Re: a graphics issue I can not figure out

You are aware the coordinate origin (0,0)  is in the upper left corner,
(not lower left, as we manually draw grids),
 and that the y axis goes down as the value of y increases?


On Wed, Mar 4, 2020 at 6:58 PM Nathan smith <[email protected]> wrote:

> Hi Group,
>
> I have recently been playing around with the drawing tools available in
> wx python.
>
> My goal was to create a grid and then plot some lines upon it.
>
> I have got the grid working, but I can not seem to position a triangle
> correctly.
>
> Here is some code which I have explained best I can:
>
> Note in the below code the variable g just refers to a way I store
> global variables.
>
> class Mywin(wx.Frame):
>   def __init__(self, parent, title):
>
>    super(Mywin, self).__init__(parent, title = title,size = (350,250),
> style=wx.DEFAULT_FRAME_STYLE)
>    self.Maximize()
>    g.center_point=self.GetClientSize()
>    g.center_point=[g.center_point.x/2, g.center_point.y/2]
>
> # this is the screen where the graph is drawn. Called from a main menu
> hence the first line.
>
>   def graph(self):
>    self.mainpanel.Hide()
>    self.Bind(wx.EVT_PAINT, self.onpaint)
>    self.Bind(wx.EVT_KEY_DOWN, self.onKeyPress)
>    self.SetBackgroundColour('WHITE')
>    self.Layout()
>    self.Fit()
>    self.Show()
>    self.SetFocus()
>
> # the paint function. to give you an example of what is in the g.lines
> variable it is something like this:
>
> g.lines=[[[1, 1], [5, 1], wx.Colour(255, 0, 0, 255), 100], [[1, 1], [1,
> 5], wx.Colour(255, 0, 0, 255), 100], [[1, 5], [5, 1], wx.Colour(255, 0,
> 0, 255), 100]]
>
>   def onpaint(self, event):
>    self.dc = wx.PaintDC(self)
>    self.dc.Clear()
>    self.pen = wx.Pen(wx.BLACK_PEN)
>    self.dc.SetPen(self.pen)
>    p1=[g.center_point[0]-(38*6), g.center_point[1]-(38*6)]
>    p2=[g.center_point[0]+(38*5), g.center_point[1]-(38*6)]
>    for x in range(11):
>     self.dc.DrawLine(p1[0],p1[1],p2[0],p2[1])
>     p1 = [p1[0],p1[1]+38]
>     p2 = [p2[0],p2[1]+38]
>    p1=[g.center_point[0]-(38*6), g.center_point[1]-(38*6)]
>    p2=[g.center_point[0]-(38*6), g.center_point[1]+(38*5)]
>    for x in range(11):
>     self.dc.DrawLine(p1[0],p1[1],p2[0],p2[1])
>     p1 = [p1[0]+38,p1[1]]
>     p2 = [p2[0]+38,p2[1]]
>    bl=[g.center_point[0]-(38*6), g.center_point[1]-(38*6)] # this is the
> bottom left corner coordinates and from this we work out where the user
> selected the line to go. (lines are made by using the arrow keys and such.)
>
>    for x in g.lines:
>      self.pen.SetColour(wx.Colour(x[2]))
>      self.pen.SetStyle(x[3])
>      self.dc.DrawLine(bl[0]+(x[0][0]*38)+10, bl[1]+(x[0][1]*38)+10,
> bl[0]+(x[1][0]*38)+10, bl[1]+(x[1][1]*38)+10)
>
>
> When ever I do this using the coordinates specified, it always puts the
> triangle in the top left, rather than the bottom left.
>
> I am doing *38 to compensate for the pixel to cm conversion.
>
> then +10 because I have this weird feeling if I draw directly over the
> grid lines wx python will not show it?
>
>
> Any help here would be appreciated.
>
> thanks'
>
> Nathan
>
>
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