This question is with regards to a 2D fighting game.

Horizontal flip, in logic, works fine for character sprites which need to face the other directiron, i.e.:

if(Player_facing==1)
draw_sprite();
else
draw_sprite_h_flip();

However, a problem arises if the characters are not centered in the graphic. For example:

Horizontally flipping it results in this

Now the main problem is, the drawing functions use the top left part of the image to be the "start" point. So when the player changes facing/direction, he actually "moves" a lot in the horizontal plane.

For a fighting game which relies on the actual sprite graphics to determine hit boxes and collision, this is of course unacceptable.

I've tried searching for some guidance on this, but I do not exactly know what this issue is called and hence turn up with mostly unrelated results. I tried manually plowing through the old posts with not much success.

As far as I can see, I would need to offset the placement of the sprites. However, my sprites are extremely varied in shape and size, and I cringe at the thought of having to manually determine, then test where the "center" point of each frame is.

Another way which I have thought of, is to tell my artists to manually determine an anchor/reference point at the feet of the character, and to extend the size of the bitmap to as much width/height as is needed to keep it right at the center (down to one pixel accuracy). This seems logically correct, but would result in, I imagine, a lot of extra effort on the part of my artists which should not be theirs (hey, artists should just draw draw draw!). Secondly, it would increase the overall size of my graphic resources and indirectly, program memory.

Thus I pose this question to the community: how would you overcome this issue?

If I am missing something blatantly obvious, please point it out to me as I am new to game design and implementation in general.

Thanks for any input

P.S: That is not my sprite, I merely use it as an example.

EDIT: wow the pictures aligned weird, but they looked fine in the preview, fixed

PPS: Why did the draw_sprite_h_flip lose its underscores?

Alas, you answered your own question.

Sometimes the obvious answer is the best one. Any other method you can come up with to solve this problem will take some amount of extra effort. When it comes down to it, adding in all those points is not as dramatic as it seems. The only tricky part is making sure each frame has the correct alignment point assigned to it. One way to do this is to encode the offset from the top left corner into the top left pixel. When the frame is loaded you read those offset coordinates from the pixel's bits and then set that pixel to transparent. Use two pixels even if you need more bits than one pixel can provide based on the bit-depth of the sprites.

--- Kris Asick (Gemini)
--- http://www.pixelships.com

On a different note, I'd consider doing the mirroring of sprites at load time rather than every time (or even cache on demand), you'd be surprised how much graphics data you can fit nowadays

POTEMKIN BUSTER

Anyway, here's another vote for adding a sprite offset to each frame. It also solves the problem of frames being of different sizes.

Well you could extend the left side of the graphic out a bit with magic pink so the graphic is actually centered in the image But that might cause some other problems later on.