drawing part of an image to a cairo surface

I am using pygtk and cairo (...wonderful stuff I must say. Thanks to all)

I am wondering how to present parts of images on my my cairo surface on a large drawingarea.

I would like to have areas within the displayed surface that appear to act clipped so I can scroll imag开发者_开发知识库es through these areas without disturbing the surrounding drawn items.

Can I cut images for part drawing onto a surface or must I just get the drawing sequence in the proper order so that the images needing to be clipped are overlain and so part hidden as required and appear clipped?

thanks for any pointers

nick

Cairo is indeed wonderful! ctx.clip() is one way to do it, using a clipping path (shown below in just pycairo, where the final draw rectangle only hits the triangular clipped area).

You could also use a transfer mode of CAIRO_OPERATOR_OUT (I think), but I'm less familiar with the transfer modes. And that would only work on the first draw, since your content would fill the alpha a bit.

(Your suggestion of "Painting Order" will work fine, too, of course!)

import cairo

WIDTH, HEIGHT = 256, 256

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

ctx.rectangle(0,0,300,300)
ctx.set_source_rgb(0,0,0)
ctx.fill()

ctx.move_to(0,0)
ctx.line_to(200,90)
ctx.line_to(90,200)
ctx.line_to(0,0)
ctx.close_path()
ctx.clip()

ctx.rectangle(0,0,300,300)
ctx.set_source_rgb(1,1,0)
ctx.fill()

surface.write_to_png("clipped.png")