Canvas drawing problems

kewlar · October 31, 2008, 9:07am

I have tried to draw into wx.lib.plot canvas and I got now some problems to
solve

In my example left mouse button will draw rectangle, the rectangle will be
drawn onto plot.canvas using wx.ClientDC(), the problem here is that now
when I resize the application, plot will be drawn again over the rectangle.
I should maybe use wx.PaintDC with EVT_PAINT but I did not get it to work,
so in my example I include code with wx.ClientDC without EVT_PAINT.

Mouse motion will draw two lines onto wx.Screen just above cursor (that's
actually tracing crosshair in my app, but didn't want to include too much
code in my example so I did make it much simplier). Ofcourse when the
crosshair is drawn again, previous crosshair must be erased, but now when
erasing the previous crosshair using self.RefreshRect(rect_area), the
refreshing will also erase the rectangle which was drawn
(http://tinypic.com/view.php?pic=vn03k1&s=4), the refreshrect seem to behave
like evt_paint only in smaller area, so moving the rectangle into
plot.canvas EVT_PAINT could also solve this problem? Or would it be possible
to take "screenshot" of the area and then using that area somehow with the
refreshrect...

I would need two layers for drawing which would be put on plot.canvas, also
drawing directly to plot.canvas (like I'm already drawing the rectangle)
could be another solution.

To make it simple: I have two problems which I would like to solve
1. drawing the rectangle so that it won't be erased when resizing windows
(using evt_paint maybe?)
2. crosshair (no, not the cursor) erases drawed rectangle when it refresh
the screen using refreshrect, see http://tinypic.com/view.php?pic=vn03k1&s=4

my code: http://pastebin.com/m29371fc
and also below:

import wx
import wx.lib.plot as plot

class MyFrame(wx.Frame):
   def __init__(self):
      wx.Frame.__init__(self, None, id=-1, title="Graph display",
size=(480,300))
      main_panel = wx.Panel(self, -1)

      #data for the plot
      data = [[1,2],[2,0],[3,1],[4,3],[5,2]]
      line = plot.PolyLine(data, colour='red', width=1)

      #plot window & bindings
      self.plot_window = plot.PlotCanvas(main_panel, -1)
      gc = plot.PlotGraphics([line], 'y-axis', 'x-axis', 'Title')
      self.plot_window.Draw(gc)
      self.plot_window.canvas.Bind(wx.EVT_LEFT_DOWN, self.mouseleftdown)
      self.plot_window.canvas.Bind(wx.EVT_MOTION, self.mousemotion)

      #sizer & layouts
      vbox_sizer = wx.BoxSizer(wx.VERTICAL)
      vbox_sizer.Add(self.plot_window, 1, wx.EXPAND|wx.ALIGN_LEFT)
      main_panel.SetAutoLayout(True)
      main_panel.SetSizer(vbox_sizer)
      main_panel.Layout()

   def mouseleftdown(self, event):
      x, y = event.GetPosition()
      print "Left Mouse Down at Point:", x, y

      pdc = wx.ClientDC( self.plot_window.canvas )
      try: dc = wx.GCDC(pdc)
      except: dc = pdc

#rectangle
rect = wx.Rect(x,y, 150, 150)

      #pencil & brush - rectangle color
      r, g, b = (34, 34, 178)
      penclr = wx.Colour(r, g, b, wx.ALPHA_OPAQUE)
      brushclr = wx.Colour(r, g, b, 128)
      dc.SetPen(wx.Pen(penclr))
      dc.SetBrush(wx.Brush(brushclr))

      #drawing the rectangel
      dc.DrawRectangleRect(rect)

   def mousemotion(self, event):
      point_x, point_y = event.GetPosition()
      print "Right Mouse Down at Point:", point_x, point_y

#converts to screen coordinates because we're drawing to screendc
point_x, point_y = self.ClientToScreenXY(point_x, point_y)

#showing the drawn object above cursor so this example doesn't look
too confusing
point_y -= 100

      #clearing the screen where the crosshair was previously located
      try:
         self.RefreshRect(self.last_drawn_crosshair)
         self.Update()
      except:
         pass

      dc = wx.ScreenDC()
      pen = wx.Pen('#000000', 1, wx.SOLID)
      pen.SetCap(wx.CAP_BUTT)
      dc.SetPen(pen)

      #drawing two lines, " a crosshair"
      size = 10
      dc.DrawLine(point_x-size, point_y, point_x+size, point_y)
      dc.DrawLine(point_x, point_y-size, point_x, point_y+size)

      #remember the area where the lines was drawn, so we can clear the area
next time
      #converting coordinates back to client coords, because the refreshing
needs client coords.
      point_x, point_y = self.plot_window.ScreenToClientXY(point_x, point_y)
      self.last_drawn_crosshair = wx.Rect(point_x-size,point_y-size, size*2,
size*2)

app = wx.PySimpleApp()
MyFrame().Show()
app.MainLoop()

···

--
View this message in context: http://www.nabble.com/Canvas-drawing-problems-tp20262194p20262194.html
Sent from the wxPython-users mailing list archive at Nabble.com.

kewlar · October 31, 2008, 9:44am

so...I added EVT_PAINT to my plot and now the crosshair drawing is also
erasing the plot picture :o
you can add these 3lines to code to see its effect:

self.plot_window.canvas.Bind(wx.EVT_PAINT, self.onpaint)

def onpaint(self, event):
dc = wx.PaintDC(event.GetEventObject())

···

--
View this message in context: http://www.nabble.com/Canvas-drawing-problems-tp20262194p20262634.html
Sent from the wxPython-users mailing list archive at Nabble.com.

Chris_Barker1 · October 31, 2008, 6:40pm

Have you read these wiki pages:

http://wiki.wxpython.org/RecipesImagesAndGraphics

They may help you out.

But the broader question is: What are you trying to do? building it on wx.lib.plot may not be the best choice.

wx.lib.floatcanvas may be a better option, or even just doing it all yourself with DCs or GCs

-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

Chris.Barker@noaa.gov

Robin · November 1, 2008, 1:40am

kewlar wrote:

I have tried to draw into wx.lib.plot canvas and I got now some problems to
solve

In my example left mouse button will draw rectangle, the rectangle will be
drawn onto plot.canvas using wx.ClientDC(), the problem here is that now
when I resize the application, plot will be drawn again over the rectangle.
I should maybe use wx.PaintDC with EVT_PAINT but I did not get it to work,
so in my example I include code with wx.ClientDC without EVT_PAINT.

Mouse motion will draw two lines onto wx.Screen just above cursor (that's
actually tracing crosshair in my app, but didn't want to include too much
code in my example so I did make it much simplier). Ofcourse when the
crosshair is drawn again, previous crosshair must be erased, but now when
erasing the previous crosshair using self.RefreshRect(rect_area), the
refreshing will also erase the rectangle which was drawn
(http://tinypic.com/view.php?pic=vn03k1&s=4), the refreshrect seem to behave
like evt_paint only in smaller area,

Correct. It actually results in a EVT_PAINT event with the given rectangle (and any others since the last EVT_PAINT) used for the update region, which means that drawing in that paint event will be clipped to that region.

so moving the rectangle into
plot.canvas EVT_PAINT could also solve this problem? Or would it be possible
to take "screenshot" of the area and then using that area somehow with the
refreshrect...

Looking at PlotCanvas.OnPaint I see that it is using a buffered Dc, so all you should need to do is to draw your stuff on to the self._Buffer bitmap and then do a RefreshRect to get PlotCanvas to paint it. If needed you can force PllotCanvas to reinitialize its buffer by calling SendSizeEvent.

···

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

kewlar · November 3, 2008, 7:51am

Robin Dunn wrote:

Looking at PlotCanvas.OnPaint I see that it is using a buffered Dc, so
all you should need to do is to draw your stuff on to the self._Buffer
bitmap and then do a RefreshRect to get PlotCanvas to paint it. If
needed you can force PllotCanvas to reinitialize its buffer by calling
SendSizeEvent.

thx, drawing to self._Buffer with dc.MemoryDC solved my problem

···

--
View this message in context: http://www.nabble.com/Canvas-drawing-problems-tp20262194p20298460.html
Sent from the wxPython-users mailing list archive at Nabble.com.