[Pythoncard-users] BitmapDrawing widget

[Kevin A. <al...@se...>]

I needed to get away from the television for a while last night, so I
started work on a BitmapDrawing widget for PythonCard. I stayed away from
the news coverage this morning as well to make a sample and put together
this rambling email. I still feel completely drained by the horrific attacks
on Tuesday, so I'm not getting much work done.

The first revision which is checked into cvs doesn't do much. It uses an
offscreen bitmap, supports setting the foregroundColor and backgroundColor,
plot(x, y), line(x1, y1, x2, y2), clear(), refresh(), autoRefresh attribute
(1 or 0), and drawText(aString, x, y); drawText uses the default font. All
the drawing and updating is brute force, it is unclear at this point what
optimizations can be made to speed up some operations.

The resourceEditor, Property Editor, and other parts of the framework don't
fully support the new widget.

One nice aspect of the widget is that it supports all the mouse events just
like the other PythonCard widgets. The doodle sample shows off just some of
these.

There are two samples, doodle and hopalong. Doodle just draws a pixel in the
current pen color while the mouse is down. Hopalong draws a mathematical
function on the screen based on the input values which can be set with the
fields at the top of the window. The drawing time is dramatically slower
when autoRefresh is true (roughly 3 - 4 times slower on my machine) and even
with autoRefresh off it can take 3.4 seconds on my AMD 1.2GHz machine to
draw 100,000 points. There is no way to cancel a drawing operation once it
is started (that is a later experiment), so be patient when drawing a large
number of points. The designs are often more interesting at the million
points or higher range. This is the same hopalong function used in one of
the turtle scripts.

The BitmapDrawing widget is experimental as are any samples that use it and
will likely change often for the next month or so; at this point I don't
even have a fixed set of design goals for the widget. I just wanted to get
something concrete into the framework to work with and help us generate
ideas.

I would like to strike a balance between ease of use, flexibility, and
speed. The current widget can be placed behind or overlapping any other
widgets, thus we can use a BitmapDrawing widget as our bitmap layer in
PythonCard probably with more flexibility than the bitmap drawing tools in
HyperCard. A separate tool will have to be provided to handle the user
interface manipulation of the widget bitmap contents like selection,
zooming, area fill, etc. I will convert the turtle sample to use the widget
sometime in the next month; eventually the turtle will just be part of the
basic PythonCard framework.

The BitmapDrawing widget is distinct from an object canvas where you can
select individual rectangles, lines, text, etc. and I expect that to be a
separate widget. Another library which people might want to look at is
PIDDLE http://piddle.sourceforge.net/ There is nothing that would prevent
doing drawing in PIDDLE and then placing the resulting bitmap into a
BitmapDrawing widget. If we want a unified drawing model that gives us the
best capabilities of PIDDLE and the underlying device contexts of
wxPython/wxWindows so that printing, drawing in PostScript, etc. are roughly
the same, that will need to be taken into account for the BitmapDrawing
widget.

One obvious problem I see with most of the current widgets is a lack of
transparency, which limits what we can do with overlapping widgets and
definitely limits the tricks that could be done with layering
BitmapDrawings. This might be a fundamental limitation of
wxPython/wxWindows.

I would like to support the Python Imaging Library, but am not sure whether
to wrap any of it or just leave its existing API exposed.

Anyway, please share your thoughts and ideas on what you would like to see
for bitmap graphics in PythonCard. You can start separate threads rather
than replying to this email if you want.

ka