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backend_template.py

00001 """
This is a fully functional do nothing backend to provide a template to
backend writers.  It is fully functional in that you can select it as
a backend with

  import matplotlib
  matplotlib.use('Template')

and your matplotlib scripts will (should!) run without error, though
no output is produced.  This provides a nice starting point for
backend writers because you can selectively implement methods
(draw_rectangle, draw_lines, etc...) and slowly see your figure come
to life w/o having to have a full blown implementation before getting
any results.

Copy this to backend_xxx.py and replace all instances of 'template'
with 'xxx'.  Then implement the class methods and functions below, and
add 'xxx' to the switchyard in matplotlib/backends/__init__.py and
'xxx' to the backends list in the validate_backend methon in
matplotlib/__init__.py and you're off.  You can use your backend with

  import matplotlib
  matplotlib.use('xxx')
  from pylab import *
  plot([1,2,3])
  show()

The files that are most relevant to backend_writers are

  matplotlib/backends/backend_your_backend.py
  matplotlib/backend_bases.py
  matplotlib/backends/__init__.py
  matplotlib/__init__.py
  matplotlib/_pylab_helpers.py

Naming Conventions

  * classes Upper or MixedUpperCase

  * varables lower or lowerUpper

  * functions lower or underscore_separated

"""

from __future__ import division

import matplotlib
from matplotlib._pylab_helpers import Gcf
from matplotlib.backend_bases import RendererBase, GraphicsContextBase,\
     FigureManagerBase, FigureCanvasBase
from matplotlib.cbook import enumerate
from matplotlib.figure import Figure
from matplotlib.transforms import Bbox


00057 class RendererTemplate(RendererBase):
    """
    The renderer handles drawing/rendering operations.

    This is a minimal do-nothing class that can be used to get started when
    writing a new backend. Refer to backend_bases.RendererBase for
    documentation of the classes methods.
    """
00065     def draw_arc(self, gc, rgbFace, x, y, width, height, angle1, angle2,
                 rotation):
        pass

00069     def draw_image(self, x, y, im, bbox):
        pass

00072     def draw_line(self, gc, x1, y1, x2, y2):
        pass

    def draw_lines(self, gc, x, y):
        pass

00078     def draw_point(self, gc, x, y):
        pass

00081     def draw_polygon(self, gcEdge, rgbFace, points):
        pass

00084     def draw_rectangle(self, gcEdge, rgbFace, x, y, width, height):
        pass

00087     def draw_text(self, gc, x, y, s, prop, angle, ismath=False):
        pass

00090     def flipy(self):
        return True

    def get_canvas_width_height(self):
        return 100, 100

00096     def get_text_width_height_descent(self, s, prop, ismath):
        return 1, 1, 1

00099     def new_gc(self):
        return GraphicsContextTemplate()

00102     def points_to_pixels(self, points):
        # if backend doesn't have dpi, eg, postscript or svg
        return points
        # elif backend assumes a value for pixels_per_inch
        #return points/72.0 * self.dpi.get() * pixels_per_inch/72.0
        # else
        #return points/72.0 * self.dpi.get()


00111 class GraphicsContextTemplate(GraphicsContextBase):
    """
    The graphics context provides the color, line styles, etc...  See the gtk
    and postscript backends for examples of mapping the graphics context
    attributes (cap styles, join styles, line widths, colors) to a particular
    backend.  In GTK this is done by wrapping a gtk.gdk.GC object and
    forwarding the appropriate calls to it using a dictionary mapping styles
    to gdk constants.  In Postscript, all the work is done by the renderer,
    mapping line styles to postscript calls.

    If it's more appropriate to do the mapping at the renderer level (as in
    the postscript backend), you don't need to override any of the GC methods.
    If it's more appropriate to wrap an instance (as in the GTK backend) and
    do the mapping here, you'll need to override several of the setter
    methods.

    The base GraphicsContext stores colors as a RGB tuple on the unit
    interval, eg, (0.5, 0.0, 1.0). You may need to map this to colors
    appropriate for your backend.
    """
    pass



########################################################################
#
# The following functions and classes are for pylab and implement
# window/figure managers, etc...
#
########################################################################

00142 def draw_if_interactive():
    """
    For image backends - is not required
    For GUI backends - this should be overriden if drawing should be done in
    interactive python mode
    """
    pass

00150 def show():
    """
    For image backends - is not required
    For GUI backends - show() is usually the last line of a pylab script and
    tells the backend that it is time to draw.  In interactive mode, this may
    be a do nothing func.  See the GTK backend for an example of how to handle
    interactive versus batch mode
    """
    for manager in Gcf.get_all_fig_managers():
        # do something to display the GUI
        pass


00163 def new_figure_manager(num, *args, **kwargs):
    """
    Create a new figure manager instance
    """
    # if a main-level app must be created, this is the usual place to
    # do it -- see backend_wx, backend_wxagg and backend_tkagg for
    # examples.  Not all GUIs require explicit instantiation of a
    # main-level app (egg backend_gtk, backend_gtkagg) for pylab
    FigureClass = kwargs.pop('FigureClass', Figure)
    thisFig = FigureClass(*args, **kwargs)
    canvas = FigureCanvasTemplate(thisFig)
    manager = FigureManagerTemplate(canvas, num)
    return manager


00178 class FigureCanvasTemplate(FigureCanvasBase):
    """
    The canvas the figure renders into.  Calls the draw and print fig
    methods, creates the renderers, etc...

    Public attribute

      figure - A Figure instance

    Note GUI templates will want to connect events for button presses,
    mouse movements and key presses to functions that call the base
    class methods button_press_event, button_release_event,
    motion_notify_event, key_press_event, and key_release_event.  See,
    eg backend_gtk.py, backend_wx.py and backend_tkagg.py
    """

00194     def draw(self):
        """
        Draw the figure using the renderer
        """
        renderer = RendererTemplate()
        self.figure.draw(renderer)

    # You should provide a print_xxx function for every file format
    # you can write.

    # If the file type is not in the base set of filetypes,
    # you should add it to the class-scope filetypes dictionary as follows:
    filetypes = FigureCanvasBase.filetypes.copy()
    filetypes['foo'] = 'My magic Foo format'

00209     def print_foo(self, filename, *args, **kwargs):
        """
        Write out format foo.  The dpi, facecolor and edgecolor are restored
        to their original values after this call, so you don't need to
        save and restore them.
        """
        pass

    def get_default_filetype(self):
        return 'foo'
    
00220 class FigureManagerTemplate(FigureManagerBase):
    """
    Wrap everything up into a window for the pylab interface

    For non interactive backends, the base class does all the work
    """
    pass

########################################################################
#
# Now just provide the standard names that backend.__init__ is expecting
#
########################################################################


FigureManager = FigureManagerTemplate


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