Move a ball in bowling game once a key is pressed - c++

Question

I have been working with bowling game in C++.
I want only one thing that I want to move the ball only once a key is pressed and the bowl moves smoothly(not like now as it moves by pressing and holding down UP-KEY).
Here is the code: -
#include <GL/glut.h>
#include <cmath>
GLfloat posX = 0.07, posY = 0.1, posZ = 0.0,
firstx1 = 0.02, firsty1 = 0.3, firstx2 = 0.07, firsty2 = 0.3, firstx3 = 0.11, firsty3 = 0.3,
secondx1 = -0.16, secondy1 = 0.3, secondx2 = -0.21, secondy2 = 0.3, secondx3 = -0.27, secondy3 = 0.3,
thirdx1 = 0.3, thirdy1 = 0.3, thirdx2 = 0.35, thirdy2 = 0.3, thirdx3 = 0.4, thirdy3 = 0.3;
double x, y, angle;
#define PI 3.1415926535898
GLint circle_points = 50;
void bottle() {
glColor3f(0.0, 0.0, 1.0);
glPointSize(9.0);
glBegin(GL_POINTS);
glVertex3f(firstx1, firsty1, 0.0);
glVertex3f(firstx2, firsty2, 0.0);
glVertex3f(firstx3, firsty3, 0.0);
glVertex3f(secondx1, secondy1, 0.0);
glVertex3f(secondx2, secondy2, 0.0);
glVertex3f(secondx3, secondy3, 0.0);
glVertex3f(thirdx1, thirdy1, 0.0);
glVertex3f(thirdx2, thirdy2, 0.0);
glVertex3f(thirdx3, thirdy3, 0.0);
glEnd();
glFlush();
}
void circ() {
glColor3f(0.0, 0.0, 1.0);
glBegin(GL_TRIANGLE_FAN);
for (int i = 0; i <= 300; i++) {
angle = 2 * PI * i / 300;
x = cos(angle) / 25;
y = sin(angle) / 20;
glVertex2d(x, y);
}
glEnd();
}
void display() {
glClearColor(1.0, 1.0, 1.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(-1.0, 1.0, -1.0, 1.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPushMatrix();
bottle();
glPopMatrix();
glPushMatrix();
glTranslatef(posX, posY, posZ);
circ();
glPopMatrix();
glutSwapBuffers();
}
float move_unit = 0.01;
void keyboardown(int key, int x, int y) {
switch (key) {
case GLUT_KEY_RIGHT:
posX += 0.3;
break;
case GLUT_KEY_LEFT:
posX -= 0.3;
break;
case GLUT_KEY_UP:
posY += move_unit;
break;
case GLUT_KEY_DOWN:
posY -= move_unit;
break;
default:
break;
}
if ((posX >= firstx1 && posX <= firstx3)
&& (posY == firsty1 && posY == firsty2 && posY == firsty3)) {
firstx1 += 0.02;
firsty1 += 0.03;
firstx2 += -0.06;
firsty2 += 0.02;
firstx3 += 0.03;
firsty3 += 0.05;
}
if ((posX <= secondx1 && posX >= secondx3)
&& (posY == secondy1 && posY == secondy2 && posY == secondy3)) {
secondx1 += 0.02;
secondy1 += 0.02;
secondx2 += -0.06;
secondy2 += 0.02;
secondx3 += 0.03;
secondy3 += 0.05;
}
if ((posX >= thirdx1 && posX <= thirdx3)
&& (posY == thirdy1 && posY == thirdy2 && posY == thirdy3)) {
thirdx1 += 0.02;
thirdy1 += 0.03;
thirdx2 += -0.07;
thirdy2 += 0.02;
thirdx3 += 0.03;
thirdy3 += 0.05;
}
glutPostRedisplay();
}
int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(500, 300);
glutInitWindowPosition(150,250);
glutCreateWindow("Balling Game");
glutDisplayFunc(display);
glutSpecialFunc(keyboardown);
glutMainLoop();
}

Answer 1

You are relying on the keyboard listener thread to do your work for you. You will need to make a position update thread, and cache the last movement command you received. The update thread will need to run regularly (e.g. 60 times a second) and update the current position of the ball every time.
The best way to do that would be to make your program more object oriented. Then you would have a "draw" thread, which simply looked at the state of the objects in your scene. It would ask the Ball objects for their current position. The Ball would know where it is based on its velocity (direction plus speed), the time elapsed since the last change in velocity, and the position at which the last change in velocity occurred.
For a first step though just store the last direction pressed and update the position at regular intervals.