Re: render.c:GetPixelOpacity() optimization ideas?

On Fri, 16 Jan 2004, Wolfgang Spraul wrote:
>
> Have there been more optimized GPO versions in the past (let's say 5 years
> ago)? (I'm asking because I doubt many machines would have been able to
> handle the enormous amount of double calculations for relatively simple
> drawing primitives back then)

This code dates from three or more years ago.  It is much faster (4X?)
than the the previous implementation.

> Would it be possible to identify some of the variables in GPO as constants
> when rendering certain primitives (let's say solid color, no aliasing, etc)?
> And then implement several GPO versions and choose the one that is just
> flexible enough but lets the compiler make use of the constants.

Certainly. Anything is possible given sufficient understanding and
time.

> Would it be possible to modify the next higher function,
> DrawPolygonPrimitive() to call GPO less/much less in certain cases?

Maybe.  Perhaps antialiasing operation can be thresholded more quickly
for a performance/quality tradeoff.

Do you have access to a high quality profiler?  I occasionally use
gcov (--enable-gcov) to do source line-level profiling.  Rather than
actually measuring time spent in functions (which is often wrong due
to the profiler overhead), it produces annotated source files
indicating how many times a given line of code was executed.  This is
a great way to find hot-spots.  It can help to determine how many
times conditional code is executed in order to decide which conditions
should be moved ahead of others in order to produce the best
short-circuit effect.

GCC supports options to use profiler output (-fprofile-arcs) to change
how it optimizes the code. I have no experience with that.

If you have a hardware emulator/analyzer for the ARM, it may offer a
high quality hardware-based profiler which allows you to profile the
application with a high degree of accuracy so you can identify the
operations which are doing the most damage.

Bob
======================================
Bob Friesenhahn
[email protected]
http://www.simplesystems.org/users/bfriesen



-------------------------------------------------------
The SF.Net email is sponsored by EclipseCon 2004
Premiere Conference on Open Tools Development and Integration
See the breadth of Eclipse activity. February 3-5 in Anaheim, CA.
http://www.eclipsecon.org/osdn