Converting projectile simulation to 3D causes drawing to disasppear? - c

Question

I have a code that successfully draws projectiles in 2D, but I need to apply changes to make it in 3D.
#include <stdio.h>
#include <GL/glut.h>
#include <math.h>
#include <unistd.h>
#define g 9.8
#define PI 3.14
#define ESC 27
void initialize(void)
{
glClearColor(0, 0, 0, 0);
glColor3f(0.0, 1.0, 0.0);
glPointSize(3.0);
glEnable(GL_POINT_SMOOTH);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, 1000, 0, 500);
}
static void keyPressFunc(unsigned char key, int x, int y)
{
switch(key) {
case ESC:
exit(1);
}
}
void display(void)
{
float Pheta, Pheta2, Pheta3,Pheta4, Vo, time, time_top, d1, d2, d3, Uox1, Uox2, Uox3;
Vo = 60;
Pheta = 60;
Pheta2 = 30;
Pheta3 = 40;
Pheta4 = 50;
time = (2 * Vo * sin(Pheta * PI / 180)) / g;
time_top = time/2;
d1 = 500;
d2 = 650;
d3 = 800;
Uox1 = (d1 - Vo * cos(Pheta * PI / 180) * 2)/2;
Uox2 = (d2 - Vo * cos(Pheta * PI / 180)* time_top)/time_top;
Uox3 = (d3 - Vo * cos(Pheta * PI / 180) * 8)/8;
for(float t=0; t < 12 ; t += 0.0005)
{
float x1 = (Vo * cos(Pheta * PI / 180) * t);
float y1 = (Vo * sin(Pheta * PI / 180) * t - 0.5 * g * t * t);
float x2 = (d1 - Uox1 * t);
float y2 = (Vo * sin(Pheta * PI / 180) * t - 0.5 * g * t * t);
float x3 = (d2 - Uox2 * t);
float y3 = (Vo * sin(Pheta * PI / 180) * t - 0.5 * g * t * t);
float x4 = (d3 - Uox3 * t);
float y4 = (Vo * sin(Pheta * PI / 180) * t - 0.5 * g * t * t);
glBegin(GL_POINTS);
glVertex2d(x1, y1);
glVertex2d(x2, y2);
glVertex2d(x3, y3);
glVertex2d(x4, y4);
if (x1+0.1 >= x4 && x4+0.1 >= x1)
{
break;
}
glEnd();
glFlush();
}
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(800, 600);
glutInitWindowPosition(0, 0);
glutCreateWindow("C-Lang-Project");
glutKeyboardFunc(keyPressFunc);
initialize();
glutDisplayFunc(display);
glutMainLoop();
}
To make it 3D, I changed glVertex2d into glVertex3d, set a variable z and added it to the glVertex3d.
The final code that I've got:
#include <stdio.h>
#include <GL/glut.h>
#include <math.h>
#include <unistd.h>
#define g 9.8
#define PI 3.14
#define ESC 27
void initialize(void)
{
glClearColor(0, 0, 0, 0);
glColor3f(0.0, 1.0, 0.0);
glPointSize(3.0);
glEnable(GL_POINT_SMOOTH);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, 1000, 0, 500);
}
static void keyPressFunc(unsigned char key, int x, int y)
{
switch(key) {
case ESC:
exit(1);
}
}
void display(void)
{
float Pheta, Pheta2, Pheta3,Pheta4, Vo, time, time_top, d1, d2, d3, Uox1, Uox2, Uox3, z;
Vo = 60;
Pheta = 60;
Pheta2 = 30;
Pheta3 = 40;
Pheta4 = 50;
time = (2 * Vo * sin(Pheta * PI / 180)) / g;
time_top = time/2;
d1 = 500;
d2 = 650;
d3 = 800;
z = 15;
Uox1 = (d1 - Vo * cos(Pheta * PI / 180) * 2)/2;
Uox2 = (d2 - Vo * cos(Pheta * PI / 180)* time_top)/time_top;
Uox3 = (d3 - Vo * cos(Pheta * PI / 180) * 8)/8;
for(float t=0; t < 12 ; t += 0.0005)
{
float x1 = (Vo * cos(Pheta * PI / 180) * t);
float y1 = (Vo * sin(Pheta * PI / 180) * t - 0.5 * g * t * t);
float x2 = (d1 - Uox1 * t);
float y2 = (Vo * sin(Pheta * PI / 180) * t - 0.5 * g * t * t);
float x3 = (d2 - Uox2 * t);
float y3 = (Vo * sin(Pheta * PI / 180) * t - 0.5 * g * t * t);
float x4 = (d3 - Uox3 * t);
float y4 = (Vo * sin(Pheta * PI / 180) * t - 0.5 * g * t * t);
glBegin(GL_POINTS);
glVertex3d(x1, y1, z);
glVertex3d(x2, y2, z);
glVertex3d(x3, y3, z);
glVertex3d(x4, y4, z);
if (x1+0.1 >= x4 && x4+0.1 >= x1)
{
break;
}
glEnd();
glFlush();
}
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(800, 600);
glutInitWindowPosition(0, 0);
glutCreateWindow("C-Lang-Project");
glutKeyboardFunc(keyPressFunc);
initialize();
glutDisplayFunc(display);
glutMainLoop();
}
But it does not show any mistake, just shows a black window.
P.S. I am using OpenGL & freeglut

Answer 1

The scene is clipped by by the near plane of the orthographic projection.
The z coordiante of the geoemtry is set z=15; but the orthographic projection is set gluOrtho2D(0, 1000, 0, 500);. gluOrtho2D sets a near plane of -1 and a far plane of 1.
The view space z coordinate has to be between the near and far plane.
Since the view space z axis points out of the viewport, the view space z coordinate is -15.
This means, if z=15 then the following condition has to be fulfilled:
near < -15 < far
Change the orthographic projection to solve the issue. Use glOrtho:
e.g.
void initialize(void)
{
// [...]
glOrtho(0, 1000, 0, 500, -20, 1);
}
Of course it is possible to switch to perspective projection. In this case you've to invert the and z coordinate.
To get all the geometry on the screen (in clip space), I recommend to increase the amount to of the z coordinate and (of course) the distance to the far plane:
e.g.
void display(void)
{
float z = -500;
// [...]
}
void initialize(void)
{
// [...]
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective( 90.0, 1000.0 / 500.0, 0.1, 1000.0 );
}
Don't implement a render loop in the event processing loop. Use glutPostRedisplay to force the display to be repainted:
float t=0;
void display(void)
{
float Pheta, Pheta2, Pheta3,Pheta4, Vo, time, time_top, d1, d2, d3, Uox1, Uox2, Uox3, z;
Vo = 60; Pheta = 60; Pheta2 = 30; Pheta3 = 40; Pheta4 = 50;
time = (2 * Vo * sin(Pheta * PI / 180)) / g;
time_top = time/2; d1 = 500; d2 = 650; d3 = 800;
z = 15;
Uox1 = (d1 - Vo * cos(Pheta * PI / 180) * 2)/2;
Uox2 = (d2 - Vo * cos(Pheta * PI / 180)* time_top)/time_top;
Uox3 = (d3 - Vo * cos(Pheta * PI / 180) * 8)/8;
float x1 = (Vo * cos(Pheta * PI / 180) * t);
float y1 = (Vo * sin(Pheta * PI / 180) * t - 0.5 * g * t * t);
float x2 = (d1 - Uox1 * t);
float y2 = (Vo * sin(Pheta * PI / 180) * t - 0.5 * g * t * t);
float x3 = (d2 - Uox2 * t);
float y3 = (Vo * sin(Pheta * PI / 180) * t - 0.5 * g * t * t);
float x4 = (d3 - Uox3 * t);
float y4 = (Vo * sin(Pheta * PI / 180) * t - 0.5 * g * t * t);
glBegin(GL_POINTS);
glVertex3d(x1, y1, z);
glVertex3d(x2, y2, z);
glVertex3d(x3, y3, z);
glVertex3d(x4, y4, z);
glEnd();
t += 0.0005;
glFlush();
glutPostRedisplay();
}