This chapter covers the drawing functions that are provided with FLTK.
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!
- 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_Widgetdraw() 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
To use the drawing functions you must first include the
<FL/fl_draw.H> header file. FLTK provides the following types of
drawing functions:
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)
Intersect 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.
Under 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.
void fl_color(Fl_Color)
Set the color for all subsequent drawing operations. Fl_Color
is an enumeration type, and all values are in the range 0-255. This
is not the X or WIN32 pixel, it is an index into 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>.
For colormapped displays, a color cell will be allocated out of
fl_colormap 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()
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)
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.
These are used to draw almost all the FLTK widgets. They draw on
exact pixel boundaries and are as fast as possible, and their behavior
will be duplicated exactly on any platform FLTK is ported to. It is
undefined whether these are affected by the
transformation matrix, so you should only call these while it is
the identity.
void fl_rectf(int x, int y, int w, int h)
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)
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.
void fl_rect(int x, int y, int w, int h)
Draw a 1-pixel border inside this bounding box.
void fl_line(int x, int y, int x1, int y1)
void fl_line(int x, int y, int x1, int y1, int x2, int y2)
Draw one or two 1-pixel thick lines between the given points.
void fl_loop(int x, int y, int x1, int y1, int x2, int y2)
void fl_loop(int x, int y, int x1, int y1, int x2, int y2, int x3,
int y3)
Outline a 3 or 4-sided polygon with 1-pixel thick lines.
void fl_polygon(int x, int y, int x1, int y1, int x2, int y2)
void fl_polygon(int x, int y, int x1, int y1, int x2, int y2, int
x3, int y3)
Fill a 3 or 4-sided polygon. The polygon must be convex.
void fl_xyline(int x, int y, int x1, int y1)
void fl_xyline(int x, int y, int x1, int y1, int x2)
void fl_xyline(int x, int y, int x1, int y1, int x2, int y3)
Draw 1-pixel wide horizontal and vertical lines. A horizontal line is
drawn first, then a vertical, then a horizontal.
void fl_yxline(int x, int y, int y1)
void fl_yxline(int x, int y, int y1, int x2)
void fl_yxline(int x, int y, int y1, int x2, int y3)
Draw 1-pixel wide vertical and horizontal lines. A vertical line is
drawn first, then a horizontal, then a vertical.
void fl_arc(int x, int y, int w, int h, double a1, double a2)
void fl_pie(int x, int y, int w, int h, double a1, double a2)
void fl_chord(int x, int y, int w, int 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.
These functions let you draw arbitrary shapes with 2-D linear
transformations. The functionality matches that found in Adobe®
PostScriptTM. The exact pixels filled in is less defined
than for the above calls, so that FLTK can take advantage of drawing
hardware. The transformed vertices are rounded to integers before
drawing the line segments. This severely limits the accuracy of these
functions for complex graphics. Use OpenGL when greater accuracy
and/or performance is required.
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(float x, float y)
void fl_scale(float x)
void fl_translate(float x, float y)
void fl_rotate(float d)
void fl_mult_matrix(float a, float b, float c, float d, float
x, float y)
Concatenate another transformation onto the current one. The rotation
angle is in degrees (not radians) and is 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_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().
void fl_vertex(float x, float y)
Add a single vertex to the current path.
void fl_curve(float x, float y, float x1, float y1, float x2, float
y2, float x3, float 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(float x, float y, float r, float start, float 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 its
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 the arc in a
clockwise direction.
void fl_circle(float x, float y, float 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()
. This draws incorrectly if the transformation is both rotated and
non-square scaled.
All text is drawn in the current font. It is
undefined whether this location or the characters are modified by the
current transformation.
void fl_draw(const char *, float x, float y)
void fl_draw(const char *, int n, float x, float y)
Draw a nul-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, as this function 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 nul-terminated string, a sequence of n
characters, or 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.
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 (i.e. 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 call to
fl_font(a,b). This can be used to save/restore the font.
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).
The following standard cursors are available:
- FL_CURSOR_DEFAULT - the default cursor, usually an arrow
- FL_CURSOR_ARROW - an arrow pointer
- 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
void fl_overlay_rect(int x, int y, int w, int h)
void fl_overlay_clear()
These functions allow you to draw interactive selection rectangles
without using the overlay hardware. 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.
To draw images, you can either do it directly from data in your
memory, or you can create Fl_Bitmap,
Fl_Image, or Fl_Pixmap
objects. 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 much faster.
Direct Image Drawing
It is undefined whether the location or drawing of the image is
affected by the current transformation, so you should only call these
when it is the identity.
void fl_draw_bitmap(const uchar *, int X, int Y, int W, int H, int
LD = 0)
This function is planned but not yet implemented (it may be impossible
under X without allocating a pixmap).
void fl_draw_image(const uchar *, int X, int Y, int W, int H, int D
= 3, int LD = 0)
void fl_draw_image_mono(const uchar *, int X, int Y, int W, int H,
int D = 1, int LD = 0)
Draw an 8-bit per color RGB or luminance 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 *, int x, int y, int w, uchar
*)
void fl_draw_image(fl_draw_image_cb, void *, int X, int Y, int W,
int H, int D = 3)
void fl_draw_image_mono(fl_draw_image_cb, void *, int X, int Y,
int W, int H, int 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, copy the data over so the x'th pixel is at
the start of the buffer.
You can assume 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, int X, int 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"
...
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).
int fl_measure_pixmap(char **data, int &w, int &h)
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 it
parsed the dimensions ok, and zero if there is any problem.
This object encapsulates the width, height, and bits of an X bitmap
(XBM), and allows you to make an Fl_Widget use a bitmap as a
label, or to just draw the bitmap directly. Under X it will create an
offscreen pixmap the first time it is drawn, and copy this each
subsequent time it is drawn.
Fl_Bitmap(const char *bits, int W, int H)
Fl_Bitmap(const uchar *bits, int W, int H)
Construct using an X bitmap. The bits pointer is simply copied to the
object, so it must point at persistent storage. The two constructors
are provided because various X implementations disagree about the type
of bitmap data. To use an XBM file use:
#include "foo.xbm"
...
Fl_Bitmap bitmap = new Fl_Bitmap(foo_bits, foo_width, foo_height);
~Fl_Bitmap()
The destructor will destroy any X pixmap created. It does not do
anything to the bits data.
void draw(int x, int y, int w, int h, int ox = 0, int oy = 0)
x,y,w,h indicates a destination rectangle. ox,oy,w,h
is a source rectangle. This source rectangle from the bitmap is drawn
in the destination. 1 bits are drawn with the current color, 0 bits
are unchanged. The source rectangle may extend outside the bitmap
(i.e. ox and oy may be negative and w and
h may be bigger than the bitmap) and this area is left unchanged.
void draw(int x, int y)
Draws the bitmap with the upper-left corner at x,y. This is
the same as doing draw(x,y,this->w,this->h,0,0).
void label(Fl_Widget *)
Change the label() and the labeltype() of the widget
to draw the bitmap. 1 bits will be drawn with the labelcolor()
, zero bits will be unchanged. You can use the same bitmap for many
widgets.
This object encapsulates the data from an XPM image, and allows you to
make an Fl_Widget use a pixmap as a label, or to just draw the
pixmap directly. Under X it will create an offscreen pixmap the
first time it is drawn, and copy this each subsequent time it is drawn
.
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)
Construct using XPM data. The data pointer is simply copied to the
object, so it must point at persistent storage. To use an XPM file do:
#include <FL/Fl_Pixmap.H>
#include "foo.xpm"
...
Fl_Pixmap pixmap = new Fl_Pixmap(foo);
~Fl_Pixmap()
The destructor will destroy any X pixmap created. It does not do
anything to the data.
void draw(int x, int y, int w, int h, int ox = 0, int oy = 0)
x,y,w,h indicates a destination rectangle. ox,oy,w,h
is a source rectangle. This source rectangle is copied to the
destination. The source rectangle may extend outside the pixmap (i.e.
ox and oy may be negative and w and h
may be bigger than the pixmap) and this area is left unchanged.
void draw(int x, int y)
Draws the image with the upper-left corner at x,y. This is
the same as doing draw(x,y,this->w,this->h,0,0).
void label(Fl_Widget *)
Change the label() and the labeltype() of the widget
to draw the pixmap. You can use the same pixmap for many widgets.
This object encapsulates a full-color RGB image, and allows you to
make an Fl_Widget use an image as a label, or to just draw the
image directly. Under X it will create an offscreen pixmap the first
time it is drawn, and copy this each subsequent time it is drawn.
Fl_Image(char uchar *data, int W, int H, int D = 3, int LD = 0)
Construct using a pointer to RGB data. W and H are
the size of the image in pixels. D is the delta between pixels
(it may be more than 3 to skip alpha or other data, or negative to flip
the image left/right). LD is the delta between lines (it may
be more than D * W to crop images, or negative to flip the
image vertically). The data pointer is simply copied to the object, so
it must point at persistent storage.
~Fl_Image()
The destructor will destroy any X pixmap created. It does not do
anything to the data.
void draw(int x, int y, int w, int h, int ox = 0, int oy = 0)
x,y,w,h indicates a destination rectangle. ox,oy,w,h
is a source rectangle. This source rectangle is copied to the
destination. The source rectangle may extend outside the image (i.e.
ox and oy may be negative and w and h
may be bigger than the image) and this area is left unchanged.
void draw(int x, int y)
Draws the image with the upper-left corner at x,y. This is
the same as doing draw(x,y,this->w,this->h,0,0).
void label(Fl_Widget *)
Change the label() and the labeltype() of the widget
to draw the image. You can use the same image for many widgets.