plotting 2D images pixel by pixel

wxPython Users
1

Hello all,

I've browsed through the (behemoth!) wxWindows reference manual, I'm a bit
overwhelmed with the huge number of classes, and thus don't know how best to do
what I want. And that is, to have some simple bitmap/canvas item on which I
can plot points pixel by pixel... (just pretend I want to implement a fractal
viewer with wxPython) What is the most sensible way of doing this? So far I've
tried with a wxBitmap+wxMemoryDC, but, oh my, wxMemoryDC::DrawPoint() is
excruciatingly slow... surely something better exists?

···

--
"The higher we soar, the smaller we appear to those who cannot fly."
          -- Friedrich Wilhelm Nietsche

2

Standard approach is to simply update a bitmap (possibly stored as a Numeric Python array) and then blit the whole thing (or a sub-set) to the wxPaintDC. You can keep a mask in the bitmap (4-bytes/pixel) to allow for not over-drawing particular pixels. You will probably also want to use one of the "buffered" wxDC sub-classes to eliminate flicker.

BTW, when people actually wrote a fractal viewer way back when, here's what it looked like :slight_smile: :

    http://wiki.wxpython.org/index.cgi/WorkingWithThreads

We should really update that code one of these days, the wx code is written in a fairly primitive style :slight_smile: .

Enjoy,
Mike

Maciej Kalisiak wrote:

···

Hello all,

I've browsed through the (behemoth!) wxWindows reference manual, I'm a bit
overwhelmed with the huge number of classes, and thus don't know how best to do
what I want. And that is, to have some simple bitmap/canvas item on which I
can plot points pixel by pixel... (just pretend I want to implement a fractal
viewer with wxPython) What is the most sensible way of doing this? So far I've
tried with a wxBitmap+wxMemoryDC, but, oh my, wxMemoryDC::DrawPoint() is
excruciatingly slow... surely something better exists?

--
_______________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://members.rogers.com/mcfletch/

3

Maciej Kalisiak wrote:

Hello all,

I've browsed through the (behemoth!) wxWindows reference manual, I'm a bit
overwhelmed with the huge number of classes, and thus don't know how best to do
what I want. And that is, to have some simple bitmap/canvas item on which I
can plot points pixel by pixel... (just pretend I want to implement a fractal
viewer with wxPython) What is the most sensible way of doing this? So far I've
tried with a wxBitmap+wxMemoryDC, but, oh my, wxMemoryDC::DrawPoint() is
excruciatingly slow... surely something better exists?

There are some things in the pipe for 2.5 that should make raw bitmap access much faster... In the meantime I'd suggest using a wxImage with the SetRGB(x, y, r, g, b) method. It doesn't have to do any API calls to set the pixel and it can then be converted to a wxBitmap for drawing when you are ready.

···

--
Robin Dunn
Software Craftsman
http://wxPython.org Java give you jitters? Relax with wxPython!

4

Robin Dunn wrote:

> So far I've
> tried with a wxBitmap+wxMemoryDC, but, oh my, wxMemoryDC::DrawPoint() is
> excruciatingly slow... surely something better exists?
>
access much faster... In the meantime I'd suggest using a wxImage with
the SetRGB(x, y, r, g, b) method. It doesn't have to do any API calls
to set the pixel and it can then be converted to a wxBitmap for drawing
when you are ready.

If you still want to use a DC, try using the DC.DrawPointList() method.
It can draw a whole list (or any python sequence) a whole lot faster
than looping through your points one by one. It's demoed in the demo
under DrawXXXList.

-Chris

···

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