## mark a section (Learn more)

require 'gtk2' # This program shows you how to create semi-transparent windows, # without any of the historical screenshot hacks. It requires # a modern system, with a compositing manager. I use xcompmgr # and the nvidia drivers with RenderAccel, and it works well. # # I'll take you through each step as we go. Minimal GTK+ knowledge is # assumed. # Only some X servers support alpha channels. Always have a fallback $supports_alpha = false def clicked(widget, event) # toggle window manager frames widget.decorated = !widget.decorated? end # This is called when we need to draw the windows contents def expose_event(widget, event) cr = widget.window.create_cairo_context if $supports_alpha cr.set_source_rgba(1.0, 1.0, 1.0, 0.0) # Transparent else cr.set_source_rgb(1.0, 1.0, 1.0) # Opaque white end # Draw the background cr.operator = Cairo::OPERATOR_SOURCE cr.paint # Draw a circle width, height = widget.size cr.set_source_rgba(1.0, 0.2, 0.2, 0.6) if width < height radius = width.to_f/2 - 0.8 else radius = height.to_f/2 - 0.8 end cr.arc(width.to_f/2, height.to_f/2, radius, 0, 2.0*3.14) cr.fill cr.stroke return false end def screen_changed(widget, old_screen = nil) # To check if the display supports alpha channels, get the colormap screen = widget.screen colormap = screen.rgba_colormap if colormap.nil? puts 'Your screen does not support alpha channels!' colormap = screen.rgb_colormap $supports_alpha = false else puts 'Your screen supports alpha channels!' $supports_alpha = true end # Now we have a colormap appropriate for the screen, use it widget.colormap = colormap return false end def main window = Gtk::Window.new window.title = "Alpha Demo" window.signal_connect('delete-event') { |widget, event| Gtk.main_quit } # Tell GTK+ that we want to draw the windows background ourself. # If we don't do this then GTK+ will clear the window to the # opaque theme default color, which isn't what we want. window.app_paintable = true # The X server sends us an expose event when the window becomes # visible on screen. It means we need to draw the contents. On a # composited desktop expose is normally only sent when the window # is put on the screen. On a non-composited desktop it can be # sent whenever the window is uncovered by another. # # The screen-changed event means the display to which we are # drawing changed. GTK+ supports migration of running # applications between X servers, which might not support the # same features, so we need to check each time. window.signal_connect('expose-event') { |widget, event| expose_event(widget, event) } window.signal_connect('screen-changed') { |widget, old_screen| screen_changed(widget, old_screen) } # toggle title bar on click - we add the mask to tell # X we are interested in this event window.decorated = false window.add_events(Gdk::Event::BUTTON_PRESS_MASK) window.signal_connect('button-press-event') { |widget, event| clicked(widget, event) } # initialize for the current display screen_changed(window) # Run the program window.show_all Gtk.main end main

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