Sign in to follow this  
eOgas

OpenGL Free Rotation of a 3D Object

Recommended Posts

eOgas    100
I'm writing a program in opengl that involves the rotation of an object in 3d space. I've been able to get rotation down, but I have the same problem as many seem to have. The first rotation I perform is as expected, but every rotation after that is affected by the first one. Say I rotate around my x axis 90 degrees. If I do this, rotations around the y-axis are no longer shown as rotations along the y-axis, because the y-axis has moved. They now appear as rotations around the z-axis. I have read many a forum post on this subject, and on every single one the response is "gimbal lock". I've read a lot about gimbal lock in the past few days, and I'm pretty sure all those people are wrong. They say use matrices, use quaternions. Your gimbal woes will disappear. I am using quaternions, and I assure you, the problem persists. How can I rotate the object and not its axes?

Share this post


Link to post
Share on other sites
Waterwalker    431
Quote:
Original post by eOgas
How can I rotate the object and not its axes?

You can't. If you rotate the object you rotate its local coordinate system ... its axes. But gimbal lock ist mostly a problem for camera classes not when rotating objects. Just keep the rotated axes of your object and use them for rotation like so:


void Object::rotateX (float angle)
{
Mat4x4 mat = Mat4x4::getRotationMatrixForAxis(angle, m_x_axis);
m_y_axis = mat * m_y_axis;
m_z_axis = mat * m_z_axis;
}


Note that the rotateX,Y,Z() methods do rotate the Y and Z, X and Z, and X and Y axis respectively. So after each call to rotate the object's corresponding axes have been rotated. Thus the following rotation does not take the standard x, y, and z axis for rotation.

Share this post


Link to post
Share on other sites
bzroom    647
You can't, this issue is always going to exist. No storage type can get around it. It's how you use the stored value and how you increment it.

You'll basically store the final transform as a quaternion, if you choose. And increment it with another. The way you compute the incremental transform will be arbitrarily chosen based on how you want the rotation to work. You could build one with 3 euler angles that are all concatenated in a particular order, as you found out. Or you can create the quaternion based off a combination of rotations about specific axis. The concatenation order will be significant here.

There is no general rule, it's all dependent on how you want it to perform. If you could describe more clearly how it should behave, I might be of some help.

For instance, if you wanted to rotate with the mouse, every time the mouse moves you get a deltaXY. You'd create two delta quaternions, each rotating deltaX, or deltaY around the current view vectors in those directions. Then you'd multiply them together, and then multiply this into your finalOrientation quaternion.

But each time you increment it, you lose the incremental value. Trying to keep it around, like using euler angles to always recompute the finalOrientation, is asking for trouble. Just store the final arbitrary orientation.

This has to be the most confusing and pointless post ever. :)

Share this post


Link to post
Share on other sites
eOgas    100
All I want is to be able to rotate the object around a stationary set of axes. It seems like I should be able to do this with a bit of trig, but I'm not quite sure how.

Share this post


Link to post
Share on other sites
bzroom    647

Quaternion modelOrientation;

void IncrementAroundStationaryAxes(float axis1delta, float axis2delta)
{
Quaternion delta1(AxisAngle(axis1, axis1delta);
Quaternion delta2(AxisAngle(axis2, axis2delta);
Quaternion totalDelta = delta1 * delta2;

modelOrientation *= totalDelta;
modelOrientation.Normalize();
}


Axis1 and Axis2 are your fixed world axes. Such as +x and +y or something..

Or you can use the camera's current world axes as your rotation axes. Or anything you choose, it's very arbitrary.

The order of delta1 and delta 2 will make a difference. The larger axis[1,2]delta's are the more you'll notice. If the deltas are small enough you wont notice at all. But if you try to do 90degrees on both deltas, the multiplication order will be very apparent.

There's nothing wrong with that, it's doing exactly what you asked it to. You just need to understand what it is EXACTLY you want it to do. In other words, the rotations must be combined in some order, that order must be chosen by you, each order will have different outcomes. There is NO way to get around this.

Share this post


Link to post
Share on other sites
eOgas    100
Thank you so much bzroom. This is a very good explanation on how this is supposed to work. I actually understand it now, and I have my rotation working flawlessly.

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  

  • Similar Content

    • By povilaslt2
      Hello. I'm Programmer who is in search of 2D game project who preferably uses OpenGL and C++. You can see my projects in GitHub. Project genre doesn't matter (except MMO's :D).
    • By ZeldaFan555
      Hello, My name is Matt. I am a programmer. I mostly use Java, but can use C++ and various other languages. I'm looking for someone to partner up with for random projects, preferably using OpenGL, though I'd be open to just about anything. If you're interested you can contact me on Skype or on here, thank you!
      Skype: Mangodoor408
    • By tyhender
      Hello, my name is Mark. I'm hobby programmer. 
      So recently,I thought that it's good idea to find people to create a full 3D engine. I'm looking for people experienced in scripting 3D shaders and implementing physics into engine(game)(we are going to use the React physics engine). 
      And,ye,no money =D I'm just looking for hobbyists that will be proud of their work. If engine(or game) will have financial succes,well,then maybe =D
      Sorry for late replies.
      I mostly give more information when people PM me,but this post is REALLY short,even for me =D
      So here's few more points:
      Engine will use openGL and SDL for graphics. It will use React3D physics library for physics simulation. Engine(most probably,atleast for the first part) won't have graphical fron-end,it will be a framework . I think final engine should be enough to set up an FPS in a couple of minutes. A bit about my self:
      I've been programming for 7 years total. I learned very slowly it as "secondary interesting thing" for like 3 years, but then began to script more seriously.  My primary language is C++,which we are going to use for the engine. Yes,I did 3D graphics with physics simulation before. No, my portfolio isn't very impressive. I'm working on that No,I wasn't employed officially. If anybody need to know more PM me. 
       
    • By Zaphyk
      I am developing my engine using the OpenGL 3.3 compatibility profile. It runs as expected on my NVIDIA card and on my Intel Card however when I tried it on an AMD setup it ran 3 times worse than on the other setups. Could this be a AMD driver thing or is this probably a problem with my OGL code? Could a different code standard create such bad performance?
    • By Kjell Andersson
      I'm trying to get some legacy OpenGL code to run with a shader pipeline,
      The legacy code uses glVertexPointer(), glColorPointer(), glNormalPointer() and glTexCoordPointer() to supply the vertex information.
      I know that it should be using setVertexAttribPointer() etc to clearly define the layout but that is not an option right now since the legacy code can't be modified to that extent.
      I've got a version 330 vertex shader to somewhat work:
      #version 330 uniform mat4 osg_ModelViewProjectionMatrix; uniform mat4 osg_ModelViewMatrix; layout(location = 0) in vec4 Vertex; layout(location = 2) in vec4 Normal; // Velocity layout(location = 3) in vec3 TexCoord; // TODO: is this the right layout location? out VertexData { vec4 color; vec3 velocity; float size; } VertexOut; void main(void) { vec4 p0 = Vertex; vec4 p1 = Vertex + vec4(Normal.x, Normal.y, Normal.z, 0.0f); vec3 velocity = (osg_ModelViewProjectionMatrix * p1 - osg_ModelViewProjectionMatrix * p0).xyz; VertexOut.velocity = velocity; VertexOut.size = TexCoord.y; gl_Position = osg_ModelViewMatrix * Vertex; } What works is the Vertex and Normal information that the legacy C++ OpenGL code seem to provide in layout location 0 and 2. This is fine.
      What I'm not getting to work is the TexCoord information that is supplied by a glTexCoordPointer() call in C++.
      Question:
      What layout location is the old standard pipeline using for glTexCoordPointer()? Or is this undefined?
       
      Side note: I'm trying to get an OpenSceneGraph 3.4.0 particle system to use custom vertex, geometry and fragment shaders for rendering the particles.
  • Popular Now