Draw cubes with random colors using OpenGL - c

Question

I want every cube to have a random color but with this code the colors keep changing all the time
int espacioX = -500;
int espacioY = -500;
for(int i=1; i<=100; i++){
for(int j=1; j<=100; j++){
randomR = (double)rand() / (RAND_MAX);
randomG = (double)rand() / (RAND_MAX);
randomB = (double)rand() / (RAND_MAX);
glColor3f(randomR,randomG,randomB);
glTranslatef(espacioX,espacioY,0);
glutSolidCube(9);
glTranslatef(-espacioX,-espacioY,0);
espacioX+=10;
}
glTranslatef(-1000,0,0);
espacioY+=10;
}
How do I make them stay in the same color while the program is running?
Edit:
This is the comple code:
#include <windows.h>
/***** OpenGL library imports. *****/
#include<gl\glut.h> //basic header file for OpenGL
//#include <gl\glaux.h> // Header File For The Glaux Library
/***** C library imports. *****/
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
int ScreenWidth = 0;
int ScreenHeight = 0;
int last_x = 0, last_y = 0,left = 1,middle = 0,right = 0;
int zoom_y = 0;
int anglex=0, angley=0, anglez=0;
int lookfrom=450;
int ang=0;
void myGlutKeyboard(unsigned char Key, int x, int y)
{
printf("%5d\n",Key);
glutPostRedisplay();
}
void init_GL_params()
{
static GLfloat light_ambient[] = { .250, .250, .250, .250 };
static GLfloat light_diffuse[] = { .250, .250, .25, .250 };
static GLfloat light_specular[] = { .250, .250, .250, .250 };
static GLfloat light1_diffuse[] = { .250, .250, .250, .0 };
static GLfloat light1_specular[] = { .250, .250, .250, .0 };
glEnable (GL_LIGHTING);
glEnable (GL_LIGHT0);
glEnable (GL_LIGHT1);
glDisable (GL_TEXTURE_2D);
glDisable (GL_TEXTURE_GEN_S);
glDisable (GL_TEXTURE_GEN_T);
glShadeModel (GL_FLAT);
glEnable (GL_DEPTH_TEST);
glDepthFunc (GL_LESS);
glEnable (GL_CULL_FACE);
glCullFace (GL_BACK);
glFrontFace (GL_CCW);
glMatrixMode (GL_PROJECTION);
glLoadIdentity();
glLightfv (GL_LIGHT0, GL_AMBIENT, light_ambient);
glLightfv (GL_LIGHT0, GL_DIFFUSE, light_diffuse);
glLightfv (GL_LIGHT0, GL_SPECULAR, light_specular);
glLightfv(GL_LIGHT1, GL_DIFFUSE, light1_diffuse);
glLightfv(GL_LIGHT1, GL_SPECULAR, light1_specular);
glLightfv (GL_LIGHT1, GL_AMBIENT, light_ambient);
glColor3f (1.0, 1.0, 1.0);
}
void setLightPosition()
{
static GLfloat light_position[] = { 100, 200.0, 10, 1.0 };
static GLfloat light1_position[] = { -0.0, 300.0, 0.0, 1.0 };
// set the light position (for some reason we have to do this in model view.
glLightfv (GL_LIGHT0, GL_POSITION, light_position);
glLightfv(GL_LIGHT1, GL_POSITION, light1_position);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glEnable(GL_COLOR_MATERIAL);
}
void myGlutDisplay(void)
{
init_GL_params();
// clear the window
glClearColor (0,0,0,0); //Color de fondo R G B
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity();
setLightPosition(); //Posici{on de la fuente de luz
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
gluPerspective(60.0f, 1.0, 1.0f, 10000.0f);
gluLookAt( //punto de vista
0 ,100 ,lookfrom , // desde donde veo xyz
0, 0, 0, // hacia donde veo xyz
0,1,0 );
glRotatef(anglex, 1.0, 0.0, 0.0);
glRotatef(angley, 0.0, 1.0, 0.0);
glRotatef(anglez, 0.0, 0.0, 1.0);
//Empieza a dibujar
int espacioX = 500;
int espacioY = 500;
double randomR, randomG, randomB;
for(int i=1; i<=100; i++){
for(int j=1; j<=100; j++){
randomR = (double)rand() / (RAND_MAX);
randomG = (double)rand() / (RAND_MAX);
randomB = (double)rand() / (RAND_MAX);
glColor3f(randomR,randomG,randomB);
glTranslatef(espacioX,espacioY,0);
glutSolidCube(9);
glTranslatef(-espacioX,-espacioY,0);
espacioX-=10;
}
glTranslatef(1000,0,0);
espacioY-=10;
}
glFlush(); // Flush The GL Pipeline
glutSwapBuffers();
}
void myGlutReshape2(int mWidth, int mHeight)
{
ScreenWidth = mWidth;
ScreenHeight = mHeight;
glViewport(0, 0, (GLsizei) ScreenWidth, (GLsizei) ScreenHeight);
glutPostRedisplay();
}
/****************************************************************/
void myGlutIdle(void)
{
glutPostRedisplay();
}
/***************************************************************/
void myGlutMouse(int button, int button_state, int x, int y){
if ( (button == GLUT_LEFT_BUTTON) && (button_state == GLUT_DOWN) )
{
last_x = x;
last_y = y;
left = 1;
middle = 0;
right = 0;
}
else if ((button == GLUT_RIGHT_BUTTON) && (button_state == GLUT_DOWN) )
{
zoom_y = y;
right = 1;
left = 0;
middle = 0;
}
}
void myGlutMotion(int x, int y){
if (left){
anglex+= (float) (y - last_y);
angley+= (float) (x - last_x);
last_x = x;
last_y = y;
}
if (right)
{
lookfrom += (y - zoom_y);
zoom_y = y;
}
}
void GlutInit(int argc, char** argv)
{
ScreenWidth = 700;
ScreenHeight = 700;
/****************************************/
/* Initialize GLUT and create window */
/****************************************/
glutInit(&argc, argv);
glutInitDisplayMode( GLUT_RGB | GLUT_DOUBLE | GLUT_STENCIL ); //set up the display as a double buffer using RGB values
glutInitWindowPosition(90, 50); //set the position of where you want the window to open
glutInitWindowSize(ScreenWidth, ScreenHeight); //set how big you want the initial window to be
glutCreateWindow("Testing Virtual Environment" ); //what do you want the window to be called (titlebar text)
//register callbacks
glutDisplayFunc(myGlutDisplay); //Register the display callback
glutReshapeFunc(myGlutReshape2); // -- Resize handler
glutKeyboardFunc(myGlutKeyboard); // -- Keyboard handler
glutMouseFunc(myGlutMouse); // -- Mouse Click handler
glutMotionFunc(myGlutMotion); // -- Mous motion handler
glutIdleFunc(myGlutIdle); // -- Idle handler
glFlush();
}
int main( int argc, char **argv )
{
GlutInit(argc, argv);
glutMainLoop();
return 0;
}
It was a sample code so I just posted the part that I edited, sorry. When I did a cube or a sphere with an specific color it always stayed the same so i didn't realiza that this refresh the image all the time. I don't really understand the whole thing so I don't know where it's refreshing the image.

Answer 1

Why not set SEED to some constant value at start of myGlutDisplay(void). That will give you the same random values each frame without any big change in your code for example like this:
void myGlutDisplay(void)
{
init_GL_params();
// clear the window
glClearColor (0,0,0,0); //Color de fondo R G B
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity();
setLightPosition(); //Posici{on de la fuente de luz
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
gluPerspective(60.0f, 1.0, 1.0f, 10000.0f);
gluLookAt( //punto de vista
0 ,100 ,lookfrom , // desde donde veo xyz
0, 0, 0, // hacia donde veo xyz
0,1,0 );
glRotatef(anglex, 1.0, 0.0, 0.0);
glRotatef(angley, 0.0, 1.0, 0.0);
glRotatef(anglez, 0.0, 0.0, 1.0);
//Empieza a dibujar
int espacioX = 500;
int espacioY = 500;
double randomR, randomG, randomB;
srand(0x98765432); // this is the SEED
for(int i=1; i<=100; i++){
for(int j=1; j<=100; j++){
randomR = (double)rand() / (RAND_MAX);
randomG = (double)rand() / (RAND_MAX);
randomB = (double)rand() / (RAND_MAX);
glColor3f(randomR,randomG,randomB);
glTranslatef(espacioX,espacioY,0);
glutSolidCube(9);
glTranslatef(-espacioX,-espacioY,0);
espacioX-=10;
}
glTranslatef(1000,0,0);
espacioY-=10;
}
glFlush(); // Flush The GL Pipeline
glutSwapBuffers();
}
The value of the SEED will give you the pattern. So changing the constant will change the colors. Beware wrong constant (like 0) can corrupt the randomness of the rand() function.

Answer 2

It seems like you are running this code inside another loop which means you are calculating your random variables every time the scene is redrawn, this would cause the colors to change and the obvious solution would be to poulate your list of cubes once and then iterate through the list drawing the cubes on each scene refresh.
However, without seeing the rest of your code it is unclear. Please include more information so we can give you a better answer.