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This is a "rough" document, but hopefully if you are interested in
adding a new paint operator to xpaint, it should make a good
staring point.
The interface to add new functions is as follows, all operations have
two functions named (where OP == Function name, ## == concatination):
void * OP ## Add(Widget w)
void OP ## Remove(Widget w, void *local)
Thus for the Pencil operation you have a PencilAdd() and PencilRemove()
function. Then what is needed is add a two lines to Operation.c, one
of GENERATE_OP( OP ), and a entry in the iconList[] table for the icon
that is displayed for the operation.
Your Add method is expected to return a pointer to whatever local
instance information that your operator might need to keep track of,
which is the argument into the Remove method. Also, usually I
use this data pointer are the information to pass into the event
methods as well.
Events handlers are added using the:
OpAddEventHandler(Widget, surface, mask, flag, function, data)
and OpRemoveEventHandler() is used to remove them. The Widget
argument should be the same ass the Widget passed into the add
function. The surface argument is weather you want events on either
the Window or the Pixmap, or both (you still are required to update
the Window if you arn't zoomed).
The first thing your operator should do before it changes the drawable
is call UndoStart{Point,Rectangle}, which will cause a new undo
buffer to be allocated for your operator.
Operators are passed an info structure, important parts are:
isFat Boolean
-- the XtWindow() is zoomed, you should only
draw on the window if you know how, when
this is set.
surface OpSurface == enum { opPixmap, opWindow }
-- what surface you are being called with
either the backing store pixmap or the
actuall window
drawable Drawable (either the window or pixmap)
-- what the drawable ID is, this in only valid
after the call to UndoStart()
filled_gc GC
-- the graphic context you should use for
all your drawing operations.
x, y int
-- The x and y position of the event,
these may be in the zoomed coordinate
on the Window, while they will always
be the real x, y for the Pixmap.
realX, realY int
-- The real x and y position of the event, if
gridding is on x,y is modified by the gridding
factor. This only should be used in rare cases
where it is non-sensical to pay attention to the
grid factor (ie flood fill).
zoom int
-- the current zoom factor, if isFat is True.
The XtNcompress value for the paint widet controlles wheather
or not motion events are compressed into a single event if
possible. Thus:
XtVaSetValues(w, XtNcompress, False, NULL);
says that your operator is interested in all motion events
(ie. the pencil, or paint brush).
Generally, if you look at the operators that I have
provided there is probably an example of every attrocity that
I might be able to think of using the above information.
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