[cairo-commit] [cairo-www] src/pyrsvg.mdwn

[Carl Worth]

 src/pyrsvg.mdwn |  126 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 126 insertions(+)

New commits:
commit 5ceb44bd27501ded824595654011c94a24645dc0
Author: Donn <donn.ingle at gmail.com>
Date:   Sun Nov 11 07:55:10 2007 -0800

    pyrsvg demos

diff --git a/src/pyrsvg.mdwn b/src/pyrsvg.mdwn
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+## How to use librsvg from Python
+
+It finally took me an entire installation of a new O/S and "locate .py | grep rsvg"(*) on my drive to find what I could not find via google : how to open an SVG file and draw it from PyCairo.
+
+I had to upgrade my O/S (to Gnu/Linux Kubuntu 7.10) in order to get the latest Python-gnome2-* packages for, buried in there, is a Python wrapper for librsvg. I don't know why it's not a stand-alone wrapper like PyCairo, but that's the way it is.
+
+The first demo is directly from the example I found on my drive.
+
+(*) You can find this demo in /usr/share/doc/python-gnome2-desktop/examples/rsvg on *buntu Gutsy 7.10
+
+    #!/usr/bin/env python
+    
+    import sys
+    import cairo
+    import rsvg
+    import gtk
+    
+    
+    BORDER_WIDTH = 10
+    
+    
+    def delete_cb(win, event):
+        gtk.main_quit()
+    
+    
+    def expose_cairo(win, event, svg):
+    
+        x, y, w, h = win.allocation
+        cr = win.window.cairo_create()
+        cr.set_source_color(win.style.fg[win.state])
+        cr.rectangle(BORDER_WIDTH, BORDER_WIDTH,
+                    w - 2*BORDER_WIDTH, h - 2*BORDER_WIDTH)
+        cr.set_line_width(5.0)
+        cr.set_line_join(cairo.LINE_JOIN_ROUND)
+        cr.stroke()
+    
+        if svg != None:
+            matrix = cairo.Matrix(3,0,0,3,0, 0)
+            #cairo.Matrix.rotate( matrix, prop.rot )
+            cr.transform (matrix)
+            svg.render_cairo(cr)
+    
+        return True
+    
+    def main():
+        win = gtk.Window ()
+        win.connect("delete-event", delete_cb)
+    
+        svg = None
+        if (len (sys.argv) > 1):
+            svg = rsvg.Handle(file=sys.argv[1])
+        else:
+            raise SystemExit("need svg file")
+    
+        win.connect("expose-event", expose_cairo, svg)
+    
+        print svg.props.width, svg.props.height, svg.props.em, svg.props.ex
+    
+        win.show_all()
+        win.connect("destroy", lambda w: gtk.main_quit())
+        gtk.main()
+    
+    if __name__ == '__main__':
+        main()
+
+##Writing an SVG file
+
+I thought I'd see how writing **out** an SVG file from Cairo works, this is a short example.
+
+
+    import cairo
+    import rsvg
+    import math
+    
+    fo = file('test.svg', 'w')
+    
+    WIDTH, HEIGHT  = 256, 256
+    
+    ## Prepare a destination surface -> out to an SVG file!
+    surface = cairo.SVGSurface (fo, WIDTH, HEIGHT)
+    
+    ## draw something - this taken from the web.
+    ctx = cairo.Context (surface)
+    ctx.scale (WIDTH/1.0, HEIGHT/1.0) # Normalizing the canvas
+    pat = cairo.LinearGradient (0.0, 0.0, 0.0, 1.0)
+    pat.add_color_stop_rgba (1, 0.7, 0, 0, 0.5) # First stop, 50% opacity
+    pat.add_color_stop_rgba (0, 0.9, 0.7, 0.2, 1) # Last stop, 100% opacity
+    ctx.rectangle (0, 0, 1, 1) # Rectangle(x0, y0, x1, y1)
+    ctx.set_source (pat)
+    ctx.fill ()
+    ctx.translate (0.1, 0.1) # Changing the current transformation matrix
+    ctx.move_to (0, 0)
+    ctx.arc (0.2, 0.1, 0.1, -math.pi/2, 0) # Arc(cx, cy, radius, start_angle, stop_angle)
+    ctx.line_to (0.5, 0.1) # Line to (x,y)
+    ctx.curve_to (0.5, 0.2, 0.5, 0.4, 0.2, 0.8) # Curve(x1, y1, x2, y2, x3, y3)
+    ctx.close_path ()
+    ctx.set_source_rgb (0.3, 0.2, 0.5) # Solid color
+    ctx.set_line_width (0.02)
+    ctx.stroke ()
+    
+    ## Do the deed.
+    surface.finish()
+
+You can use 'svgdisplay' (if you have the binary), Inkscape, Firefox or the first demo app to view test.svg
+
+##A feedback loop
+
+What happens when you feed the snake it's tail?
+
+    import cairo
+    import rsvg
+    
+    fo = file('test.svg', 'w')
+    
+    WIDTH, HEIGHT  = 256, 256
+    surface = cairo.SVGSurface (fo, WIDTH, HEIGHT)
+    
+    ctx = cairo.Context (surface)
+    
+    svg = rsvg.Handle(file="test2.svg")
+    svg.render_cairo(ctx)
+    
+    surface.finish()
+
+Well, it works! test.svg comes in and comes out as test2.svg. I don't think it proves anything, but it's fun.
+