středa 20. května 2009

Cairo PDF - text vs. curves

When I started to use Cairo, I was at first surprised and then pleased by finding out that the text in PDF export was converted into curves. However, later I found that cairo also supports normal text and embedding of fonts in PDF. Because both can be useful in different situations, I would like to show in this post how both can be achieved in PyCairo (the Cairo bindings to Python).
The basic difference is in the PyCairo context object method you use to create the text. The two possibilities are:
  • show_text(text)
  • text_path(text)

The first one puts a normal text into the drawing (and embeds fonts), while the second creates a path for the text, which can later be filled (or stroked), thus converting the text into curves.
The following code demonstrates this feature:

import cairo
width, height = 200, 100
# create the surface and context
surface = cairo.PDFSurface( "output.pdf", width, height)
context = cairo.Context( surface)
# white background
context.set_source_rgb( 1, 1, 1)
context.rectangle( 0, 0, width, height)
# draw the text
context.set_font_size( 32)
context.select_font_face( "Arial")
context.move_to( 10, 40)
context.set_source_rgb( 0, 0, 0.5)
# text as curves
context.text_path( "Hello curves")
context.move_to( 30, 80)
# text as text
context.show_text( "Hello text")
# finalization

When you run this code, you will get a small PDF document called output.pdf in which part of the text will be selectable as normal text and part will not, because it is converted to curves.
As mentioned, the text path can be also used for stroking, which will produce a nice text outline:

Žádné komentáře: