faster line rendering

[artemp]

needs testing but possibility we should be using u8 for thin lines:

"You might be able to speed the
rendering up a little if you use the scanline_p8 type (the packed version)
for thicker strokes and the unpacked version (scanline_u8) for thin strokes"

http://comments.gmane.org/gmane.comp.graphics.agg/3610

{{{

!diff

Index: src/agg/process_line_symbolizer.cpp

--- src/agg/process_line_symbolizer.cpp (revision 3296)
+++ src/agg/process_line_symbolizer.cpp (working copy)
@@ -69,7 +69,7 @@
ras_ptr->reset();
ras_ptr->gamma(agg::gamma_linear(0.0, stroke_.get_gamma()));

• agg::scanline_p8 sl;
• agg::scanline_u8 sl;
  metawriter_with_properties writer = sym.get_metawriter();
  for (unsigned i=0;i<feature.num_geometries();++i)
  {
  }}}

[artemp]

[springmeyer] generally we have to find a way to draw lines faster. we should review clipping and consider testing rasterizer_outline_aa as per: http://old.nabble.com/-AGG--Newbie-question%3A-How-to-learn--tt404602.html#a459319

[artemp]

[springmeyer] also, initializing agg::scaline_u8 outside of function call: http://permalink.gmane.org/gmane.comp.graphics.agg/2859

[artemp]

[springmeyer] http://article.gmane.org/gmane.comp.graphics.agg/2857
http://article.gmane.org/gmane.comp.graphics.agg/2860

[artemp]

[springmeyer] http://article.gmane.org/gmane.comp.graphics.agg/2776

[artemp]

[springmeyer] Closting - great boost by exposing faster "outline_aa" method of rendering lines in r3298 as a text_symbolizer property that can be enabled with rasterizer=fast.

Also, u8 does not appear any faster than p8 for thin lines and world borders, and I also could not detect benefit of single creation of u8 class as member of renderer.