3D shapes and Rotation in Opengl ES 2.0

It will be helpful to go through Previous tutorial before reading this one. LINK

Now, we will change the structure of Vertex a little. Position array is now of size 3 to handle x, y as well as z.

struct Vertex {

    float Position[3];

    float Color[4];

};

Our rotation matrix

void ApplyRotationX(float degrees)

{

    float radians = degrees * 3.14159f / 180.0f;

    float s = std::sin(radians);

    float c = std::cos(radians);

    float zRotation[16] = {

        1, 0, 0, 0,

        0, c, s, 0,

        0, -s, c, 0,

        0, 0, 0, 1

    };

    

    GLint modelviewUniform = glGetUniformLocation(buildProgram, "Modelview");

    glUniformMatrix4fv(modelviewUniform, 1, 0, &zRotation[0]);

}

void ApplyRotationY(float degrees)

{

    float radians = degrees * 3.14159f / 180.0f;

    float s = std::sin(radians);

    float c = std::cos(radians);

    float zRotation[16] = {

        s, 0, c, 0,

        0, 1, 0, 0,

        c, 0, -s, 0,

        0, 0, 0, 1

    };

    

    GLint modelviewUniform = glGetUniformLocation(buildProgram, "Modelview");

    glUniformMatrix4fv(modelviewUniform, 1, 0, &zRotation[0]);

}

void ApplyRotationXY(float degrees)

{

    float radians = degrees * 3.14159f / 180.0f;

    float s = std::sin(radians);

    float c = std::cos(radians);

    float zRotation[16] = {

        s, 0, c, 0,

        s*c, c, -s* s, 0,

        c*c, -s, -c * s, 0,

        0, 0, 0, 1

    };

    

    GLint modelviewUniform = glGetUniformLocation(buildProgram, "Modelview");

    glUniformMatrix4fv(modelviewUniform, 1, 0, &zRotation[0]);

}

Arrays of vertex and indices

// Define the positions and colors(R,G,B,A) of 8 vertices of square.

const Vertex Vertices[] = {

    {{0, 0, 0}, {1, 0, 0, 1}},

    {{0, 0.5, 0},  {0, 1, 0, 1}},

    {{0.5, 0.5, 0},  {1, 1, 0, 1}},

    {{0.5, 0, 0}, {1, 0, 1, 1}},

    {{0, 0, 0.5}, {0, 1, 1, 1}},

    {{0, 0.5, 0.5},  {0, 0.5, 0, 1}},

    {{0.5, 0.5, 0.5},  {0.5, 0.5, 0, 1}},

    {{0.5, 0, 0.5}, {0.5, 0, 0.5, 1}},

  

};

//Define the order of vertices for 12 triangles/

//0,1,2 forms first triangle

//2,3,0 form second triangle.

const GLubyte Indices[] = {

    0, 1, 2,

    2, 3, 0,

    4,5,6,

    6,7,4,

    0,1,4,

    1,4,5,

    1,2,6,

    1,5,6,

    2,3,6,

    3,6,7,

    0,3,4,

    3,4,7,

    

};

And finally drawing

       // Drawing code

    glClearColor(1.0f, 1.0f, 1.0f, 1);

    glClear(GL_COLOR_BUFFER_BIT);

    

    switch (rotateAlong) {

        case 1:

            ApplyRotationX(degreesX);

            break;

        case 2:ApplyRotationY(degreesY);

            break;

        default:ApplyRotation(degreesZ);

            break;

    }

    

    

    

    

    glEnableVertexAttribArray(_positionSlot);

    glEnableVertexAttribArray(_colorSlot);

    

    

    //Lets give these functions pointer to head of vertex array.

    GLsizei stride = sizeof(Vertex);

    const GLvoid* pCoords = &Vertices[0].Position[0];

    const GLvoid* pColors = &Vertices[0].Color[0];

    

   //Attribute changed from 2 (when we had drawn square) to 3 (dealing with cube x,y and z)

    glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, stride, pCoords);

    glVertexAttribPointer(_colorSlot, 4, GL_FLOAT, GL_FALSE, stride, pColors);

    

    //Draw the 12 triangles and (12*3=)36 indices.

    const GLvoid* bodyIndices = &Indices[0];

    glDrawElements(GL_TRIANGLES,12* 3, GL_UNSIGNED_BYTE, bodyIndices);

    

    glDisableVertexAttribArray(_positionSlot);

    glDisableVertexAttribArray(_colorSlot);    

    

    [mimContext presentRenderbuffer:GL_RENDERBUFFER];

In order to know about rotation matrix, read this LINK
It tells you about matrix used for rotation around x, y and z axis. For rotation around X as well Y (mixed rotation) we just multiply rotation matrix of X and Y axis.

There are 3 sliders with which  you can rotate the cube along X, Y and Z axis.

     //Solo Rotation along either of X,Y or Z.

    switch (rotateAlong) {

        case 1:

            ApplyRotationX(degreesX);

            break;

        case 2:ApplyRotationY(degreesY);

            break;

        default:ApplyRotation(degreesZ);

            break;

    }

    //Comment above lines in switch in code

    //Uncomment following lines to see mixed rotation.

    //Mixed Rotation along X and Y

    ApplyRotationXY(40);

    

Check out screenshot:

You can download the code HERE