Source code for gaphas.tool.zoom

from gi.repository import Gtk

from gaphas.view import GtkView


class Zoom:
    def __init__(self, matrix):
        self.matrix = matrix
        self.x0 = 0
        self.y0 = 0
        self.sx = 1.0
        self.sy = 1.0

    def begin(self, x0, y0):
        self.x0 = x0
        self.y0 = y0
        self.sx = self.matrix[0]
        self.sy = self.matrix[3]

    def update(self, scale):
        if self.sx * scale < 0.2:
            scale = 0.2 / self.sx
        elif self.sx * scale > 20.0:
            scale = 20.0 / self.sx

        m = self.matrix
        sx = m[0]
        sy = m[3]
        ox = (m[4] - self.x0) / sx
        oy = (m[5] - self.y0) / sy
        dsx = self.sx * scale / sx
        dsy = self.sy * scale / sy
        m.translate(-ox, -oy)
        m.scale(dsx, dsy)
        m.translate(+ox, +oy)


def zoom_tool(view: GtkView) -> Gtk.GestureZoom:
    """Create a zoom tool as a Gtk.Gesture.

    Note: we need to keep a reference to this gesture, or else it will be destroyed.
    """
    zoom = Zoom(view.matrix)
    gesture = (
        Gtk.GestureZoom.new(view)
        if Gtk.get_major_version() == 3
        else Gtk.GestureZoom.new()
    )
    gesture.set_propagation_phase(Gtk.PropagationPhase.CAPTURE)
    gesture.connect("begin", on_begin, zoom)
    gesture.connect("scale-changed", on_scale_changed, zoom)
    return gesture


def on_begin(
    gesture: Gtk.GestureZoom,
    sequence: None,
    zoom: Zoom,
) -> None:
    _, x0, y0 = gesture.get_point(sequence)
    zoom.begin(x0, y0)


def on_scale_changed(gesture: Gtk.GestureZoom, scale: float, zoom: Zoom) -> None:
    zoom.update(scale)