[Bug 28604] 2gis laggy map redraw

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=28604

--- Comment #6 from Yuri Khan <yurivkhan at gmail.com> 2011-11-12 09:57:49 CST ---
I have investigated the issue further and here’s what I found.

I added trace output to dibdrv_Polyline, logging the number of points and the
time it took to draw. I get values like 45ms per polyline; the most popular
point count is 5 (suggesting a quadrangle).

The time is mostly spent actually drawing lines, in calls to solid_pen_lines
which calls solid_pen_line which handles clipping to the current region and
calls bres_line_with_bias which implements the Bresenham line drawing algorithm
and for each pixel calls the callback function solid_pen_line_callback which
calls solid_rects for a single-pixel rectangle. (Which looks like a lot of
function-call overhead which also cannot be optimized out by inlining because
of the callback.)

I also tried bypassing the whole function, by adding a “return TRUE;” at the
top. The slowdown no longer reproduced, and the only part of functionality that
suffered was the railroads — the white sections were not painted.

So it seems to me that the alternative way (which, if I understand correctly,
involves round-tripping to the X server) is faster than Wine’s Bresenham. (This
also explains the similar slowness when running 2gis over ssh with X
forwarding. When the X server is on the local machine (including ssh -Y
localhost), round-tripping is fast; on another machine on the same 100Mbit
switch it is slow.)

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