTML links only ! -->
+void fl_curve(float x, float y, float x1, float y1, float x2, float y2,
+float x3, float y3)
+
+\par
+Add a series of points on a Bezier curve to the path.  The curve ends
+(and two of the points) are at <tt>x,y</tt> and <tt>x3,y3</tt>.
+
+<A NAME="fl_arc"></A> <!-- For old HTML links only ! -->
+void fl_arc(float x, float y, float r, float start, float end)
+
+\par
+Add a series of points to the current path on the arc of a
+circle; you can get elliptical paths by using scale and rotate
+before calling fl_arc(). <tt>x,y</tt> are the center of
+the circle, and <tt>r</tt> is its radius. fl_arc()
+takes <tt>start</tt> and <tt>end</tt> angles that are measured
+in degrees counter-clockwise from 3 o'clock.  If <tt>end</tt> is
+less than <tt>start</tt> then it draws the arc in a clockwise
+direction.
+
+<A NAME="fl_circle"></A> <!-- For old HTML links only ! -->
+void fl_circle(float x, float y, float r)
+
+\par
+fl_circle() is equivalent to fl_arc(...,0,360) but
+may be faster. It must be the <I>only</I> thing in the path: if you
+want a circle as part of a complex polygon you must use fl_arc().
+
+\par
+\b Note:
+fl_circle() draws incorrectly if the transformation is both rotated and
+non-square scaled.
+
+<A name="text"></A> <!-- For old HTML links only ! -->
+\subsection ssect_Text Drawing Text
+
+All text is drawn in the
+<A href="#fl_font">current font</A>.
+It is undefined whether this location or the characters are
+modified by the current transformation.
+
+<A NAME="fl_draw"></A> <!-- For old HTML links only ! -->
+void fl_draw(const char *, int x, int y) <br>
+void fl_draw(const char *, int n, int x, int y)
+
+\par
+Draw a nul-terminated string or an array of <tt>n</tt> characters
+starting at the given location. Text is aligned to the left and to
+the baseline of the font. To align to the bottom, subtract fl_descent() from
+<i>y</i>. To align to the top, subtract fl_descent() and add fl_height().
+This version of fl_draw provides direct access to
+the text drawing function of the underlying OS. It does not apply any 
+special handling to control characters. 
+
+void fl_draw(const char *, int x, int y, int w, int h,
+Fl_Align align, Fl_Image *img = 0, int draw_symbols = 1)
+
+\par
+Fancy string drawing function which is used to draw all the
+labels. The string is formatted and aligned inside the passed
+box.  Handles '\\t' and '\\n', expands all other control
+characters to ^X, and aligns inside or against the edges of the
+box described by <i>x</i>, <i>y</i>, <i>w</i> and <i>h</i>. See 
+Fl_Widget::align() for values for <tt>align</tt>. The value
+<tt>FL_ALIGN_INSIDE</tt> is ignored, as this function always
+prints inside the box.
+
+\par
+If <tt>img</tt> is provided and is not <tt>NULL</tt>, the
+image is drawn above or below the text as specified by the
+<tt>align</tt> value.
+
+\par
+The <tt>draw_symbols</tt> argument specifies whether or not
+to look for symbol names starting with the "@" character.
+
+\par
+The text length is limited to 1024 caracters per line.
+
+<A NAME="fl_measure"></A> <!-- For old HTML links only ! -->
+void fl_measure(const char *, int &w, int &h, int draw_symbols = 1)
+
+\par
+Measure how wide and tall the string will be when printed by
+the <tt>fl_draw(...align)</tt> function. If the incoming
+<tt>w</tt> is non-zero it will wrap to that width.
+
+<A NAME="fl_height"></A> <!-- For old HTML links only ! -->
+int fl_height()
+
+\par
+Recommended minimum line spacing for the current font.  You
+can also just use the value of <tt>size</tt> passed to
+<A href="#fl_font"><tt>fl_font()</tt></A>.
+
+<A NAME="fl_descent"></A> <!-- For old HTML links only ! -->
+int fl_descent()
+
+\par
+Recommended distance above the bottom of a fl_height() tall box to draw
+the text at so it looks centered vertically in that box.
+
+<A NAME="fl_width"></A> <!-- For old HTML links only ! -->
+float fl_width(const char*) <br>
+float fl_width(const char*, int n) <br>
+float fl_width(uchar)
+
+\par
+Return the pixel width of a nul-terminated string, a sequence of <tt>n</tt>
+characters, or a single character in the current font.
+
+<A NAME="fl_shortcut_label"></A> <!-- For old HTML links only ! -->
+const char *fl_shortcut_label(ulong)
+
+\par
+Unparse a shortcut value as used by Fl_Button or Fl_Menu_Item
+into a human-readable string like "Alt+N".  This only
+works if the shortcut is a character key or a numbered function
+key. If the shortcut is zero an empty string is returned. The
+return value points at a static buffer that is overwritten with
+each call.
+
+<A name="fonts"></A> <!-- For old HTML links only ! -->
+\subsection ssect_Fonts Fonts
+
+FLTK supports a set of standard fonts based on the Times,
+Helvetica/Arial, Courier, and Symbol typefaces, as well as
+custom fonts that your application may load. Each font is
+accessed by an index into a font table.
+
+Initially only the first 16 faces are filled in. There are
+symbolic names for them: FL_HELVETICA,
+FL_TIMES, FL_COURIER, and modifier values
+FL_BOLD and FL_ITALIC which can be added to
+these, and FL_SYMBOL and FL_ZAPF_DINGBATS.
+Faces greater than 255 cannot be used in Fl_Widget
+labels, since Fl_Widget stores the index as a byte.
+
+<A name="fl_font"></A> <!-- For old HTML links only ! -->
+void fl_font(int face, int size)
+
+\par
+Set the current font, which is then used by the routines
+described above. You may call this outside a draw context if
+necessary to call fl_width(), but on X this will open
+the display.
+
+\par
+The font is identified by a <tt>face</tt> and a
+<tt>size</tt>. The size of the font is measured in
+<tt>pixels</tt> and not "points". Lines should be spaced
+<tt>size</tt> pixels apart or more.
+
+<A NAME="fl_size"></A> <!-- For old HTML links only ! -->
+int fl_font() <br>
+int fl_size()
+
+\par
+Returns the face and size set by the most recent call to
+fl_font(a,b). This can be used to save/restore the font.
+
+<A NAME="character_encoding"></A> <!-- For old HTML links only ! -->
+\subsection ssect_CharacterEncoding Character Encoding
+
+FLTK 1 supports western character sets using the eight bit encoding
+of the user-selected global code page. For MS Windows and X11, the code
+page is assumed to be Windows-1252/Latin1, a superset to ISO 8859-1. 
+On Mac OS X, we assume MacRoman.
+
+FLTK provides the functions fl_latin1_to_local(), 
+fl_local_to_latin1(), fl_mac_roman_to_local(), and
+fl_local_to_mac_roman() to convert strings between both
+encodings. These functions are only required if your source
+code contains "C"-strings with international characters and 
+if this source will be compiled on multiple platforms.
+
+<!-- Editor's note:
+   ** Caution: the following text contains utf-8 encoded characters.
+   ** be careful when using non-utf-8-aware editors !
+-->
+
+Assuming that the following source code was written on MS Windows, 
+this example will output the correct label on OS X and X11 as well.
+Without the conversion call, the label on OS X would read 
+<tt>Fahrvergn¸gen</tt> with a deformed umlaut u ("cedille",
+html "&cedil;").
+\code
+  btn = new Fl_Button(10, 10, 300, 25);
+  btn->copy_label(fl_latin1_to_local("Fahrvergnügen"));
+\endcode
+
+\note	If your application uses characters that are not part of both
+	encodings, or it will be used in areas that commonly use different
+	code pages, you might consider upgrading to FLTK 2 which supports
+	UTF-8 encoding. 
+
+\todo	drawing.dox: I fixed the above encoding problem of these \&cedil;
+	and umlaut characters, but this text is obsoleted by FLTK 1.3
+	with utf-8 encoding, or must be rewritten accordingly:
+	How to use native (e.g. Windows "ANSI", or ISO-8859-x)
+	encoding in embedded strings for labels, error messages
+	and more. Please check this (utf-8) encoding on different
+	OS'es and with different language and font environments.
+
+For more information about character encoding, unicode and utf-8
+see chapter \ref unicode.
+
+<A name="overlay"></A> <!-- For old HTML links only ! -->
+\subsection ssect_Overlay Drawing Overlays
+
+These functions allow you to draw interactive selection rectangles
+without using the overlay hardware. FLTK will XOR a single rectangle
+outline over a window.
+
+void fl_overlay_rect(int x, int y, int w, int h); <br>
+void fl_overlay_clear();
+
+\par
+fl_overlay_rect() draws a selection rectangle, erasing any
+previous rectangle by XOR'ing it first. fl_overlay_clear()
+will erase the rectangle without drawing a new one.
+
+\par
+Using these functions is tricky. You should make a widget
+with both a handle() and draw() method.
+draw() should call fl_overlay_clear() before
+doing anything else.  Your handle() method should call
+window()->make_current() and then
+fl_overlay_rect() after FL_DRAG events, and
+should call fl_overlay_clear() after a
+FL_RELEASE event.
+
+
+<A NAME="images"></A> <!-- For old HTML links only ! -->
+\section drawing_images Drawing Images
+
+To draw images, you can either do it directly from data in
+your memory, or you can create a Fl_Image object. The advantage of
+drawing directly is that it is more intuitive, and it is faster
+if the image data changes more often than it is redrawn. The
+advantage of using the object is that FLTK will cache translated
+forms of the image (on X it uses a server pixmap) and thus
+redrawing is <I>much</I> faster.
+
+\subsection ssect_DirectImageDrawing Direct Image Drawing
+
+The behavior when drawing images when the current
+transformation matrix is not the identity is not defined, so you
+should only draw images when the matrix is set to the identity.
+
+<A NAME="fl_draw_image"></A> <!-- For old HTML links only ! -->
+void fl_draw_image(const uchar *, int X, int Y, int W, int H,
+int D = 3, int LD = 0) <br>
+void fl_draw_image_mono(const uchar *, int X, int Y, int W, int H,
+int D = 1, int LD = 0)
+
+\par
+Draw an 8-bit per color RGB or luminance image.  The pointer
+points at the "r" data of the top-left pixel. Color
+data must be in <tt>r,g,b</tt> order. <tt>X,Y</tt> are where to
+put the top-left corner. <tt>W</tt> and <tt>H</tt> define the
+size of the image. <tt>D</tt> is the delta to add to the pointer
+between pixels, it may be any value greater or equal to
+<tt>3</tt>, or it can be negative to flip the image
+horizontally. <tt>LD</tt> is the delta to add to the pointer
+between lines (if 0 is passed it uses <tt>W * D</tt>), and may
+be larger than <tt>W * D</tt> to crop data, or negative to flip
+the image vertically.
+
+\par
+It is highly recommended that you put the following code before the
+first show() of <I>any</I> window in your program to get rid
+of the dithering if possible: 
+
+\code
+Fl::visual(FL_RGB);
+\endcode
+
+\par
+Gray scale (1-channel) images may be drawn. This is done if
+<tt>abs(D)</tt> is less than 3, or by calling
+fl_draw_image_mono(). Only one 8-bit sample is used for
+each pixel, and on screens with different numbers of bits for
+red, green, and blue only gray colors are used. Setting
+<tt>D</tt> greater than 1 will let you display one channel of a
+color image.
+
+\par
+\b Note:
+The X version does not support all possible visuals.
+If FLTK cannot draw the image in the current visual it
+will abort. FLTK supports any visual of 8 bits or less,
+and all common TrueColor visuals up to 32 bits.
+
+typedef void (*fl_draw_image_cb)(void *, int x, int y, int w, uchar *) <br>
+void fl_draw_image(fl_draw_image_cb, void *, int X, int Y, int W, int H,
+int D = 3) <br>
+void fl_draw_image_mono(fl_draw_image_cb, void *, int X, int Y, int W, int H,
+int D = 1)
+
+\par
+Call the passed function to provide each scan line of the
+image.  This lets you generate the image as it is being drawn,
+or do arbitrary decompression of stored data, provided it can be
+decompressed to individual scan lines easily.
+
+\par
+The callback is called with the <tt>void *</tt> user data
+pointer which can be used to point at a structure of information
+about the image, and the <tt>x</tt>, <tt>y</tt>, and <tt>w</tt>
+of the scan line desired from the image. 0,0 is the upper-left
+corner of the image, <I>not <tt>X,Y</tt></I>. A pointer to a
+buffer to put the data into is passed. You must copy <tt>w</tt>
+pixels from scanline <tt>y</tt>, starting at pixel <tt>x</tt>,
+to this buffer.
+
+\par
+Due to cropping, less than the whole image may be requested.
+So <tt>x</tt> may be greater than zero, the first <tt>y</tt> may
+be greater than zero, and <tt>w</tt> may be less than
+<tt>W</tt>. The buffer is long enough to store the entire <tt>W * D</tt>
+pixels, this is for convenience with some decompression
+schemes where you must decompress the entire line at once:
+decompress it into the buffer, and then if <tt>x</tt> is not
+zero, copy the data over so the <tt>x</tt>'th pixel is at the
+start of the buffer.
+
+\par
+You can assume the <tt>y</tt>'s will be consecutive, except
+the first one may be greater than zero.
+
+\par
+If <tt>D</tt> is 4 or more, you must fill in the unused bytes
+with zero.
+
+<A NAME="fl_draw_pixmap"></A> <!-- For old HTML links only ! -->
+int fl_draw_pixmap(char **data, int X, int Y, Fl_Color = FL_GRAY)
+
+\par
+Draws XPM image data, with the top-left corner at the given position.
+The image is dithered on 8-bit displays so you won't lose color space
+for programs displaying both images and pixmaps. This function returns
+zero if there was any error decoding the XPM data.
+
+\par
+To use an XPM, do:
+
+\code
+#include "foo.xpm"
+...
+fl_draw_pixmap(foo, X, Y);
+\endcode
+
+\par
+Transparent colors are replaced by the optional
+Fl_Color argument. To draw with true transparency you must
+use the Fl_Pixmap class.
+
+<A NAME="fl_measure_pixmap"></A> <!-- For old HTML links only ! -->
+int fl_measure_pixmap(char **data, int &w, int &h)
+
+\par
+An XPM image contains the dimensions in its data. This
+function finds and returns the width and height. The return
+value is non-zero if the dimensions were parsed ok and zero if
+there was any problem.
+
+\subsection ssect_DirectImageReading Direct Image Reading
+
+FLTK provides a single function for reading from the current
+window or off-screen buffer into a RGB(A) image buffer.
+
+<A NAME="fl_read_image"></A> <!-- For old HTML links only ! -->
+uchar *fl_read_image(uchar *p, int X, int Y, int W, int H, int alpha = 0);
+
+\par
+Read a RGB(A) image from the current window or off-screen
+buffer. The <tt>p</tt> argument points to a buffer that can hold
+the image and must be at least <tt>W*H*3</tt> bytes when reading
+RGB images and <tt>W*H*4</tt> bytes when reading RGBA images. If
+<tt>NULL</tt>, <tt>fl_read_image()</tt> will create an array of
+the proper size which can be freed using <tt>delete[]</tt>.
+
+\par
+The <tt>alpha</tt> parameter controls whether an alpha
+channel is created and the value that is placed in the alpha
+channel. If 0, no alpha channel is generated.
+
+<A name="Fl_Image"></A> <!-- For old HTML links only ! -->
+\subsection ssect_Fl_Image Image Classes
+
+FLTK provides a base image class called Fl_Image which supports
+creating, copying, and drawing images of various kinds, along
+with some basic color operations. Images can be used as labels
+for widgets using the image() and deimage() methods or drawn directly.
+
+The Fl_Image class does almost nothing by itself, but is instead 
+supported by three basic image types:
+
+\li Fl_Bitmap
+\li Fl_Pixmap
+\li Fl_RGB_Image
+
+The Fl_Bitmap class encapsulates a mono-color bitmap image.
+The draw() method draws the image using the current drawing
+color.
+
+The Fl_Pixmap class encapsulates a colormapped image.
+The draw() method draws the image using the colors in the
+file, and masks off any transparent colors automatically.
+
+The Fl_RGB_Image class encapsulates a full-color 
+(or grayscale) image with 1 to 4 color components. Images with 
+an even number of components are assumed to contain an 
+alpha channel that is used for transparency. The transparency 
+provided by the draw() method is either a 24-bit 
+blend against the existing window contents or a "screen door" 
+transparency mask, depending on the platform and screen color depth. 
+
+<A NAME="fl_can_do_alpha_blending"></A> <!-- For old HTML links only ! -->
+char fl_can_do_alpha_blending()
+
+\par
+fl_can_do_alpha_blending() will return 1, if your
+platform supports true alpha blending for RGBA images, or 0, 
+if FLTK will use screen door transparency.
+
+FLTK also provides several image classes based on the three
+standard image types for common file formats:
+
+\li Fl_GIF_Image 
+\li Fl_JPEG_Image 
+\li Fl_PNG_Image 
+\li Fl_PNM_Image 
+\li Fl_XBM_Image 
+\li Fl_XPM_Image
+
+Each of these image classes load a named file of the
+corresponding format. The Fl_Shared_Image class
+can be used to load any type of image file - the class examines
+the file and constructs an image of the appropriate type.
+
+Finally, FLTK provides a special image class called Fl_Tiled_Image to
+tile another image object in the specified area. This class can be
+used to tile a background image in a Fl_Group widget, for example.
+
+virtual void copy(); <br>
+virtual void copy(int w, int h);
+
+\par
+The copy() method creates a copy of the image. The second form
+specifies the new size of the image - the image is resized using the
+nearest-neighbor algorithm.
+
+void draw(int x, int y, int w, int h, int ox = 0, int oy = 0);
+
+\par
+The draw() method draws the image object.
+<tt>x,y,w,h</tt> indicates a destination rectangle.
+<tt>ox,oy,w,h</tt> is a source rectangle. This source rectangle
+is copied to the destination. The source rectangle may extend
+outside the image, i.e. <tt>ox</tt> and <tt>oy</tt> may be
+negative and <tt>w</tt> and <tt>h</tt> may be bigger than the
+image, and this area is left unchanged.
+
+void draw(int x, int y)
+
+\par
+Draws the image with the upper-left corner at <tt>x,y</tt>.
+This is the same as doing draw(x,y,img->w(),img->h(),0,0).
+
+<A NAME="offscreen"></A> <!-- For old HTML links only ! -->
+\subsection ssect_Offscreen Offscreen Drawing
+
+Sometimes it can be very useful to generate a complex drawing
+in memory first and copy it to the screen at a later point in 
+time. This technique can significantly reduce the amount of
+repeated drawing. Fl_Double_Window uses offscreen rendering
+to avoid flickering on systems that don't support 
+double-buffering natively.
+
+<A NAME="fl_create_offscreen"></A> <!-- For old HTML links only ! -->
+Fl_Offscreen fl_create_offscreen(int w, int h)
+
+\par
+Create an RGB offscreen buffer with <tt>w*h</tt> pixels.
+
+<A NAME="fl_delete_offscreen"></A> <!-- For old HTML links only ! -->
+void fl_delete_offscreen(Fl_Offscreen)
+
+\par
+Delete a previously created offscreen buffer. All drawings are lost.
+
+<A NAME="fl_begin_offscreen"></A> <!-- For old HTML links only ! -->
+void fl_begin_offscreen(Fl_Offscreen)
+
+\par
+Send all subsequent drawing commands to this offscreen buffer. 
+FLTK can draw into a buffer at any time. There is no need to wait for 
+an Fl_Widget::draw() to occur.
+
+<A NAME="fl_end_offscreen"></A> <!-- For old HTML links only ! -->
+void fl_end_offscreen()
+
+\par
+Quit sending drawing commands to this offscreen buffer.
+
+<A NAME="fl_copy_offscreen"></A> <!-- For old HTML links only ! -->
+void fl_copy_offscreen(int x, int y, int w, int h,
+Fl_Offscreen osrc, int srcx, int srcy)
+
+\par
+Copy a rectangular area of the size <tt>w*h</tt> from <tt>srcx, srcy</tt>
+in the offscreen buffer into the current buffer at <tt>x, y</tt>.
+
+\htmlonly
+<hr>
+<a class="el" href="index.html">[Index]</a> &nbsp;&nbsp;
+<a class="el" href="editor.html">[Previous]&nbsp; 4 - Designing a Simple Text Editor</a>&nbsp;
+<a class="el" href="events.html">[Next]&nbsp; 6 - Handling Events</a>&nbsp;
+\endhtmlonly
+*/