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Difference between revisions of "AGI/Specifications/Overview"

Add information about cyan pixels on the priority screen.
m (AGISpecifications/Overview moved to AGI Specifications/Overview: fixing subpage feature)
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==Control lines and priority information==
==Control lines and priority information==


In the AGI interpreter, the priority bands and control lines are drawn on the same screen. This can lead to problems when the interpreter wants to know the priority of a pixel that has a control line drawn over it. The way that the interpreter deals with this is to search downwards until it finds a pixel that isn't a control line and it assumes that the pixel it is looking at is the same priority as the one it found by searching downwards (increasing Y). Usually this will be the pixel immediately below but for some pixels this can be as far away as twenty pixels or more!! In some games this can cause a noticeable visual error if you are aware of it. For example, you could walk behind a strip of grass that thinks it is part of the tree below it (KQ1, room 20, blue control line beside left hand tree). There are also a number of other one pixel visual errors that are virtually unnoticeable if you don't know they are there.
In the AGI interpreter, the priority bands and control lines are drawn on the same screen. This can lead to problems when the interpreter wants to know the priority of a pixel that has a control line drawn over it. The way that the interpreter deals with this is to search downwards until it finds a pixel that isn't a control line and it assumes that the pixel it is looking at is the same priority as the one it found by searching downwards (increasing Y). Usually this will be the pixel immediately below but for some pixels this can be as far away as twenty pixels or more! In some games this can cause a noticeable visual error if you are aware of it. For example, you could walk behind a strip of grass that thinks it is part of the tree below it (KQ1, room 20, blue control line beside left hand tree). There are also a number of other one pixel visual errors that are virtually unnoticeable if you don't know they are there.
 
An important point to note is that cyan pixels, which normally indicate a "water" condition, should not be skipped over during this process; only pixel values 0, 1 and 2 are skipped over. Room 6 of KQ3 (the kitchen) is a prime example: the majority of the floor is cyan on the priority screen, and should appear behind the ego.


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