I would to add a visual motion effect for when my characters slash a weapon in my game (like a sword).
The motion is a perfect circle around the character.

Here's an example : http://www.consoles-emulators.com/wp-content/uploads/2006/12/god-of-war-20050318074311125.jpg of course my game is in 2D

How would I go about generating that ?

- Multiple images of the full animation
- Render rotated circle slices following the weapon
- ?

There are several ways to come up with what you want. What I would do is go with the "Render rotated circle slices" technique Draw a circle with a gradient along the circumference black-to-white. Set that as the alpha channel.

To draw it just do a BlitRotated (I believe you're using OpenLayer) around the center coordinate and increment the roatation so it aligns with the swipe of the weapon.

Hmm. I would probably store the two points (top and bottom of the "effect"-part of the sword) in a list (well, a deque probably), interpolate with bezier (to get a nice number of points) and render them as a quad. If the effect should be used for the full weapon, you could just use a triangle fan with the characters hand (or whatever) as the center point (though that would probably look funky if the character moved).

sigh It's just a regular ribbon trail, from the looks of it. It's hardly a sophisticated technique.

It just means to overlay, but I guess in this case it doesn't really fit because it mainly has to do with overlaying graphics over a sprite to make it look like he/she is wearing different items, like a paper doll. Still it's a simple way of doing it, and it would work, but I'm sure it's not very efficient.

Actually, has anyone ever played Brain Lord? The animation for the weapon alone doesn't include any slash effect and is instead more "build in" to the sheet itself, which makes it look a lot more realistic in my opinion.

http://www.allegro.cc/files/attachment/592451

I probably would have done it very similarly to X-G, but you could also go with a more particle-ish system. I think it works better for 2D games (but not very well for 3D). Every x frames, push a new particle onto the related emitter that has the same sprite as your weapon, and maybe colorize it blue or white with additive blending to give the blade a nice ghostly appearance. Each "particle" should fade pretty quickly, otherwise it would look very strange.

Thanks for the comments.

I'm aware of all that, it's just that I wonder what technique to use to actually draw that slice of circle...

About the old game and Castlevania, I dont like those effects :/

I know how to check for the blade movement over time... but the ribbon effect you're talking about, I've never heard of it. Care to explain what it's about ?

Forgive my ignorance of texture mapping, but how does one stretch a texture across it?

To do it that well you almost certainly want hardware acceleration. Each sprite leaving a trail keeps a list of coordinates and angles the sprite has moved through, then quads are drawn between each pair of points so that their width is perpendicular at each side to the angle the sprite was at when it passed through them.

...which is a lot easier to say than do, but that's how you do it. Kinda like the snakes in Nibbles style games.

Or another, less accurate, but easier method that doesn't require acceleration is to drop sprites behind the sprite leaving the trail at timed intervals, which then forms the trail.

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

An emitter particle and normal particles which have a certain lifespan then fade out dramatically at the end?

True!

Bitmap.BlitDistorted oslt?