gtk: Thin drawn polygons hide "clearline" lines, arcs, text

[Robert Fitzsimons]

With the gtk hid. In the latest git revision, it's also been present for a while.

When the "clearline" attribute is set on a line/arc/text, if it then intersects with a polygon on the same layer, the intersecting part isn't visible in "Thin draw/Thin draw poly" modes.

To reproduce:
- Open pcb.
- Draw a rectangle/polygon.
- Deselect "New lines, arcs clear polygons", in the settings menu.
- Draw a new line which starts outside and then enters and ends in the polygon.
- Select "Thin draw ploy", in the settings menu.

The part of the line that enters the polygon has been clipped, is invisible. Though with a bit of care you can find end point with the mouse cursor.

[Robert Fitzsimons (robfitz273k)]

For transparent objects to work in OpenGL the opaque objects need to rendered first.
http://www.opengl.org/archives/resources/faq/technical/transparency.htm#blen0020

Note: This might have an effect on the lesstif hid?

[Robert Fitzsimons (robfitz273k)]

A similar problem also exists with overlapping polygons in the same layer.

[Robert Fitzsimons (robfitz273k)]

This patch replaces the previous version. It splits the rendering of polygons into two parts for thin drawn mode, first the polygons contour and then later the transperent filling.

Tested with gtk and lesstif hids.

[Chad Parker (parker-charles)]

Branch LP1072500 implements a fix for this.

It more or less takes the same approach as the original patches, but the code base has diverged somewhat since they were submitted, and have they have bit-rotten.

[Chad Parker (parker-charles)]

Please test branch LP1072500 and report back.

It will be merged into master next weekend if I don't hear back from anyone.

[Chad Parker (parker-charles)]

Used for observing polygon transparency in thindraw mode.

[Bert Timmerman (bert-timmerman)]

OK, seems to work as advertised.

Thanks Chad ;-)