Apple II Megademo Is Countin’ Cycles and Takin’ Names

The demoscene is an active place to this day, with enthusiasts around the world continuing to push the envelope as far as the capabilities of machines are concerned. [Deater], along with a skilled team, produced this Apple II Megademo which won first place at Demosplash 2018.

The demo starts with an intentional tease, with an emulated C64 BASIC startup screen which splits to reveal the title card. White-on-blue text isn’t the easiest on the Apple II, due to palette limitations, but it’s necessary for the joke to work. The following scenes make heavy use of mode-switching techniques in the middle of drawing the screen. Single screens are made up of various sections in LORES, HIRES, and even text modes. The term “cycle-counting” refers to the fact that the demo is written to operate in a cycle-exact fashion. This is necessary to achieve the mode-switching effects and to make the most of the limited resources of the Apple II.

It’s a demo that, like many others, does the right things in the wrong way to achieve its impressive results, and is a worthy competition winner. [Deater] has kindly provided an FAQ and source code for those who wish to study it further.

If you’ve written a mindblowing demo yourself, be sure to notify the tips line. Video after the break.

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Retro Rebuild Recreates SGI Workstation Demos On The Go

When [Lawrence] showed us the Alice4 after Maker Faire Bay Area last weekend it wasn’t apparent how special the system was. The case is clean and white, adorned only with a big red button below a 7″ screen with a power switch around the back. When the switch is flicked the system boots to display a familiar animation and drops you at a menu. Poking around from here elicits a variety of self-contained graphics demos, some interactive. So this is a Raspberry Pi in a box playing videos, right? Not even close.

Often retro computing focuses on personal computer systems. When they were new the 8-bit graphics or intricate 2D sprites were state of the art, but now their appeal tends towards learning opportunities and the thrill of nostalgia. This may still be true of Alice4, the system [Brad, Lawrence, Mike, and Chris] put together to run Silicon Graphics (SGI) demos from the mid 1980’s but it’s not the whole story. [Lawrence] and [Brad] had both worked at SGI during its heyday and had fond memories of the graphics demos that shipped with those mammoth workstation. So they built Alice4 from the FPGA up to run those very same demos in real-time.

Thanks to Moore’s law, today’s embedded systems put yesterday’s powerhouses within reach. [Lawrence] and [Brad] found the old demo code in a ratty FTP server, and tailor-made Alice4’s software and hardware to run them natively. [Brad] wrote a libgl which implements the subset of the IrisGL API needed to support their selected set of demos. The libgl emits sets of triangles to the SDRAM where [Lawrence’s] HDL running on the onboard FPGA fetches them to interpolate color and depth and draw the result on-screen. Together they allow the $99 Altera Cyclone V development board at Alice4’s heart to run these state of the art demos in the palm of your hand.

Alice4 is open source and extensively documented. Peruse the archeology of reverse engineering the graphics API or the discussion of FIFO design in the FPGA. If those don’t sate your appetite check out a video of Alice4 in action after the break.

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JeVois Machine Vision Camera Nails Demo Mode

JeVois is a small, open-source, smart machine vision camera that was funded on Kickstarter in early 2017. I backed it because cameras that embed machine vision elements are steadily growing more capable, and JeVois boasts an impressive range of features. It runs embedded Linux and can process video at high frame rates using OpenCV algorithms. It can run standalone, or as a USB camera streaming raw or pre-processed video to a host computer for further action. In either case it can communicate to (and be controlled by) other devices via serial port.

But none of that is what really struck me about the camera when I received my unit. What really stood out was the demo mode. The team behind JeVois nailed an effective demo mode for a complex device. That didn’t happen by accident, and the results are worth sharing.

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Does This Demo Remind You of Mario Kart? It Should!

Here’s a slick-looking VGA demo written in assembly by [Yianni Kostaris]; it’s VGA output from an otherwise stock ATmega2560 at 16MHz with no external chips involved. If you’re getting some Super Mario Kart vibes from how it looks, there’s a good reason for that. The demo implements a form of the Super Nintendo’s Mode 7 graphics, which allowed for a background to be efficiently texture-mapped, rotated, and scaled for a 3D effect. It was used in racing games (such as Super Mario Kart) but also in many others. A video of the demo is embedded below.

[Yianni] posted the original demo a year earlier, but just recently added detailed technical information on how it was all accomplished. The AVR outputs VGA signals directly, resulting in 100×120 resolution with 256 colors, zipping along at 60 fps. The AVR itself is not modified or overclocked in any way — it runs at an entirely normal 16MHz and spends 93% of its time handling interrupts. Despite sharing details for how this is done, [Yianni] hasn’t released any code, but told us this demo is an offshoot from another project that is still in progress. It’s worth staying tuned because it’s clear [Yianni] knows his stuff.

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Tying Knots with Industrial Robots

We’re not ashamed to admit that we desperately want a pair of high-end industrial robot arms to play around with. We don’t know where we’d put them — maybe the living room? — but we know that we’d figure something out.
This demo aims to get Boy Scouts interested in robotics by applying the beastly arms to something that all kids love, learning to tie knots. (If you ask us, they’ve got it backwards.) Anyway, there are two videos embedded below for you to peek at.

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Don’t Mess With Texas – The TI-99/4A Megademo

The demoscene is a hotbed of masterful assembly programming, particularly when it comes to platforms long forgotten by the passage of technology and time. There’s a certain thrill to be had in wringing every last drop of performance out of old silicon, particularly if it’s in a less popular machine. It’s that mindset that created Don’t Mess With Texas – a glorious megademo running on the TI-99/4A.

Entered in the oldskool demo contest at Syncrony 2017, the demo took out the win for [DESiRE], a group primarily known for demos on the Amiga – a far more popular platform in the scene. The demo even includes a Boing Ball effect as a cheeky nod to their roots. Like any good megademo, the different personalities and tastes brings a huge variety of effects to the show – there’s a great take on vintage shooters a la Wolfenstein in there too. [jmph] shared a few more details on the development process over on pouet.net.

The TI-99/4A wasn’t the easiest machine to develop for. It’s got a 16-bit CPU hamstrung by an 8-bit bus, and only 256 bytes of general purpose RAM. Despite the group’s best attempts, the common 32K RAM expansion present in the floppy drive controller is a requirement to run the demo. Just to make things harder, the in-built BASIC is too slow for any real use and there’s no function to allow the use of in-line assembly instructions. The group had to resort to a cartridge-based assembler to get the job done.

In the machine’s favour, it has a great sound chip put to brilliant use – the demo’s soundtrack will take you right back to the glory days of chiptune. It’s also got strong graphics capabilities for the era on par with, if not better than, the Commodore 64. The video subsystem in the TI works so hard that it’s the only DIP in the machine that gets a heatsink! The demo does a great job of pushing the machine to its limits in this regard.

If you’re suddenly feeling a strong attraction to the TI-99/4A, don’t worry – it’s got a cult following all its own. You can even find USB adapters & IDE controllers if you want to build a fully loaded rig, or play a stunning port of Flappy Bird if that tickles your fancy.

[Thanks to Gregg for the tip!]

Helicopter Pendulum is PID-licious

If you’ve ever tried to tune a PID system, you have probably encountered equal parts overwhelming math and black magic folk wisdom. Or maybe you just let the autotune take over. If you really want to get some good intuition for motion control algorithms, PID included, nothing beats a little hands-on experimentation.

To get you started, [Clovis] wrote in with his budget propeller-based PID demo platform (Portuguese, translated shockingly well here).

The basic setup is a potentiometer glued to a barbecue skewer with a mini-quadcopter motor and rotor on the end of it. A microcontroller reads the voltage and PWMs the propeller through a MOSFET. The goal is to have the pendulum hover stably in midair, controlled by whatever algorithms you can dream up on the controller. [Clovis]’ video demonstrates on-off and PID control of the fan. Adding a few more potentiometers (one for P, I, and D?) would make hands-on tweaking even more interactive.

In all, it’s a system that will only set you back a few bucks, but can teach you more than you’d learn in a month in college. Chances are good that you’re not going to have exactly the same brand of sardine can on hand that he did, but some improvisation is called for here.

If you don’t know why you’d like to master open-loop closed-loop control algorithms, here’s one of the best advertisements that we’ve seen in a long time. But you don’t have to start out with hand-wound hundred-dollar motors, or precisely machined bits. As [Clovis] demonstrates, you can make do with a busted quadcopter and whatever you find in your kitchen.

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