Opengl Translation on Model Matrix malforms result

user4641064 :

I am trying to build a model matrix where I apply some common transformations like scaling, rotation and translation. I was following a tutorial here: https://solarianprogrammer.com/2013/05/22/opengl-101-matrices-projection-view-model/. I know that matrixes are not commutative so I think I paid attention to get the correct order of transformations.

But when I try to translate my model it gets stretched into the corresponding axis instead of translating. Here is how it looks:

I would appreciate any help. :)

Vertex shader

# version 330

in vec3 in_pos;
in vec3 in_col;
in vec3 in_norm;

// uniform wie eine konstante, kann einmal per frame geaender werden und gillt fuer alle vertices
uniform mat4 mvp; // mat4 = 4x4 Matrix

// out stream to fragment shader
out vec4 frag_pos;
out vec4 frag_col;
out vec4 frag_norm;

// column major
void main() {
    gl_Position = mvp * vec4(in_pos, 1.0);
    frag_pos = vec4(in_pos,1.0);
    // transparent frag_col = vec4(in_col,0.5);
    frag_col = vec4(in_col,1);
    frag_norm = vec4(in_norm,1.0);
}

Java transformations

float aspectRatio = (float) HEIGHT /(float)WIDTH;

float[][] rotX = new float[][] {
        {1.0f,0.0f,0.0f,0.0f},
        {0.0f,(float)Math.cos(thetaX),(float)-Math.sin(thetaX),0.0f},
        {0.0f,(float)Math.sin(thetaX),(float)Math.cos(thetaX),0.0f},
        {0.0f,0.0f,0.0f,1.0f}
};

float[][] rotY = new float[][] {
        {(float)Math.cos(thetaY),0.0f,(float)Math.sin(thetaY),0.0f},
        {0.0f,1.0f,0.0f,0.0f},
        {(float)-Math.sin(thetaY),0.0f,(float)Math.cos(thetaY),0.0f},
        {0.0f,0.0f,0.0f,1.0f}
};

float[][] rotZ = new float[][] {
        {(float)Math.cos(thetaZ),(float)-Math.sin(thetaZ),0.0f,0.0f},
        {(float)Math.sin(thetaZ),(float)Math.cos(thetaZ),0.0f,0.0f},
        {0.0f,0.0f,1.0f,0.0f},
        {0.0f,0.0f,0.0f,1.0f}
};

float[][] translation = new float[][] {
        {1.0f,0.0f,0.0f,transX},
        {0.0f,1.0f,0.0f,transY},
        {0.0f,0.0f,1.0f,transZ},
        {0.0f,0.0f,0.0f,1.0f}
};

float[][] scaleMatrix = new float[][] {
        {scale,0.0f,0.0f,0.0f},
        {0.0f,scale,0.0f,0.0f},
        {0.0f,0.0f,scale,0.0f},
        {0.0f,0.0f,0.0f,1.0f}
};

float[][] aspect = new float[][] {
        {aspectRatio,0.0f,0.0f,0.0f},
        {0.0f,1.0f,0.0f,0.0f},
        {0.0f,0.0f,1.0f,0.0f},
        {0.0f,0.0f,0.0f,1.0f}
};

float[][] rotationMatrix = Matrix.matMult(rotZ,Matrix.matMult(rotY,rotX));
float[][] matrix = Matrix.matMult(translation,Matrix.matMult(rotationMatrix,scaleMatrix));

float[] model = Matrix.matrixToFloatVector(Matrix.matMult(matrix,aspect));

FloatBuffer fb = BufferUtils.createFloatBuffer(16);
fb.put(model);

fb.flip();  // Reset pointer
// "upload" to graphics card
glUniformMatrix4fv(uLocMVP, false, fb);

Rabbid76 :

See The OpenGL Shading Language 4.6, 5.4.2 Vector and Matrix Constructors, page 110:

To initialize a matrix by specifying vectors or scalars, the components are assigned to the matrix elements in column-major order.

mat4(float, float, float, float,  // first column
     float, float, float, float,  // second column
     float, float, float, float,  // third column
     float, float, float, float); // fourth column

This means you have to transpose the matrix before setting the uniform variable of type mat4.

This can be done automatically by setting the 3rd parameter of glUniformMatrix4fv true:

glUniformMatrix4fv(uLocMVP, true, fb)

---

Instead you can transpose the initialization and swap the matrix multiplications (Matrix.matMult), too.