In June 1990, Sonic the Hedgehog debuted at the ‘90 Tokyo Toy Show, with a radically different appearance to what it became at its release a year later. In its legacy, this parallax demo became a famous piece of Sonic lost media. Especially as of the 2020s, many people including myself have attempted to recreate the parallax demo, but doing such a task would require lots of research. That’s what I’m doing here today, to write about how I believe the foreground parallax works in this demo. The foreground parallax I’ll be referring to here involves things that display above the level, such as the moving trees, rocks, and clouds. I won’t be talking about the clouds in this one though, as that is its own (still unsolved) mystery. -------------------------------------------------------------------------------------------------------------------------------------------- For many years, people have assumed this was achieved entirely based on sprites. It was found out that the tree in the final version of Green Hill Zone was constructed to work like a sprite, further supporting the idea. Unfortunately, all attempts at replicating the foreground using sprites resulted in the scanline sprite limit being reached. Later on, a pattern was found in these sprites, where they loop every 1024 pixels. This is equal to every 512 pixels of Sonic movement as these sprites move at double the speed of the camera. Spoiler: IMAGE: Loop demonstration, separated Spoiler: IMAGE: Loop demonstration, overlapped A later discovery has shown that these sprites were placed on a 16x16 grid, equal to two tiles, or one level block. The below image is an example. Spoiler: IMAGE: Offset demonstration -------------------------------------------------------------------------------------------------------------------------------------------- Being aligned in such a way seems odd for seemingly free-form sprites. That gave me the idea, what if these aren’t even sprites at all? You may be able to notice that the bottom of the background isn’t visible in any of the currently available screenshots, as the level terrain overlaps it. You may also notice that in one case, the tree overlaps another tree above the ground, but nothing overlaps in front of the ground. Spoiler: IMAGE: Overlap demonstration What’s my idea here? These are high priority background tiles. Now, this doesn’t completely rule out sprites being used, but just only when they're above the ground. Below the ground, they are background tiles. Spoiler: IMAGE: Sprites and background usage clarification The sprites and background tiles would move in sync with each other, making it look like there was a seamless third plane scrolling along with everything else. Due to that, the background plane would look something like this: Spoiler: IMAGE: Replica background plane demonstration [assets from Project Tokyo Debut 1990 by Laffy Taffy] A similar method of parallax was used in Sonic the Hedgehog 2 and Sonic the Hedgehog CD, in Aquatic Ruin and Quartz Quadrant respectively. -------------------------------------------------------------------------------------------------------------------------------------------- Putting it all together, the foreground parallax is constructed of both sprites that go above the ground, and high priority background tiles that overlay the ground. This is supported by things only overlapping above the ground, and how each object is on a 16x16 grid.
