scaling is moving the object

Question

Video Link for the issue.

https://www.youtube.com/watch?v=iqX1RPo4NDE&feature=youtu.be

This is what i want to attain.

https://www.youtube.com/watch?v=bWwYV0VhXqs

Here after scaling the object i can move pivot independently , position of the pivot does not affect the position of the object.

These are my matrices. when i move the pivot point to one unit in x and if the scaling is set to 1 than everthing works fine.

the pivot point has moved to one unit and the cube has stayed in its position.

But when i first scale the object to 0.5 and than move the pivot point than the cube follows the pivot point , which should not be he case as i am only moving pivot point.

Please help me with this , how can i keep the cube in position.

Though i am moving the axis not the cube so the cube should stay in original position.

glm::mat4x4 Container::GetPositionMatrix()
{
    // posx  is the x position of the object.
    // posy  is the y position of the object.
    // posz  is the y position of the object.
    glm::mat4 TransformationPosition = glm::translate(glm::mat4x4(1.0),
    glm::vec3(posx, posy, posz ));
    return TransformationPosition;
}

glm::mat4x4 Container::GetRotationMatrix()
{
    // posx  is the x positon of the object
    // pivotx is the x position on the pivot point
    // rotx is the x rotation of the object
    glm::vec3 pivotVector(posx - pivotx, posy - pivoty, posz - pivotz);
    glm::mat4 TransPivot = glm::translate(glm::mat4x4(1.0f), pivotVector);
    glm::mat4 TransPivotInverse = glm::translate(glm::mat4x4(1.0f), 
    glm::vec3( -pivotVector.x , -pivotVector.y , -pivotVector.z));
    glm::mat4 TransformationRotation(1.0);
    TransformationRotation = glm::rotate(TransformationRotation, 
        glm::radians(rotx), glm::vec3(1.0, 0.0, 0.0));
    TransformationRotation = glm::rotate(TransformationRotation, 
        glm::radians(roty), glm::vec3(0.0, 1.0, 0.0));
    TransformationRotation = glm::rotate(TransformationRotation, 
        glm::radians(rotz ), glm::vec3(0.0, 0.0, 1.0));
    return  TransPivotInverse * TransformationRotation * TransPivot;
}

glm::mat4x4 Container::GetScalingMatrix()
{
    // posx  is the x positon of the object
    // pivotx is the x  position on the pivot point
    // scax is the x scaling of the object
    glm::vec3 pivotVector(posx - pivotx, posy - pivoty, posz - pivotz);
    glm::mat4 TransPivot = glm::translate(glm::mat4x4(1.0f), pivotVector);
    glm::mat4 TransPivotInverse = glm::translate(glm::mat4x4(1.0f),
        glm::vec3(-pivotVector.x, -pivotVector.y, -pivotVector.z));
    glm::mat4 TransformationScale = glm::scale(glm::mat4x4(1.0 ), 
        glm::vec3(scax, scay, scaz));
    return  TransPivotInverse * TransformationScale * TransPivot;
}

final matrix for the Object position.

TransformationPosition * TransformationRotation * TransformationScaling

This is my final matrix for the pivot point

 PivotPointPosition = MatrixContainerPosition * MatrixPivotPointPosition * 
 MatrixRotationContainer * MatrixScaleContainer

Answer 1

The object should be orientated and located as follows:

The reference point (pivotx, pivoty, pivotz) is a point in object space.
The object has to be scaled (scax, scay, scaz) and rotated (rotx, roty, rotz) relative to the reference point (pivotx, pivoty, pivotz).
The point (posx, posy, posz) defines the position of the object in the scene, where the reference point has finally to be placed.

Do the following steps:

1. Scale the object to the desired size, with respect to the reference point:

glm::mat4 GetScalingMatrix()
{
    glm::vec3 refVector(pivotx, pivoty, pivotz);

    glm::mat4 TransRefToOrigin   = glm::translate(glm::mat4(1.0f), -refVector);
    glm::mat4 TransRefFromOrigin = glm::translate(glm::mat4(1.0f),  refVector);

    glm::vec3 scale = glm::vec3(scax, scay, scaz);
    glm::mat4 TransformationScale = glm::scale(glm::mat4(1.0), scale);
    return TransRefFromOrigin * TransformationScale * TransRefToOrigin;
}

2. Rotate the scaled object around the pivot, like in the answer to one of your previous questions (How to use Pivot Point in Transformations):

glm::mat4 GetRotationMatrix()
{
    glm::vec3 pivotVector(pivotx, pivoty, pivotz);

    glm::mat4 TransPivotToOrigin   = glm::translate(glm::mat4(1.0f), -pivotVector);
    glm::mat4 TransPivotFromOrigin = glm::translate(glm::mat4(1.0f),  pivotVector);

    glm::mat4 TransformationRotation(1.0);
    TransformationRotation = glm::rotate(TransformationRotation, 
        glm::radians(rotx), glm::vec3(1.0, 0.0, 0.0));
    TransformationRotation = glm::rotate(TransformationRotation, 
        glm::radians(roty), glm::vec3(0.0, 1.0, 0.0));
    TransformationRotation = glm::rotate(TransformationRotation, 
        glm::radians(rotz), glm::vec3(0.0, 0.0, 1.0));

    return  TransPivotFromOrigin * TransformationRotation * TransPivotToOrigin;
}

3. Move the scaled and rotated object to its final position (posx, posy, posz).

glm::mat4 GetPositionMatrix()
{
    glm::vec3 trans = glm::vec3(posx-pivotx, posy-pivoty, posz-pivotz);
    glm::mat4 TransformationPosition = glm::translate(glm::mat4(1.0), trans);
    return TransformationPosition;
}

The order matters:

glm::mat4 model = GetPositionMatrix() * GetRotationMatrix() * GetScalingMatrix(); 

---

All this can be simplified:

// translate "pivot" to origin 
glm::mat4 ref2originM = glm::translate(glm::mat4(1.0f), -glm::vec3(pivotx, pivoty, pivotz));        

// scale
glm::mat4 scaleM = glm::scale(glm::mat4(1.0), glm::vec3(scax, scay, scaz));

// rotate
glm::mat4 rotationM(1.0);
rotationM = glm::rotate(rotationM, glm::radians(rotx), glm::vec3(1.0, 0.0, 0.0));
rotationM = glm::rotate(rotationM, glm::radians(roty), glm::vec3(0.0, 1.0, 0.0));
rotationM = glm::rotate(rotationM, glm::radians(rotz), glm::vec3(0.0, 0.0, 1.0));

// translate to "pos"
glm::mat4 origin2posM = glm::translate(glm::mat4(1.0), glm::vec3(posx, posy, posz));

// concatenate matrices
glm::mat4 model = origin2posM * rotationM * scaleM * ref2originM;