BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  naive question - does screen refresh rate affect animation?          BorlandTalk.com Forum Index -> Delphi Graphics View previous topic :: View next topic   Author Message Warrick Wilson Guest Posted: Wed Apr 26, 2006 4:03 pm    Post subject: naive question - does screen refresh rate affect animation? I'm bouncing between a number of projects, and there's one case where we have a text crawl going from right to left across the bottom of a screen. It's actually a Java applet in a TWebBrowser control, but there's a noticable "hesitation" that's periodic (or at least somewhat predictable). I've tried doing something similar in a Delphi app a while ago - both in an ActiveX control and just a plain Windows app - and I'd still see these hesitations and some tearing on redraws. There were messages floating around about how to do such graphics, and some helped, and I know I'll be revisting that little project before the summer's over. However, I've got a more fundamental question that may pertain to some graphics and multimedia things I've been seeing: Does the monitor's refresh rate have any bearing on flicker or tearing or ??? For example, if I want something to update at 30 frames per second, but my monitor is updating at 75 Hz, do I have a built-in problem? Sort of like how fluorescent lights can cause funny patterns on monitors when the refresh rates don't match? Or is the problem I'm seeing with animation more likely related to trying to update large areas of the screen in a poor fashion? Thanks. Back to top Mike Williams (TeamB) Guest Posted: Wed Apr 26, 2006 6:03 pm    Post subject: Re: naive question - does screen refresh rate affect animati Mike Williams (TeamB) wrote: Quote: which you would see even if the screen had animation Sorry, I meant to say: which you would see even if the screen had *no* animation -- -Mike (TeamB) Back to top Mike Williams (TeamB) Guest Posted: Wed Apr 26, 2006 6:03 pm    Post subject: Re: naive question - does screen refresh rate affect animati Warrick Wilson wrote: Quote: Or is the problem I'm seeing with animation more likely related to trying to update large areas of the screen in a poor fashion? That's my guess. If your refresh rate is 75Hz that's really too fast for you to see flicker caused by the refresh itself - which you would see even if the screen had animation - and instead the flicker is from the actual drawing code itself. -- -Mike (TeamB) Back to top Jens Gruschel Guest Posted: Wed Apr 26, 2006 7:03 pm    Post subject: Re: naive question - does screen refresh rate affect animat Quote: Does the monitor's refresh rate have any bearing on flicker or tearing or ??? For example, if I want something to update at 30 frames per second, but my monitor is updating at 75 Hz, do I have a built-in problem? Sort of like how fluorescent lights can cause funny patterns on monitors when the refresh rates don't match? Or is the problem I'm seeing with animation more likely related to trying to update large areas of the screen in a poor fashion? No, you can make your drawings whenever you want. But of course it's not shown immediately, but when the cathode ray crosses your drawings, or parts of it, the next time (it's similar for TFTs). This can result in flickering. It's even possible that you don't see your drawings at all, if you draw something, then delete it again (restoring the original image), while the cathode ray is on its way back to the top of the screen (there is a short vertical retrace pause where nothing is refreshed at all). So the best thing you could do is make your drawings during the vertical retrace, or at least make sure you don't cross the ray while drawing (on the C64 this was the trick to have more sprites on the screen than the hardware did support, they were not there at the same time, only the ones near the ray did exist). In single task operating systems like MS DOS you can easily ask the graphic card whether it's vertical retrace time or not (using port $3DA) and wait a bit to sync your animation with the screen. In multi task operating systems like Windows that's not possible. Wasting CPU cycles is just one problem (but well, modern graphic cards are signaling it by hardware interrupt AFAIK). And normally it's not necessary. The worst thing which can happen is that you see a horizontal line moving across the screen, if you refresh a smooth animation periodically. That's because it can happen that the upper part is drawn to a region just refreshed, and the lower part "outruns" the ray and is shown immediately (it can be the other way round, too, but on modern systems that's not very likely). So you see the old frame above that line, and the new frame below that line. The line itself is not really visible, we just think we see it, because we notice there is a difference between the upper and the lower part. While for most applications that doesn't matter, often you won't even notice it, of course that's very bad for games and similar applications. That's why DirectX allows you to synchronize your drawings with the screen refresh rate. Of course now the frame rate cannot exceed the refresh rate (that's why some gamers turn that feature off). It's only possible if you have full control over the screen. DirectX has an "exclusive" mode, not allowing other tasks to make drawings to the screen at the same time. So this "exclusive" mode is a special full screen mode. It also allows you to update the whole screen at once, by drawing to a back buffer, which then is activated during the vertical retrace - of course that's not possible if different applications share the same screen. -- Jens Gruschel http://www.pegtop.net Back to top Roger Lascelles Guest Posted: Fri Apr 28, 2006 2:03 am    Post subject: Re: naive question - does screen refresh rate affect animat "Warrick Wilson" <warrickw (AT) mercuryonline (DOT) com> wrote in message news:444f9954$1 (AT) newsgroups (DOT) borland.com... Quote: Does the monitor's refresh rate have any bearing on flicker or tearing or ??? For example, if I want something to update at 30 frames per second, but my monitor is updating at 75 Hz, do I have a built-in problem? Sort of like how fluorescent lights can cause funny patterns on monitors when the refresh rates don't match? Or is the problem I'm seeing with animation more likely related to trying to update large areas of the screen in a poor fashion? If you go to http://www.trichview.com/vcllist/ and download the TFlickerFreePaintbox, you get a nice demo program which shows two shapes moving across the screen. One shows "tearing", the other does not. You will be able to see if the tearing effect is the same as the trouble you have. As well, you can see one way to solve the problem - you draw to an offscreen bitmap which is then blitted to screen. Underneath, the API BitBlt() function actually dumps the bitmap to screen. Even if you don't use BitBlt(), the tearing effect can definitely be reduced by drawing more cleverly. For example, if you let Windows or the VCL erase the background at each step, then you paint a new color over it, you are liable to see a burst of the erase color if the computer is "busy" for a moment. Another trick is to only update the small area of the screen which has changed and leave the rest untouched. I think the "tearing" is actually a bar of another color briefly displayed, and not a distortion of the image. In the TFlickerFreePaintbox demo, the shapes move so slowly that the tearing can't be a strobing effect - and is so pronounced that it can't be vertical refresh related, so my guess is that the CPU has obeyed an interrupt and gone off to do some other task - remember Windows is not a real time OS and has a lot of processes running, some of which involve delays. It is just a matter of time before a time consuming interrupt comes and takes away the CPU in the middle of the drawing code. That would explain why the randomness of the effect. I produce a CAD program which uses straight TCanvas drawing functions and the drawing is imperceptibly quick because minimal areas are redrawn and the predominant background color only is always redrawn first. Once in a while on a slow PC you catch a slight flicker - probably an interrupt during a draw. Roger Lascelles Back to top Warrick Wilson Guest Posted: Fri Apr 28, 2006 5:03 pm    Post subject: Re: naive question - does screen refresh rate affect animat "Roger Lascelles" <rogerlasAToptusnet.com.au> wrote in message news:44516acd$1 (AT) newsgroups (DOT) borland.com... Quote: "Warrick Wilson" <warrickw (AT) mercuryonline (DOT) com> wrote in message news:444f9954$1 (AT) newsgroups (DOT) borland.com... If you go to http://www.trichview.com/vcllist/ and download the TFlickerFreePaintbox, you get a nice demo program which shows two shapes moving across the screen. One shows "tearing", the other does not. You will be able to see if the tearing effect is the same as the trouble you have. As well, you can see one way to solve the problem - you draw to an offscreen bitmap which is then blitted to screen. Underneath, the API BitBlt() function actually dumps the bitmap to screen. Even if you don't use BitBlt(), the tearing effect can definitely be reduced by drawing more cleverly. For example, if you let Windows or the VCL erase the background at each step, then you paint a new color over it, you are liable to see a burst of the erase color if the computer is "busy" for a moment. Another trick is to only update the small area of the screen which has changed and leave the rest untouched. I think the "tearing" is actually a bar of another color briefly displayed, and not a distortion of the image. Thanks for the pointer. I looked at the program you mentioned, and it suggests that it's out-dated due to DoubleBuffered being a parameter on new panel implementations. I ran it, and there is an obvious difference in appearance. But event with the bottom image, I was still getting an odd effect on the redraw. It doesn't show up when I try and do a screen capture. But what I see is something like this (where everything is against the left margins below) (original) | | | | What I see part way thru | | | | Doesn't happen every time. What I'm trying to get is a smooth scroll/animation, and it seems that the larger the area to be drawn, the worse off the effect becomes. And it doesn't happen every time the draw takes place - it just happens "sometimes". My screen is set to 60 Hz refresh, so it's probably not in the frequency of the redraw (I set the timer to 16, and I realize there's some "slop" in how accurate that's going to be). Back to top Jens Gruschel Guest Posted: Fri Apr 28, 2006 8:03 pm    Post subject: Re: naive question - does screen refresh rate affect animat Quote: (original) | | | | What I see part way thru | | | | That's what I meant in my post. It's no flickering but some kind of "time moire effect". You cannot avoid it if you don't synchronize your animation with the vertical retrace. In Windows 9x this can be done since you can access the ports directly (but I don't recommend it). In Windows NT/2K/XP using DirectX or OpenGL is the only solution AFAIK (or maybe writing your own driver). -- Jens Gruschel http://www.pegtop.net Back to top Roger Lascelles Guest Posted: Sat Apr 29, 2006 4:04 am    Post subject: Re: naive question - does screen refresh rate affect animat "Jens Gruschel" <nospam (AT) thisurldoesnotexist (DOT) com> wrote in message news:44526d18$1 (AT) newsgroups (DOT) borland.com... Quote: That's what I meant in my post. It's no flickering but some kind of "time moire effect". You cannot avoid it if you don't synchronize your animation with the vertical retrace. Warrick mentioned a timer set to "16" in his own program. If he means 16 ms that is 62.5Hz - and strobing ("time moire") effects are possible against the 60Hz vertical frequency. That is a very fast timer - about as fast a a PC can handle. Most GDI animations are at somthing like 5Hz. If your program is for commercial distribution, you can forget the fast timer. DirectX will get this speed well up and synchronise your graphics card and program. As downloaded the program "TFlickerFreePaintBox" redraws its image at 1 Hz rate and at that frequency looks perfect to me. if you look at http://planet-source-code.com/vb/scripts/BrowseCategoryOrSearchResults.asp?t xtCriteria=flicker+free&blnWorldDropDownUsed=TRUE&txtMaxNumberOfEntriesPerPa ge=10&blnResetAllVariables=TRUE&lngWId=7&B1=Quick+Search&optSort=Alphabetica l or http://tinyurl.com/hn2og you can see another BitBlt() animation which runs in a loop, pretty well as fast as your PC can go. With my hardware and eyes, this looks perfect, with no strobing. Results may vary depending on how much background work your PC is doing. Windows makes no guarantees as to CPU availability. Results may also depend on your graphics hardware. By the way, DoubleBuffered property uses BitBlt() internally for an identical result. Roger Lascelles Back to top Roger Lascelles Guest Posted: Sat Apr 29, 2006 4:04 am    Post subject: Re: naive question - does screen refresh rate affect animat "Roger Lascelles" <rogerlasAToptusnet.com.au> wrote in message news:4452df5a (AT) newsgroups (DOT) borland.com... Quote: http://planet-source-code.com/vb/scripts/BrowseCategoryOrSearchResults.asp?t xtCriteria=flicker+free&blnWorldDropDownUsed=TRUE&txtMaxNumberOfEntriesPerPa ge=10&blnResetAllVariables=TRUE&lngWId=7&B1=Quick+Search&optSort=Alphabetica l or http://tinyurl.com/hn2og Oops! Tthere are two items at that link - its "Flicker Free Graphics !" by "Scottie G" . Roger Lascelles Back to top Jens Gruschel Guest Posted: Sat Apr 29, 2006 12:03 pm    Post subject: Re: naive question - does screen refresh rate affect animat Quote: As downloaded the program "TFlickerFreePaintBox" redraws its image at 1 Hz rate and at that frequency looks perfect to me. Yes, of course, for such slow animations (much slower than the screen refresh rate) the effect is still there, but it's nearly invisible. It also depends on what your animation looks like. I posted a very simple example project to b.p.attachments. For horizontal scrolling you'll see the effect when the scrolling speed exceeds some limit. -- Jens Gruschel http://www.pegtop.net Back to top Warrick Wilson Guest Posted: Sun Apr 30, 2006 8:03 pm    Post subject: Re: naive question - does screen refresh rate affect animat "Jens Gruschel" <nospam (AT) thisurldoesnotexist (DOT) com> wrote in message news:44534757 (AT) newsgroups (DOT) borland.com... Quote: As downloaded the program "TFlickerFreePaintBox" redraws its image at 1 Hz rate and at that frequency looks perfect to me. Yes, of course, for such slow animations (much slower than the screen refresh rate) the effect is still there, but it's nearly invisible. It also depends on what your animation looks like. I posted a very simple example project to b.p.attachments. For horizontal scrolling you'll see the effect when the scrolling speed exceeds some limit. Jens, Thanks for the example. I've played with it a little over the past couple of days and you're right - it really starts to show the effect when I get the trackbar position up to about 4. I set it up to move the opposite direction and it does the same thing, and it seems more pronounced. I think that's just a visual effect trick from the eye, though. I'm going to play with it some more. In my case, I want to actually move a larger image through the "viewport" that the PaintBox in your example would be.I was hoping to do it smoothly. Using a full-screen DirectX or OpenGL isn't currently an option in my application (I'm assuming I'd need to run full-screen "exclusive mode", rather than trying to set up an small window.) Thanks again... 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