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I am trying to get Z-Ordering working. Objects are(supposed to be) drawn in order of their Y position, from least to greatest. So that objects which are higher(lower Y value) on the screen appear behind those which are lower(higher Y value). What is the best way to do this? (I have to do it for every frame) Jonoxon

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The articles section of GameDev gives some answers while a quick search on the web may point you to the tutorials for programming Pocket PC by Jacco Bikker aka The Phantom.

Ghostly yours,
Red.

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You''ll find details on a quicksort algorithm. The first sort will take the longest. Hopefully afterwards your objects will stay in y order (in your linked list or however you represent them) from frame to frame. Some suggest a quicker algorithm for a mostly sorted list (bubblesort or radix?) for subsequent sorts.

You may need to experiment to find the one that''s right for you.

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Quicksort's worst-case scenario is on a nearly-ordered list. Randomize the list if the implementation you're using doesn't already. Or, like Waverider said, choose another algorithm for subsequent sorts.

(NOTE: I do not know anything about z-sorting, just talking about sorting in general)

[edited by - Thrump on June 6, 2002 12:11:40 PM]

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Yes, I did read all of the articles on sorting algorithms and search the internet etc. I am currently using a system where I scan all the objects, and put the order into a separate array that tells the engine what order to blt the sprites.

I guess what I''m looking for is the best algorithm for an array that changes every frame. It''s FF1(Final Fantasy on SNES) style sprites that move around alot. I could just block the sprites from going behind each other, but I want to allow that.

Jonoxon

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Insertion sort''s a really nice sort if you know which of your sprites are moving...

Bubble sort''s also good if only a few elements are out of place.

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Thanks for the suggtestions, they were a great help.

Here is the code I''m currently using, it''s basically a bubble sort. Sorry for the lack of commentataion, but it should be pretty easy to figure out. I do this once per frame.

bool bOK;

for(int i=0;i=i; //Make the list

do {
bOK=true;
for(i = 0; i if(m_actors[i].pt.y >= m_actors[i+1].pt.y) {
int temp;
temp=m_iZOrder[i];
m_iZOrder[i]=m_iZOrder[i+1];
m_iZOrder[i+1]=temp;
}
}
}
while(!bOK);

for(int h=0;h<2-NUM_SPRITES;h++) {
i=m_iZOrder[h];
Blt(actor[i]);
}

Jonoxon

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