I think I may have found possible reasons for a slowdown, and I’d like your help in analyzing this as a possible solution.
My game is a 2D tile-based game.
The current world area is 128 by 128 tiles, each of which is 64 pixels.
The viewable area is 512x512 pixels, or 8 tiles on a side.
You should be able to move one tile in one second. Most characters have 8 frames of animation to display in that time, so I’d like to achieve 32 fps. (there are times in the game you should move faster, like on a speed potion).
Here is what I’m doing to paint the screen:
I have a thread that just draws the background. This is done the moment you start a movement… it uses two buffers and switches the buffers when movement stops, so it can take up 1000 ms to draw. I doubt this drawing is an issue.
To create the offScreenBuffer, which is FINALLY painted to the screen, I first blit the current BackgroundBuffer +/- the scrolling offsets… this is one g.drawImage().
The foreground images must be interleaved with character images to achieve the depth illusion, so unfortunately they MUST be redrawn every frame. I have drawing rules which state that top-right is furthest away, and bottom-left is closest, giving us a diagonal “perspective” so to speak. In order to paint these images, I got the first thing I could think of to work: a nested loop that draws top-to-bottom, right-to-left.
This results in 192 checks to see if anything is there needing to be painted. And I think it is slow to do this.
I am wondering whether I should load foreground tiles, those non-moving images in the game that interleave with characters (trees, fountains, etc), into a Quadtree.
I’m thinking of creating a Quadtree that holds an object called MapCell, which contains three variables: foreground, character, and flying. If anything there needs to be painted, I’d just draw the image right then. My reasoning is that although g.drawImage might be slow, the following loop is likely slower:
for ( int i = iRowOffset - 4; i < iRowOffset + 3; i++ )
{
for (int j = iColOffset -4; j < iColOffset + 3; j++ )
{
// Check if foreground tile exists at map[i][j]
// draw it if there
// Check if character exists at map[i][j]
// draw it if there
// Check if flying character exists at map[i][j]
// draw it if there
}
}
Now, I don’t know how long it takes to complete the checks, but I know for a fact this loop runs in O(n2) and is guaranteed to run at that rate.
At maximum this has 192 drawImage() calls, but that should never happen; the screen should never be that full.
Would it make more sense to get a range from a Quadtree, which may or may not have objects at the appropriate positions, and just iterate through that list?
Is my logic sound, or am I not looking at the fps problem the right way?