Gergely Kontra

#!/usr/bin/env ruby

require 'gtk2'
require 'rational'

=begin
A drawing area, which can be panned and zoomed.
(requires rational)
Panning is done with middle mouse drag, zooming is with the scrollwheel.
To zoom only into x or y axis, hold down the shift or ctrl keys respectively.
You must create the following method:
expose_event event, cairo, coordinates
where
event is the expose event
cairo is the cairo context
coordinates is an array with the [xstart, ystart, xend, yend] coordinates
=end
class DragZoomDrawingArea < Gtk::DrawingArea
    type_register

    def initialize
        super

        @xscale = @yscale = 1.to_r
        @xoffset = @yoffset = 0.to_r
        @xscalestep = @yscalestep = 2.to_r
        @drag_sig_handlers = []

        signal_connect('expose-event') {|widget, event|
            cairo = window.create_cairo_context
            cairo.scale(@xscale, @yscale)
            cairo.translate(@xoffset, @yoffset)

            alloc = allocation
            width, height = alloc.width, alloc.height

            xstart = (0.to_r - @xoffset) / @xscale
            xend = (width.to_r - @xoffset) / @xscale

            ystart = (0.to_r - @yoffset) / @yscale
            yend = (height.to_r - @yoffset) / @yscale

            expose_event widget, event, cairo, [xstart, ystart, xend, yend]
            true
        }

        signal_connect('scroll-event') {|widget, event|
            do_xscale = do_yscale = true

            if event.state & Gdk::Window::ModifierType::SHIFT_MASK != 0
                do_yscale = false
            end
            if event.state & Gdk::Window::ModifierType::CONTROL_MASK != 0
                do_xscale = false
            end

            xscale_old, yscale_old = @xscale, @yscale
            case event.direction
            when Gdk::EventScroll::DOWN
                @xscale /= @xscalestep if do_xscale
                @yscale /= @yscalestep if do_yscale
            when Gdk::EventScroll::UP
                @xscale *= @xscalestep if do_xscale
                @yscale *= @yscalestep if do_yscale
            end

            @xoffset = event.x.to_i.to_r / @xscale - (event.x.to_i / xscale_old - @xoffset)
            @yoffset = event.y.to_i.to_r / @yscale - (event.y.to_i / yscale_old - @yoffset)
            queue_draw
        }

        @motion_cb = proc {|widget, event|
            deltax, deltay = event.x.to_i.to_r - @startx.to_i, event.y.to_i.to_r - @starty.to_i
            @xoffset += deltax / @xscale
            @yoffset += deltay / @yscale
            @startx, @starty = event.x, event.y
            queue_draw
        }

        signal_connect('button-press-event') {|widget, event|
            if(event.button == 2)
                @startx, @starty = event.x, event.y
                @drag_sig_handlers << signal_connect('motion-notify-event', &@motion_cb)
            end
        }

        signal_connect('button-release-event') {|widget, event|
            if(event.button == 2)
                @drag_sig_handlers.reject!{|s| signal_handler_disconnect(s); true}
            end
        }

        add_events(Gdk::Event::SCROLL_MASK |
            Gdk::Event::BUTTON_PRESS_MASK |
            Gdk::Event::BUTTON_RELEASE_MASK |
            Gdk::Event::POINTER_MOTION_MASK)
    end
end

class MyWindow < Gtk::Window
    def initialize
        super('interactive graph')
        set_size_request(500,500)
        signal_connect("delete-event") { Gtk.main_quit;true }


        drawing_area = DragZoomDrawingArea.new
        def drawing_area.expose_event widget, event, cairo, disp
            cairo.set_source_rgb(1,0,0)
            cairo.rectangle(100, 100, 50, 50)
            cairo.stroke
        end
        add(drawing_area)
        show_all
    end
end

app = MyWindow.new

Gtk.main