kicad-developers team mailing list archive

[Seth Hillbrand <seth@xxxxxxxxxxxxx>]

Am 2019-05-10 12:33, schrieb Tomasz Wlostowski:
> Hi,
>
> I've been recently playing with Victor's huge 32-layer PCB design and
> trying to improve the performance of pcbnew for larger designs. This
> board causes even pretty decent PCs to crash/render glitches due to
> pcbnew's enormous VBO (Vertex Buffer) memory consumption.
>
> It turns out it's caused by the way KiCad renders filled zones:
> - the inside of a zone is drawn/plotted as a filled polygon with 
> 0-width
> boundary. This one not a problem - we already triangulate the polygons
> and I recently developed a patch for the OpenGL GAL that allows reusing
> vertices of triangulated polys in the VBO/Index buffer to further 
> reduce
> memory footprint.
> - the thick outline is drawn with rounded segments with the width =
> minimum width of the polygon. Since we don't have arcs in polygons, 
> each
> of round features (e.g. vias) surrounded by a zone gets a ton of tiny
> segments in the polygon outline. Each rounded segment in OpenGL is
> composed of 2 triangles, hence 6 vertices (that can't be reused...). 
> For
> Victor's board it means 1 GB (sic!) of the VBO goes for outlines of the
> polygons alone. Disabling the outline drawing makes the renderer work
> smooth again.


What about moving the knock-out code to the relative-error calculation 
first?  Vias probably don't need 32 segments around the edge.  Look at 
buildZoneFeatureHoleList().  We currently use 32 as the minimum value 
for segments per circle, so each via with a cutout has 32 segments, each 
of which have 32*3 points for the rounded edges.  So that's 3k worth of 
points per via.  If we moved to the relative error for the vias, most 
would be at ~14 segments (for a 6-mil via with 6 mil clearance) or only 
588 points.

Most of the code for the relative calculation is in place already.  We 
need to finish updating routines line 
TransformShapeWithClearanceToPolygon() and Inflate() to remove their 
dependence on segment count.

This might avoid the need for massive overhaul of the graphics engine.

-Seth