Miter joins of rectangles with tiny height aren't rendered

Migrated from https://bugs.launchpad.net/inkscape/+bug/168957

Steps to reproduce:

• open badmiterlimit_new.svg
• select the only object
• open fill and stroke dialog
• in the stroke style tab, change the join type to round, bevel, and miter
• (observe rendering of the ends of the path)

To see how zoom and height affect this

• open badmiterlimit.svg, which shows more examples of these rectangles with differing thickness (example file taken from launchpad issue)
• zoom in and out
• (observe some paths being rendered with or without the join at different zoom levels)

What happened?

• For miter and bevel joins, the joins aren't rendered
• Appearance depends on zoom factor, and how small the height actually is (per https://bugs.launchpad.net/inkscape/+bug/168957/comments/8)
  • some zooms show the correct rendering, some don't
  • stroke to path converts to wrong appearance too (but effect there is not dependent on zoom)
• Inconsistent behaviour between printing, pdf/png export and Inkscape display

What should have happened?

• For all joins, the stroke should extend the whole width of the canvas
  • no change in behaviour even when stroke-miterlimit is set to 1000 or other large values
• Printing, pdf/png/other exports will have differing behaviour based on resolution, etc.
• Different renderers display it differently, e.g. firefox renders the joins, xviewer (rsvg?) does not.

Sample attachments:

• Second example file, showing how zoom and thickness affects the rendering, from bug-importer on launchpad: badmiterlimit.svg
  • Comparison at different zoom levels:
    • 
• Minimal file: badmiterlimit_new.svg
• File from launchpad issue, created in Inkscape Entwurf1.svg -

Version Info:

• 1.1-dev (3ee125b4ad, 2020-10-26) Linux Mint 20
• Inkscape 0.92pre1 15073 (GTK3) Arch
• 0.92.x rev. 15044 (inkscape@74b8d7e2), Windows XP
• Various tests on launchpad (I believe these displayed Entwurd1.svg in Inkscape correctly, but not on export)
  • Inkscape 0.45.1, built Mar 21 2007, Windows XP
  • 0.48.5 Windows XP
  • 0.91 Windows XP (problems at higher zooms)
  • r11859 (inkscape@75e147ea) (cairo 1.11.2), Windows XP
• On 2012-11-12, jazzynico comments

  Also affects the trunk versions of Inkscape (with cairo rendering) Reproduced on XP with revision 11859 [inkscape@75e147ea] (cairo 1.11.2) and 11871 [inkscape@0516dc2e] (cairo 1.12.8, local test).

• vonHalenbach (lustik) wrote on 2007-12-22: replicated SVN 16763. I exported the attached svg to cairo pdf. But i seem to have an old version of cairo installed. My cairo is 1.4.2 i don't know if this is relevant.