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# Copyright (C) 2006, Red Hat, Inc.
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the
# Free Software Foundation, Inc., 59 Temple Place - Suite 330,
# Boston, MA 02111-1307, USA.
""" Units conversions and constants
The purpose of the module is to keep Sugar independent from the
screen size, factory and DPI. There a few use cases that needs
to be considered:
- The XO display. The screen DPI is 201 and the screen
resolution is 1200x900. The screen factor is 4:3.
- The Sugar emulator runned on traditional screens. Resolution
is variable, ranging from 800x600 up to 1200x900. The DPI
is usually but not necessarily 96. The screen factor is
either 4:3 or 16:9
- Other embedded devices. DPI, screen resolution and screen
factor are variable.
To achieve the goal a few rules needs to be respected when
writing code for Sugar:
- Never use absolute positioning. Use the layout facilities
provided by HippoCanvas. If you need custom layouts make
sure they adapt to different screen resolutions.
- Never specify sizes, fonts, borders or padding using pixels.
Instead use the device independt units provided by this
module.
We are currently providing the following resolution independent
units:
- Points.
- Grid. One cell of the screen grid as specificed by the HIG.
- Microgrid. One microcell of the screen grid as
specificed by the HIG.
- A set of icon sizes as specified by the HIG (standard, small,
medium, large, xlarge).
Just scaling UI elements on the base of the screen DPI is not
enough to provide a good experience. For example on smaller
screens smaller fonts or icons might be acceptable to gain
screen aestate. For this reason a constant zoom factor is
applied to all the transformation from resolution independent
units to device units.
"""
import gtk
_MAX_ZOOM_FACTOR = 2.0
_ZOOM_CONSTANT = 650.0
def _compute_zoom_factor():
screen_width = gtk.gdk.screen_width()
if _screen_dpi == 201.0 and screen_width == 1200:
return 1.0
else:
return min(_MAX_ZOOM_FACTOR, screen_width / _ZOOM_CONSTANT)
_gtk_xft_dpi = gtk.settings_get_default().get_property('gtk-xft-dpi')
_screen_dpi = float(_gtk_xft_dpi / 1024)
_dpi_factor = _screen_dpi / 201.0
_zoom_factor = _compute_zoom_factor()
STANDARD_ICON_SCALE = 1.0 * _dpi_factor * _zoom_factor
SMALL_ICON_SCALE = 0.5 * _dpi_factor * _zoom_factor
MEDIUM_ICON_SCALE = 1.5 * _dpi_factor * _zoom_factor
LARGE_ICON_SCALE = 2.0 * _dpi_factor * _zoom_factor
XLARGE_ICON_SCALE = 2.75 * _dpi_factor * _zoom_factor
def points_to_device(points):
return int(points * _zoom_factor)
def points_to_pixels(points):
return int(points * _screen_dpi / 72.0 * _zoom_factor)
def grid_to_pixels(units):
return int(units * 75.0 * _dpi_factor * _zoom_factor)
def microgrid_to_pixels(units):
return int(units * 15.0 * _dpi_factor * _zoom_factor)
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