Subversion Repositories or1k

                        MINI-X TUTORIAL
                        David I. Bell
                        19 May 91

This is a simple tutorial on using the mini-X graphics system.  Much of this
is a lot easier to understand if you are familiar to X.  I am not going to
try to explain every concept in detail here, nor how to put it all together
to make really fancy programs.  Instead, I am only going to tell you just
enough to let you make some simple graphics programs which work.  Experience
with simple test programs will enable you to build much fancier graphics
programs much easier than trying to decipher what I could tell you.

I am assuming that you basically know what a screen, pixels, colors,
keyboards, mice, buttons, and windows are.  However, you probably don't
know exactly what the properties of windows in this system are.  Also, you
might not know two other concepts which are important here, which are
graphics contexts and events.  So these things will be explained in this
tutorial.


WINDOWS

Windows are rectangular areas which can be drawn into.  Windows have a
position, specified by the x and y coordinates of their upper left corners,
and also a size, specified by their width and height.  Windows are arranged
in a tree structure, with the parent windows controlling the child windows.
The top of the tree is known as the root window.  The root window is always
present, and represents the total screen area.

Each child window is clipped by its parent window.  This means that a window
can be very large, but the only part of the window that can ever be seen is
the part which shows through its parent window.  This applies recursively,
so that all of the parents of a window limit its visibility.  The position
of a window is specified relative to its parent, and not absolutely.  This
means that for example, when a window is moved, then all of its children will
move with it.  The position of a window can be negative.

Windows which have the same parent can clip each other.  That is, there is a
defined order among the children of a window as to which is more important.
If two sibling windows overlap, then the more important window will be visible
in preference to the less important window.  The precedence of visibility
of siblings can be dynamically adjusted.  Clipping can also occur on a window
by earlier siblings of any of the window's parents.

Windows can be mapped or unmapped.  Unmapped windows are not visible, and
cause no events.  They can be thought of as "in storage" or offscreen.
When a window is mapped, then it can become visible on the screen.  Children
of an unmapped window are implicitly also unmapped.  So a window is not
visible until it and all of its parents are mapped.  A newly created window
starts off unmapped.

Windows have a background color.  A newly mapped window is filled with its
background color.  Clearing the window later, or having obscured portions
of the window become visible again, will fill the region with the background.
The client program can then draw into the window to make it look correct.

Windows may have a border.  A border is a set of rectangles adjacent to the
four sides of the window which is drawn in a specified color, with a
specified width.  This makes pretty lines around the window, for example.
The border cannot be drawn in by the program.  Borders are optional, so
that a window with a border width of zero has no border at all.  Borders
are "around" the window, so that they do not affect the coordinates of the
window.  Whether or not a window has borders, its position determines the
location of the upper left corner which can be drawn into.

Windows can have a cursor associated with them.  The graphics server tracks
the location of the mouse, and maintains the position of a graphics cursor
on the screen.  This cursor can automatically change its shape and colors as
it moves between different windows.  The use of different cursors for different
windows can be used to provide a powerful clue to the user as to what will
happen if a mouse button is pressed in a window.  Newly created windows
inherit the same cursor as their parent.

There are two types of windows, input-output and input-only windows.
Input-output windows are normal windows which are visible and can be drawn
into.  Input-only windows are invisible, have no border, and cannot be
drawn into.  Their purpose is to catch events, and to enable the cursor
to be changed in different regions of a visible window.  The only children
of input-only windows are also input-only windows.

Windows are identified by integers called window ids.  The root window has
a constant window id value of GR_ROOT_WINDOW_ID.  The root window does not
need creating, and cannot be unmapped, moved, resized, or destroyed.
However, it can be drawn into and events can be delivered to it.  New windows
can be created from existing windows.  Their window ids are not constants,
but once created the window id remains until the window is destroyed.  Window
ids are not reused as windows are created and destroyed.


GRAPHICS CONTEXTS

When drawing objects such as lines, there are many parameters that can be
specified for the function call that affect the operation.  Besides the
minimum information needed for the function such as the endpoint coordinates,
there are extra parameters that are less important and less variable.
Examples of these extra parameters are color, width (thin or thick), style
(dashed, dotted), and drawing operation (setting, XORing).  Instead of
requiring the specifying of each of these extra parameters for every function
call, graphics contexts are used.  Graphics contexts are just a collection
of specific combinations of these extra parameters.  The many possible
extra parameters to each function are replaced by just one extra parameter,
which is the graphics context.

For example, instead of a function call like:
        drawline(window, x1, y1, x2, y2, color, width, style, operation);

you have instead
        drawline(window, gc, x1, y1, x2, y2),

where the graphics context contains within itself the parameters color, width,
style, and operation.

Graphics contexts are stored in the graphics server, and are identified by
unique numbers in a way similar to window ids.  Your program must allocate
graphic contexts, which then can be used in drawing functions.  A newly
allocated graphics context is supplied with default parameters, such as a
foreground color of white, drawing operation of setting, and width of 0.
You can modify the parameters associated with the graphics context one by
one, by for example, setting the foreground color to black.

A single graphics context could be used for every drawing operation by
constantly setting the parameters associated with it to the values needed
for each drawing call.  But this is inefficient.  The reason that multiple
graphics contexts can be allocated is so that you can minimize the setting of
their parameters.  By presetting the parameters of several graphics contexts
to commonly used values in your program, you can avoid changing them later.
For example, you can call one graphics context white_gc, and another graphics
context black_gc, and then use the correct graphics context in the drawing
functions to draw in either black or white.

The parameters contained within a graphics context are currently the
following:

Drawing mode.
Specifies the operation performed when drawing each pixel.  One of:
        GR_MODE_SET     draw pixels as given (default)
        GR_MODE_XOR     draw pixels using XOR
        GR_MODE_OR      draw pixels using OR
        GR_MODE_AND     draw pixels using AND

Text font.
A small integer identifying the font for drawing text.  The first few are
built-in to the device driver, others must be loaded by the graphics server.
The default font is 0.

Foreground color.
The color that is used to draw almost all objects with, such as lines,
points, ellipses, text, bitmaps, and filled areas.  Default is white.

Background color.
The color used for some functions in addition to the foreground color.
For bitmaps and text, this is the color used for the zero bits.  The
default background color is black.  The drawing of this color can be
disabled by the next parameter.

UseBackground flag.
This is a boolean value which indicates whether or not the background
color is actually to be drawn for bitmaps, text, and the GrArea8 function.
The default is GR_TRUE.


EVENTS

Events are the way in which the graphics system notifies your program
of asychronous changes in the state of the screen, mouse, or keyboard.
Whenever the state changes, your program is notified of this change and
can act on it.  The word "event" is used both for the actual change
that took place, and also for the data that is returned to your program
which describes the change.

Events are generated for various different types of changes that may be useful
for your program to know.  Events directly related to the hardware are the
keyboard and mouse events.  Keyboard events are generated for each key which
is pressed (and released, if possible).  The event contains the character
which caused the event.  Mouse events are generated when a button on the
mouse is pressed or released, or when the mouse position moves.  The event
contains the buttons which are pressed, and the current position of the mouse.
Other events are more subtle, and are based on non-physical changes, such
as having the mouse move into or out of specific windows.

Events are generally tied to individual windows.  Your program can enable
or disable which kinds of events it wants for each window.  Part of the data
associated with an event is the window associated with the event.  For
example, if a key is pressed on the keyboard, the event for that key will
indicate which window that key is for.  You program can then act differently
for different windows.  Events which you have not indicated an interest in
are simply discarded.

The keyboard and mouse events can propagate upwards through the window tree
and be delivered to some parent window.  This occurs if the window does
not select for the event, but one of the parent windows does.  Part of the
information returned about these events is the window that accepted the event,
and also the original window which caused the event.  Therefore, your program
can determine which child window an event was for without having to select
for the event for each child.  Events other than keyboard and mouse events
never propagate.

The window that keyboard events are delivered to depends on the current
mouse position or on the "input focus".  The input focus is a way of
specifying that keyboard events are to be delivered to a particular window,
no matter where the mouse is currently pointing.  Your program can change
the input focus as desired.  If the input focus is set to the root window,
then the keyboard events will be delivered to the window which contains
the mouse pointer (or one of its parents).

Events are returned to your program as a structure containing the information
about the event.  This information is the event type, the window id which
the event is associated with, and other event-specific data.  Events are
stored in a queue, and are delivered to your program one by one as requested.
The order of the events is preserved.  Your program can either simply ask
for the next available event (waiting for one if none are yet available),
or it can check to see if an event is available without waiting.  The
delivering of events only occurs when you request an event.  So even though
events themselves are asychronous, the reading of them is synchronous.
There are no "interrupts" for events, you must explicitly ask for them.

The important thing about programming with events is that your program
should be written to run "upside-down".  That is, you do not have a main
routine which checks that the mouse has been moved, or the keyboard has
been typed on, or which window the mouse is in.  Instead, your main routine
just waits for an event, and then dispatches on its type and which window
it is for.  Generally, you must keep some state information to remember
what is happening in your program.  For example, if the user wants to click
the button in a window to indicate where some text should be inserted, then
your program cannot simply detect the mouse click, and then wait for the
text to be typed.  Instead, when the mouse is clicked, it should just
remember the position of the mouse and set a flag to indicate that text
typing is allowed,  When the keyboard event arrives, this saved information
then enables you to draw the text at the correct location.  Your program
basically becomes one large state machine.

One obscure event is the exposure event.  This is sent to your program when
a window requires redrawing.  Due to lack of memory space, the graphics server
does not attempt to save the data from the parts of windows which are
covered by other windows.  Therefore, when the obscured parts of the window
are uncovered, your program must be told to redraw those parts.  The exposure
event contains a rectangular area which requires drawing (which may in fact
be larger than the area which was actually uncovered).  Your program can
either just redraw that area, or if more convenient, redraw the whole window.
The area to be redrawn has already been cleared to the window's background
color.  When a window is mapped, an exposure event is sent for the window.
Therefore, you should not explicitly draw into a window when it is first
created and mapped, but should instead just wait for the exposure event, and
then draw it.  In this way, the code to draw the window only resides in one
place in your program, and you prevent redundant drawing of the window.
If you are drawing the complete window on all exposure events, then it
might be useful to use GrPeekEvent to examine the next event too.  If it
is also an exposure event for the same window, then you can read it by using
GrGetNextEvent, and thereby prevent redundant redrawing.  Of course, to
be able to redraw the window, you may need to save extra data in order to
regenerate the drawing commands.  (Pixmaps are one way of doing this in
the future, but they are not currently implemented.)

The following is a description of the various types of events which are
available, and (in parenthesis) the typedef name for the structure that
returns the event.  Each event has a type field, which can be used to
distinguish between the various events.  For details on the other data
within the structures, refer to graphics.h.  The typedef GR_EVENT is a
union which contains all of the possible event structures.


GR_EVENT_TYPE_NONE      (GR_EVENT)
        This indicates that no event has occurred.

GR_EVENT_TYPE_EXPOSURE  (GR_EVENT_EXPOSURE)
        This is generated when a window needs redrawing because it is either
        newly mapped, or has been uncovered by another window.  This returns
        the window id, and the x, y, width, and height of the area within
        the window which needs redrawing.

GR_EVENT_TYPE_BUTTON_DOWN       (GR_EVENT_BUTTON)
        This is generated when a button is pressed down on the mouse.
        This returns the window id which generated the event, the window id
        which actually contains the mouse, the current position of the mouse,
        the buttons which are currently down on the mouse, the buttons
        which were just pressed down, and the current modifier flags.

GR_EVENT_TYPE_BUTTON_UP         (GR_EVENT_BUTTON)
        This is generated when a button is released on the mouse.  This
        returns data similarly to button down.

GR_EVENT_TYPE_MOUSE_ENTER       (GR_EVENT_GENERAL)
        This is generated when the mouse enters a window.  This returns the
        window id which generated the event.

GR_EVENT_TYPE_MOUSE_EXIT        (GR_EVENT_GENERAL)
        This is generated when the mouse leaves a window.  This returns
        the window id which generated the event.

GR_EVENT_TYPE_MOUSE_MOTION      (GR_EVENT_MOUSE)
        Mouse motion is generated for every motion of the mouse, and is
        used to track the entire history of the mouse.  Mouse motion
        generates many events and causes lots of overhead.  This returns
        data similarly to mouse enter.

GR_EVENT_TYPE_MOUSE_POSITION    (GR_EVENT_MOUSE)
        Mouse position ignores the history of the motion, and only reports the
        latest position of the mouse by only queuing the latest such event for
        any single client (good for rubber-banding).  This returns data
        similarly to mouse enter.

GR_EVENT_TYPE_KEY_DOWN          (GR_EVENT_KEYSTROKE)
        This indicates that a key has been pressed on the keyboard.
        This returns the window id which generated the event, the window id
        which actually contains the pointer (if the pointer is outside of
        the event window, this will be the event window), the current position
        of the mouse, the current buttons on the mouse which are down, the
        current modifier flags, and the character which was typed.

GR_EVENT_TYPE_KEY_UP            (GR_EVENT_KEYSTROKE)
        This indicates that a key has been released on the keyboard.  This
        event is not necessarily available, and should not be depended on.
        This returns data similarly to key down.

GR_EVENT_TYPE_FOCUS_IN          (GR_EVENT_GENERAL)
        This indicates that the input focus has just changed to this window.
        This returns the window id which got focus.

GR_EVENT_TYPE_FOCUS_OUT         (GR_EVENT_GENERAL)
        This indicates that the input focus has just left this window.
        This returns the window id which lost focus.


To select for events, you use GrSelectEvents, and specify the window which
wants to receive the events, and also specify a mask indicating the events
you wish to receive.  The mask is the logical OR of individual bit values
representing the event types.  The mask names are the same as the event
names, except that the "_TYPE_" string is replaced by "_MASK_".  For
example, the mask associated with the event GR_EVENT_TYPE_FOCUS_IN is
GR_EVENT_MASK_FOCUS_IN.

If you select for both button down and button up events, then the mouse
will be implicitly "grabbed" when any button is pressed down in that window.
This means that the mouse position and button down and up events will be
delivered only to that window, and the cursor shape won't change, even if
the mouse leaves that window.  The implicit grabbing ends after the last
button is released.  While this grabbing occurs, the input focus is also
not changed as the mouse is moved.


MODIFIER AND MOUSE BUTTONS

Modifiers are the status of special keyboard shift-like keys.  The state
of these keys can be read as up or down, and don't generate any characters
by themselves.  These keys are for things like SHIFT, CTRL, and ALT.
They are returned as bit values OR'd together in various events.  Not all
of these modifiers may be implemented.  The GrGetScreenInfo function returns
the modifiers that are implemented.  The following modifiers are defined:

        GR_MODIFIER_SHIFT       shift key is down
        GR_MODIFIER_CTRL        ctrl key is down
        GR_MODIFIER_META        meta (or ALT) key is down
        GR_MODIFIER_ANY         any of the modifiers is down


The mouse button state are returned as bit values OR'd together in various
events.  Not all of these buttons may be implemented.  The GrGetScreenInfo
function returns the buttons that are implemented.  The following mouse
buttons are defined:

        GR_BUTTON_1             button 1 is down (left)
        GR_BUTTON_2             button 2 is down (middle)
        GR_BUTTON_3             button 3 is down (right)
        GR_BUTTON_ANY           any of the buttons is down


BITMAPS

Bitmaps are defined as an array of GR_BITMAP values, which are unsigned shorts.
Each word is 16 bits, which specify foreground and background values, with 1
being foreground and 0 being background.  Higher order bits in the word
represent pixels to the left of the lower order bits.  Bitmaps have a width
and a height, measured in pixels.  The width does not need to be a multiple
of 16.  In this case, remaining bits in the last word of a row are unused,
so that each row starts with a new bitmap word.  The GR_BITMAP_SIZE macro can
be used to allocate the proper number of bitmap words for a bitmap, as in:

        GR_BITMAP_SIZE(width, height).

The symbol GR_MAX_BITMAP_SIZE is the number of bitmap words required for
the maximum sized cursor.


ERROR CODES

Calls to the graphics libraries may produce errors.  Most errors that
occur are due to specifying a window or graphics context which does not
exist, or attempting an operation which is illegal.  Many things are allowed
even if pointless, such as drawing outside of the window boundaries, or
while a window is not mapped.  The things which return errors are those
which definitely indicate a program bug, attempts to exceed the system
limits, or a fatal device error.

In order to be as efficient as possible, error codes are not returned by
individual function calls.  Instead, if a function fails, an error event
is generated which will eventually be noticed by the program at a possibly
much later time.  This allows many drawing requests to be sent at one time
without having to worry about the status of each one.

Error events are detected when the program checks for events, such as
by calling GrGetNextEvent.  At this point, if an error had occurred, a
special error handler routine is called to notice the error.  If the program
had not set up its own error handler, a default one is called which will
disconnect from the server, print out an indication of the error, and exit
the program.

The following is a list of the possible errors:

GR_ERROR_BAD_WINDOW_ID          the specified window id is unknown
GR_ERROR_BAD_GC_ID              the specified graphics context id is unknown
GR_ERROR_BAD_CURSOR_SIZE        the specified cursor is too large
GR_ERROR_MALLOC_FAILED          no more memory is available in the server
GR_ERROR_BAD_WINDOW_SIZE        the specified window size is illegal
GR_ERROR_KEYBOARD_ERROR         an error occurred reading from the keyboard
GR_ERROR_MOUSE_ERROR            an error occurred reading from the mouse
GR_ERROR_INPUT_ONLY_WINDOW      drawing was attempted in an input-only window
GR_ERROR_ILLEGAL_ON_ROOT_WINDOW an illegal operation was attempted on the root
GR_ERROR_TOO_MUCH_CLIPPING      complexity of windows exceeded clipping limits
GR_ERROR_SCREEN_ERROR           an error occurred talking to the screen driver
GR_ERROR_UNMAPPED_FOCUS_WINDOW  attempted to set focus to an unmapped window
GR_ERROR_BAD_DRAWING_MODE       illegal drawing mode specified for a GC


SCREEN PROPERTIES

You do not have to hard code the size of the screen or the number of colors
available in your program.  Instead, you can find this information out
dynamically after the connection is made to the graphics server, by using
the GrGetScreenInfo call.  This returns the above information, and in addition
returns the color values for black and white, the aspect ratio of pixels,
the number of built-in fonts available, and the modifiers and buttons which
are available.  The aspect ratio is useful for drawing objects which need
to be scaled correctly, such as circles.  The aspect ratio is the quotient
of xdpcm and ydpcm, which are integer values.


typedef struct {
        GR_SIZE         rows;           /* number of rows on screen */
        GR_SIZE         cols;           /* number of columns on screen */
        GR_SIZE         xdpcm;          /* dots/centimeter in x direction */
        GR_SIZE         ydpcm;          /* dots/centimeter in y direction */
        GR_COLOR        maxcolor;       /* maximum legal color value */
        GR_COLOR        black;          /* the color black */
        GR_COLOR        white;          /* the color white */
        GR_COUNT        fonts;          /* number of built-in fonts */
        GR_BUTTON       buttons;        /* buttons which are implemented */
        GR_MODIFIER     modifiers;      /* modifiers which are implemented */
} GR_SCREEN_INFO;


INCLUDE FILE AND GRAPHICS LIBRARY

To use the graphics server, your program must include "graphics.h".
This should be put into /usr/include, so that your program simply has
the following line at the top:
        #include <graphics.h>

Including this file gives you all of the definitions you need to use the
graphics library.  These are the typedefs, function declarations, event
structures, and various constants.

When loading your program, you need to load the graphics server into the
program by using the -lgraph option in the cc command.  For example, if
your program is called myprog, then you could build it using the following:
        cc -o myprog myprog.c -lgraph


TYPEDEFS

The following is a list of the typedefs in the include file, and a short
description of their purpose.  Refer to their definitions in graphics.h
to find out what their actual C base type is.  Most are shorts, unsigned
shorts, or longs.

GR_COORD        coordinate value (x, y locations, signed)
GR_SIZE         size value (widths, heights, signed)
GR_COUNT        number of items (signed)
GR_COLOR        full color value (32 bit value for full generality)
GR_COLOR8       eight bit color value (8 bit value for efficient storage)
GR_BITMAP       bitmap unit (single words of 16 bits for bitmaps)
GR_MODE         drawing mode (setting, xoring, anding, oring)
GR_CHAR         text character (normal chars)
GR_ID           resource ids (window, graphics context, pixmap)
GR_DRAW_ID      drawable id (window, pixmap)
GR_WINDOW_ID    window id (identifies individual window)
GR_PIXMAP_ID    pixmap id (identifies individual pixmaps, not yet used)
GR_GC_ID        graphics context id (identifies indiviual graphics contexts)
GR_FONT         font number (identifies individual fonts, first few built-in)
GR_BOOL         boolean value (GR_TRUE or GR_FALSE)
GR_FUNC         function codes (not for clients to use)
GR_ERROR        error value (reasons for graphics calls to fail)
GR_EVENT_TYPE   event types (identifies the type of event)
GR_BUTTON       button flags (which mouse buttons are depressed)
GR_MODIFIER     modifier flags (CTRL, SHIFT, etc)
GR_EVENT_MASK   event masks (mask values corresponding to event types)
GR_FUNC_NAME    function name (for error reporting)
GR_ERROR_FUNC   error function (for defining error handlers)


The following typedefs may be useful to your program.  None of the library
functions (currently) accept any of these structures as arguments, except
for the GrPoly and GrFillPoly routines, which use GR_POINT.


typedef struct {
        GR_COORD        x;              /* x coordinate */
        GR_COORD        y;              /* y coordinate */
} GR_POINT;

typedef struct {
        GR_COORD        x1;             /* x coordinate of first point */
        GR_COORD        y1;             /* y coordinate of first point */
        GR_COORD        x2;             /* x coordinate of second point */
        GR_COORD        y2;             /* y coordinate of second point */
} GR_LINE;

typedef struct {
        GR_COORD        x;              /* x coordinate of center */
        GR_COORD        y;              /* y coordinate of center */
        GR_SIZE         rx;             /* radius in x direction */
        GR_SIZE         ry;             /* radius in y direction */
} GR_ELLIPSE;

typedef struct {
        GR_COORD        x;              /* x coordinate of top left corner */
        GR_COORD        y;              /* y coordinate of top left corner */
        GR_SIZE         width;          /* width of rectangle */
        GR_SIZE         height;         /* height of rectangle */
} GR_RECT;


LIMITS

The coordinate system is limited to integers in the range GR_COORD_MIN
to GR_COORD_MAX.  This is -32768 to 32767, and fits in a short.

The maximum size of a cursor definition is GR_MAX_CURSOR_SIZE, which is
16 pixels by 16 pixels.

The complexity of overlapping windows is limited to GR_MAX_CLIPRECTS regions,
which is 200.  Each window which overlaps another requires another 1 to 4
regions depending on its position and size.


GRAPHICS CALLS


int
GrOpen()
Open a connection to the graphics server.  This must be the first graphics
function used by your program.  Currently, this sets the screen into
graphics mode.  Returns zero if successful, -1 on failure.


void
GrClose()
Close the connection to the graphics server, first flushing any graphics
calls that have been buffered.  Currently, this sets the screen back into
text mode.  This (currently) should be called before your program exits,
otherwise the screen will be left in graphics mode.  If this occurs, you
can run the 'tm' program to reset the terminal to text mode.


GR_ERROR_FUNC
GrSetErrorHandler(func)
        GR_ERROR_FUNC   func;           /* function to handle errors */
Set an error handling routine, which will be called on any errors from
the server (when events are asked for by the client).  If zero is given,
then a default routine will be used which will describe the error and exit.
Returns the previous error handler (0 if none).  When an error occurs,
the error handling function is called with the following parameters:
GR_ERROR, GR_FUNC_NAME, and GR_ID.  These are the error code, the name
of the function which failed, and a resource id (0 if not meaningful).
The error routine can return if desired, but without corrective action
new errors will probably occur soon.


void
GrGetScreenInfo(sip)
        GR_SCREEN_INFO  *sip;           /* location to return info into */
Return useful information about the screen.  This information returned
has been documented above.


void
GrGetFontInfo(font, fip)
        GR_FONT         font;           /* font number */
        GR_FONT_INFO    *fip;           /* address of font info */
Return useful information about the specified font number.  This information
is the font number, the height of the font, the maximum width of any
character in the font, the height of the baseline, a flag indicating whether
or not the font is fixed-width, and a table of the individual widths of each
character in the font.  If the font is unknown, the returned font number is
set to zero and the remainder of the information is undefined.  Refer to
graphics.h for a definition of the fields of GR_FONT_INFO.


void
GrGetGCInfo(gc, gcip)
        GR_GC_ID        gc;             /* graphics context */
        GR_GC_INFO      *gcip;          /* address of graphics context info */
Return useful information about the specified graphics context.  This
information is the graphics context id, the current font, the foreground
and background colors, and so on.  If the graphics context is unknown,
the returned id is 0, and the other information is undefined.  Refer to
graphics.h for a definition of the fields of GR_GC_INFO.


void
GrGetGCTextSize(gc, cp, len, retwidth, retheight, retbase)
        GR_GC_ID        gc;             /* graphics context containing font */
        GR_CHAR         *cp;            /* address of text string */
        GR_SIZE         len;            /* length of text string */
        GR_SIZE         *retwidth;      /* returned width of string */
        GR_SIZE         *retheight;     /* returned height of string */
        GR_SIZE         *retbase;       /* returned height of baseline */
Return the size of a text string for the font in a graphics context.
This is the width of the string, the height of the string, and the height
above the bottom of the font of the baseline for the font.  The returned
sizes are in pixels.


void
GrGetNextEvent(ep)
        GR_EVENT        *ep;            /* address where event is returned */
Return the next event from the event queue, waiting for it if necessary.
If a graphics error had occurred, the error handler will be called at this
point.  This routine first flushes any buffered graphics commands.  The
GR_EVENT is a union of all the possible events.  The type field of the union
indicates which of the possible events took place, and then the correct
element of the union can be used to access that particular event type's data.


void
GrCheckNextEvent(ep)
        GR_EVENT        *ep;            /* address where event is returned */
Return the next event from the event queue if one is ready.
If one is not ready, then the event type GR_EVENT_TYPE_NONE is returned.
Therefore, this routine never blocks.  This routine first flushes any
buffered graphics commands.


void
GrPeekEvent(ep)
        GR_EVENT        *ep;            /* address where event is returned */
Return the next event from the event queue if one is ready, without removing
it from the queue.  If one is not ready, then the type GR_EVENT_TYPE_NONE
is returned.  This routine never blocks.  This routine first flushes any
buffered graphics commands.


void
GrSelectEvents(wid, eventmask)
        GR_WINDOW_ID    wid;            /* window id */
        GR_EVENT_MASK   eventmask;      /* mask of events wanted */
Select events for a window for this client.  The events are a bitmask
specifying the events desired for this window.  This totally replaces
any previously selected event mask for the window.


GR_WINDOW_ID
GrNewWindow(parent, x, y, width, height, bordersize, background, bordercolor)
        GR_WINDOW_ID    parent;         /* parent id */
        GR_COORD        x;              /* x position relative to parent */
        GR_COORD        y;              /* y position relative to parent */
        GR_SIZE         width;          /* width */
        GR_SIZE         height;         /* height */
        GR_SIZE         bordersize;     /* size of border */
        GR_COLOR        background;     /* background color */
        GR_COLOR        bordercolor;    /* border color */
Allocate a new input-output window which is a child of the specified window.
A new top-level window is made by specifying a parent of GR_ROOT_WINDOW_ID.
The x and y position is the upper left corner of the window, relative to
the parent's upper left corner.  These corners are only for the drawable
area of the windows, so that the border does not affect the position.  An
input-output window cannot be made as a child of an input-only window.  The
new window starts off unmapped, and must be mapped before it can be seen.
The new window inherits the cursor of the parent window, and initially is
set to select no events.  This routine returns the window id of the window
which can be used in other calls.


GR_WINDOW_ID
GrNewInputWindow(parent, x, y, width, height)
        GR_WINDOW_ID    parent;         /* parent id */
        GR_COORD        x;              /* x position relative to parent */
        GR_COORD        y;              /* y position relative to parent */
        GR_SIZE         width;          /* width */
        GR_SIZE         height;         /* height */
Allocate a new input-only window which is a child of the specified window.
An input-only window is invisible, and cannot be drawn into.  It's only
purposes are that it can select events, and can have it's own cursor.  The
new window starts off unmapped, and must be mapped before it is effective.
The new window inherits the cursor of the parent window, and initially is
set to select no events.  This routine returns the window id of the window
which can be used in other calls.


void
GrDestroyWindow(wid)
        GR_WINDOW_ID    wid;            /* window to destroy */
This unmaps and then destroys the specified window, and all of its children.
The root window cannot be destroyed.  After destroying a window, you must be
careful about handling events which refer to the dead window, but which have
not been read yet.


void
GrGetWindowInfo(wid, wip)
        GR_WINDOW_ID    wid;            /* window id to find out about */
        GR_WINDOW_INFO  *wip;           /* location to return info into */
Return useful information about the specified window.  Refer to the
graphics.h include file for the definition of GR_WINDOW_INFO to see
what data is returned.  If the window id is not valid, an error is NOT
generated.  Instead, the wid value in the returned structure is set to
zero, and the other fields are not defined.


GR_GC_ID
GrNewGC()
Allocate a new graphics context with default parameters.  These defaults are:
background of black, foreground of white, font as font 0, and drawing mode
as setting.  This routine returns the id for the graphics context which can
be used in other calls.


GR_GC_ID
GrCopyGC(gc)
        GR_GC_ID        gc;             /* graphics context to copy */
Allocate a new graphics context which is a copy of another one.  The new
graphics context has the same parameter values as the old one, but is then
independent.  This routine returns the id for the graphics context which
can be used in other calls.


void
GrDestroyGC(gc)
        GR_GC_ID        gc;             /* graphics context to destroy */
Destroy an existing graphics context.


void
GrMapWindow(wid)
        GR_WINDOW_ID    wid;            /* window to be mapped */
Map the window to make it (and possibly its children) visible on the screen.
This paints the border and background of the window, and creates an
exposure event to tell the client to draw into it.


void
GrUnmapWindow(wid)
        GR_WINDOW_ID    wid;            /* window to be unmapped */
Unmap the window to make it and its children invisible on the screen.


void
GrRaiseWindow(wid)
        GR_WINDOW_ID    wid;            /* window to be raised */
Raise the window to the highest level among its siblings.  This means that
this window will be visible in preference to those siblings.  Siblings are
windows which have the same parent as this window.


void
GrLowerWindow(wid)
        GR_WINDOW_ID    wid;            /* window to be lowered */
Lower the window to the lowest level among its siblings.  This means that
this window will be covered by any siblings which overlap it.


void
GrMoveWindow(wid, x, y)
        GR_WINDOW_ID    wid;            /* window to be lowered */
        GR_COORD        x;              /* new relative x position */
        GR_COORD        y;              /* new relative y position */
Move the window to the specified position relative to its parent.


void
GrResizeWindow(wid, width, height)
        GR_WINDOW_ID    wid;            /* window to be lowered */
        GR_SIZE         width;          /* new width of window */
        GR_SIZE         height;         /* new height of window */
Resize the window to be the specified size.  Resizing of a window can
generate exposure events.


void
GrClearWindow(wid, exposeflag)
        GR_WINDOW_ID    wid;            /* window id */
        GR_BOOL         exposeflag;     /* nonzero to cause an exposure */
Clear the specified window by setting it to its background color.
If the exposeflag is nonzero, then this also creates an exposure
event for the window.


void
GrSetFocus(wid)
        GR_WINDOW_ID    wid;            /* window id */
Set the focus to a particular window.  This makes keyboard events only
visible to that window or children of it, depending on the pointer location.
Setting the focus window to the root window makes the input focus track
the pointer (which is the default).


void
GrSetBorderColor(wid, color)
        GR_WINDOW_ID    wid;            /* window id */
        GR_COLOR        color;          /* color for border */
Set the border of a window to the specified color.


void
GrSetCursor(wid, width, height, hotx, hoty, foreground, background,
        fgbitmap, bgbitmap)

        GR_WINDOW_ID    wid;            /* window id to set cursor for */
        GR_SIZE         width;          /* width of cursor */
        GR_SIZE         height;         /* height of cursor */
        GR_COORD        hotx;           /* relative x position of hot spot */
        GR_COORD        hoty;           /* relative y position of hot spot */
        GR_COLOR        foreground;     /* foreground color of cursor */
        GR_COLOR        background;     /* background color of cursor */
        GR_BITMAP       *fgbitmap;      /* foreground bitmap */
        GR_BITMAP       *bgbitmap;      /* background bitmap */
Specify a new cursor for a window.  This cursor will only be used within
that window, and by default for its new children.  The cursor is defined
by giving its width and height, its foreground and background colors, its
foreground and background bitmaps, and its "hot spot" position.  If a pixel
is specified for both the foreground and background bitmaps, then the
foreground has precedence.  The hot spot is an offset from the upper left
corner of the bitmap, and is the location in the cursor which is important.


void
GrMoveCursor(x, y)
        GR_COORD        x;              /* new x position of cursor */
        GR_COORD        y;              /* new y position of cursor */
Move the cursor to the specified absolute screen coordinates.
The coordinates are that of the defined hot spot of the cursor.
The cursor's appearance is changed to that defined for the window
in which the cursor is moved to.


void
GrFlush()
Flush the graphics buffer so that all previous requests will be executed.
This is only needed if you do not check events quickly and want to see the
results on the screen soon, since checking for events does an automatic flush.


void
GrSetGCForeground(gc, foreground)
        GR_GC_ID        gc;             /* graphics context id */
        GR_COLOR        foreground;     /* foreground color */
Set the foreground color in a graphics context.  The default is white.


void
GrSetGCBackground(gc, background)
        GR_GC_ID        gc;             /* graphics context id */
        GR_COLOR        background;     /* background color */
Set the background color in a graphics context.  The default is black.


void
GrSetGCUseBackground(gc, flag)
        GR_GC_ID        gc;             /* graphics context id */
        GR_BOOL         flag;           /* TRUE if background is drawn */
Set whether or not the background color is drawn in bitmaps and text.
This affects GrBitmap, GrArea8, and GrText.  The default is GR_TRUE.


void
GrSetGCMode(gc, mode)
        GR_GC_ID        gc;             /* graphics context id */
        GR_MODE         mode;           /* drawing mode */
Set the drawing mode in a graphics context.  The drawing mode is one of
GR_MODE_SET, GR_MODE_XOR, GR_MODE_AND, or GR_MODE_OR.  The default is
GR_MODE_SET.


void
GrSetGCFont(gc, font)
        GR_GC_ID        gc;             /* graphics context id */
        GR_FONT         font;           /* text font */
Set the font used for text drawing in a graphics context.
The font is a number identifying one of several fonts.
Font number 0 is always available, and is the default font.


void
GrLine(id, gc, x1, y1, x2, y2)
        GR_DRAW_ID      id;
        GR_GC_ID        gc;
        GR_COORD        x1;
        GR_COORD        y1;
        GR_COORD        x2;
        GR_COORD        y2;
Draw a line in the specified drawable using the specified graphics context.


void
GrRect(id, gc, x, y, width, height)
        GR_DRAW_ID      id;
        GR_GC_ID        gc;
        GR_COORD        x;
        GR_COORD        y;
        GR_SIZE         width;
        GR_SIZE         height;
Draw the boundary of a rectangle in the specified drawable using the
specified graphics context.


void
GrFillRect(id, gc, x, y, width, height)
        GR_DRAW_ID      id;
        GR_GC_ID        gc;
        GR_COORD        x;
        GR_COORD        y;
        GR_SIZE         width;
        GR_SIZE         height;
Fill a rectangle in the specified drawable using the specified graphics
context.  The boundary of this rectangle is identical to that drawn by
the GrRect function.


void
GrEllipse(id, gc, x, y, rx, ry)
        GR_DRAW_ID      id;
        GR_GC_ID        gc;
        GR_COORD        x;
        GR_COORD        y;
        GR_SIZE         rx;
        GR_SIZE         ry;
Draw the boundary of an ellipse in the specified drawable with
the specified graphics context.


void
GrFillEllipse(id, gc, x, y, rx, ry)
        GR_DRAW_ID      id;
        GR_GC_ID        gc;
        GR_COORD        x;
        GR_COORD        y;
        GR_SIZE         rx;
        GR_SIZE         ry;
Fill an ellipse in the specified drawable using the specified
graphics context.


void
GrBitmap(id, gc, x, y, width, height, bitmaptable)
        GR_DRAW_ID      id;
        GR_GC_ID        gc;
        GR_COORD        x;
        GR_COORD        y;
        GR_SIZE         width;
        GR_SIZE         height;
        GR_BITMAP       *bitmaptable;
Draw a rectangular area in the specified drawable using the specified
graphics context, as determined by the specified bit map.  This differs
from rectangle drawing in that the rectangle is drawn using the foreground
color and possibly the background color as determined by the bit map.
Bits which are 1 are the foreground, and bits which are 0 are the background.
Each row of bits is aligned to the next bitmap word boundary (so there can
be padding at the end of each row).  The background bit values are only
written if the usebackground flag is set in the GC.


void
GrArea8(id, gc, x, y, width, height, colortable)
        GR_DRAW_ID      id;
        GR_GC_ID        gc;
        GR_COORD        x;
        GR_COORD        y;
        GR_SIZE         width;
        GR_SIZE         height;
        GR_COLOR8       *colortable;
Draw a rectangular area in the specified drawable using the specified
graphics context.  This differs from rectangle drawing in that the
color values for each pixel in the rectangle are specified.  The color
values are estricted to 8 bit values.  The color table is indexed row by
row from left to right.  Table values whose color matches the background
color are only written if the usebackground flag is set in the GC.


void
GrReadArea8(id, x, y, width, height, colortable)
        GR_DRAW_ID      id;
        GR_COORD        x;
        GR_COORD        y;
        GR_SIZE         width;
        GR_SIZE         height;
        GR_COLOR8       *colortable;
Read the color values from the specified rectangular area of the specified
drawable into a supplied buffer.  If the drawable is a window which is
obscured by other windows, then the returned values will include the values
from the covering windows.  Regions outside of the screen boundaries, or
from unmapped windows will return black.


void
GrPoint(id, gc, x, y)
        GR_DRAW_ID      id;
        GR_GC_ID        gc;
        GR_COORD        x;
        GR_COORD        y;
Draw a point in the specified drawable using the specified graphics context.


void
GrPoly(id, gc, count, pointtable)
        GR_DRAW_ID      id;
        GR_GC_ID        gc;
        GR_COUNT        count;
        GR_POINT        *pointtable;
Draw a polygon in the specified drawable using the specified graphics
context.  The polygon is only complete if the first point is repeated at
the end.  Note: currently if the polygon crosses itself, and the drawing
mode is set to XOR, then the individual line segments will affect each
other.  The endpoints of the lines are correct, however.


void
GrFillPoly(id, gc, count, pointtable)
        GR_DRAW_ID      id;
        GR_GC_ID        gc;
        GR_COUNT        count;
        GR_POINT        *pointtable;
Draw a filled polygon in the specified drawable using the specified
graphics context.  The last point may be a duplicate of the first point,
but this is not required.  Note: currently only convex polygons are
filled properly.


void
GrText(id, gc, x, y, str, count)
        GR_DRAW_ID      id;
        GR_GC_ID        gc;
        GR_COORD        x;
        GR_COORD        y;
        GR_CHAR         *str;
        GR_COUNT        count;
Draw a text string at the specified location in the specified drawable
using the specified graphics context.  The background of the characters
are only drawn if the usebackground flag in the GC is set.


EXAMPLE PROGRAM

The following simple program opens the graphics, creates a window, prints
some text in it, waits for the mouse to be clicked in the window, then exits.


#include <stdio.h>
#include <graphics.h>

#define MARGIN  50                      /* margin around window */


main()
{
        GR_WINDOW_ID    wid;            /* window id */
        GR_GC_ID        gc;             /* graphics context id */
        GR_EVENT        event;          /* current event */
        GR_SCREEN_INFO  si;             /* screen information */

        if (GrOpen() < 0) {
                fprintf(stderr, "Cannot open graphics\n");
                exit(1);
        }

        GrGetScreenInfo(&si);

        wid = GrNewWindow(GR_ROOT_WINDOW_ID, MARGIN, MARGIN,
                si.cols - MARGIN * 2, si.rows - MARGIN * 2,
                1, si.black, si.white);

        GrSelectEvents(wid, GR_EVENT_MASK_BUTTON_DOWN | GR_EVENT_MASK_EXPOSURE);
        GrMapWindow(wid);
        gc = GrNewGC();

        while (1) {
                GrGetNextEvent(&event);
                switch (event.type) {
                        case GR_EVENT_TYPE_BUTTON_DOWN:
                                if (event.button.wid != wid)
                                        break;
                                GrClose();
                                exit(0);

                        case GR_EVENT_TYPE_EXPOSURE:
                                if (event.exposure.wid == wid)
                                        GrText(wid, gc, 50, 50, "EXIT", 4);
                                break;
                }
        }
}


For a more complete demonstration program, see the file "demo.c" in the
/usr/src/graphics/clients directory.