• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
Rickard_Hermansson

Parent child relatioship using quaternions

7 posts in this topic

Hello.

I have two game objects.

The final world transform of each object is calculated by concatenating the objects local transform with that parents transform, like so:
world =  Matrix.Scaling(scale) * Matrix.RotationQuaternion(orientation) * Matrix.Translation(position)
world *= parent.world;
Now, to my problem.

the scenario is:

1. I pitch objectA 90 deg around the world x-axis (position is (0,0,0))
2. I move objectB a few units along the x-axis (position is (3,0,0))
3. I set the objectA as the parent of objectB

Now I decide to yaw objectB in world space, the operation would be (using quaternions):
objectB.orientation = qYaw * objectB.orientation;
BbjectB will rotate around the world z-axis since it is parallel to the parents y-axis.

I need to account for the parent's oerientaton when performing rotations in world space, and I have no idéa how
to do that. I have tried to use the conjugate of the parents orientation, but without success. Edited by Rickard_Hermansson
0

Share this post


Link to post
Share on other sites
Just premultiply your quaternion orientation by your parents quaternion orientation?

 

Do you mean when creating my world matrix or when performing the rotaion?

 

currently the object position,orientation, and scale is relative to the parent.

 

premultiplying it would mean that the orientation is stored relative to the world rather than the parent?

0

Share this post


Link to post
Share on other sites
Perform the rotation in local space but then premultiply the resulting quaternion by the parents orientation quaternion, then convert to a matrix... that should work as long as there is no non-uniform scale. q = q1 * q2 is the rotation quaternion for q1 followed by q2.
0

Share this post


Link to post
Share on other sites
I asume this mean I should no longer use tha parent world matrix.
The code for creating the world matrix now looks like:
How ever, the result is the same.
if (parent != null)            {                Quaternion q = orientation * parent.orientation;                Vector3 p = parent.Position + position;                p = Vector3.Transform(p, parent.orientation);                world = Matrix.Scaling(scale) * Matrix.RotationQuaternion(q) * Matrix.Translation(p);                               // world *= parent.world;            }            else            {                world = Matrix.Scaling(scale) * Matrix.RotationQuaternion(orientation) * Matrix.Translation(position);            }

if i do:
childMesh.Transform.Roll(deltaTime * 5f, TransformSpace.World);
The child will rotate around the y-axis because of the parent orientation and I wan't it tor rotate around the z-axis. Edited by Rickard_Hermansson
0

Share this post


Link to post
Share on other sites

The code for making th rotations

 

 /* The rotation we wan't too add to this orientation*/
            Quaternion q = Quaternion.RotationAxis(axis, angle);
            q.Normalize();
            switch (space)
            {
                case TransformSpace.World:
                        orientation = q * orientation;
                    break;

                case TransformSpace.Local:
                    
                    orientation = orientation * q;
                    break;
            }
0

Share this post


Link to post
Share on other sites

Well I made a mistake.

 

Since the parent is rotated forward the inital rotation of the child will also be rotated forward.

I used, being a bit stupid, a unit cube to visualize the child, so I did not notice that it had the same inital orientation of the parent. (ofcoruse it did!)

 

Thank you for your help!

0

Share this post


Link to post
Share on other sites

I asked around in tge Ogre 3D forum how it's done there. I seems that the quaternion multiplication order differs from ogre and sharp dx (atleast is seems that way), I have asked on their forum. In ogre the multplication order is right to left.

in the XNA documentation is say the product of a quaternion multiplication = Q2 * Q1, e.g right to left.

any ways, my code for rotating in the desired transform space :

 

   case TransformSpace.Parent:

              relativeOrientation =  relativeOrientation * q;
              break;

    case TransformSpace.World:

             relativeOrientation = WorldOrientation * q * worldOrientationInverse * relativeOrientation;                   
             break;

     case TransformSpace.Local:

               relativeOrientation = q * relativeOrientation;
               break;

Now, the order of multiplication here is the reverse of what ogre is using.
When I send the worldmatrix to the shader I have to transpose it, Sharp DX use row major and the HLSL shader expect matrices as column major. So I transpose the world matrix before sending it to the shader.

Is this why I must reverse the order?

 

Edited by Rickard_Hermansson
0

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0