Steve44 on Aug 29, Not the poster but yes, the Spectrum was at about 3. I posted a link in another reply about something similar. Have a look at this flood fill, this was zipping along at full speed. That looks like a traditional flood fill which is a different case but I might be wrong. Leaderboard had vector graphics so the program knew analytically where the polygon edges are and it could simply write bytes in the bitmap, in most cases without reading back pixels. Let's say C64 had roughly, in practise, about 15k cycles per frame.
Quick calculation shows that filling the entire x screen in a trivial loop is k cycles for instructions alone, plus any delays should the graphics chip read the memory at the same time. Add to that vector math and the fact that not the whole screen will be filled and we should be able to count filling the scene in terms of frames, not several seconds.
Leaderboard might have sloppy routines to make it 'watchable' but I suspect C64 can fill faster than that if made to. Filled vectors were notoriously hard on C64 as both the bandwidth usage and cpu cycles spent on math rack up. Yet games like Rescue in Fractalus had simpler but still filled vectors in real time. Early 3D games are primarily limited on how they handle occlusion. If your scene is designed favorably e. Leaderboard is using a kind of painter's algorithm to do everything, which is flexible but requires using overdraw, and by itself, will produce rendering errors in many scenes because the depth will be sorted per object or per triangle, versus per pixel.
Filled triangle rasterization is particularly expensive to compute and requires a fair amount of numeric precision, both of which compound the issue of using overdraw.
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Fractalus does not use these techniques for terrain - although the exact implementation is idiosyncratic, it's ultimately filling an outline that defines the horizon, and then adds texture to the landscape with dot patterns. Bear in mind, it doesn't render to the full screen either, it's mostly HUD, while Leaderboard is a little more expansive. A similar technique was used in Last Ninja 2, where the 3d isometric screens would be visibly redrawn, with the objects drawn one over another. It was actually a very cool effect. Don't know if the underlying technical reasons were similar though.
Another problem with double buffering is the need to perform the copy of the buffer. This is trivial now, but not quite so in the early years. I grew up way behind the tech curve -- we had a few 1MHz computers in our non-US university lab and a single 4 MHz machine with a color monitor, wow which seemed super fast. As frames are often similar only a small portion really changes , on those slow machines many folks preferred to update a small portion of the single buffer at the right time instead of copying the whole thing.
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Often, the buffer was never copied. Instead, the video card is told to read from the old back buffer which is the new front buffer , and the old front buffer which the video card was drawing from last frame becomes the new back buffer. This only requires a few instructions, so can easily be done during the monitor's vertical blank.
That is entirely dependant on the hardware. Some machines could, some couldn't, and some could but mucked it up. The Spectrum couldn't so you either wrote to the live video display or used some method of copying. Some systems also had hardware sprites which weren't part of the main video ram, they were overlaid by hardware. You could also do some fun stuff with those such as rewriting them as the scanline progressed down the screen to fudge a lot more hardware sprites.
I'm out of the industry now but one of the major parts of games programming was pushing the hardware way beyond what it was designed to do. Now, as far as I understand, you write for an API. Race that beam! For simpler things, not 3D, sorting objects and a single buffer render still work just fine. Well, except that to prevent tearing, you have to draw just behind the monitor's refresh line well, at least when we had cathodic monitors.
And that required an awful lot of super accurate timing on PC at least. Or, draw just ahead of it. I think that is a matter of perspective. The idea being to have the graphics there for the display device to render them. Once it has done that, they are no longer needed, until next frame.
Doing that actually needs only a small buffer, but is timing intense, also compute and write demanding. If one has a sprite capability, and or a larger, or full frame buffer, just write from the top down, starting at the beginning of blank from the previous frame. Drawing behind works simplest assuming a full frame buffer, so the new follows the old once the display has pushed those pixels to eyeballs. Or more, depending. Render into the one the display is not using. This is more coarse, but can be less complex to arrange. The timing depends. If one is working scanline by scanline, yeah.
Need accurate timing. When working with screen regions, or just a blanking period, the requirement is relaxed. Really, all you need is to understand the speed of the object draw engine and a quick sort to insure the initial part of the frame is drawn in time for the display. Screen regions also work well when the renderer cannot get a full frame drawn every display frame.
There, a priority system will draw what is needed, delay that which is not. I enjoy doing ths kind of programming.
A full double buffer is a luxury :D. Cool stuff! Perhaps one could have even written some routines to kinda abstract that? HelloNurse on Aug 27, An "engine" could take care of synchronizing rendering with reading, but the difficult part is application specific: ensuring that rendering fits in the specified number of CPU cycles. For many cases, one ends up writing a little kernel that manages the display.
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Break the display into whatever elements make sense, and insure timing is all sorted. Run tests to get maximums. Once it is running, the rest feeds it with pointers to objects, and lists or the objects get generated dynamically at display time. Various schemes apply to overtime requirements. In old Williams arcade games, one method was to just move baddies to a non displayed region.
Aggresive players would fire off a ton of shots to trigger this.
Another is to delay animation or movement. The kernel can do that, but it gets more complex and slow. Dumber kernels are faster. Higher level code can manage what the kernel has to do. One thing is smart to do though, and that is to have the display kernel fail gracefully. Use hardware timers, or loop counters to prevent overdraw and the loss of display sync normally associated with that condition. That was a great video.
Enjoyable talk. At one point, they were drawing tiles, the walls associated with them, objects, etc Moving objects would end up between tiles and the sprite would be cut off by a different tile draw. Worse, there was no sort order that worked for all cases. They ended up creating, what the speaker called "an ai" to move the object away from the draw conflict, get it all drawn, then move the player back, just ahead of the actual motion In hindsight, they could have just decoupled the walls from the tiles and it all could have been a lot simpler!
The bit era meant that machines had a bit more memory to play with so double-buffering became a common technique on platforms like the Amiga. True, and on the Amiga it was especially nice since the location of the frame buffer was under software control, so no need to copy a full screen's worth of pixels anywhere.
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To swap, just tell write the new frame buffer base address to the appropriate custom chip registers, and you're done. Since the swap should be synchronized to the beam, the actual write typically happened in a copper list anyway, so that's what you really write to in order to do the swap. It all brings me back to being a teenager and discovering these things. If this article tickles your fancy, you should read the whole book. Bob did a great job on it!
It's all available on the website for free, or you can pay for a nice copy if you'd like to support his efforts. Thank you for the compliment!
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Thank you for the book! The chapter on the prototype pattern was the first time that I fully grokked the Factory pattern. And, your's is the only resource I've found that has thoughtfully constructive thoughts on singletons. Neil44 on Aug 27, On games this can be quite expensive in terms of frames per second and smoothness because of how it interacts with the monitors refresh rate. Now the user sees the same image for two frames then a jump and your frames per second has fallen off a cliff.
AMD has this standard for interacting with the monitor refresh now called FreeSync. The downside is that you tend to have a visible seam or "tear" in the image when the buffer flips. The real problem is that you need to be pushing a framerate at least as high your monitor's refresh rate, and ideally 2x your refresh rate. That's undesirable in a world where you don't have infinite money to spend on hardware. AMD has the advantage of not needing special hardware in the monitor, but it usually comes with the disadvantage of only being able to sync over a narrow range, such as Hz.
Some monitors have as narrow as a hz sync range, and many of them tend to flicker once they get down to the lower end of their sync range. There are currently a total of three FreeSync monitors on the market that don't totally suck. Nimelrian on Aug 27, I don't notice any issues with judder when my framerate goes below the range for 1 or 2 frames. Your info is out of date. LFC only works on models that already have a wide sync range, which is the reason that stuff like Hz panels are a problem in the first place. Finally you'll explore basic 3D modeling with Autodesk 3ds Max, and you'll learn how to enhance your games with sound effects, collisions, and more.
The final chapter of the book shows you how to put all your new knowledge together and build your own full game! All you need to get started are some basic computer skills and a love of games. No previous programming experience required! Stay ahead with the world's most comprehensive technology and business learning platform. With Safari, you learn the way you learn best.
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