Mouse: Moving the Camera III

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);
	glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
	glutInitWindowPosition(100,100);
	glutInitWindowSize(320,320);
	glutCreateWindow("Lighthouse3D - GLUT Tutorial");

	// register callbacks
	glutDisplayFunc(renderScene);
	glutReshapeFunc(changeSize);
	glutIdleFunc(renderScene);

	glutIgnoreKeyRepeat(1);
	glutKeyboardFunc(processNormalKeys);
	glutSpecialFunc(pressKey);
	glutSpecialUpFunc(releaseKey);

	// here are the two new functions
	glutMouseFunc(mouseButton);
	glutMotionFunc(mouseMove);

	// OpenGL init
	glEnable(GL_DEPTH_TEST);

	// enter GLUT event processing cycle
	glutMainLoop();

	return 1;
}

Check the next page to see the full source code.