Thoughts about 2D animations.

I know that I shouldn't think of such things like animation systems (considering that I'll write my final exam tomorrow) but it's just something that got to my mind yesterday while I was falling asleep.

Actually I'm using a fairly simple approach for animations.
To create a animated graphic in my engine you got to use the following syntax (The parameters should be self explanatory):

  GraphicsFactory::createAnimatedGraphic(Uint32  animationStepTimeInMilliseconds,Uint8 animationSteps,bool autostart)

After you created the object you can add a graphic to it via:

 animatedGraphicObject.loadGraphic("graphic.png");

(I know its a strange way, but I'll stick with this for now)

When the graphic gets drawn, only the current animationframe will get drawn.

Example:




This System works great for a normal walkcycle like this, but if you have an animation like this:






The system isn't the best solution.

The reason for that is the bounding box (bounding boxes are used for collision detection and are almost always as big as the animation frame) of each animation frame. In the walkcycle example the size of each frame never changes (its always 24x32), but if you see at the second example, especially this frame:





you'll might notice that this frame (109x49) is way bigger than the other frames (62x44 and 80x44).

If the above mentioned system is used, the bounding box of each frame is equally to the bounding box of the biggest frame. (I hope you get what I'm trying to say)

This is a big disadvantage IMHO because if a bounding box collision is detected, the collision system goes into pixel perfect collision deteciton (at least in my engine), which is way more expensive than the bounding box collision.

To avoid this problem I thought of the following approach.

At the point where the user determines the amount of animation frames, the size of each animation frame is known. (Width of the graphic / amount of animation frames = size of the biggest animation frame).

The next step would be to check each pixel of each animation frame for its color value to determine the real bounding box of each animation frame by comparing the color value of the current pixel with the color value of the images color key (The color key is the color in the image that is invisible later in the actual game).

After that step, each animation frame can be packed into an array, so you get a nice animation with perfectly fitting bounding boxes for each frame :)