How to capture keyboard input to stop an animation in opengl code. - opengl

Question

I have some code to move a toy car from left to right.
I want to transform the code to stop its movement by the pressing of any key for example 's'....could someone help me do that...here is my code so far.
#include <GL/glut.h> // Header File For The GLUT Library
#include <GL/gl.h> // Header File For The OpenGL32 Library
#include <GL/glu.h> // Header File For The GLu32 Library
//#include <unistd.h> // Header File For sleeping.
/* ASCII code for the escape key. */
#define ESCAPE 27
/* The number of our GLUT window */
int window;
/* rotation angle for the triangle. */
float rtri = 0.0f;
/* rotation angle for the quadrilateral. */
float rquad = 0.0f;
/* A general OpenGL initialization function. Sets all of the initial parameters. */
// We call this right after our OpenGL window is created.
void InitGL(int Width, int Height)
{
// This Will Clear The Background Color To Black
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClearDepth(1.0); // Enables Clearing Of The Depth Buffer
glDepthFunc(GL_LESS); // The Type Of Depth Test To Do
glEnable(GL_DEPTH_TEST); // Enables Depth Testing
glShadeModel(GL_SMOOTH); // Enables Smooth Color Shading
glMatrixMode(GL_PROJECTION);
glLoadIdentity(); // Reset The Projection Matrix
gluPerspective(45.0f,(GLfloat)Width/(GLfloat)Height,0.1f,100.0f);
glMatrixMode(GL_MODELVIEW);
}
/* The function called when our window is resized (which shouldn't happen, because we're fullscreen) */
void ReSizeGLScene(int Width, int Height)
{
if (Height==0) // Prevent A Divide By Zero If The Window Is Too Small
Height=1;
glViewport(0, 0, Width, Height); // Reset The Current Viewport And Perspective Transformation
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f,(GLfloat)Width/(GLfloat)Height,0.1f,100.0f);
glMatrixMode(GL_MODELVIEW);
}
float ballX = -0.5f;
float ballY = 0.0f;
float ballZ = 0.0f;
void drawBall(void) {
glColor3f(0.0, 1.0, 0.0); //set ball colour
glTranslatef(ballX,ballY,ballZ); //moving it toward the screen a bit on creation
//glRotatef(ballX,ballX,ballY,ballZ);
glutSolidSphere (0.3, 20, 20); //create ball.
glTranslatef(ballX+1.5,ballY,ballZ); //moving it toward the screen a bit on creation
glutSolidSphere (0.3, 20, 20); //
}
/* The main drawing function. */
void DrawGLScene()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear The Screen And The Depth Buffer
glLoadIdentity(); // Reset The View
glTranslatef(rtri,0.0f,-6.0f); // Move Left 1.5 Units And Into The Screen 6.0
//glRotatef(rtri,1.0f,0.0f,0.0f); // Rotate The Triangle On The Y axis
// draw a triangle (in smooth coloring mode)
glBegin(GL_POLYGON); // start drawing a polygon
glColor3f(1.0f,0.0f,0.0f); // Set The Color To Red
glVertex3f(-1.0f, 1.0f, 0.0f); // Top left
glVertex3f(0.4f, 1.0f, 0.0f);
glVertex3f(1.0f, 0.4f, 0.0f);
glColor3f(0.0f,1.0f,0.0f); // Set The Color To Green
glVertex3f( 1.0f,0.0f, 0.0f); // Bottom Right
glColor3f(0.0f,0.0f,1.0f); // Set The Color To Blue
glVertex3f(-1.0f,0.0f, 0.0f);// Bottom Left
//glVertex3f();
glEnd(); // we're done with the polygon (smooth color interpolation)
drawBall();
rtri+=0.005f; // Increase The Rotation Variable For The Triangle
if(rtri>2)
rtri=-2.0f;
rquad-=15.0f; // Decrease The Rotation Variable For The Quad
// swap the buffers to display, since double buffering is used.
glutSwapBuffers();
}
/* The function called whenever a key is pressed. */
void keyPressed(unsigned char key, int x, int y)
{
/* sleep to avoid thrashing this procedure */
// usleep(100);
/* If escape is pressed, kill everything. */
if (key == ESCAPE)
{
/* shut down our window */
glutDestroyWindow(window);
/* exit the program...normal termination. */
exit(0);
}
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_ALPHA | GLUT_DEPTH);
/* get a 640 x 480 window */
glutInitWindowSize(640, 480);
/* the window starts at the upper left corner of the screen */
glutInitWindowPosition(0, 0);
/* Open a window */
window = glutCreateWindow("Moving Car");
/* Register the function to do all our OpenGL drawing. */
glutDisplayFunc(&DrawGLScene);
/* Go fullscreen. This is as soon as possible. */
//glutFullScreen();
/* Even if there are no events, redraw our gl scene. */
glutIdleFunc(&DrawGLScene);
/* Register the function called when our window is resized. */
glutReshapeFunc(&ReSizeGLScene);
/* Register the function called when the keyboard is pressed. */
glutKeyboardFunc(&keyPressed);
/* Initialize our window. */
InitGL(640, 480);
/* Start Event Processing Engine */
glutMainLoop();
return 1;
}

Answer 1

conditionally disable the following bit of code:
rtri+=0.005f; // Increase The Rotation Variable For The Triangle
if(rtri>2)
rtri=-2.0f;
rquad-=15.0f; // Decrease The Rotation Variable For The Quad
this can be done by adding the following to the keyPressed function
if (key == S)
{
updateGeom = false;//stop updating
}
if (key == D)
{
updateGeom = true;//start updating
}
and changing the above mentioned code as
if(updageGeom){
rtri+=0.005f; // Increase The Rotation Variable For The Triangle
if(rtri>2)
rtri=-2.0f;
rquad-=15.0f; // Decrease The Rotation Variable For The Quad
}
you need to add a global boolean updateGeom as well