Object rotation around pivot point issue

Question

I'm trying to rotate the model based on my mouse click position. Each time I click the mouse, the rotate point is recalculated, but after I rotate the model and choose another rotate point, the model shifts. I don't know what is wrong with my implement. If I need to provide more information to receive helps, just tell me.

This is the render function:

private void Render()
{
    glControl1.MakeCurrent();
    GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
    GL.MatrixMode(MatrixMode.Modelview);
    GL.PushMatrix();
    GL.LoadIdentity();

    GL.Translate(transX, transY, 0);
    GL.Translate(rotatePoint.point);
    GL.Rotate(angleX, 0, 1, 0);
    GL.Rotate(-angleY, 1, 0, 0);
    GL.Translate(-rotatePoint.point);

    SetupViewport();
    pco.Render();
    GL.PopMatrix();
}

SetupViewport function:

private void SetupViewport()
{
    int w = glControl1.ClientSize.Width;
    int h = glControl1.ClientSize.Height;

    GL.MatrixMode(MatrixMode.Projection);
    GL.LoadIdentity();
    float aspect = w / (float)h;
    float n = scaling;
    float left = -n * 0.5f, right = n * 0.5f, down = -n * 0.5f / aspect, up = n * 0.5f / aspect;

    if (w <= h)
    {
        GL.Ortho(-1, 1, -aspect, aspect, -1, 1);
    }
    else
    {
        GL.Ortho(left, right, down, up, -10.0f, 10.0f);
    }
    GL.Viewport(0, 0, w, h);
}

This is when I rotate around the original state:

The model shifted after rotate but when I rotate the model back to the original state, it stops shifting:

While I don't know the solution to this issue, following may help: 1) Start dragging at a specific point. 2) Drag around and after dragging move your mouse back to that point. 3) If nothing got shifted, it could be that something with the mouse delta input is not working. Also I recommend converting videos to GIF format and pasting them in this question rather than a YouTube link, because that way you ensure that all people reading this question know what your problem is. — CheckerT
– CheckerT, Commented Jul 30, 2024 at 12:11
@CheckerT If I rotate the model back to the beginning state, the model won't shift. Personally, I think its because the rotatePoint calculation is not based on the new state after rotating the model. Btw, thanks, I'll add the gif into my question. — nghia_pham
– nghia_pham, Commented Jul 30, 2024 at 12:27

nghia_pham · Accepted Answer · 2024-08-08 08:04:23Z

In my code, I didn't save the previous state and then multiply that previous state to the transformation I did earlier.

The problem is I keep creating a new model matrix base on the origin state so that make my model shifts when I choose a new pivot base on the NEW STATE but meanwhile reset the state to origin. Have to save the previous matrix to use it later, I do these steps (Example code):

// Global variable
Matrix4d prevModelMatrix = Matrix4d.Identity;
Matrix4d modelMatrix = Matrix4d.Identity;

function Render() {
  ...
  GL.LoadMatrix(modelMatrix);
  ...
  Transformation... (Use offset instead of using new rotate and translate value to avoid accumulating)
  For example: 
    - GL.Rotate(offsetAngleX, 1,0,0);
}

// Reset offsets to 0 to avoid Render() function still use the offset to transform the scene
function MouseUp() {
  offsetAngleX = 0;
  ...
}
```

Stack Exchange Network

Object rotation around pivot point issue

1 Answer 1

You must log in to answer this question.

Hot Network Questions

Object rotation around pivot point issue

1 Answer 1

You must log in to answer this question.

Related

Hot Network Questions