Help end child hunger

Mouse: Moving the Camera III

Prev: The Mouse Next: The Code So Far II

In the previous example we changed the orientation of the camera with the keyboard. In here we are going to use the mouse instead.

When the user presses the mouse left button we are going to record the X position of the mouse. As the mouse moves will check the new X position, and based on the difference we’ll set a variable <I>deltaAngle</I>. This variable will be added to the initial angle to compute the direction of the camera.

A variable to store the X position where the mouse is clicked is also required.

float deltaAngle = 0.0f;
int xOrigin = -1;

Note that xOrigin is initialized to a value that never occurs when the mouse is pressed (it must be at least zero). This will enable us to distinguish if the user is pressing the left button or any other button.

The next function is responsible for processing the button state changes:

void mouseButton(int button, int state, int x, int y) {

	// only start motion if the left button is pressed
	if (button == GLUT_LEFT_BUTTON) {

		// when the button is released
		if (state == GLUT_UP) {
			angle += deltaAngle;
			xOrigin = -1;
		else  {// state = GLUT_DOWN
			xOrigin = x;

Notice that the var xOrigin is set to -1 when the left button is released.

The function to process the motion of the mouse is now presented:

void mouseMove(int x, int y) {

	// this will only be true when the left button is down
	if (xOrigin >= 0) {

		// update deltaAngle
		deltaAngle = (x - xOrigin) * 0.001f;

		// update camera's direction
		lx = sin(angle + deltaAngle);
		lz = -cos(angle + deltaAngle);

In the main function we have to register the two new callback functions:

int main(int argc, char **argv) {

	// init GLUT and create window
	glutInit(&argc, argv);
	glutCreateWindow("Lighthouse3D - GLUT Tutorial");

	// register callbacks


	// here are the two new functions

	// OpenGL init

	// enter GLUT event processing cycle

	return 1;

Check the next page to see the full source code.


Prev: The Mouse Next: The Code So Far II

  9 Responses to “Mouse: Moving the Camera III”

  1. Hi i have followed these tutorials and love them thanks

    how would we implement strafe in the left and right direction?

    please feel free to email me to explain how this can be achieved



    • You can strafe by using the cross product of the camera look direction and a vector pointed up (0,1,0) to get a vector pointed to the camera’s right. Since we don’t care about the look direction’s y axis the rightX becomes -lz and the rightZ becomes lx. Here’s some code:

      void ComputeCameraPosition(float deltaX, float deltaY)
      CameraX += deltaY * CameraLX * CameraMoveSpeed;
      CameraZ += deltaY * CameraLZ * CameraMoveSpeed;

      float rightX = -CameraLZ;
      float rightZ = CameraLX;

      CameraX += deltaX * rightX * CameraMoveSpeed;
      CameraZ += deltaX * rightZ * CameraMoveSpeed;

  2. I ‘ m having trouble moving the camera. For example i can move in the Z axis back and front and also using one more glut button to move faster however when i rotate the camera in the X axis the camera rotates all right but then all movements stop and I cannot move anymore and only rotate in the X axis only. I am using freeglut if it matters

  3. Hi, maybe you can post some examples how to move camera in all directions? in this tutorial you can move it only in x and z axis… but if i want it to move y axis too?
    thank you.

    • The second and fifth arguments in the gluLookAt function are the camera y and the y in the line of sight, just change those to set the y.

  4. Very useful tutorial, thanks!!
    However, if I try to run this program (I got no errors from the compiler), it appears a window that says:
    “The procedure entry point _glutIgnoreKeyRepeat@4 could not be located in the dynamic link library GULT32.dll”….
    Do you have any idea of what does it means?

    • Hi, if you have translated the message as is then the culprit is “GULT32.dll”. It should be GLUT32.dll. Otherwise can you provide more info on your setup please?

      • Sorry, the message was: “The procedure entry point _glutIgnoreKeyRepeat@4 could not be located in the dynamic link library GLUT32.dll”
        I use Visual C++ 2008 Express edition, with the GLUT 3.7
        The previous codes of your tutorial work well. It seems that I have a problem
        with glutIgnoreKeyRepeat() and glutSpecialUpFunc()…

        • Humm, not sure what the problem might be… Maybe checking for multiple versions of GLUT in your system.

 Leave a Reply




You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>