12.2. Drawing Methods

There are a general set of methods that can be used to draw onto the drawing area 'canvas'. These drawing methods work for any gtk.gdk.Drawable which is a gtk.gdk.Window or a gtk.gdk.Pixmap. The drawing methods are:

  drawable.draw_point(gc, x, y)

gc is the Graphics Context to be used to do the drawing.

x and y are the coordinates of the point.

  drawable.draw_line(gc, x1, y1, x2, y2)

gc is the Graphics Context.

x1 and y1 specify the starting point of the line. x2 and y2 specify the ending point of the line.

  drawable.draw_rectangle(gc, filled, x, y, width, height)

where gc is the Graphics Context.

filled is a boolean indicating the rectangle should be filled with the foreground color if TRUE or not filled, if FALSE.

x and y are the top left corner of the rectangle.

width and height are the width and height of the rectangle.

  drawable.draw_arc(gc, filled, x, y, width, height, angle1, angle2)

gc is the Graphics Context.

filled is a boolean indicating the arc should be filled with the foreground color if TRUE or not filled, if FALSE.

x and y are the top left corner of the bounding rectangle. width and height are the width and height of the bounding rectangle.

angle1 is the start angle of the arc, relative to the 3 o'clock position, counter-clockwise, in 1/64ths of a degree.

angle2 is the end angle of the arc, relative to angle1, in 1/64ths of a degree counter clockwise.

  drawable.draw_polygon(gc, filled, points)

gc is the Graphics Context.

filled is a boolean indicating the polygon should be filled with the foreground color if TRUE or not filled, if FALSE.

points is a list of coordinate pairs in tuples e.g. [ (0,0), (2,5), (3,7), (4,11) ] of the points to be drawn as a connected polygon.

  drawable.draw_string(font, gc, x, y, string)

  drawable.draw_text(font, gc, x, y, string)

font is the gtk.gdk.Font to use to render the string.

gc is the Graphics Context.

x and y are the coordinates of the point to start rendering the string i.e the left baseline.

string is the string of characters to render.

Note

Both the draw_string() and draw_text() methods are deprecated - use a pango.Layout instead with the draw_layout() method.

  drawable.draw_layout(gc, x, y, layout)

gc is the Graphics Context.

x and y are the coordinates of the point to start rendering the layout.

layout is the pango.Layout that is to be rendered.

  drawable.draw_drawable(gc, src, xsrc, ysrc, xdest, ydest, width, height)

gc is the Graphics Context.

src is the source drawable.

xsrc and ysrc are the coordinates of the top left rectangle in the source drawable.

xdest and ydest are the coordinates of the top left corner in the drawing area.

width and height are the width and height of the source drawable area to be copied to the drawable. If width or height is -1 then the full width or height of the drawable is used.

  drawable.draw_image(gc, image, xsrc, ysrc, xdest, ydest, width, height)

gc is the Graphics Context.

image is the source image.

xsrc and ysrc are the coordinates of the top left rectangle in the source drawable.

xdest and ydest are the coordinates of the top left corner in the drawing area.

width and height are the width and height of the source drawable area to be copied to the drawable. If width or height is -1 then the full width or height of the image is used.

  drawable.draw_points(gc, points)

gc is the Graphics Context.

points is a list or tuple of coordinate pairs in tuples e.g. [ (0,0), (2,5), (3,7), (4,11) ] of the points to be drawn.

  drawable.draw_segments(gc, segs)

gc is the Graphics Context.

segs is a list or tuple of start and end coordinate pairs in tuples e.g. [ (0,0, 1,5), (2,5, 1,7), (3,7, 1,11), (4,11, 1,13) ] of the line segments to be drawn.

  drawable.draw_lines(gc, points)

gc is the Graphics Context.

points is a list or tuple of coordinate pairs in tuples e.g. [ (0,0), (2,5), (3,7), (4,11) ] of the points to be connected with lines.

  drawable.draw_rgb_image(gc, x, y, width, height, dith, rgb_buf, rowstride)

  drawable.draw_rgb_32_image(gc, x, y, width, height, dith, buf, rowstride)

  drawable.draw_gray_image(gc, x, y, width, height, dith, buf, rowstride)

gc is the Graphics Context.

x and y are the top left corner of the image bounding rectangle.

width and height are the width and height of the image bounding rectangle.

dith is the dither mode as described below

For the draw_rgb_image() method, rgb_buf is the RGB Image data packed in a string as a sequence of 8-bit RGB pixel triplets. For the draw_rgb_32_image() method, buf is the RGB Image data packed in a string as a sequence of 8-bit RGB pixel triplets with 8-bit padding (4 characters per RGB pixel). For the draw_gray_image() method, buf is the gray image data packed in a string as 8-bit pixel data.

rowstride is the number of characters from the start of one row to the start of the next row of the image. rowstride usually defaults to: 3 * width for the draw_rgb_image() method; 4 * width for the draw_rgb_32_image(); and, width for the draw_gray_image() method. If rowstride is 0 the line will be replicated height times.

The dither modes are:

  RGB_DITHER_NONE    # Never use dithering.

  RGB_DITHER_NORMAL  # Use dithering in 8 bits per pixel (and below) only.

  RGB_DITHER_MAX     # Use dithering in 16 bits per pixel and below.

The drawingarea.py example program demonstrates the use of most of the DrawingArea methods. Figure 12.1 shows the resulting display:

Figure 12.1. Drawing Area Example

Drawing Area Example

The drawingarea.py source code is below and uses the gtk.xpm pixmap:

    1	#!/usr/bin/env python
    2	
    3	# example drawingarea.py
    4	
    5	import pygtk
    6	pygtk.require('2.0')
    7	import gtk
    8	import operator
    9	import time
   10	import string
   11	
   12	class DrawingAreaExample:
   13	    def __init__(self):
   14	        window = gtk.Window(gtk.WINDOW_TOPLEVEL)
   15	        window.set_title("Drawing Area Example")
   16	        window.connect("destroy", lambda w: gtk.main_quit())
   17	        self.area = gtk.DrawingArea()
   18	        self.area.set_size_request(400, 300)
   19	        self.pangolayout = self.area.create_pango_layout("")
   20	        window.add(self.area)
   21	        self.area.connect("expose-event", self.area_expose_cb)
   22	        self.area.show()
   23	        window.show()
   24	
   25	    def area_expose_cb(self, area, event):
   26	        self.style = self.area.get_style()
   27	        self.gc = self.style.fg_gc[gtk.STATE_NORMAL]
   28	        self.draw_point(10,10)
   29	        self.draw_points(110, 10)
   30	        self.draw_line(210, 10)
   31	        self.draw_lines(310, 10)
   32	        self.draw_segments(10, 100)
   33	        self.draw_rectangles(110, 100)
   34	        self.draw_arcs(210, 100)
   35	        self.draw_pixmap(310, 100)
   36	        self.draw_polygon(10, 200)
   37	        self.draw_rgb_image(110, 200)
   38	        return gtk.TRUE
   39	
   40	    def draw_point(self, x, y):
   41	        self.area.window.draw_point(self.gc, x+30, y+30)
   42	        self.pangolayout.set_text("Point")
   43	        self.area.window.draw_layout(self.gc, x+5, y+50, self.pangolayout)
   44	        return
   45	
   46	    def draw_points(self, x, y):
   47	        points = [(x+10,y+10), (x+10,y), (x+40,y+30),
   48	                  (x+30,y+10), (x+50,y+10)]
   49	        self.area.window.draw_points(self.gc, points)
   50	        self.pangolayout.set_text("Points")
   51	        self.area.window.draw_layout(self.gc, x+5, y+50, self.pangolayout)
   52	        return
   53	
   54	    def draw_line(self, x, y):
   55	        self.area.window.draw_line(self.gc, x+10, y+10, x+20, y+30)
   56	        self.pangolayout.set_text("Line")
   57	        self.area.window.draw_layout(self.gc, x+5, y+50, self.pangolayout)
   58	        return
   59	
   60	    def draw_lines(self, x, y):
   61	        points = [(x+10,y+10), (x+10,y), (x+40,y+30),
   62	                  (x+30,y+10), (x+50,y+10)]
   63	        self.area.window.draw_lines(self.gc, points)
   64	        self.pangolayout.set_text("Lines")
   65	        self.area.window.draw_layout(self.gc, x+5, y+50, self.pangolayout)
   66	        return
   67	
   68	    def draw_segments(self, x, y):
   69	        segments = ((x+20,y+10, x+20,y+70), (x+60,y+10, x+60,y+70),
   70	            (x+10,y+30 , x+70,y+30), (x+10, y+50 , x+70, y+50))
   71	        self.area.window.draw_segments(self.gc, segments)
   72	        self.pangolayout.set_text("Segments")
   73	        self.area.window.draw_layout(self.gc, x+5, y+80, self.pangolayout)
   74	        return
   75	
   76	    def draw_rectangles(self, x, y):
   77	        self.area.window.draw_rectangle(self.gc, gtk.FALSE, x, y, 80, 70)
   78	        self.area.window.draw_rectangle(self.gc, gtk.TRUE, x+10, y+10, 20, 20)
   79	        self.area.window.draw_rectangle(self.gc, gtk.TRUE, x+50, y+10, 20, 20)
   80	        self.area.window.draw_rectangle(self.gc, gtk.TRUE, x+20, y+50, 40, 10)
   81	        self.pangolayout.set_text("Rectangles")
   82	        self.area.window.draw_layout(self.gc, x+5, y+80, self.pangolayout)
   83	        return
   84	
   85	    def draw_arcs(self, x, y):
   86	        self.area.window.draw_arc(self.gc, gtk.FALSE, x+10, y, 70, 70,
   87	                                  0, 360*64)
   88	        self.area.window.draw_arc(self.gc, gtk.TRUE, x+30, y+20, 10, 10,
   89	                                  0, 360*64)
   90	        self.area.window.draw_arc(self.gc, gtk.TRUE, x+50, y+20, 10, 10,
   91	                                  0, 360*64)
   92	        self.area.window.draw_arc(self.gc, gtk.TRUE, x+30, y+10, 30, 50,
   93	                                  210*64, 120*64)
   94	        self.pangolayout.set_text("Arcs")
   95	        self.area.window.draw_layout(self.gc, x+5, y+80, self.pangolayout)
   96	        return
   97	
   98	    def draw_pixmap(self, x, y):
   99	        pixmap, mask = gtk.gdk.pixmap_create_from_xpm(
  100	            self.area.window, self.style.bg[gtk.STATE_NORMAL], "gtk.xpm")
  101	
  102	        self.area.window.draw_drawable(self.gc, pixmap, 0, 0, x+15, y+25,
  103	                                       -1, -1)
  104	        self.pangolayout.set_text("Pixmap")
  105	        self.area.window.draw_layout(self.gc, x+5, y+80, self.pangolayout)
  106	        return
  107	
  108	    def draw_polygon(self, x, y):
  109	        points = [(x+10,y+60), (x+10,y+20), (x+40,y+70),
  110	                  (x+30,y+30), (x+50,y+40)]
  111	        self.area.window.draw_polygon(self.gc, gtk.TRUE, points)
  112	        self.pangolayout.set_text("Polygon")
  113	        self.area.window.draw_layout(self.gc, x+5, y+80, self.pangolayout)
  114	        return
  115	
  116	    def draw_rgb_image(self, x, y):
  117	        b = 80*3*80*['\0']
  118	        for i in range(80):
  119	            for j in range(80):
  120	                b[3*80*i+3*j] = chr(255-3*i)
  121	                b[3*80*i+3*j+1] = chr(255-3*abs(i-j))
  122	                b[3*80*i+3*j+2] = chr(255-3*j)
  123	        buff = string.join(b, '')
  124	        self.area.window.draw_rgb_image(self.gc, x, y, 80, 80,
  125	                                 gtk.gdk.RGB_DITHER_NONE, buff, 80*3)
  126	        self.pangolayout.set_text("RGB Image")
  127	        self.area.window.draw_layout(self.gc, x+5, y+80, self.pangolayout)
  128	        return
  129	
  130	def main():
  131	    gtk.main()
  132	    return 0
  133	
  134	if __name__ == "__main__":
  135	    DrawingAreaExample()
  136	    main()