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- Gradient Sizes -
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The actual height of the gradient in an emulator seems to depend on the gradient
itself. However, the following are *approximations* of how many scanlines should
be used to cover up the entire backdrop--the actual number of scanlines needed
will vary.

Scrolling Mode
 None:     ~130 scanlines (use a fixed 224-scanline HDMA gradient instead)
 Slow:     ~140 scanlines (consider using a fixed 224-scanline HDMA gradient)
 Variable: ~224 scanlines
 Constant: ~320 scanlines