Drawing Things in FLTK
This chapter covers the drawing functions that are provided with 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 fltk::Widget::draw(). To write
code here, you must subclass one of the existing fltk::Widget
classes and implement your own version of draw().
- You can also write boxtypes and labeltypes. These are small structures
with functions in them that rae called by existing
fltk::Widget::draw() methods. Pointers to these
structures are stored in the widget's box() ,
labeltype(), and possibly other properties.
- You can write fltk::Image classes, which
can then be put into the fltk::Widget::image() and be called by
existing fltk::Widget::draw() methods.
- You can call
fltk::Window::make_current() to do incremental update of a
widget. Use
fltk::Widget::window() to find the window.
To use the drawing functions you must first include the
<fltk/draw.h> header file. FLTK provides the following types of
drawing functions:
FLTK provides an arbitrary 2-D linear transformation (ie rotation,
scale, skew, reflections, and translation). This is very similar to
PostScript, PDF, and SVG.
Due to limited graphics capabilities of some systems, all
drawing methods that take 4 integer values (defining a box) only
transform the x and y values, and round them to the nearest
integer. You should use functions that take floating-point coordinates
if you want accurately scaled drawings.
Save and restore the current transformation. The maximum depth of the
stack is 10.
Concatenate another transformation onto the current one. The rotation
angle is in degrees (not radians) and is counter-clockwise.
fltk::translate(int,int) is provided because it is much faster than
the floating-point version. However C++ will not "resolve" which one
you want to call if you try passing doubles as arguments. To get it to
compile, make sure you cast the arguments to float (add 'f' after
floating-point constants). Use the 'f' versions (ie sinf(), cosf(),
etc) of the math functions from <fltk/math.h> to produce floats
and get maximum calculation speed.
Replace the current transform with the identity transform, which puts
0,0 in the top-left corner of the window and each unit is 1 pixel in
size.
Replace x and y with the transformed coordinates.
Replace x and y with the transformed coordinates, rounded to the
nearest integer.
Replace x and y with the tranformed coordinates, ignoring
translation. This transforms a vector which is measuring a distance
between two positions, rather than a position.
You can limit all your drawing to a region by calling fltk::push_clip(), and put the drawings
back by using fltk::pop_clip(). Fltk
may also set up clipping before draw() is called to limit the drawing
to the region of the window that is damaged.
When drawing you can also test the current clip region with
fltk::not_clipped() and fltk::clip_box(). By using these
to skip over complex drawings that are clipped you can greatly speed
up your program's redisplay.
Notice that the width and height of the clipping region is measured
in transformed coordianates.
Pushes the intersection of the current region and this
rectangle onto the clip stack.
Remove the rectangle from the current clip region, thus making it a
more complex shape. This does not push the stack, it just replaces
the top of it. This does not work on X or Win32 unless
fltk::push_clip() has been called at least once.
Pushes an empty clip region on the stack so nothing will be clipped.
This lets you draw outside the current clip region. You should not
use this :-)
Restore the previous clip region. You must call
fltk::pop_clip() exactly once for every time you call
fltk::clip(). If you return to FLTK with the clip stack not
empty unpredictable results occur.
Return non-zero if the intersection of the rectangle and the current
clip region is non-zero. If this returns zero you don't have to draw
anything in that rectangle. Under X this returns 1 if the
interesection is equal to the rectangle, and 2 if the intersection is
only part of the rectangle.
Find the smallest rectangle that surrounds the intersection of the
rectangle x,y,w,h with the current clip region. This
"bounding box" is returned in X,Y,W,H. The return value is
non-zero if the bounding box is different than the rectangle. If the
intersection is empty then W and H are set to zero.
This can be used to limit complex pixel operations (like drawing
images) to the smallest rectangle needed to update the visible area.
Set the color for all subsequent drawing operations. fltk::Color is a typedef for a 32-bit integer
containing r,g,b bytes and an "index" byte. The index is used if
r,g,b is zero. For instance 0xFF008000 is 255 red, zero
green, and 128 blue.
(On non-TrueColor X displays fltk rounds the desired color to the
nearest color in a small (200) set of colors and allocates that from X
to avoid consuming the entire colormap. On Windows colormapped displays
the system dithering is used for all colors, which looks lousy, but
Windows does not have the defective X behavior and thus you usually
are not forced to set the screen to 8-bit mode)
Returns the last fltk::color() that was set. This can be used
for state save/restore.
Set how to draw lines (the "pen"). If you change this it is your
responsibility to set it back to the default with
fltk::line_style(0).
style is a bitmask in which you 'or' 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.
- fltk::SOLID -------
- fltk::DASH - - - -
- fltk::DOT ·········
- fltk::DASHDOT - · - ·
- fltk::DASHDOTDOT - ·· - ··
- fltk::CAP_FLAT
- fltk::CAP_ROUND
- fltk::CAP_SQUARE (extends past end point 1/2 line width)
- fltk::JOIN_MITER (pointed)
- fltk::JOIN_ROUND
- fltk::JOIN_BEVEL (flat)
width 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.
dashes 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 null pointer or a zero-length
array results in a solid line. Odd array sizes are not supported and
result in undefined behavior. The dashes array does not work on
Windows 95/98, use the dash styles instead.
These functions let you draw arbitrary shapes with 2-D linear
transformations. The functionality matches that found in Adobe®
PostScriptTM. 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.
Clear the current "path". This is normally done by fltk::fill() or any
other drawing command.
Add a single vertex to the current path. (If you are familiar with
PostScript, this does a "moveto" if the path is clear or fltk::closepath
was done last, otherwise it does a "lineto").
fltk::vertex(int,int) is provided because it is much faster than
the floating-point version. However C++ will not "resolve" which one
you want to call if you try passing doubles as arguments. To get it to
compile, make sure you cast the arguments to float (add 'f' after
floating-point constants). Use the 'f' versions (ie sinf(), cosf(),
etc) of the math functions from <fltk/math.h> to produce floats
and get maximum calculation speed.
Add a whole set of vertices to the current path. This is much faster
than calling fltk::vertex once for each point.
Add a set of vertices to the current path where the coordinates are
in the units returned by fltk::transform().
This is used by fltk::curve() and can be used by
other code to calculate shapes.
Similar to drawing another vertex back at the starting point, but fltk
knows the path is closed. The next fltk::vertex will start a new
disconnected part of the shape.
It is harmless to call fltk::closepath() several times in a
row, or to call it before the first point. Sections with less than 3
points in them will not draw anything when filled.
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.
Add a series of points to the current path on the arc of an
ellipse. The ellipse in inscribed in the x,y,w,h rectangle,
and the start and end angles are measured in degrees
counter-clockwise from 3 o'clock, 45 points at the upper-right corner
of the rectangle. If end is less than start then
it draws the arc in a clockwise direction.
Does closepath() and then adds a series of points on the edge of an
ellipse inscribed in the given rectangle, then another closepath().
This tries to take advantage of the primitive drawing provided by X
and Win32, which means it only draws the right thing if the rotation
is a multiple of 90 degrees, or if the shape is a circle. Currently
there can only be one ellipse or circle in a path.
fltk::circle() draws a circle of radius r centered on the point
x,y. The result is always a circle, irregardless of scale. This also
tries to take advantage of the X/Win32 graphics primitives like fltk::ellipse.
Draw a point (one pixel) for every vertex in the path, then clear the
path.
Draw a line between all the points in the path (see fltk::line_type() for
ways to set the thicknesss and dot pattern of the line), then clear
the path.
Does fltk::closepath() and then fill with the current color, and
then clear the path.
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.
Does fltk::fill(), then sets the current color to
linecolor and does fltk::stroke with the same closed
path, and then clears the path.
These graphics will go directly to the primitives provided by X or
GDI. Only the x,y coordinates are transformed and in most cases they
are rounded to the nearest integer.
Draw a line inside this bounding box (currently correct only
for 0-thickness lines).
Color a rectangle that exactly fills the given bounding box.
Draw a straight line between the two points.
These functions match the rather limited circle drawing code provided
by X and WIN32. The advantage over using fltk::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. Only the integer
translation of the current transformation is obeyed on most systems.
The allowed types are:
- fltk::PIE fills a pie-slice shape
- fltk::CHORD join the ends of the arc with a straight line
and fill.
- fltk::ARC stroke the curved edge of the arc.
See fltk::Font for a description of what can be
passed as a font. For most uses one of the built-in constant fonts
like fltk::HELVETICA can be used.
Set the current font and font scaling so the size is size
pixels. The size is unaffected by the current transformation matrix
(you may be able to use fltk::transform() to
get the size to get a properly scaled font).
The size is given in pixels. Many pieces of software express sizes
in "points" (for mysterious reasons, since everything else is measured
in pixels!). To convert these point sizes to pixel sizes use the
following code:
const fltk::Screen_Info& info = fltk::info();
float pixels_per_point = info.height/(info.height_mm*(72/25.4));
float font_pixel_size = font_point_size*pixels_per_point;
Set the current font by name. Exactly what names work depend on your
system, it is best to use fltk::list_fonts to see what
is provided. See fltk::find_font for how the
name and attributes are interpreted.
The encoding determines how the bytes sent to fltk::draw are turned into glyphs. If the current font
cannot do the encoding, some default encoding will be used (for
instance the Symbol font always works without having to set the
encoding).
In current implementations you must call fltk::font(...)
after this for the change in encoding to take effect.
The only way
to find out what encodings are going to work is to call fltk::Font::encodings().
In general you should set this on startup to your locale, and leave
it alone. We hope to support UTF-8 encoding by default in fltk in the
future. It is likely that when this happens support for fltk::encoding()
will be removed.
The default is "iso8859-1"
fltk::Font fltk::font()
Returns the current font.
Returns the current font size.
const char* fltk::encoding();
Returns the current encoding.
Returns the vertical size of the font according to the system. I
recommended that you use fltk::size() instead for portability
and because many X fonts return erroneous values for this. Notice that
the dimension is in transformed coordinates.
Recommended distance above the bottom of a fltk::height() tall
box to draw the text at so it looks centered vertically in that box.
Notice that the dimension is in transformed coordinates.
Return the pixel width of a nul-terminated string, or a string of
length n bytes. Notice that the dimension is in transformed
coordinates.
Draw a nul-terminated string or an array of n bytes
starting at the given location.
Draw an array of n bytes starting at the given location,
which is given in actual device units, such as those returned by fltk::transform(). You must use this if you wish
to accurately append pieces of text together.
void fltk::draw(const char*, int x, int y, int w, int h, fltk::Flags)
Fancy string drawing function which is used to draw all the labels.
The string is formatted and aligned inside the passed box (only the
x/y are transformed, the width and height are in device units).
Handles '\t' and '\n', expands all other control characters to ^X, and
aligns inside or against the edges of the box. See fltk::Labeltype_::draw() for values
for the flags (fltk::ALIGN_INSIDE is ignored, it acts like it is
always on).
Measure how wide and tall the string will be when printed by the
fltk::draw(...align) function. If the incoming w is
non-zero it will wrap to that width. Notice that the dimensions are
in transformed coordinates.
If you plan to draw the same image many times, you may want an fltk::Image subclass such as fltk::Bitmap, fltk::RGB_Image, or fltk::Pixmap and call draw() on them. 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. In addition, on current systems, fltk::Image is the
only way to get transparency or to draw 1-bit bitmaps.
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.
Currently the image is only affected by the integer portion of the
current transformation. This may change in future versions!
Draw an 8-bit per color RGB or luminance image. The pointer points at
the byte of red 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:
fltk::visual(fltk::RGB);
Gray scale (1-channel) images may be drawn. This is done if abs(D)
is less than 3, or by calling fltk::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 (*fltk::draw_image_cb)(void*, int x, int y, int w, uchar
*)
void fltk::draw_image(fltk::draw_image_cb, void*, int X, int Y, int W,
int H, int D = 3)
void fltk::draw_image_mono(fltk::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.