[plot] closest function for item

[vallsv]

Item provides a pick method to reach data index at a specific location. This is based on the backend and can't be used for position far away from the item.

It would be good to provide a closest function.

• At least taking a x/y position
• At least processing only visible elements
• At least computing distances based on the display (then taking care of log scale)
• At least for curve items
• Returning at least the closest data index, and computed distance

[vallsv]

Here is my current implementation.

It do not manage the log scale, nor the visible data.

    def __closest(self, curve, x, y):
        """Returns the closest point from a curve item"""
        xx = curve.getXData()
        yy = curve.getYData()
        if xx is None or len(xx) > 0:
            return None, None
        xdata, ydata = self.__plot.pixelToData(x, y)
        xcoef, ycoef = self.__plot.pixelToData(1, 1)
        if xcoef == 0:
            xcoef = 1
        if ycoef == 0:
            ycoef = 1
        xcoef, ycoef = 1 / xcoef, 1 / ycoef
        dist = ((xx - xdata) * xcoef) ** 2 + ((yy - ydata) * ycoef) ** 2
        index = numpy.nanargmin(dist)
        xdata, ydata = xx[index], yy[index]
        pos = self.__plot.dataToPixel(xdata, ydata)
        if pos is None:
            return None, None
        xdata, ydata = pos
        dist = numpy.sqrt((x - xdata) ** 2 + (y - ydata) ** 2)
        return index, dist