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# Copyright (c) 2005 Ruby-GNOME2 Project Team
# This program is licenced under the same licence as Ruby-GNOME2.
#
# $Id: rotated_text.rb,v 1.2 2005/03/05 15:01:16 mutoh Exp $
=begin
= Rotated Text
This demo shows how to use GDK and Pango to draw rotated and transformed text.
The use of Gdk::PangoRenderer in this example is a somewhat advanced technique; most applications can simply use Gdk::Drawable#draw_layout.
We use it here mostly because that allows us to work in user coordinates - that is, coordinates prior to the application of the transformation matrix, rather than device coordinates.
As of GTK+-2.6, the ability to draw transformed and anti-aliased graphics as shown in this example is only present for text.
With GTK+-2.8, a new graphics system called "Cairo" will be introduced that provides these capabilities and many more for all types of graphics.
=end
require 'common'
module Demo
class RotatedText < BasicWindow
RADIUS = 150
N_WORDS = 10
FONT = "Sans Bold 27"
def initialize
super('Rotated Text')
unless Gtk.check_version?(2, 6, 0)
add(Gtk::Label.new("This sample requires GTK+ 2.6.0 or later"))
return
end
drawing_area = Gtk::DrawingArea.new
add(drawing_area)
drawing_area.modify_bg(Gtk::STATE_NORMAL, Gdk::Color.new(65535, 65535, 65535))
drawing_area.signal_connect("expose_event") do
matrix = Pango::Matrix.new
# Get the default renderer for the screen, and set it up for drawing
renderer = Gdk::PangoRenderer.get_default(drawing_area.screen)
renderer.drawable = drawing_area.window
renderer.gc = style.black_gc
width = drawing_area.allocation.width
height = drawing_area.allocation.height
# Set up a transformation matrix so that the user space coordinates for
# the centered square where we draw are [-RADIUS, RADIUS], [-RADIUS, RADIUS]
# We first center, then change the scale
device_radius = [width, height].min / 2.0
matrix.translate!(device_radius + (width - 2 * device_radius) / 2.0,
device_radius + (height - 2 * device_radius) / 2.0)
matrix.scale!(device_radius / RADIUS, device_radius / RADIUS)
# Create a PangoLayout, set the font and text
context = Gdk::Pango.context
layout = Pango::Layout.new(context)
layout.text = "Text"
layout.font_description = Pango::FontDescription.new(FONT)
# Draw the layout N_WORDS times in a circle
(0...N_WORDS).each do |i|
rotated_matrix = matrix.dup
angle = 360 * i / N_WORDS.to_f
# Gradient from red at angle == 60 to blue at angle == 300
red = 65535 * (1 + Math.cos((angle - 60) * Math::PI / 180.0)) / 2
color = Gdk::Color.new(red, 0, 65535 - red)
renderer.set_override_color(Pango::Renderer::PART_FOREGROUND, color)
rotated_matrix.rotate!(angle)
context.matrix = rotated_matrix
# Inform Pango to re-layout the text with the new transformation matrix
layout.context_changed
width, height = layout.size
renderer.draw_layout(layout, - width / 2, - RADIUS * Pango::SCALE)
end
# Clean up default renderer, since it is shared
renderer.set_override_color(Gdk::PangoRenderer::PART_FOREGROUND, nil)
renderer.drawable = nil
renderer.gc = nil
end
end
end
end
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