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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
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The graphics library
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<HR>
<H1>Chapter 22: The graphics library</H1>
The <TT>graphics</TT> library provides a set of portable drawing primitives.
Drawing takes place
in a separate window that is created when <TT>open</TT><TT>_</TT><TT>graph</TT> is called.<BR>
<BR>
<FONT COLOR=purple>Unix:</FONT>
<BLOCKQUOTE>
This library is implemented under the X11 windows system.
Programs that use the <TT>graphics</TT> library must be linked as follows:
<PRE>
ocamlc -custom <I>other options</I> graphics.cma <I>other files</I> \
-cclib -lgraphics -cclib -lX11
</PRE>
For interactive use of the <TT>graphics</TT> library, do:
<PRE>
ocamlmktop -custom -o mytop graphics.cma -cclib -lgraphics \
-cclib -lX11
./mytop
</PRE>
Here are the graphics mode specifications supported by <TT>open</TT><TT>_</TT><TT>graph</TT> on
the X11 implementation of this library:
the argument to <TT>open</TT><TT>_</TT><TT>graph</TT> has the format
<TT>"</TT><I>display-name</I> <I>geometry</I><TT>"</TT>,
where <I>display-name</I> is the name of the X-windows display to
connect to, and <I>geometry</I> is a standard X-windows geometry
specification. The two components are separated by a space. Either can
be omitted, or both. Examples:
<DL COMPACT=compact>
<DT>
<TT>open</TT><TT>_</TT><TT>graph "foo:0"</TT><DD>
connects to the display <TT>foo:0</TT> and creates a window with the default geometry
<DT><TT>open</TT><TT>_</TT><TT>graph "foo:0 300x100+50-0"</TT><DD>
connects to the display <TT>foo:0</TT> and creates a window 300 pixels wide
by 100 pixels tall, at location (50,0)
<DT><TT>open</TT><TT>_</TT><TT>graph " 300x100+50-0"</TT><DD>
connects to the default display and creates a window 300 pixels wide
by 100 pixels tall, at location (50,0)
<DT><TT>open</TT><TT>_</TT><TT>graph ""</TT><DD>
connects to the default display and creates a window with the default
geometry.
</DL>
</BLOCKQUOTE>
<FONT COLOR=purple>Windows:</FONT>
<BLOCKQUOTE>
This library is available only under the toplevel application
<TT>ocamlwin.exe</TT>. Before using it, the Caml part of this library must be
loaded in-core, either by typing
<PRE>
#load "graphics.cmo";;
</PRE>
in the input windows or by using the ``Load'' entry of the ``File''
menu.
</BLOCKQUOTE>The screen coordinates are interpreted as shown in the figure below.
Notice that the coordinate system used is the same as in mathematics:
<I>y</I> increases from the bottom of the screen to the top of the screen,
and angles are measured counterclockwise (in degrees).
Drawing is clipped to the screen.
<BR>
<BR>
<DIV ALIGN=center>
<IMG SRC="libgraph.gif">
</DIV>
<BR>
<H2>22.1 Module <TT>Graphics</TT>: machine-independent graphics primitives</H2><A NAME="s:Graphics"></A>
<A NAME="@manual828"></A><PRE>
exception Graphic_failure of string
</PRE>
<A NAME="@manual829"></A><BLOCKQUOTE>
Raised by the functions below when they encounter an error.
</BLOCKQUOTE>
<H3>Initializations </H3>
<PRE>
val open_graph: string -> unit
</PRE>
<A NAME="@manual830"></A><BLOCKQUOTE>
Show the graphics window or switch the screen to graphic mode.
The graphics window is cleared and the current point is set
to (0, 0). The string argument is used to pass optional
information on the desired graphics mode, the graphics window
size, and so on. Its interpretation is implementation-dependent.
If the empty string is given, a sensible default is selected.
</BLOCKQUOTE>
<PRE>
val close_graph: unit -> unit
</PRE>
<A NAME="@manual831"></A><BLOCKQUOTE>
Delete the graphics window or switch the screen back to
text mode.
</BLOCKQUOTE>
<PRE>
val clear_graph : unit -> unit
</PRE>
<A NAME="@manual832"></A><BLOCKQUOTE>
Erase the graphics window.
</BLOCKQUOTE>
<PRE>
val size_x : unit -> int
val size_y : unit -> int
</PRE>
<A NAME="@manual833"></A><A NAME="@manual834"></A><BLOCKQUOTE>
Return the size of the graphics window. Coordinates of the screen
pixels range over <CODE>0 .. size_x()-1</CODE> and <CODE>0 .. size_y()-1</CODE>.
Drawings outside of this rectangle are clipped, without causing
an error. The origin (0,0) is at the lower left corner.
</BLOCKQUOTE>
<H3>Colors </H3>
<PRE>
type color = int
</PRE>
<BLOCKQUOTE>
A color is specified by its R, G, B components. Each component
is in the range <CODE>0..255</CODE>. The three components are packed in
an <CODE>int</CODE>: <CODE>0xRRGGBB</CODE>, where <CODE>RR</CODE> are the two hexadecimal digits for
the red component, <CODE>GG</CODE> for the green component, <CODE>BB</CODE> for the
blue component.
</BLOCKQUOTE>
<PRE>
val rgb: int -> int -> int -> color
</PRE>
<A NAME="@manual835"></A><BLOCKQUOTE>
<CODE>rgb r g b</CODE> returns the integer encoding the color with red
component <CODE>r</CODE>, green component <CODE>g</CODE>, and blue component <CODE>b</CODE>.
<CODE>r</CODE>, <CODE>g</CODE> and <CODE>b</CODE> are in the range <CODE>0..255</CODE>.
</BLOCKQUOTE>
<PRE>
val set_color : color -> unit
</PRE>
<A NAME="@manual836"></A><BLOCKQUOTE>
Set the current drawing color.
</BLOCKQUOTE>
<PRE>
val black : color
val white : color
val red : color
val green : color
val blue : color
val yellow : color
val cyan : color
val magenta : color
</PRE>
<A NAME="@manual837"></A><A NAME="@manual838"></A><A NAME="@manual839"></A><A NAME="@manual840"></A><A NAME="@manual841"></A><A NAME="@manual842"></A><A NAME="@manual843"></A><A NAME="@manual844"></A><BLOCKQUOTE>
Some predefined colors.
</BLOCKQUOTE>
<PRE>
val background: color
val foreground: color
</PRE>
<A NAME="@manual845"></A><A NAME="@manual846"></A><BLOCKQUOTE>
Default background and foreground colors (usually, either black
foreground on a white background or white foreground on a
black background).
<CODE>clear_graph</CODE> fills the screen with the <CODE>background</CODE> color.
The initial drawing color is <CODE>foreground</CODE>.
</BLOCKQUOTE>
<H3>Point and line drawing </H3>
<PRE>
val plot : int -> int -> unit
</PRE>
<A NAME="@manual847"></A><BLOCKQUOTE>
Plot the given point with the current drawing color.
</BLOCKQUOTE>
<PRE>
val point_color : int -> int -> color
</PRE>
<A NAME="@manual848"></A><BLOCKQUOTE>
Return the color of the given point.
</BLOCKQUOTE>
<PRE>
val moveto : int -> int -> unit
</PRE>
<A NAME="@manual849"></A><BLOCKQUOTE>
Position the current point.
</BLOCKQUOTE>
<PRE>
val current_point : unit -> int * int
</PRE>
<A NAME="@manual850"></A><BLOCKQUOTE>
Return the position of the current point.
</BLOCKQUOTE>
<PRE>
val lineto : int -> int -> unit
</PRE>
<A NAME="@manual851"></A><BLOCKQUOTE>
Draw a line with endpoints the current point and the given point,
and move the current point to the given point.
</BLOCKQUOTE>
<PRE>
val draw_arc : int -> int -> int -> int -> int -> int -> unit
</PRE>
<A NAME="@manual852"></A><BLOCKQUOTE>
<CODE>draw_arc x y rx ry a1 a2</CODE> draws an elliptical arc with center
<CODE>x,y</CODE>, horizontal radius <CODE>rx</CODE>, vertical radius <CODE>ry</CODE>, from angle
<CODE>a1</CODE> to angle <CODE>a2</CODE> (in degrees). The current point is unchanged.
</BLOCKQUOTE>
<PRE>
val draw_ellipse : int -> int -> int -> int -> unit
</PRE>
<A NAME="@manual853"></A><BLOCKQUOTE>
<CODE>draw_ellipse x y rx ry</CODE> draws an ellipse with center
<CODE>x,y</CODE>, horizontal radius <CODE>rx</CODE> and vertical radius <CODE>ry</CODE>.
The current point is unchanged.
</BLOCKQUOTE>
<PRE>
val draw_circle : int -> int -> int -> unit
</PRE>
<A NAME="@manual854"></A><BLOCKQUOTE>
<CODE>draw_circle x y r</CODE> draws a circle with center <CODE>x,y</CODE> and
radius <CODE>r</CODE>. The current point is unchanged.
</BLOCKQUOTE>
<PRE>
val set_line_width : int -> unit
</PRE>
<A NAME="@manual855"></A><BLOCKQUOTE>
Set the width of points and lines drawn with the functions above.
Under X Windows, <CODE>set_line_width 0</CODE> selects a width of 1 pixel
and a faster, but less precise drawing algorithm than the one
used when <CODE>set_line_width 1</CODE> is specified.
</BLOCKQUOTE>
<H3>Text drawing </H3>
<PRE>
val draw_char : char -> unit
val draw_string : string -> unit
</PRE>
<A NAME="@manual856"></A><A NAME="@manual857"></A><BLOCKQUOTE>
Draw a character or a character string with lower left corner
at current position. After drawing, the current position is set
to the lower right corner of the text drawn.
</BLOCKQUOTE>
<PRE>
val set_font : string -> unit
val set_text_size : int -> unit
</PRE>
<A NAME="@manual858"></A><A NAME="@manual859"></A><BLOCKQUOTE>
Set the font and character size used for drawing text.
The interpretation of the arguments to <CODE>set_font</CODE> and
<CODE>set_text_size</CODE> is implementation-dependent.
</BLOCKQUOTE>
<PRE>
val text_size : string -> int * int
</PRE>
<A NAME="@manual860"></A><BLOCKQUOTE>
Return the dimensions of the given text, if it were drawn with
the current font and size.
</BLOCKQUOTE>
<H3>Filling </H3>
<PRE>
val fill_rect : int -> int -> int -> int -> unit
</PRE>
<A NAME="@manual861"></A><BLOCKQUOTE>
<CODE>fill_rect x y w h</CODE> fills the rectangle with lower left corner
at <CODE>x,y</CODE>, width <CODE>w</CODE> and height <CODE>h</CODE>, with the current color.
</BLOCKQUOTE>
<PRE>
val fill_poly : (int * int) array -> unit
</PRE>
<A NAME="@manual862"></A><BLOCKQUOTE>
Fill the given polygon with the current color. The array
contains the coordinates of the vertices of the polygon.
</BLOCKQUOTE>
<PRE>
val fill_arc : int -> int -> int -> int -> int -> int -> unit
</PRE>
<A NAME="@manual863"></A><BLOCKQUOTE>
Fill an elliptical pie slice with the current color. The
parameters are the same as for <CODE>draw_arc</CODE>.
</BLOCKQUOTE>
<PRE>
val fill_ellipse : int -> int -> int -> int -> unit
</PRE>
<A NAME="@manual864"></A><BLOCKQUOTE>
Fill an ellipse with the current color. The
parameters are the same as for <CODE>draw_ellipse</CODE>.
</BLOCKQUOTE>
<PRE>
val fill_circle : int -> int -> int -> unit
</PRE>
<A NAME="@manual865"></A><BLOCKQUOTE>
Fill a circle with the current color. The
parameters are the same as for <CODE>draw_circle</CODE>.
</BLOCKQUOTE>
<H3>Images </H3>
<PRE>
type image
</PRE>
<BLOCKQUOTE>
The abstract type for images, in internal representation.
Externally, images are represented as matrices of colors.
</BLOCKQUOTE>
<PRE>
val transp : color
</PRE>
<A NAME="@manual866"></A><BLOCKQUOTE>
In matrices of colors, this color represent a ``transparent''
point: when drawing the corresponding image, all pixels on the
screen corresponding to a transparent pixel in the image will
not be modified, while other points will be set to the color
of the corresponding point in the image. This allows superimposing
an image over an existing background.
</BLOCKQUOTE>
<PRE>
val make_image : color array array -> image
</PRE>
<A NAME="@manual867"></A><BLOCKQUOTE>
Convert the given color matrix to an image.
Each sub-array represents one horizontal line. All sub-arrays
must have the same length; otherwise, exception <CODE>Graphic_failure</CODE>
is raised.
</BLOCKQUOTE>
<PRE>
val dump_image : image -> color array array
</PRE>
<A NAME="@manual868"></A><BLOCKQUOTE>
Convert an image to a color matrix.
</BLOCKQUOTE>
<PRE>
val draw_image : image -> int -> int -> unit
</PRE>
<A NAME="@manual869"></A><BLOCKQUOTE>
Draw the given image with lower left corner at the given point.
</BLOCKQUOTE>
<PRE>
val get_image : int -> int -> int -> int -> image
</PRE>
<A NAME="@manual870"></A><BLOCKQUOTE>
Capture the contents of a rectangle on the screen as an image.
The parameters are the same as for <CODE>fill_rect</CODE>.
</BLOCKQUOTE>
<PRE>
val create_image : int -> int -> image
</PRE>
<A NAME="@manual871"></A><BLOCKQUOTE>
<CODE>create_image w h</CODE> returns a new image <CODE>w</CODE> pixels wide and <CODE>h</CODE>
pixels tall, to be used in conjunction with <CODE>blit_image</CODE>.
The initial image contents are random, except that no point
is transparent.
</BLOCKQUOTE>
<PRE>
val blit_image : image -> int -> int -> unit
</PRE>
<A NAME="@manual872"></A><BLOCKQUOTE>
<CODE>blit_image img x y</CODE> copies screen pixels into the image <CODE>img</CODE>,
modifying <CODE>img</CODE> in-place. The pixels copied are those inside the
rectangle with lower left corner at <CODE>x,y</CODE>, and width and height
equal to those of the image. Pixels that were transparent in
<CODE>img</CODE> are left unchanged.
</BLOCKQUOTE>
<H3>Mouse and keyboard events </H3>
<PRE>
type status =
{ mouse_x : int; (* X coordinate of the mouse *)
mouse_y : int; (* Y coordinate of the mouse *)
button : bool; (* true if a mouse button is pressed *)
keypressed : bool; (* true if a key has been pressed *)
key : char } (* the character for the key pressed *)
</PRE>
<BLOCKQUOTE>
To report events.
</BLOCKQUOTE>
<PRE>
type event =
Button_down (* A mouse button is pressed *)
| Button_up (* A mouse button is released *)
| Key_pressed (* A key is pressed *)
| Mouse_motion (* The mouse is moved *)
| Poll (* Don't wait; return immediately *)
</PRE>
<BLOCKQUOTE>
To specify events to wait for.
</BLOCKQUOTE>
<PRE>
val wait_next_event : event list -> status
</PRE>
<A NAME="@manual873"></A><BLOCKQUOTE>
Wait until one of the events specified in the given event list
occurs, and return the status of the mouse and keyboard at
that time. If <CODE>Poll</CODE> is given in the event list, return immediately
with the current status. If the mouse cursor is outside of the
graphics window, the <CODE>mouse_x</CODE> and <CODE>mouse_y</CODE> fields of the event are
outside the range <CODE>0..size_x()-1, 0..size_y()-1</CODE>. Keypresses
are queued, and dequeued one by one when the <CODE>Key_pressed</CODE>
event is specified.
</BLOCKQUOTE>
<H3>Mouse and keyboard polling </H3>
<PRE>
val mouse_pos : unit -> int * int
</PRE>
<A NAME="@manual874"></A><BLOCKQUOTE>
Return the position of the mouse cursor, relative to the
graphics window. If the mouse cursor is outside of the graphics
window, <CODE>mouse_pos()</CODE> returns a point outside of the range
<CODE>0..size_x()-1, 0..size_y()-1</CODE>.
</BLOCKQUOTE>
<PRE>
val button_down : unit -> bool
</PRE>
<A NAME="@manual875"></A><BLOCKQUOTE>
Return <CODE>true</CODE> if the mouse button is pressed, <CODE>false</CODE> otherwise.
</BLOCKQUOTE>
<PRE>
val read_key : unit -> char
</PRE>
<A NAME="@manual876"></A><BLOCKQUOTE>
Wait for a key to be pressed, and return the corresponding
character. Keypresses are queued.
</BLOCKQUOTE>
<PRE>
val key_pressed : unit -> bool
</PRE>
<A NAME="@manual877"></A><BLOCKQUOTE>
Return <CODE>true</CODE> if a keypress is available; that is, if <CODE>read_key</CODE>
would not block.
</BLOCKQUOTE>
<H3>Sound </H3>
<PRE>
val sound : int -> int -> unit
</PRE>
<A NAME="@manual878"></A><BLOCKQUOTE>
<CODE>sound freq dur</CODE> plays a sound at frequency <CODE>freq</CODE> (in hertz)
for a duration <CODE>dur</CODE> (in milliseconds).
</BLOCKQUOTE>
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