Question

The following code demonstrates a problem with certain wx cursors on Windows (OSX cursors have a white outline)… namely, they are all black, and therefore completely invisible on a black background.

import wx
app = wx.PySimpleApp()
f = wx.Frame(None)
f.SetBackgroundColour(wx.Color(0))
f.SetCursor(wx.StockCursor(wx.CURSOR_CROSS))
f.Show()
app.MainLoop()

I wonder if anyone has found a way to patch the windows icons, or if there is a fix for it that I am unaware of.

The more specific problem I am having is that matplotlibs’ wx backend uses the wx.CURSOR_CROSS for zooming on imshow plots, which I am using to display images that are mostly black. I’ve yet to find a way to customize the cursors that mpl chooses, but I figured I’d pose the question while I dig.

Thanks,
Adam

Note: Using wxPython version 2.8.10.1 and matplotlib versions 0.99 and 1.0

PROGRESS:
I seem to be able to at least make my own cursor by doing the following, but I’m extremely frustrated to find that there is no way for me to include the color white anywhere. The documentation on this is horrendous.

import numpy as np
buf = np.ones((16,16,3), dtype='uint8') * 127   # pixels untouched by the following operations will outline the crosshair shape (wish they could be white)
buf[7,:,:] = 0        # horizontal black line
buf[:,7,:] = 0        # vertical black line
buf[:6,:6, :] = 255   # evidently values > 127 are interpreted as alpha
buf[9:,:6, :] = 255
buf[9:, 9:, :] = 255
buf[:6, 9:, :] = 255
im = wx.ImageFromBuffer(16, 16, buf.tostring()) # passing a separate alpha buffer just gets ignored
im.SetOptionInt(wx.IMAGE_OPTION_CUR_HOTSPOT_X, 7)
im.SetOptionInt(wx.IMAGE_OPTION_CUR_HOTSPOT_Y, 7)
cursor = wx.CursorFromImage(im)

Answer 1

Welp, here’s what I came up with. Handling the mouse_enter and mouse_leave events isn’t good enough since the matplotlib navigation toolbar will set the cursor after the fact, so we need to set it on mouse motion.

I wasn’t able to get a white outline around the crosshair icon, but I got close enough for now. so here it is.

# Bind mouse motion events in the canvas
self.figure.canvas.mpl_connect('motion_notify_event', self.on_mouse_move)

# ...

def on_mouse_move(self, evt):
    #
    # LAAAME SAUCE -- Crosshair cursor is all black on Windows making it
    #    virtually invisible on dark images. Use custom cursor instead.
    #
    if (sys.platform.lower().startswith('win') and 
        evt.inaxes and
        self.navtoolbar.mode == 'Zoom to rect mode'):  # NOTE: There are no constants for the navbar modes
        #
        # Build the crosshair cursor image as a numpy array.
        # Sadly I can't figure out how to make a white outline since every
        # value above 127 is apparently transparent.
        # Soooo the outline is yellow.
        #
        # Best docs I could find: http://wxruby.rubyforge.org/doc/cursor.html
        #
        buf = np.ones((16,16,3), dtype='uint8') * 255
        buf[:,:,2] = 1
        buf[7,1:-1,:] = buf[1:-1,7,:] = 0
        buf[:6,:6,:] = buf[9:,:6,:] = buf[9:,9:,:] = buf[:6,9:,:] = 255
        #
        # NOTE: I tried making an alpha channel and doing 
        #  wx.ImageFromBuffer(16, 16, buf.tostring(), alpha_buffer.to_string())
        # ...no good. wx just ignores the channel.
        #
        im = wx.ImageFromBuffer(16, 16, buf.tostring())
        im.SetOptionInt(wx.IMAGE_OPTION_CUR_HOTSPOT_X, 7)
        im.SetOptionInt(wx.IMAGE_OPTION_CUR_HOTSPOT_Y, 7)
        cursor = wx.CursorFromImage(im)
        self.figure.canvas.SetCursor(cursor)