Friday, May 31, 2013

Modern OpenGL tutorial Rotation, Scalling and Translation Matrix using GML (OpenGL Mathematics)

In previous article perspective projection I have shown you how to do perspective projection. Now its time to do Scalling, Translation and Rotation which are very important task. In ancient version of OpenGL for these operation opengl provide funcition like glRotate, glScale, glTranslate but in modern opengl this function are not available so we are using GLM (OpenGL Mathematics) for doing such task. From this article I have change the source code with OOP. I have made two reusable classes Program and Shader.

All the code in this series of articles is available from github:  You can download a zip of all the files from that page, or you can clone the repository if you are familiar with git.

GLM function for rotation, scalling and translation is given below.
// Projection matrix : 45° Field of View, aspect ratio, display range : 1 unit <-> 200 units
    projectionMatrix = glm::perspective(45.0f, (float)SCREEN_SIZE.x / (float)SCREEN_SIZE.y, 1.0f, 200.0f);
    // Camera matrix
    viewMatrix       = glm::lookAt(
                            glm::vec3(0,0,1), // Camera is at (4,3,3), in World Space
                            glm::vec3(0,0,0), // and looks at the origin
                            glm::vec3(0,1,0)  // Head is up (set to 0,-1,0 to look upside-down)

    // Model matrix : an identity matrix (model will be at the origin)
    modelMatrix= glm::mat4(1.0f);// Changes for each model !
    modelMatrix= glm::translate(modelMatrix,glm::vec3(0,0,-5));//translating to negative z-axis
    modelMatrix= glm::scale(modelMatrix,glm::vec3(2,2,2));//scalling by 2x
    modelMatrix= glm::rotate(modelMatrix, -rotationAngle, glm::vec3(0,0,1));//rotating in clockwise direction

For continuous rotaton, to update the value of  rotationAngle I have made the update function.
    // update the scene based on the time elapsed since last update
    void Update(float secondsElapsed) {
    const GLfloat degreesPerSecond = 100.0f;
    rotationAngle += secondsElapsed * degreesPerSecond;
    while(rotationAngle > 360.0f) rotationAngle -= 360.0f;

Next Chapter: Playing with Color

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