The Mega Drive has two background planes that can be scrolled independently of each other either horizontally, vertically, or on both axes.
A parallax effect can be created by scrolling the planes at different rates relative to each other. This effect adds a sense of depth by having the more distant background scroll at a slower rate than the foreground.
Here are the two planes from the Revenge of Shinobi example:
The foreground, Plane A, scrolls at a rate of two pixels per frame, while the background, Plane B, scrolls at a rate of one pixel per frame.
The VDP also supports a window plane, which is actually rendered as a portion of Plane A. The window plane never scrolls and is typically used to display player information. The above Revenge of Shinobi example shows the window plane on Plane A.
Here is an example from Twinkle Tale of vertical full-screen scrolling:
Horizontal and vertical scrolling are achieved in the same way, although the horizontal scroll offsets are stored in VRAM while the vertical scroll offsets have their own area of memory called VSRAM (Vertical Scroll RAM). Horizontal and vertical scrolling can be combined to scroll diagonally, as well.
List of Effects:
- Full-Screen Scrolling
- Row / Column Scrolling
- Line Scrolling
- Multi-Jointed Characters
- Tilting / Rotation
- Shadow and Highlight
- Palette Swapping
- Vertical Scaling
- Sprite Raster Effects
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