Position the square on the left after it reaches the top - c++

Question

#include <stdio.h> // this library is for standard input and output
#include "glut.h"// this library is for glut the OpenGL Utility Toolkit
#include <math.h>
float squareX = 0.0f;
float squareY = -0.3f;
float squareZ = 0.0f;
static int flag = 1;
void drawShape(void) {
glTranslatef(squareX, squareY, squareZ);
glBegin(GL_POLYGON);
glColor3f(1.0, 0.0, 0.0);
glVertex2f(162, 50);
glVertex2f(162, 10);
glVertex2f(220, 10);
glVertex2f(220, 50);
glVertex2f(162, 50);
glEnd();
}
void initRendering() {
glEnable(GL_DEPTH_TEST);
}
// called when the window is resized
void handleResize(int w, int h) {
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0f, (float)w, 0.0f, (float)h, -1.0f, 1.0f);
}
void drawScene() {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
drawShape();
glutSwapBuffers();
}
// make the square go up
void update(int value) {
if (flag) {
squareY += 1.0f;
if (squareY > 400.0) {
flag = 0;
}
}
glutPostRedisplay();
glutTimerFunc(25, update, 0);
}
// make the square go right
/* void update(int value) {
if (flag) {
squareX += 1.0f;
if (squareX > 400.0) {
flag = 0;
}
}
glutPostRedisplay();
glutTimerFunc(25, update, 0);
} */
int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(400, 400);
glutCreateWindow("Moving Square");
initRendering();
glutDisplayFunc(drawScene);
glutReshapeFunc(handleResize);
glutTimerFunc(25, update, 0);
glutMainLoop();
return(0);
}
I have uploaded this code before but this time I made the square go all the way up. The code just moves the square up, but I don't know how to position it on the left once it reaches the top, so then I can make it move to the right. I have uploaded a demonstration on how I want it to look below.
Preview:
What I want it to do next:

Answer 1

I recommend to initialize the variables squareX, squareY and squareZ with the start position of the rectangle:
float squareX = 162.0f;
float squareY = 0.0f;
float squareZ = 0.0f;
Do not draw a rectangle specific position, but draw a rectangle on the position (0,0) with a length (width, height). Let the model matrix (set by glTranslatef), do the job of the positioning:
void drawShape(void)
{
float width = 58.0f;
float height = 40.0f;
glTranslatef(squareX, squareY, squareZ);
glBegin(GL_POLYGON);
glColor3f(1.0, 0.0, 0.0);
glVertex2f(0, 0);
glVertex2f(width, 0);
glVertex2f(width, height);
glVertex2f(0, height);
glVertex2f(0, 0);
glEnd();
}
Use a variable state, which has stated the direction of the current movement:
int state = 1; // 0: stop; 1: move up; 2: move right
If the rectangle a certain position has reached, then the state has to be changed and a the new start position can be set. At the final position, the rectangle can stop or the process can even be restarted:
void update(int value)
{
if (state == 1) // 1 : move up
{
squareY += 1.0f;
if (squareY > 400.0)
{
state = 2;
squareX = 0.0f;
squareY = 180.0f;
}
}
else if (state == 2) // 2 : move right
{
squareX += 1.0f;
if (squareX > 400.0)
{
state = 0;
// restart
//state = 1;
//squareX = 162.0f;
//squareY = 0.0f;
}
}
glutPostRedisplay();
glutTimerFunc(25, update, 0);
}