Resource centre for ZX Spectrum games
using Manic Miner and Jet Set Willy game engines
Archive of the
Manic Miner & Jet Set Willy Yahoo! Group
messages
|
|
|
|
|
Message: 7167
Author: ian.rushforth
Date: 02/02/2018
Subject: Non-aesthetic effect of the Cell Graphics Bug
I've just discovered a possible side-effect of the Cell Graphics Bug which can occur in the Manic Miner game engine, and which is more than merely an aesthetic concern.
If you POKE #CE5E, #06 and then proceed in-game to the cavern 'Miner Willy Meets the Kong Beast', you will observe that the POKE has tweaked the bottom pixel-row of the 'stalactite' Fire cells, giving rise to a match with the colour attribute for the switch.
This causes the Cell Graphics Bug to change the way that the switches are drawn in the cavern. In particular, note the way that the sixth graphic byte of the switch has been altered from the intended value (#08, as specified at the primary address #CE65 and copied to #8065 in the cavern buffer).
That, in turn, has a couple of knock-on effects upon execution of the routine at #9135 (and its subroutine at #921B) which handles the switches:
- the opening wall automatically opens as soon as Willy enters the cavern (the routine thinks that the first switch has already been flipped);
- touching the second switch does not cause the Kong Beast to fall from its perch (again, the program thinks that the switch has already been flipped, but the second CALL to the subroutine works in a different way to the first CALL - compare and contrast the code around #9144 with #917C - and therefore the flipped status of the second switch is never detected and acted upon).
|
|
|