FlipX / FlipY with IK - XNA

Vermeulen

I am trying to move an IK constraint ingame to have the character focus on the cursor. I am finding that I need to set FlipY = true for the IK to work (since I think XNA's Y axis is inverted).

Is using FlipX and FlipY not possible with inverse kinetics? Is there another way I can flip/mirror the character, like with the skeletonRenderer? Or maybe flip/mirror the animation at some separate step

Here is a video of the setup in Spine:

And trying it ingame (first with the character not flipped, then it flipped):

thanks,

Vermeulen

Nate

Sorry for the long delay.

It looks like a bug with IK, however the raptor example has IK and it seems to work fine when flipped. Maybe you can email a executable XNA example so I can repro the problem?

Vermeulen

I altered the example source to demonstrate:
https://dl.dropboxusercontent.com/u/170 ... ne-xna.zip

Use W and S keys to switch FlipY

Nate

I'm really very sorry it took so long to get to your issue. 🙁

I was a bit confused so I moved the gun goal so it wasn't so far from the tip of the gun:
Loading Image
This made it easier to see where the gun should be pointing.

Next I changed how the local bone position is set:

var state = Mouse.GetState();
float worldX = state.X - skeleton.X, worldY = state.Y - skeleton.Y;
float localX, localY;
Gun.Target.Parent.WorldToLocal(worldX, worldY, out localX, out localY);
Gun.Target.X = localX;
Gun.Target.Y = localY;

WorldToLocal is required to transform the coordinates from the skeleton world coordinates to the bone's parent coordinates.

Finally, I found and fix a bug with single bone IK when using a y-up coordinate system or when the skeleton or bones are flipped. Fix is in Git!

BinaryCats

@Nate, you know there is a similar bug with all of the runtimes (atleast unity plug in and c runtime). Could this be the same fix? if so, have you updated all of the runtimes or just xna?

Nate

All runtimes got the fix.

BinaryCats

woo thank you

Hi,

I just checked it with unity (using the latest runtime) and the problem still persists. When an IK is manipulating two bones and the X is flipped it works fine, but if the IK is manipulating one bone then it does not resolve correctly. Is there something special that needs to be called?

Its also worth noting it happens in editor too.