Chapter XXX - Drawing Things in FLTK

When can you draw things in FLTK?

• The most common is inside the virtual method Fl_Widget::draw(). To write code here, you must subclass one of the existing Fl_Widget classes and implement your own version of draw().

• You can also write boxtypes and labeltypes. These are small procedures that can be called by existing Fl_Widget draw() methods. These "types" are identified by an 8-bit index that is stored in the widget's box(), labeltype(), and possibly other properties.

• You can call Fl_Window::make_current() to do incremental update of a widget (use Fl_Widget::window() to find the window). Under X this only works for the base Fl_Window class, not for double buffered, overlay, or OpenGL windows!

FLTK Drawing functions
#include <FL/fl_draw.H>

• Clipping
• Colors
• Fast Shapes
• Complex Shapes
• Text
• Images
• Cursor
• Overlay
• Using OpenGL

Clipping

You can limit all your drawing to a rectangular region by calling fl_clip, and put the drawings back by using fl_pop_clip. This rectangle is measured in pixels (it is unaffected by the current transformation matrix).

In addition, the system may provide clipping when updating windows, this clip region may be more complex than a simple rectangle.

void fl_clip(int x, int y, int w, int h);

Intesect the current clip region with a rectangle and push this new region onto the stack.

void fl_pop_clip();

Restore the previous clip region. You must call fl_pop_clip() once for every time you call fl_clip(). If you return to FLTK with the clip stack not empty unpredictable results occur.

int fl_not_clipped(int x, int y, int w, int h);

Returns true if any of the rectangle intersects the current clip region. If this returns false you don't have to draw the object. On X this returns 2 if the rectangle is partially clipped, and 1 if it is entirely inside the clip region.

int fl_clip_box(int x, int y, int w, int h,
    int& X, int& Y, int& W, int& H);

Intersect the rectangle x,y,w,h with the current clip region and returns the bounding box of the result in X,Y,W,H. Returns non-zero if the resulting rectangle is different than the original. This can be used to limit the necessary drawing to a rectangle. W and H are set to zero if the rectangle is completely outside the region.

Colors

void fl_color(Fl_Color);

Set the color for all subsequent drawing operations. Fl_Color is an enumeration type, all values are in the range 0-255. This is not the X pixel, it is an internal table! The table provides several general colors, a 24-entry gray ramp, and a 5x8x5 color cube. All of these are named with poorly-documented symbols in <FL/Enumerations.H>.

Under X, a color cell will be allocated out of fl_colormap each time you request an fl_color the first time. If the colormap fills up then a least-squares algorithim is used to find the closest color.

Fl_Color fl_color();

Returns the last fl_color() that was set. This can be used for state save/restore.

void Fl::set_color(Fl_Color, uchar r, uchar g, uchar b);
void Fl::get_color(Fl_Color, uchar &, uchar &, uchar &);

Set or get an entry in the fl_color index table. You can set it to any 8-bit rgb color. On X, if the index has been requested before, the pixel is free'd. No pixel is allocated until fl_color(i) is used again, and there is no guarantee that the same pixel will be used next time.

void fl_color(uchar r, uchar g, uchar b);

Set the color for all subsequent drawing operations. The closest possible match to the rgb color is used. Under X this works perfectly for TrueColor visuals. For colormap visuals the nearest index in the gray ramp or color cube is figured out, and fl_color(i) is done with that, this can result in two approximations of the color and is very inaccurate!

Fast Shapes

All arguments are integers.

void fl_rectf(x, y, w, h);

Color a rectangle that exactly fills the given bounding box.

void fl_rectf(x, y, w, h, uchar r, uchar g, uchar b);

Color a rectangle with "exactly" the passed r,g,b color. On screens with less than 24 bits of color this is done by drawing a solid-colored block using fl_draw_image() so that dithering is produced. If you have 24 bit color, this fills the rectangle with a single pixel value and is about 1 zillion times faster.

void fl_rect(x, y, w, h);

Draw a 1-pixel border inside this bounding box.

void fl_line(x, y, x1, y1);
void fl_line(x, y, x1, y1, x2, y2);

Draw one or two 1-pixel thick lines between the given points.

void fl_loop(x, y, x1, y1, x2, y2);
void fl_loop(x, y, x1, y1, x2, y2, x3, y3);

Outline a 3 or 4-sided polygon with 1-pixel thick lines.

void fl_polygon(x, y, x1, y1, x2, y2);
void fl_polygon(x, y, x1, y1, x2, y2, x3, y3);

Fill a 3 or 4-sided polygon. The polygon must be convex.

void fl_xyline(x, y, x1, y1);
void fl_xyline(x, y, x1, y1, x2);
void fl_xyline(x, y, x1, y1, x2, y3);

Draw 1-pixel wide horizontal and vertical lines. A horizontal line is drawn first, then a vertical, then a horizontal.

void fl_yxline(x, y, y1);
void fl_yxline(x, y, y1, x2);
void fl_yxline(x, y, y1, x2, y3);

Draw 1-pixel wide vertical and horizontal lines. A vertical line is drawn first, then a horizontal, then a vertical.

void fl_arc(x, y, w, h, double a1, double a2);
void fl_pie(x, y, w, h, double a1, double a2);
void fl_chord(x, y, w, h, double a1, double a2);

High-speed ellipse sections. These functions match the rather limited circle drawing code provided by X and MSWindows. The advantage over using fl_arc 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, a2 must be greater or equal to a1.

fl_arc draws a 1-pixel thick line (notice this has a different number of arguments than the fl_arc described below.

fl_pie draws a filled-in pie slice. This slice may extend outside the line drawn by fl_arc, to avoid this use w-1 and h-1.

fl_chord is not yet implemented.

Complex Shapes

All arguments are float.

void fl_push_matrix();
void fl_pop_matrix();

Save and restore the current transformation. The maximum depth of the stack is 4.

void fl_scale(x, y);
void fl_scale(x);
void fl_translate(x, y);
void fl_rotate(d);
void fl_mult_matrix(a, b, c, d, x, y);

Concat another transformation to the current one. The rotation angle is in degrees (not radians) counter-clockwise.

void fl_begin_line();
void fl_end_line();

Start and end drawing 1-pixel thick lines.

void fl_begin_loop();
void fl_end_loop();

Start and end drawing a closed sequence of 1-pixel thick lines.

void fl_begin_polygon();
void fl_end_polygon();

Start and end drawing a convex filled polygon.

void fl_begin_complex_polygon();
void fl_gap();
void fl_end_complex_polygon();

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 seperate 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). For portability, you should only draw polygons that appear the same whether "even/odd" or "non-zero" "winding rules" are used to fill them. This mostly means that holes should be drawn in the opposite direction of the outside.

fl_gap() should only be called between fl_begin/end_complex_polygon(). To outline the polygon, use fl_begin_loop() and replace each fl_gap() with fl_end_loop();fl_begin_loop().

void fl_vertex(x, y);

Add a single vertex to the current path.

void fl_curve(int x,int y,int x1,int y1,int x2,int y2,int x3,int y3);

Add a series of points on a Bezier curve to the path. The curve ends (and two of the points) are at x,y and x3,y3.

void fl_arc(x, y, r, start, end);

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 this). x,y are the center of the circle, and r is it's radius. fl_arc() takes start and end angles that are measured in degrees counter-clockwise from 3 o'clock. If end is less than start then it draws clockwise.

void fl_circle(x, y, r);

fl_circle() is equivalent to fl_arc(...,0,360) but may be faster. It must be the only thing in the path: if you want a circle as part of a complex polygon you must use fl_arc(). Under Xlib and MSWindows this draws incorrectly if the transformation is both rotated and non-square scaled.

Text

void fl_draw(const char*, float x, float y);
void fl_draw(const char*, int n, float x, float y);

Draw a null terminated string or an array of n characters starting at the given location.

void fl_draw(const char*, int x,int y,int w,int h, Fl_Align);

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. See Fl_Widget::align() for values for align. The value FL_ALIGN_INSIDE is ignored, this always prints inside the box.

void fl_measure(const char*, int& w, int& h);

Measure how wide and tall the string will be when printed by the fl_draw(...align) function. If the incoming w is non-zero it will wrap to that width.

int fl_height();

Recommended minimum line spacing for the current font. You can also just use the value of size passed to fl_font().

int fl_descent();

Recommended distance above the bottom of a fl_height() tall box to draw the text at so it looks centered vertically in that box.

float fl_width(const char*);
float fl_width(const char*, int n);
float fl_width(uchar);

Return the width of a null-terminated string, a sequence of n characters, and a single character.

const char* fl_shortcut_label(ulong);

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.

Fonts

void fl_font(int face, int size);

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.

The font is identified by a face and a size. The size of the font is measured in pixels (ie. it is not "resolution [in]dependent"). Lines should be spaced size pixels apart (or more).

The face is an index into an internal 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 it stores the index as a byte.

int fl_font();
int fl_size();

Returns the face and size set by the most recent fl_font(a,b). This can be used to save/restore the font.

const char* Fl::get_font(int face);

Get the string for this face. This string is different for each face. Under X this value is passed to XListFonts to get all the sizes of this face.

const char* Fl::get_font_name(int face, int* attributes=0);

Get a human-readable string describing the family of this face. This is useful if you are presenting a choice to the user. There is no guarantee that each face has a different name. The return value points to a static buffer that is overwritten each call.

The integer pointed to by attributes (if the pointer is not zero) is set to zero, FL_BOLD(1) or FL_ITALIC(2) or FL_BOLD|FL_ITALIC (maybe more attributes will be defined in the future). To locate a "family" of fonts, search forward and back for a set with non-zero attributes, these faces along with the face with a zero attribute before them constitute a family.

int get_font_sizes(int face, int*& sizep);

Return an array of sizes in sizep. The return value is the length of this array. The sizes are sorted from smallest to largest and indicate what sizes can be given to fl_font() that will be matched exactly (fl_font() will pick the closest size for other sizes). A zero in the first location of the array indicates a scalable font, where any size works, although the array may list sizes that work "better" than others. Warning: the returned array points at a static buffer that is overwritten each call. Under X this will open the display.

int Fl::set_font(int face, const char*);

Change a face. The string pointer is simply stored, the string is not copied, so the string must be in static memory.

int Fl::set_font(int face, int from);

Copy one face to another.

int Fl::set_fonts(const char* = 0);

FLTK will open the display, and add every font on the server to the face table. It will attempt to put "families" of faces together, so that the normal one is first, followed by bold, italic, and bold italic.

The optional argument is a string to describe the set of fonts to add. Passing NULL will select only fonts that have the ISO8859-1 character set (and are thus usable by normal text). Passing "-*" will select all fonts with any encoding as long as they have normal X font names with dashes in them. Passing "*" will list every font that exists (on X this may produce some strange output). Other values may be useful but are system dependent. On MSWindows NULL selects fonts with ISO8859-1 encoding and non-NULL selects all fonts.

Return value is how many faces are in the table after this is done.

Bitmaps, Pixmaps and Images

Cursor

void fl_cursor(Fl_Cursor, Fl_Color=FL_WHITE, Fl_Color=FL_BLACK);

Change the cursor. Depending on the system this may affect the cursor everywhere, or only when it is pointing at the window that is current when you call this. For portability you should change the cursor back to the default in response to FL_LEAVE events.

The type Fl_Cursor is an enumeration defined in <Enumerations.H>. The double-headed arrows are bitmaps provided by FLTK on X, the others are provided by system-defined cursors. Under X you can get any XC_cursor value by passing Fl_Cursor((XC_foo/2)+1).

• FL_CURSOR_DEFAULT (0) usually an arrow
• FL_CURSOR_ARROW
• FL_CURSOR_CROSS - crosshair
• FL_CURSOR_WAIT - watch or hourglass
• FL_CURSOR_INSERT - I-beam
• FL_CURSOR_HAND - hand (uparrow on MSWindows)
• FL_CURSOR_HELP - question mark
• FL_CURSOR_MOVE - 4-pointed arrow
• FL_CURSOR_NS - up/down arrow
• FL_CURSOR_WE - left/right arrow
• FL_CURSOR_NWSE - diagonal arrow
• FL_CURSOR_NESW - diagonal arrow
• FL_CURSOR_NONE - invisible

Overlay rectangle

void fl_overlay_rect(int x, int y, int w, int h);
void fl_overlay_clear();

Big kludge to draw interactive selection rectangles without using the overlay. FLTK will xor a single rectangle outline over a window. Calling this will erase any previous rectangle (by xor'ing it), and then draw the new one. Calling fl_overlay_clear() will erase the rectangle without drawing a new one. Using this 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.

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Drawing Images in FLTK

This function is planned but not yet implemented (it may be impossible under X without allocating a pixmap).

void fl_draw_image(const uchar*, X, Y, W, H, D = 3, LD = 0);
void fl_draw_image_mono(const uchar*, X, Y, W, H, D = 1, LD = 0);

Draw an 8-bit per color rgb image. The pointer points at the "r" data of the top-left pixel. Data must be in r,g,b order. X, Y are where to put the top-left corner. W and H define the size of the image. D is the delta to add to the pointer between pixels, it may be any value greater or equal to 3, or it can be negative to flip the image horizontally. LD is the delta to add to the pointer between lines (if 0 is passed it uses W*D), and may be larger than W*D to crop data, or negative to flip the image vertically.

It is highly recommended that you put the following code before the first show() of any window in your program to get rid of the dithering if possible:

Fl::visual(FL_RGB)

Gray scale (1-channel) images may be drawn. This is done if abs(D) 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 D greater than 1 will let you display one channel of a color image.

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*, x, y, w, uchar*);
void fl_draw_image(fl_draw_image_cb, void*, X, Y, W, H, D = 3);
void fl_draw_image_mono(fl_draw_image_cb, void*, X, Y, W, H, D = 1);

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).

The callback is called with the void* user data pointer (this can be used to point at a structure of information about the image), and the x, y, and w of the scan line desired from the image. 0,0 is the upper-left corner (not X,Y). A pointer to a buffer to put the data into is passed. You must copy w pixels from scanline y, starting at pixel x, to this buffer.

Due to cropping, less than the whole image may be requested. So x may be greater than zero, the first y may be greater than zero, and w may be less than W. The buffer is long enough to store the entire W*D pixels, this is for convienence with some decompression schemes where you must decompress the entire line at once: decompress it into the buffer, and then if x is not zero, memcpy the data over so the x'th pixel is at the start of the buffer.

You can assumme the y's will be consecutive, except the first one may be greater than zero.

If D is 4 or more, you must fill in the unused bytes with zero.

int fl_draw_pixmap(char** data, X, Y, Fl_Color=FL_GRAY);

Draw XPM image data, with the top-left corner at the given position. The images 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.

To use an XPM, do "#include "foo.xpm"" and then "fl_draw_pixmap(foo, X, Y)".

In the current version the XPM data is converted to 8-bit full color and passed through fl_draw_image(). This is obviously not the most efficient way to do it, and has the same visual limitations as listed above for fl_draw_image(). Transparent colors are replaced by the optional Fl_Color argument (this may change in the future).

FLTK supports some (questionable) enhancements to the XPM format.

int fl_measure_pixmap(char** data, int &w, int &h);

An XPM image contains the dimensions in it's data. This function finds and returns the width and height. The return value is non-zero if it parsed the dimensions ok, and zero if there is any problem.

The current implementation converts the pixmap to 8 bit color data and uses fl_draw_image() to draw it. Thus you will get dithered colors on an 8 bit screen.

Fl_Pixmap(char * const * data);

~Fl_Pixmap()

void draw(int x, int y, int w, int h, int ox=0, int oy=0);

void draw(int x, int y);

void label(Fl_Widget *);

See fl_draw_image() for what happens. On 8 bit screens dithering is used.

Fl_Image(char uchar *data, int W, int H, int D=3, int LD=0);

~Fl_Image()

void draw(int x, int y, int w, int h, int ox=0, int oy=0);

void draw(int x, int y);

void label(Fl_Widget *);

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FLTK enhancements to the XPM format

I made some additions to XPM that may be good, or intensely disliked by X purists. I do not know if the changes are compatable with current XPM.

The change was to make a "compressed colormap" that avoids XParseColor(), and gives the actual color values (which is really what everybody wants!). Only colormaps of this form, and ones where the colors are named as "#rrggbb", will be portable to non-X platforms.

A compressed colormap is indicated by the number of colors being negative. The colormap is then given as an array of 4*numcolors characters. Each color is described by 4 characters: the index character, and the red, green, and blue value (for 2-character indexes each color needs 5 characters).

XPM files support a single transparent index. I require this index to be ' ' (space). To indicate that ' ' is transparent, it should be first in the color table. To make ' ' not be transparent, put it somewhere other than first in the table.

To make the XPM files easily parseable, but still portable to most C compilers, I suggest the following format:

/* XPM */
static char * name[] = {
/* width height ncolors chars_per_pixel */
"64 64 -4 1 ",
/* colormap */
"\
 \x50\x50\x80\
.\xff\xff\x00\
r\xff\x00\x00\
b\x00\x00\x00",
/* pixels */
"        bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb        ",
"        bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb        ",
"        bb............................................bb        ",
...

All lines starting with "/*" are optional. Parsers should handle '\' at the end of the line and \xNN and \NNN characters. This requires the C compiler to parse \xNN characters.

Chapter XXX - Drawing Things in FLTK

When can you draw things in FLTK?

• The most common is inside the virtual method Fl_Widget::draw(). To write code here, you must subclass one of the existing Fl_Widget classes and implement your own version of draw().

• You can also write boxtypes and labeltypes. These are small procedures that can be called by existing Fl_Widget draw() methods. These "types" are identified by an 8-bit index that is stored in the widget's box(), labeltype(), and possibly other properties.

• You can call Fl_Window::make_current() to do incremental update of a widget (use Fl_Widget::window() to find the window). Under X this only works for the base Fl_Window class, not for double buffered, overlay, or OpenGL windows!

FLTK Drawing functions
#include <FL/fl_draw.H>

• Clipping
• Colors
• Fast Shapes
• Complex Shapes
• Text
• Images
• Cursor
• Overlay
• Using OpenGL

Clipping

You can limit all your drawing to a rectangular region by calling fl_clip, and put the drawings back by using fl_pop_clip. This rectangle is measured in pixels (it is unaffected by the current transformation matrix).

In addition, the system may provide clipping when updating windows, this clip region may be more complex than a simple rectangle.

void fl_clip(int x, int y, int w, int h);

Intesect the current clip region with a rectangle and push this new region onto the stack.

void fl_pop_clip();

Restore the previous clip region. You must call fl_pop_clip() once for every time you call fl_clip(). If you return to FLTK with the clip stack not empty unpredictable results occur.

int fl_not_clipped(int x, int y, int w, int h);

Returns true if any of the rectangle intersects the current clip region. If this returns false you don't have to draw the object. On X this returns 2 if the rectangle is partially clipped, and 1 if it is entirely inside the clip region.

int fl_clip_box(int x, int y, int w, int h,
    int& X, int& Y, int& W, int& H);

Intersect the rectangle x,y,w,h with the current clip region and returns the bounding box of the result in X,Y,W,H. Returns non-zero if the resulting rectangle is different than the original. This can be used to limit the necessary drawing to a rectangle. W and H are set to zero if the rectangle is completely outside the region.

Colors

void fl_color(Fl_Color);

Set the color for all subsequent drawing operations. Fl_Color is an enumeration type, all values are in the range 0-255. This is not the X pixel, it is an internal table! The table provides several general colors, a 24-entry gray ramp, and a 5x8x5 color cube. All of these are named with poorly-documented symbols in <FL/Enumerations.H>.

Under X, a color cell will be allocated out of fl_colormap each time you request an fl_color the first time. If the colormap fills up then a least-squares algorithim is used to find the closest color.

Fl_Color fl_color();

Returns the last fl_color() that was set. This can be used for state save/restore.

void Fl::set_color(Fl_Color, uchar r, uchar g, uchar b);
void Fl::get_color(Fl_Color, uchar &, uchar &, uchar &);

Set or get an entry in the fl_color index table. You can set it to any 8-bit rgb color. On X, if the index has been requested before, the pixel is free'd. No pixel is allocated until fl_color(i) is used again, and there is no guarantee that the same pixel will be used next time.

void fl_color(uchar r, uchar g, uchar b);

Set the color for all subsequent drawing operations. The closest possible match to the rgb color is used. Under X this works perfectly for TrueColor visuals. For colormap visuals the nearest index in the gray ramp or color cube is figured out, and fl_color(i) is done with that, this can result in two approximations of the color and is very inaccurate!

Fast Shapes

All arguments are integers.

void fl_rectf(x, y, w, h);

Color a rectangle that exactly fills the given bounding box.

void fl_rectf(x, y, w, h, uchar r, uchar g, uchar b);

Color a rectangle with "exactly" the passed r,g,b color. On screens with less than 24 bits of color this is done by drawing a solid-colored block using fl_draw_image() so that dithering is produced. If you have 24 bit color, this fills the rectangle with a single pixel value and is about 1 zillion times faster.

void fl_rect(x, y, w, h);

Draw a 1-pixel border inside this bounding box.

void fl_line(x, y, x1, y1);
void fl_line(x, y, x1, y1, x2, y2);

Draw one or two 1-pixel thick lines between the given points.

void fl_loop(x, y, x1, y1, x2, y2);
void fl_loop(x, y, x1, y1, x2, y2, x3, y3);

Outline a 3 or 4-sided polygon with 1-pixel thick lines.

void fl_polygon(x, y, x1, y1, x2, y2);
void fl_polygon(x, y, x1, y1, x2, y2, x3, y3);

Fill a 3 or 4-sided polygon. The polygon must be convex.

void fl_xyline(x, y, x1, y1);
void fl_xyline(x, y, x1, y1, x2);
void fl_xyline(x, y, x1, y1, x2, y3);

Draw 1-pixel wide horizontal and vertical lines. A horizontal line is drawn first, then a vertical, then a horizontal.

void fl_yxline(x, y, y1);
void fl_yxline(x, y, y1, x2);
void fl_yxline(x, y, y1, x2, y3);

Draw 1-pixel wide vertical and horizontal lines. A vertical line is drawn first, then a horizontal, then a vertical.

void fl_arc(x, y, w, h, double a1, double a2);
void fl_pie(x, y, w, h, double a1, double a2);
void fl_chord(x, y, w, h, double a1, double a2);

High-speed ellipse sections. These functions match the rather limited circle drawing code provided by X and MSWindows. The advantage over using fl_arc 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, a2 must be greater or equal to a1.

fl_arc draws a 1-pixel thick line (notice this has a different number of arguments than the fl_arc described below.

fl_pie draws a filled-in pie slice. This slice may extend outside the line drawn by fl_arc, to avoid this use w-1 and h-1.

fl_chord is not yet implemented.

Complex Shapes

All arguments are float.

void fl_push_matrix();
void fl_pop_matrix();

Save and restore the current transformation. The maximum depth of the stack is 4.

void fl_scale(x, y);
void fl_scale(x);
void fl_translate(x, y);
void fl_rotate(d);
void fl_mult_matrix(a, b, c, d, x, y);

Concat another transformation to the current one. The rotation angle is in degrees (not radians) counter-clockwise.

void fl_begin_line();
void fl_end_line();

Start and end drawing 1-pixel thick lines.

void fl_begin_loop();
void fl_end_loop();

Start and end drawing a closed sequence of 1-pixel thick lines.

void fl_begin_polygon();
void fl_end_polygon();

Start and end drawing a convex filled polygon.

void fl_begin_complex_polygon();
void fl_gap();
void fl_end_complex_polygon();

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 seperate 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). For portability, you should only draw polygons that appear the same whether "even/odd" or "non-zero" "winding rules" are used to fill them. This mostly means that holes should be drawn in the opposite direction of the outside.

fl_gap() should only be called between fl_begin/end_complex_polygon(). To outline the polygon, use fl_begin_loop() and replace each fl_gap() with fl_end_loop();fl_begin_loop().

void fl_vertex(x, y);

Add a single vertex to the current path.

void fl_curve(int x,int y,int x1,int y1,int x2,int y2,int x3,int y3);

Add a series of points on a Bezier curve to the path. The curve ends (and two of the points) are at x,y and x3,y3.

void fl_arc(x, y, r, start, end);

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 this). x,y are the center of the circle, and r is it's radius. fl_arc() takes start and end angles that are measured in degrees counter-clockwise from 3 o'clock. If end is less than start then it draws clockwise.

void fl_circle(x, y, r);

fl_circle() is equivalent to fl_arc(...,0,360) but may be faster. It must be the only thing in the path: if you want a circle as part of a complex polygon you must use fl_arc(). Under Xlib and MSWindows this draws incorrectly if the transformation is both rotated and non-square scaled.

Text

void fl_draw(const char*, float x, float y);
void fl_draw(const char*, int n, float x, float y);

Draw a null terminated string or an array of n characters in the current font, starting at the given location.

void fl_draw(const char*, int x,int y,int w,int h, Fl_Align);

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. See Fl_Widget::align() for values for align. The value FL_ALIGN_INSIDE is ignored, this always prints inside the box.

void fl_measure(const char*, int& w, int& h);

Measure how wide and tall the string will be when printed by the fl_draw(...align) function. If the incoming w is non-zero it will wrap to that width.

int fl_height();

Recommended minimum line spacing for the current font. You can also just use the value of size passed to fl_font().

int fl_descent();

Recommended distance above the bottom of a fl_height() tall box to draw the text at so it looks centered vertically in that box.

float fl_width(const char*);
float fl_width(const char*, int n);
float fl_width(uchar);

Return the width of a null-terminated string, a sequence of n characters, and a single character.

const char* fl_shortcut_label(ulong);

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.

Fonts

void fl_font(int face, int size);

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.

The font is identified by a face and a size. The size of the font is measured in pixels (ie. it is not "resolution [in]dependent"). Lines should be spaced size pixels apart (or more).

The face is an index into an internal 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 it stores the index as a byte.

int fl_font();
int fl_size();

Returns the face and size set by the most recent fl_font(a,b). This can be used to save/restore the font.

const char* Fl::get_font(int face);

Get the string for this face. This string is different for each face. Under X this value is passed to XListFonts to get all the sizes of this face.

const char* Fl::get_font_name(int face, int* attributes=0);

Get a human-readable string describing the family of this face. This is useful if you are presenting a choice to the user. There is no guarantee that each face has a different name. The return value points to a static buffer that is overwritten each call.

The integer pointed to by attributes (if the pointer is not zero) is set to zero, FL_BOLD(1) or FL_ITALIC(2) or FL_BOLD|FL_ITALIC (maybe more attributes will be defined in the future). To locate a "family" of fonts, search forward and back for a set with non-zero attributes, these faces along with the face with a zero attribute before them constitute a family.

int get_font_sizes(int face, int*& sizep);

Return an array of sizes in sizep. The return value is the length of this array. The sizes are sorted from smallest to largest and indicate what sizes can be given to fl_font() that will be matched exactly (fl_font() will pick the closest size for other sizes). A zero in the first location of the array indicates a scalable font, where any size works, although the array may list sizes that work "better" than others. Warning: the returned array points at a static buffer that is overwritten each call. Under X this will open the display.

int Fl::set_font(int face, const char*);

Change a face. The string pointer is simply stored, the string is not copied, so the string must be in static memory.

int Fl::set_font(int face, int from);

Copy one face to another.

int Fl::set_fonts(const char* = 0);

FLTK will open the display, and add every font on the server to the face table. It will attempt to put "families" of faces together, so that the normal one is first, followed by bold, italic, and bold italic.

The optional argument is a string to describe the set of fonts to add. Passing NULL will select only fonts that have the ISO8859-1 character set (and are thus usable by normal text). Passing "-*" will select all fonts with any encoding as long as they have normal X font names with dashes in them. Passing "*" will list every font that exists (on X this may produce some strange output). Other values may be useful but are system dependent. On MSWindows NULL selects fonts with ISO8859-1 encoding and non-NULL selects all fonts.

Return value is how many faces are in the table after this is done.

Bitmaps, Pixmaps and Images

Cursor

void fl_cursor(Fl_Cursor, Fl_Color=FL_WHITE, Fl_Color=FL_BLACK);

Change the cursor. Depending on the system this may affect the cursor everywhere, or only when it is pointing at the window that is current when you call this. For portability you should change the cursor back to the default in response to FL_LEAVE events.

The type Fl_Cursor is an enumeration defined in <Enumerations.H>. The double-headed arrows are bitmaps provided by FLTK on X, the others are provided by system-defined cursors. Under X you can get any XC_cursor value by passing Fl_Cursor((XC_foo/2)+1).

• FL_CURSOR_DEFAULT (0) usually an arrow
• FL_CURSOR_ARROW
• FL_CURSOR_CROSS - crosshair
• FL_CURSOR_WAIT - watch or hourglass
• FL_CURSOR_INSERT - I-beam
• FL_CURSOR_HAND - hand (uparrow on MSWindows)
• FL_CURSOR_HELP - question mark
• FL_CURSOR_MOVE - 4-pointed arrow
• FL_CURSOR_NS - up/down arrow
• FL_CURSOR_WE - left/right arrow
• FL_CURSOR_NWSE - diagonal arrow
• FL_CURSOR_NESW - diagonal arrow
• FL_CURSOR_NONE - invisible

Overlay rectangle

void fl_overlay_rect(int x, int y, int w, int h);
void fl_overlay_clear();

Big kludge to draw interactive selection rectangles without using the overlay. FLTK will xor a single rectangle outline over a window. Calling this will erase any previous rectangle (by xor'ing it), and then draw the new one. Calling fl_overlay_clear() will erase the rectangle without drawing a new one. Using this 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.

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