artemp/mapnik — Issue #585: Text halo not correctly rendered after Cairo scaling
Author: artemp
Created: 2011-10-11 16:27:04+00:00
State: open
Labels: Cairo_Renderer

In MapOSMatic, we are currently working on a new version of our map rendering engine (still based on Mapnik, of course ;-). We are running into a weird issue with the halo_radius attribute of the TextSymbolizer. It appears the halo is not properly rendered across Cairo scaling, which we didn't do before.

Now, we tell Mapnik to render its map in a "big enough" surface that is then scaled down with Cairo (using CairoContext.scale) to fit into a certain area on the Cairo surface.

I'm not sure how to describe the problem, but the halo (which apparently is a thin white path following the glyph of each letter) doesn't behave properly when rescaled. Attached are screenshots of the PDF and SVG outputs.

We have another problem with text rendering when scaling that only happens when rendering to PNG. I'm not sure if it's related, so I'll create a separate ticket with another screenshot for it.