How do I specify a keyboard's directional keys in glut? - opengl

Question

I wanna use up, down, left, right as part of the controls of an opengl + glut application. How do I refer to the keys inside my 'keyboard' function (the one that I pass to glutKeyboardFunc)?

Answer 1

You need glutSpecialFunc.
For example -
#include<GL/gl.h>
#include<GL/glut.h>
#include<stdio.h>
void
init(void)
{
/*initialize the x-y co-ordinate*/
glClearColor(0,0,0,0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(-320, 319,-240, 239);
glClear (GL_COLOR_BUFFER_BIT);
glFlush();
}
void
catchKey(int key, int x, int y)
{
if(key == GLUT_KEY_LEFT)
printf("Left key is pressed\n");
else if(key == GLUT_KEY_RIGHT)
printf("Right key is pressed\n");
else if(key == GLUT_KEY_DOWN)
printf("Down key is pressed\n");
else if(key == GLUT_KEY_UP)
printf("Up key is pressed\n");
}
int
main(int argc, char *argv[])
{
double x_0, y_0, x_1, y_1;
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(640, 480);
glutInitWindowPosition(400, 400);
glutCreateWindow("Special key");
init();
glutSpecialFunc(catchKey);
glutMainLoop();
}

Answer 2

your functions should be something like these
void handleSpecialKeypress(int key, int x, int y) {
switch (key) {
case GLUT_KEY_LEFT:
isLeftKeyPressed = true;
if (!isRightKeyPressed) {
DO SOMETHING HERE;
}
break;
case GLUT_KEY_RIGHT:
isRightKeyPressed = true;
if (!isLeftKeyPressed) {
DO SOMETHING HERE;
}
break;
}
}
void handleSpecialKeyReleased(int key, int x, int y) {
switch (key) {
case GLUT_KEY_LEFT:
isLeftKeyPressed = false;
break;
case GLUT_KEY_RIGHT:
isRightKeyPressed = false;
break;
}
}
and you also need to invoke these in your main() method
glutSpecialFunc(handleSpecialKeypress);
glutSpecialUpFunc(handleSpecialKeyReleased);
The variables isRightKeyPressed and isLeftKeyPressed are global variables I defined.