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Guest FPSFREAK

Why does FPS drop in FS9?

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A simple question, right? ;)I've made a few observations in the last week or so, mostly since installing UT. To qualify, these are observations I've made on my computer, and may or may not be similar in your hands. My machine is a P4/2.26/533 768MB PC2100 RAM ti4600 128MB (stock clock) XP Home FS9 at 1024x768x32 w2xAA,4xAF Almost everything maxed (but default.xml deleted), FPS either unlimited (avg=30 fps high and dry, 12 fps at KEWR, 18 fps at KBOS) or locked at 18 (stays there except in full overcast or at some major airports like KEWR or KJFK).1.) When in slew mode, FPS skyrockets.2.) When in top-down view, FPS skyrockets.3.) At some airports, such as KBOS, FPS is really high, and unaffected by AI traffic, while other airports, such as KEWR, never see high FPS.I've done some testing to see what affects this framerate. In short, i've concluded nothing. I've adjusted sliders for autogen/scenery/weather/you name it from left to right, top to bottom, and I can only gain a few FPS at KEWR, while my frames are great at KBOS even with everything on (and with 100% ultimate traffic, mind you - there are as many planes tooling around the tarmac at boston as newark). I even went to the scenery library and inactivated the new york satellite photo scenery, and that had NO effect on frame rate at all.What surprises me is the top-down view (ctrl-s) and slew modes. Why should the frame rate be so high in those views? Everything is textured. All the AI is drawn with shadows and reflections. Water effects are visible. At a wide angle of zoom, the visibility is quite high (long distance) even in top down view. Certainly the view from the cockpit in slew mode is identical in terms of everything, yet FPS is much much higher.I started to suspect the panel, so I closed the panel either by pressing shift-1 or by cycling with W. No change. (as an aside, I do find that VCs work much more efficiently if you close the 2D panel with shift-1 before switching views - similar to another report from the 2D users' side about deleting VC gauges).I'm wondering what you all think about this. Why should frame rates be so high in slew and top-down compared to the normal views?sg

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To put it quite simply.......A lot less for the card and machine to render. Top down shows limited AC textures to render and a lot less terrain textures to render. As far as slew mode goes I wouldn't judge anything while in that mode. Not a true representation of the performance of the sim.It all comes down to what the box has to render at any given time. When you run your bench's are you being sure to use the same WX for each one?. Using realtime WX or using a different WX scenario for each bench will/can have a major impact on framerates.Bobby

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>When you run your bench's are you being sure to use the>same WX for each one?. Using realtime WX or using a different>WX scenario for each bench will/can have a major impact on>framerates.Absolutely. I usually compare three weather scenarios - The fair weather theme, a real weather set that I downloaded and archived using getweather a few weeks ago (fair, with high surface wind), and a real weather set with drizzle and overcast (again archived with getweather). Its the combination of the two that gets me. Slew has to render everything except the flight model - but in terms of graphics, its all there. Not to minimize that - I (hope) am sure the flight dynamics requires a massive amount of CPU time. But that's why top down surprizes me. I'm not sure there are fewer or smaller textures being drawn. Buildings and AI planes look very similar. Zooming way out, a large amount of ground and autogen is visible...sg

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In the case of top-down, the difference (improvement) may be due to clipping. Clipping is the algorithm that deals with scenery off the screen, whether it is behind you, to the sides, etc.... When you're in top-down view, what is behind you? Yep--sky... Not a lot to do as far as clipping is concerned. One of my first attempts at writing code--long before the days of DirectX, was writing a little 3-d sim very similar in look to the early versions of FS--I wrote it about 16 years ago. FPS was pretty good (mind you I wrote the program for an Atari ST running at 8MHZ). But the clipping algorithms--especially those dealing with what is behind the viewpoint, always had a hit in performance, which one would notice as an object like a building moved behind the viewpoint.As for slew, the flight model takes up more cpu juice than you might think. I know almost all of us have dissed it for what it can't do, but it's pretty amazing for what it can do. A lot of math is going on behind the scenes for that. Going back to my example above, I never created a decent flight model for my sim. I actually "fudged" it and wrote a model that simply looked at an aircraft's altitude, and adjusted the ground speed accordingly. Had I coded a flight model, it would have had a performance penalty.Going back to clipping, it is one of the reasons why a seemingly simple airport like Newark may have less performance than some of the detailed ones. Around Newark, there is a ton of scenery to clip....-John

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Well now you didn't say you wanted the "COMPLEX" answer Lol. Great explanation of what I said John. :)Bobby

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