Well, last night I gave a talk at one of the ever-brilliant Oxford Geek Nights, and in case you’re baying for the slides I used (all seven of them), you can find them at this wonderful OGN7 LastGraph Slides link. If you live within punting distance of Oxford, you should really try to come to the next one on August 27th. If not; well, they put videos up on the site…
In a related note, I am enjoying the improvement on my slide-making capabilities via Inkscape. Previously, PDFs exported to massive file sizes and tying the individual pages together wasn’t easy. Now, the new Cairo export in Inkscape (the same PDF export library LastGraph uses, yay) makes reasonably-sized PDFs, and pdftk munges them together easily and in record time. One day I’ll give in and use an actual presentation program.
After much work, lastgraph3’s beta is now out. Please be warned that it may not work, may explode, and may abduct your cat, dog or goldfish in the process of failing.
Apart from that, please feel free to give it a try at lastgraph3.aeracode.org. Report any and all problems back to me, either here, or at my email or something similar.
Oh, and it’s also very slow at fetching until I re-negotiate fast fetching with last.fm, since I’ve moved IP.
Update: I’ve decided to make this one of those public, neverending betas, so LastGraph is now basically open for anyone and everyone to use. The last feature I added was LastGraph Premium, my new way of soliciting donations (this time, you can donate, and in return get a few extra features). I’m still not sure about it, but I’ve had some emails before from people who would have liked it, so we’ll see how it turns out.
LastGraph has been given a much needed refresh, including a tweak to the render nodes to stop them running out of file handles/memory/disk space, and the main site so it in fact remembers when it deletes XML caches to free up space rather than wandering around going “I’m sure I put that file somewhere…”.
I may also actually implement expiry soon, as my S3 bill is finally above $5. Yay…
One of the overwhelming horrors of designing for the web (or so it would appear from a lot of the mockups I’ve seen) is that designers (and people who are just bored of Arial and Times New roman) want to make their titles on web pages using non-standard fonts. “But that’s shockingly non-accessible and uses more bandwidth”, I hear you cry; well, there’s a reason the alt tag is around, and why broadband is much more common.
Well, perhaps this isn’t the sole reason, but nonetheless it’s a more than feasible idea these days to have headings, titles and short lines of text using fonts a user doesn’t have installed on their system. And, until the spec for embedding fonts is finialised in around 2065, there are two main options:
So, we need header images. One horribly labour-intensive way of doing this is making them manually in Generic Graphics Editor 8.6. However, since we’re sensible people, we’ll generate them on the fly. And, since we’re sensible people, we’ll be using Django*, so we need to write some nice Python code.
I’ll be using Cairo to generate graphics, in part because it’s a nice library, and is pretty common these days. You’ll need the Python Cairo bindings; on debian-like systems, this is the package python-cairo; in other places, your mileage may vary.
The key to making Cairo work with Django is wrapping a Cairo canvas in a django view. For this reason, I have this function lying around:
def render_image(drawer, width, height):
import os, tempfile, cairo
# We render to a temporary file, since Cairo can’t stream nicely
filename = tempfile.mkstemp()[1]
# We render to a generic Image, being careful not to use colour hinting
surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, int(width), int(height))
font_options = surface.get_font_options()
font_options.set_antialias(cairo.ANTIALIAS_GRAY)
context = cairo.Context(surface)
# Call our drawing function on that context, now.
drawer(context)
# Write the PNG data to our tempfile
surface.write_to_png(filename)
surface.finish()
# Now stream that file’s content back to the client
fo = open(filename)
data = fo.read()
fo.close()
os.unlink(filename)
return HttpResponse(data, mimetype=”image/png”)
The idea is, you pass it a function which will draw the image onto a context, and the image’s width and height, and it takes care of all the boring tedium of wrapping cairo and django together.
Now, that’s not very useful by itself, is it? Time to draw some text!
Firstly, as an aside, we need a way of seeing how big a certain text string will be for a given font and size, so we can render an image just big enough for it. This function achieves that:
def text_bounds(text, size, font="Sans", weight=cairo.FONT_WEIGHT_NORMAL, style=cairo.FONT_SLANT_NORMAL):
import cairo
surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, 1, 1)
context = cairo.Context(surface)
context.select_font_face(font, style, weight)
context.set_font_size(size)
width, height = context.text_extents(text)[2:4]
return width, height
Yes, yes, it’s somewhat cryptic, but it does the job. Now, we can write a text-rendering view!
def render_title(request, text, size=60):
# Get some variables pinned down
size = int(size) * 3
font = “Meta”
width, height = text_bounds(text, size, font)
def draw(cr):
import cairo
# Paint the background white. Replace with 1,1,1,0 for transparent PNGs.
cr.set_source_rgba(1,1,1,1)
cr.paint()
# Some black text
cr.set_source_rgba(0,0,0,1)
cr.select_font_face(font, cairo.FONT_SLANT_NORMAL, cairo.FONT_WEIGHT_NORMAL)
cr.set_font_size(size)
# We need to adjust by the text’s offsets to center it.
x_bearing, y_bearing, width, height = cr.text_extents(text)[:4]
cr.move_to(-x_bearing,-y_bearing)
# We stroke and fill to make sure thinner parts are visible.
cr.text_path(text)
cr.set_line_width(0.5)
cr.stroke_preserve()
cr.fill()
return render_image(draw, width, height)
Here, we construct the draw function with a simple text drawing command, and run the wrapper.
There’s some interesting text positioning going on up there; for more on this, and cairo in general, read through the excellent Cairo Tutorial for Python Programmers.
The last thing is to add an appropriate URL into your URLconf, such as
(r'^title/([^\/]+)/(\d+)/$’, “render_title”)
And then, when you browse to /title/HelloWorld/20/, you’ll hopefully get a nice PNG of your new title! Then, you can just use img tags instead of titles, in this sort of style:
<img src="/title/{{ item.title }}/20" alt="{{ item.title }}" />
This process is quite quick, but not without a small cost of processing power; if you’re using it a lot, think about some sort of caching. Apart from that, be happy with your newfound title freedom…
* Or possily Pylons. As long as you don’t go and cavort with those Gems On Guiderails people, or heaven forbid the [PH/AS]P guys…
