d-wilson

How were they done the first time? Did people use something like a chip clip?

Is this site gone again?

Don't know the answer to either of those, and it wouldn't surprise me if the Jr. and 7800 had different results. Probably wouldn't hurt to get some others to take photos of Stay Frosty and post it with which Atari it was on. As you probably know, the position counters for all the objects get advanced once every colour clock during the active part of the screen. Horizontal motion works by advancing those counters once every four colour clocks during the inactive part of the screen until the HMOVE counter matches the value in the HMxxx register for an object. The trick in the starfield effect is to change the HMxxx value just in time so that it never matches with the HMOVE counter and therefore the object's position counter will keep getting extra clock pulses. On the TIA77 the extra HMOVE pulses will simply overlap with the normal clock pulses that advance the position counters and therefore have no effect during the active part of the line (That's different on the TIA89, but that's a different subject.) The problem is that the same clock pulses are also used to advance the counters in the display circuit of the movable objects. And there the two different clock pulses happening at almost the same time might cause some side effects due to some race conditions. The visual consequences of these side effects might differ due to the chip revision, the age of the TIA, the temperature etc. That's why you are getting different starfields on different VCSs. IIRC the by far most common starfield pattern I have found is like this: The missile gets shiftet 17 pixels to the left in each scanline. When the missile is supposed to be displayed over the first pixel of a PF block, it gets extended one pixel to the left. So the missile is two pixels wide and connects two PF blocks. In the next line where the missile would be displayed at the last pixel of a PF block, it doesn't get displayed at all. What happens when you use wider missiles or the player or the ball still needs to be researched. Also what happens when you trigger a HMOVE in the active part of the scanline when there are still objects to be displayed in that part of the line also needs researching. Just mentioning it so you know that you'll still have lots more fun until you can consider Stella's TIA emulation to be perfect. Does anybody know how many different versions of the TIA chip there are? Can somebody write a program that will tell you what version you have in your system?