Pmw.ScrolledCanvas

Name

Pmw.ScrolledCanvas() - canvas with optional scrollbars

Inherits

Pmw.MegaWidget

Description

A scrolled canvas consists of a standard canvas widget with optional scrollbars which can be used to scroll the canvas. The scrollbars can be dynamic, which means that a scrollbar will only be displayed if it is necessary, that is, if the scrollregion of the canvas is larger than the canvas.

Options

Options for this megawidget and its base classes are described below.

borderframe

Initialisation option. If true, the borderframe component will be created. The default is 0.

canvasmargin

Initialisation option. The margin around the items in the canvas. Used by the resizescrollregion() method. The default is 0.

hscrollmode

The horizontal scroll mode. If 'none', the horizontal scrollbar will never be displayed. If 'static', the scrollbar will always be displayed. If 'dynamic', the scrollbar will be displayed only if necessary. The default is 'dynamic'.

labelmargin

Initialisation option. If the labelpos option is not None, this specifies the distance between the label component and the rest of the megawidget. The default is 0.

labelpos

Initialisation option. Specifies where to place the label component. If not None, it should be a concatenation of one or two of the letters 'n', 's', 'e' and 'w'. The first letter specifies on which side of the megawidget to place the label. If a second letter is specified, it indicates where on that side to place the label. For example, if labelpos is 'w', the label is placed in the center of the left hand side; if it is 'wn', the label is placed at the top of the left hand side; if it is 'ws', the label is placed at the bottom of the left hand side.

If None, a label component is not created. The default is None.

scrollmargin

Initialisation option. The distance between the scrollbars and the enclosing canvas widget. The default is 2.

usehullsize

Initialisation option. If true, the size of the megawidget is determined solely by the width and height options of the hull component.

Otherwise, the size of the megawidget is determined by the width and height of the canvas component, along with the size and/or existence of the other components, such as the label, the scrollbars and the scrollmargin option. All these affect the overall size of the megawidget. The default is 0.

vscrollmode

The vertical scroll mode. If 'none', the vertical scrollbar will never be displayed. If 'static', the scrollbar will always be displayed. If 'dynamic', the scrollbar will be displayed only if necessary. The default is 'dynamic'.

Components

Components created by this megawidget and its base classes are described below.

borderframe

A frame widget which snuggly fits around the canvas, to give the appearance of a canvas border. It is created with a border so that the canvas, which is created without a border, looks like it has a border. By default, this component is a tkinter.Frame.

canvas

The canvas widget which is scrolled by the scrollbars. If the borderframe option is true, this is created with a borderwidth of 0 to overcome a known problem with canvas widgets: if a widget inside a canvas extends across one of the edges of the canvas, then the widget obscures the border of the canvas. Therefore, if the canvas has no border, then this overlapping does not occur. By default, this component is a tkinter.Canvas.

horizscrollbar

The horizontal scrollbar. By default, this component is a tkinter.Scrollbar. Its component group is Scrollbar.

hull

This acts as the body for the entire megawidget. Other components are created as children of the hull to further specialise this class. By default, this component is a tkinter.Frame.

label

If the labelpos option is not None, this component is created as a text label for the megawidget. See the labelpos option for details. Note that to set, for example, the text option of the label, you need to use the label_text component option. By default, this component is a tkinter.Label.

vertscrollbar

The vertical scrollbar. By default, this component is a tkinter.Scrollbar. Its component group is Scrollbar.

Methods

Only methods specific to this megawidget are described below. For a description of its inherited methods, see the manual for its base class Pmw.MegaWidget. In addition, methods from the tkinter.Canvas class are forwarded by this megawidget to the canvas component.

bbox(*args)

This method is explicitly forwarded to the canvas component's bbox() method. Without this explicit forwarding, the bbox() method (aliased to grid_bbox()) of the hull would be invoked, which is probably not what the programmer intended.

interior()

Return the canvas widget within which the programmer should create graphical items and child widgets. This is the same as component('canvas').

resizescrollregion()

Resize the scrollregion of the canvas component to be the bounding box covering all the items in the canvas plus a margin on all sides, as specified by the canvasmargin option.

Example

The image at the top of this manual is a snapshot of the window (or part of the window) produced by the following code.

class Demo:
    def __init__(self, parent):
        # Create the ScrolledCanvas.
        self.sc = Pmw.ScrolledCanvas(parent,
                borderframe = 1,
                labelpos = 'n',
                label_text = 'ScrolledCanvas',
                usehullsize = 1,
                hull_width = 400,
                hull_height = 300,
        )

        # Create a group widget to contain the scrollmode options.
        w = Pmw.Group(parent, tag_text='Scroll mode')
        w.pack(side = 'bottom', padx = 5, pady = 5)

        hmode = Pmw.OptionMenu(w.interior(),
                labelpos = 'w',
                label_text = 'Horizontal:',
                items = ['none', 'static', 'dynamic'],
                command = self.sethscrollmode,
                menubutton_width = 8,
        )
        hmode.pack(side = 'left', padx = 5, pady = 5)
        hmode.invoke('dynamic')

        vmode = Pmw.OptionMenu(w.interior(),
                labelpos = 'w',
                label_text = 'Vertical:',
                items = ['none', 'static', 'dynamic'],
                command = self.setvscrollmode,
                menubutton_width = 8,
        )
        vmode.pack(side = 'left', padx = 5, pady = 5)
        vmode.invoke('dynamic')

        buttonBox = Pmw.ButtonBox(parent)
        buttonBox.pack(side = 'bottom')
        buttonBox.add('yview', text = 'Show\nyview', command = self.showYView)
        buttonBox.add('scroll', text = 'Page\ndown', command = self.pageDown)
        buttonBox.add('center', text = 'Center', command = self.centerPage)

        # Pack this last so that the buttons do not get shrunk when
        # the window is resized.
        self.sc.pack(padx = 5, pady = 5, fill = 'both', expand = 1)

        self.sc.component('canvas').bind('<1>', self.addcircle)

        testEntry = tkinter.Entry(parent)
        self.sc.create_line(20, 20, 100, 100)
        self.sc.create_oval(100, 100, 200, 200, fill = 'green')
        self.sc.create_text(100, 20, anchor = 'nw',
                text = 'Click in the canvas\nto draw ovals',
                font = testEntry.cget('font'))
        button = tkinter.Button(self.sc.interior(),
                text = 'Hello,\nWorld!\nThis\nis\na\nbutton.')
        self.sc.create_window(200, 200,
                anchor='nw',
                window = button)

        # Set the scroll region of the canvas to include all the items
        # just created.
        self.sc.resizescrollregion()

        self.colours = ('red', 'green', 'blue', 'yellow', 'cyan', 'magenta',
                'black', 'white')
        self.oval_count = 0
        self.rand = 12345

    def sethscrollmode(self, tag):
        self.sc.configure(hscrollmode = tag)

    def setvscrollmode(self, tag):
        self.sc.configure(vscrollmode = tag)

    def addcircle(self, event):
        x = self.sc.canvasx(event.x)
        y = self.sc.canvasy(event.y)
        width = 10 + self.random() % 100
        height = 10 + self.random() % 100
        self.sc.create_oval(
            x - width, y - height, x + width, y + height,
            fill = self.colours[self.oval_count])
        self.oval_count = (self.oval_count + 1) % len(self.colours)
        self.sc.resizescrollregion()

    # Simple random number generator.
    def random(self):
        self.rand = (self.rand * 125) % 2796203
        return self.rand

    def showYView(self):
        print(self.sc.yview())

    def pageDown(self):
        self.sc.yview('scroll', 1, 'page')

    def centerPage(self):
        top, bottom = self.sc.yview()
        size = bottom - top
        middle = 0.5 - size / 2
        self.sc.yview('moveto', middle)