VectorStorm Blog

So here’s a fun one for you all.  I mentioned that I had achieved some speed boosts for rendering based upon insights from gDEBugger.  On the basis of that, I’ve been setting up some more intelligent rendering code which doesn’t tell OpenGL to do something that it was already doing.

In brief, what was happening before was that MT2 (and all VectorStorm games) would render every object in the scene one at a time, setting up OpenGL to render that object individually (“Turn fog on.  Turn lighting on.  Turn zbuffer on, turn writing into color channels on, turn glow effect off, etc.”), even though 95% of those settings were the same on every object in the scene.

Now what happens is that each object registers those state changes onto a new object (the “vsRendererState”), and immediately before rendering, all those queued state changes are made.  Previously if (for example) the first object in a scene is using a texture and the second object is also using a texture, I’d be telling OpenGL “okay, turn on texture support”, render the first object, then “turn off texture support now”, and then “okay, turn on texture support again” before rendering the second object.  Now, it leaves texture support on until it actually starts rendering an object which isn’t using a texture;  it only changes the settings which are actually changing, instead of just naively setting everything.

Note that to make this work, I had to remove compiled display list support.  There’s simply no good way to keep track of OpenGL’s internal state when compiled display lists are being used.  But compiled display lists were really replaced by VBOs long ago, so this shouldn’t cause concern.  It’s similar to when I removed CPU-side shaders, and overlays.  Old technologies which have been superceded by faster, better ones.  :)

The screenshot today is what happens when there’s a bug in the code (in this case, not applying rendering state changes before performing post-render effects).

The Windows version of the new VectorStorm multithreading code is now in place and working, and in the live trunk.  (Has been for about week, now;  I apparently forgot to post about it!)

I’ve also been playing a bit with gDEBugger, an OpenGL profiler/analyser/etc, which is now free (was previously quite expensive to license).  It’s nowhere near PIX in terms of power and insight, but it’s as close as we have under OpenGL at the moment.  And you can’t argue with the price.  And it works on all the major platforms, which is pretty awesome to see.  I’ve already made some sizeable rendering speed boosts for VectorStorm just on the basis of its insights into MMORPG Tycoon 2, and will have more in the near future.  Once I have these mostly sorted out, I’ll port them back into trunk as well.

This tool has also pointed out that lots of the techniques VectorStorm’s core rendering architecture use have been declared obsolete as of OpenGL 3.1.  Which surprised me, since I kind of designed VectorStorm for OpenGL 1.4 (which was the most that my ancient laptop could handle at the time);  I really didn’t think that the interfaces I was using would last all the way up to 3.1!  But it does suggest that someday I should be thinking about looking forward to the more modern revisions of OpenGL;  purging some of my old rendering architecture, and replacing it with more modern approaches.  That won’t be until after MT2, though, unless MT2 really calls for some modern rendering techniques.  (I’d really like to have some basic shadows.  But otherwise, I’m not too fussed over fancy rendering techniques for MT2).