Sam wrote:
> Apologies if this has been asked previously but I had no luck searching
> the archive.
nope, this is s new one.
> I am using FloatCanvas to construct a mapping tool and my
> world coordinates are in the projection I am using (NZTM). This is all
> working quite nicely but I wish to add scale and direction images such
> that they are placed using pixel coordinates.
That does make sense. It's interesting that I've never had the use case
myself yet.
> This is so they remain in
> place unscaled as the user pans and zooms. Is there a simple way of
> doing this? I have tried subclassing Bitmap (and creating a new
> PixelBitmap class) where I have edited the _Draw function to not scale
> the coordinates (pixel coordinates are passed in).
You'd think that would work, but...
I don't see the
> print message I put in the modified _Draw function and I don't get any
> error messages and when I zoomtofit everything disappears (obviously the
> pixel coords are still being treated as world coords, which is not what
> I want!!).
I thin the problem is that FloatCanvas doesn't try to draw objects that
aren't within the present view. It does that by checking if the bounding
box of the object overlaps with the windows, and it does that in world
coordinates.
This is a bit of a design error -- It would be better if the Canvas told
each object to draw, and the object itself would figure out whether to
draw or not, so you could have objects that would always be drawn.
You can't simple make the bounding box of your object huge, as the
bounding box is also used to determine the global bounding box (used for
zoom_to_fit, etc).
However for your use case, if you know the bounds of your map ahead of
time, you could set the BoundingBox of your object to the full extent
you need, then it would always have its _draw method called, and I think
your trick would work.
Another option is to make it a Grid object, and put it on the top of the
canvas with:
Canvas.GridOver = Grid
That feature is there so that you can draw a grid (or graticule) over
everything else, and it will always get drawn, without a bounding box
check. This isn't a grid, but it should work for you use case also. All
you need is an object with a _Draw method:
def _Draw(self, dc, Canvas):
do some drawing...
You've got the Canvas object, so you can get other attributes you may
need, like Canvas.
I've enclosed and example of that approach, along with the bitmap it needs.
Vitor Bosshard wrote:
> The canvas has PixelToWorld and WorldToPixel conversion functions.
>
> So, having your fixed pixel coords, you can just redraw your objects
> at the recalculated world coords whenever you pan or zoom.
I don't think the events are in place to be able to do that at the right
time.
-Chris
--
Christopher Barker, Ph.D.
Oceanographer
Emergency Response Division
NOAA/NOS/OR&R (206) 526-6959 voice
7600 Sand Point Way NE (206) 526-6329 fax
Seattle, WA 98115 (206) 526-6317 main reception
[email protected]
_______________________________________________
FloatCanvas mailing list
[email protected]
http://paulmcnett.com/cgi-bin/mailman/listinfo/floatcanvas
