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using Manic Miner and Jet Set Willy game engines
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Message: 7193
Author: ian.rushforth
Date: 16/04/2018
Subject: Re: wraparound / mm
I wrote:
> Instead, when Willy is falling off the bottom of a Manic Miner cavern, the lower part of his sprite is drawn at
> the top of the cavern (although in the first time-frame, his lower half may not be visible if the Air INK
> and PAPER settings match).
To clarify something arising from that latter point: in the first time-frame, an attribute value corresponding to Willy's white INK OR'd with the BRIGHT/PAPER settings of the background is written to the primary attribute buffer for the cells in the top two cell-rows through which Willy is falling whilst he is straddling the boundary between the bottom and top of the cavern.
That creates de facto Water cells in the location at the top of the cavern where Willy fell through, and so in subsequent time-frames (once the primary-to-secondary buffer copying takes place at the start of the next pass through the Main Loop), the bottom of Willy's sprite is visible there (he is passing through pixel-less Water cells so his sprite is displayed in the attribute that was written to those cells. i.e. white INK and the BRIGHT/PAPER settings for the cavern's Air).
Those de facto Water cells are 'standonable', and therefore prevent Willy from falling through the bottom of the cavern at the same x-coordinate for a second time (unless he dies and the cavern is refreshed in the intervening period).
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