scale_factor breaks font rendering in 2.1; was ok in 2.0

[woodpeck]

I'm setting a scale_factor of 2.0 on the agg renderer and this breaks font rendering in Mapnik 2.1. I'm using more or less the standard OSM Mapnik style. A test tile with scale 1.0 look ok:

The same tile rendered with scale_factor 2.0 in Mapnik 2.0 (2.0.1+dev20120507.git.7fe677d-1~precise1) looks right (icons are not scaled but that's a different issue):

However with Mapnik 2.1 (2.1.0+dev20120627.git.d9880ef-1~precise1) I am seeing:

It almost looks as if the font rendering engine was reverting to unifont for some reason.

[artemp]

@woodpeck - should be fixed in bf60dd9

@herm - can you check the fix doesn't break new text placement logic?

[herm]

Looks good to me.

[springmeyer]

This change seems to work in simple tests: basically it has no effect when scale_factor is 1, but when greater now allows larger text rather than just larger spacing. But it broke 4 of the visual tests. @herm - can you see if you can figure out if the tests are valid or if they need to be updated?

[woodpeck]

Confirm fixed in my test case as well, using almost-latest trunk (not yet including your above halo fix):

Thank you!

[springmeyer]

Great to hear @woodpeck! Thanks for reporting.

[herm]

Sorry, my last comment was wrong. The line in font_engine_freetype.cpp is actually needed. What the code does is:

• Calculate the size of all characters (which might have different font sizes) and pass them to placement finder so it doesn't have to ask freetype again and again.
• Find placement
• Render all characters at their calculated positions with the correct font size.

If you don't set the font size in the last step you end up with all characters being the size of the last character.