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# Zerratar

Member Since 05 Sep 2013
Offline Last Active Jul 26 2015 02:05 PM

### In Topic: How I tackled my performance issues developing an Android game in Unity

26 July 2015 - 01:51 PM

Hey frob!

I must agree, this does aim at game development in Unity in general and not really specifically for just Android!
So these apply in all cases ;-)

I've been using Unity now for almost 3 years and I've enjoyed every single bit of it. But I've also learned incredibly much during this period.
I was hoping that this would help out others that was encountering the same issues I once did.

/Karl

### In Topic: Help with rotation issue

23 September 2013 - 01:44 PM

Well, if you simply want to rotate the arm around its shoulder. You can use the following:

```var m = Mouse.GetState();
Vector2 mousePos = new Vector2(m.X, m.Y);

Vector2 distance = mousePos - p1;
// calculate angle to rotate
float angle =
(float)Math.Atan2(distance.Y, distance.X);

spriteBatch.Begin();
spriteBatch.Draw(armAndGunTexture, p1.X, p.Y, null, Color.White, angle, Vector2.Zero,1f, SpriteEffects.None, 0);
spriteBatch.End();```

I hope this helped

### In Topic: Making a 3D model face the direction it's moving

09 September 2013 - 06:08 AM

It Worked!!!

Thanks Zerratar that worked perfectly!

code below is just a small sample of how I tested it

Vector3 NewPosition = new Vector3(55, 0, 77);

```  if (currentKeyboardState.IsKeyDown(Keys.Left))
{

RotationQuat = GetRotation(NewPosition);
}
```

and Thanks again guys for responding to my post

Hurray! I'm glad it worked for you!

### In Topic: Making a 3D model face the direction it's moving

05 September 2013 - 04:09 AM

Hi football94!

You can calculate the rotation between the two world points (Vector3)

This is what I used in my game:

```	public Quaternion GetRotation(Vector3 targetPos)
{
return GetRotation(this.Position, targetPos);
}

public Quaternion GetRotation(Vector3 entityPos, Vector3 targetPos)
{
// the new forward vector, so the avatar faces the target
Vector3 newForward = Vector3.Normalize(entityPos - targetPos);

// calc the rotation so the avatar faces the target
var src = Vector3.Forward;

var dest = newForward;

src.Normalize();
dest.Normalize();

float d = Vector3.Dot(src, dest);

if (d >= 1f)
{
return Quaternion.Identity;
}
if (d < (1e-6f - 1.0f))
{
Vector3 axis = Vector3.Cross(Vector3.UnitX, src);

if (axis.LengthSquared() == 0)
{
axis = Vector3.Cross(Vector3.UnitY, src);
}

axis.Normalize();
return Quaternion.CreateFromAxisAngle(axis, MathHelper.Pi);
}

float s = (float)Math.Sqrt((1 + d) * 2);
float invS = 1 / s;

Vector3 c = Vector3.Cross(src, dest);
Quaternion q = new Quaternion(invS * c, 0.5f * s);
q.Normalize();

return q;
}
```

NewPosition = should be the target (future) position that your model is moving towards.

Quaternion RotationQuat = GetRotation(NewPosition);

then you need to store your RotationQuat and do NOT update it until your new "future" position is changed.

otherwise the model will rotate back the moment you stop moving.

for (int i = 0; i < bones.Length; i++)
{
bones[i] *=
Matrix.CreateFromQuaternion(RotationQuat)
* Matrix.CreateTranslation(position)
* Matrix.CreateWorld(Translation, Vector3.Forward, Vector3.Up); //Move the models position
...

I hope this helped

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