OpenGL moving objects from corner - c

Question

I have an openGL program thats using GLUT and I'm stuck with moving it from the top left corner to bottom right when i resize the window. I'm trying to get a ratio down and i cant figure it out.
#include <stdio.h>
#include <stdlib.h>
#include <GLUT/glut.h>
//global variables
GLsizei wh = 500, ww = 500;
double height;
double width;
double top = 500;
double bottom = 450;
int right = 50;
int left = 0;
double ratiowidth = 500/500;
double ratioheight = 500/500;
void myinit(){
glClearColor (0.0, 0.0, 0.0, 0.0);
}
void reshape(int w, int h){
if(h == 0){
h = 1;
}
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, (GLsizei) w, 0, (GLsizei)h);
glViewport(0,0,w,h);
glMatrixMode(GL_MODELVIEW);
int difference = h - wh;
int difference2 = w - ww;
left = left + difference2;
right = right + difference2;
wh = (GLsizei)h;
ww = (GLsizei)w;
height = h;
width = w;
}
void mouse(int button, int state, int x, int y){
if(button == GLUT_LEFT_BUTTON && state == GLUT_DOWN){
top = height;
bottom = height - 50;
right = 50;
left = 0;
ratiowidth = width/height;
ratioheight = height/width;
}
if(button == GLUT_RIGHT_BUTTON && state == GLUT_DOWN){
exit(0);
}
}
void display(){
glClear (GL_COLOR_BUFFER_BIT);
glColor3i (rand(), rand(), rand());
glBegin(GL_POLYGON);
glVertex3f (left,top,0.0);
glVertex3f (right, top, 0.0);
glVertex3f (right, bottom, 0.0);
glVertex3f (left, bottom, 0.0);
glEnd();
if(bottom == 0 || bottom < 0)
bottom = 0;
else{
left = left + ratiowidth;
right = right + ratiowidth;
top = top - ratioheight;
bottom = bottom - ratioheight;
}
glutSwapBuffers();
usleep(10000);
glutPostRedisplay();
}
int main(int argc, char** argv) {
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(ww, wh);
glutInitWindowPosition(100,100);
glutCreateWindow("moving Square");
myinit();
glutReshapeFunc(reshape);
glutDisplayFunc(display);
glutMouseFunc(mouse);
glutMainLoop();
return 0;
}

Answer 1

glBegin(GL_POLYGON);
glVertex3f (left,top,0.0);
glVertex3f (right, top, 0.0);
glVertex3f (right, bottom, 0.0);
glVertex3f (left, bottom, 0.0);
glEnd();
Careful with your winding order. glFrontFace() defaults to GL_CCW. Perhaps you meant this:
glBegin(GL_POLYGON);
glVertex3f (left, bottom, 0.0);
glVertex3f (right, bottom, 0.0);
glVertex3f (right, top, 0.0);
glVertex3f (left,top,0.0);
glEnd();
EDIT: This is what I think you were trying to do:
#include <GL/glut.h>
struct State
{
double x; // in units
double y;
double xvel; // in units per second
double yvel;
};
State curState = { 0 };
void myinit()
{
curState.xvel = 100;
curState.yvel = 100;
}
void Integrate( State* state, double dt )
{
state->x += state->xvel * dt;
state->y += state->yvel * dt;
}
double GetSeconds()
{
return glutGet(GLUT_ELAPSED_TIME) / 1000.0f;
}
void reshape(int w, int h)
{
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, (GLsizei)w, 0, (GLsizei)h);
}
void mouse(int button, int state, int x, int y)
{
if(button == GLUT_LEFT_BUTTON && state == GLUT_UP)
{
curState.x = 0;
curState.y = 0;
}
if(button == GLUT_RIGHT_BUTTON && state == GLUT_UP)
{
exit(0);
}
}
void display()
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glClear (GL_COLOR_BUFFER_BIT);
float w = 20;
float h = 20;
float x = curState.x;
float y = curState.y;
glColor3ub(rand()%255, rand()%255, rand()%255);
glBegin(GL_QUADS);
glVertex2f( x - w/2, y - h/2 );
glVertex2f( x + w/2, y - h/2 );
glVertex2f( x + w/2, y + h/2 );
glVertex2f( x - w/2, y + h/2 );
glEnd();
static double lastTime = GetSeconds();
double curTime = GetSeconds();
Integrate( &curState, curTime - lastTime );
lastTime = curTime;
glutSwapBuffers();
}
void timer(int extra)
{
glutPostRedisplay();
glutTimerFunc(16, timer, 0);
}
int main(int argc, char** argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(500, 500);
glutInitWindowPosition(100,100);
glutCreateWindow("moving Square");
myinit();
glutReshapeFunc(reshape);
glutTimerFunc(0, timer, 0);
glutDisplayFunc(display);
glutMouseFunc(mouse);
glutMainLoop();
return 0;
}
Be aware that there are probably some C++-isms in there :)