offset < 0 for simple outline line symbology for polygon creates rounded corners

[qgib]

Author Name: Mathieu Pellerin - nIRV (Mathieu Pellerin - nIRV)
Original Redmine Issue: 10605
Affected QGIS version: master
Redmine category:symbology
Assignee: Martin Dobias

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During the development of upcoming QGIS 2.4, offset for a polygon layer's simple outline line symbology was improved and now relies on a GEOS buffer operation. While it's an overall improvement, it has a create a huge change in rendering:

• Under QGIS 2.2, a negative offset value will keep the offset'ed line's original angles (see QGIS_22-straight_angles.png)
• Under QGIS 2.4, a negative offset value will created rounded angles (see QGIS_24-rounded_angles.png)

While the rounded angle is expected when outputting a buffer, I don't think the user expects that behavior when offsetting a polygon outline. I have mixed feelings as to what should be the appropriate behavior, but after giving it some thoughts, I think the QGIS 2.2 drawing is the right. The 2.2 drawing of polygon's simple outline line with negative offset value also behaves the same as if your offsetting a line layer, which IMO is important.

In addition to the above, any project relying on this styling prior to 2.4 will obviously render very differently too, which should be considered.

Crossing fingers GEOS can do straight angle buffers :)

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• QGIS_24-rounded_angles.png (Mathieu Pellerin - nIRV)
• QGIS_22-straight_angles.png (Mathieu Pellerin - nIRV)

[qgib]

Author Name: Martin Dobias (@wonder-sk)

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• assigned_to_id was changed from Alvaro Huarte to Martin Dobias

[qgib]

Author Name: Martin Dobias (@wonder-sk)

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Fixed in changeset "ed1d08d435091e2890773b984c64fa96202b9f51".

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• status_id was changed from Open to Closed