Line Rendering Artifacts

I’m investigating ways of removing nasty little rendering bugs which occur when Maperitive draws something that should be a continuous polyline, but has to be rendered in several separate segments because these segments belong to different layers of painter’s algorithm.

Here’s the bug under the microscope:

I’ve turned the transparency to visualize the actual endings of several line segments. The bug is in the missing pieces of line/curve at the bottom right.

There are some workarounds for it, but of them are perfect. The first one is setting the line-start-cap : round property:

This removes the artifacts between segments, but you end up with an ugly rounded end of lines.

The next one is setting the line-start-cap property to square value:

Now you’ll have nice square end of lines, but you’ll also have new artifacts between line segment joins.

Other possible solutions:

• Extending each line segment a pixel or two in both directions.
• Drawing additional joins between unconnected segments once all layers have been drawn. Could be problematic.
• Some modification of the painter’s algorithm that would allow rendering of polylines as single continuous segments. Now we’re in the SciFi region.

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