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Cairo module

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  Cairo module Poul Riis <priisdk@gmail.com> - 2015-02-03 13:00 -0800
    Re: Cairo module Travis Griggs <travisgriggs@gmail.com> - 2015-02-03 14:19 -0800
      Re: Cairo module Poul Riis <priisdk@gmail.com> - 2015-02-04 13:21 -0800
        Re: Cairo module Cousin Stanley <cousinstanley@gmail.com> - 2015-02-04 15:56 -0700
          Re: Cairo module Cousin Stanley <cousinstanley@gmail.com> - 2015-02-04 16:00 -0700
    Re: Cairo module Michiel Overtoom <motoom@xs4all.nl> - 2015-02-04 08:58 +0100

#85171 — Cairo module

I just tried the Cairo Python module.
I ran the test file below.
It works perfectly but instead of saving the resulting image as a file I want to see it displayed directly on the screen.
How can I do that?

Poul Riis




import math
import cairo

WIDTH, HEIGHT = 256, 256

surface = cairo.ImageSurface (cairo.FORMAT_ARGB32, WIDTH, HEIGHT)
ctx = cairo.Context (surface)

ctx.scale (WIDTH, HEIGHT) # 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 ()

surface.write_to_png ("example.png") # Output to PNG 

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#85179

> On Feb 3, 2015, at 1:00 PM, Poul Riis <priisdk@gmail.com> wrote:
> 
> I just tried the Cairo Python module.
> I ran the test file below.
> It works perfectly but instead of saving the resulting image as a file I want to see it displayed directly on the screen.
> How can I do that?
> 

I have quiet a bit of experience with Cairo (I wrote language bindings for it in Smalltalk and had the time of my life with it there); I have no experience with the pycairo bindings.

> 
> import math
> import cairo
> 
> WIDTH, HEIGHT = 256, 256
> 
> surface = cairo.ImageSurface (cairo.FORMAT_ARGB32, WIDTH, HEIGHT)

This is your basic problem right here. And ImageSurface is for creating an Image (sometimes called a raster graphic or bitmap). If you want to display directly to your screen, you need to create a surface that binds to your screen’s display functionality. There is one for each main operating system:

Win32Surface
XLibSurface
QuartzSurface (I see that this is missing from the pycairo documentation, but it is in the cairo documentation, and the pycairo.c file at least has some reference to it)

Allocating one of these involves getting handles (and other information) for a given window on screen of your host OS and creating the surface from it.


> ctx = cairo.Context (surface)
> 
> ctx.scale (WIDTH, HEIGHT) # 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 ()
> 
> surface.write_to_png ("example.png") # Output to PNG 
> -- 
> https://mail.python.org/mailman/listinfo/python-list

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#85234

Could you be a little more specific (giving, for instance, a full working example)?
I tried to interchange
 surface = cairo.ImageSurface (cairo.FORMAT_ARGB32, WIDTH, HEIGHT) 
with
 surface = cairo.Win32Surface (cairo.FORMAT_ARGB32, WIDTH, HEIGHT) 
but that didn't seem to work.

Could matplotlib be used to show the image?

Poul Riis

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#85237

> ....
> Could matplotlib be used to show the image?

  You might consider using python-imaging
  to display the image after writing it 
  from cairo .... 

  import image
  ....
  surface.write_to_png ( "x_surface.png" ) 

  img = Image.open( "x_surface.png" )

  img.show( command = 'display' )


-- 
Stanley C. Kitching
Human Being
Phoenix, Arizona

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#85238

> You might consider using python-imaging
> to display the image after writing it
> from cairo ....
> 
> import image

  import statement should be .... 

  import Image

  note uppercase I ....


-- 
Stanley C. Kitching
Human Being
Phoenix, Arizona

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#85200

Hi Poul,

I recently used cairo in a python project (https://github.com/luismqueral/jumpcityrecords). To see the cairo drawing directly on the screen I wrote a minimal Gtk application. It's in the 'src' directory and is called 'randomdraw.py'. Maybe it is of some help to you.

Greetings,

-- 
"You can't actually make computers run faster, you can only make them do less." - RiderOfGiraffes

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