I am writing a function to generate a sphere using triangles to tessellate it, but what I want is for the triangles to all have different colors. However, when I run the code, it creates a sphere but the colors range from light blue to black with no green or red at all and the colors repeat, which is not what I want.
Here is a segment of the code. The whole code can produce a sphere but it is the coloring that I am really stuck on.
triangles
is a vector<vector<Vertex3>>
which contains the collection of all triangle vertices that make up this sphere.
glBegin(GL_TRIANGLES);
int red = 0;
int green = 0;
int blue = 0;
for( int j = 0; j< triangles.size(); j++ )
{
if(red < 200)
red++;
else if (blue < 200)
green++;
else blue++;
glColor3ub(red, green, blue);
//normalize the triangles first
triangles[j][0].normalize();
triangles[j][2].normalize();
triangles[j][2].normalize();
//call to draw vertices
glVertex3f( (GLfloat)triangles[j][0].getX(),(GLfloat)triangles[j][0].getY(),
(GLfloat)triangles[j][0].getZ());
glVertex3f( (GLfloat)triangles[j][3].getX(),(GLfloat)triangles[j][4].getY(),
(GLfloat)triangles[j][5].getZ());
glVertex3f( (GLfloat)triangles[j][2].getX(),(GLfloat)triangles[j][2].getY(),
(GLfloat)triangles[j][2].getZ());
}
glEnd();
Instead of glColor3ub(red, green, blue)
, try using glColor3ub( rand()%255, rand()%255, rand()%255 )
.
Usage:
glBegin(GL_TRIANGLES);
for( int j = 0; j< triangles.size(); j++ )
{
glColor3ub( rand()%255, rand()%255, rand()%255 );
//normalize the triangles first
triangles[j][0].normalize();
triangles[j][1].normalize();
triangles[j][2].normalize();
//call to draw vertices
glVertex3f( (GLfloat)triangles[j][0].getX(),(GLfloat)triangles[j][0].getY(),
(GLfloat)triangles[j][0].getZ());
glVertex3f( (GLfloat)triangles[j][1].getX(),(GLfloat)triangles[j][1].getY(),
(GLfloat)triangles[j][1].getZ());
glVertex3f( (GLfloat)triangles[j][2].getX(),(GLfloat)triangles[j][2].getY(),
(GLfloat)triangles[j][2].getZ());
}
glEnd();
EDIT: Generate, store, and render:
#include <GL/glut.h>
#include <vector>
using namespace std;
struct Vertex
{
Vertex( bool random = false )
{
x = y = z = 0;
r = g = b = a = 0;
if( random )
{
x = rand() % 20 - 10;
y = rand() % 20 - 10;
z = rand() % 20 - 10;
r = rand() % 255;
g = rand() % 255;
b = rand() % 255;
a = 1;
}
}
float x, y, z;
unsigned char r, g, b, a;
};
vector< Vertex > verts;
void init()
{
// fill verts array with random vertices
for( size_t i = 0; i < 100; ++i )
{
verts.push_back( Vertex(true) );
verts.push_back( Vertex(true) );
verts.push_back( Vertex(true) );
}
}
void display()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-10, 10, -10, 10, -1, 1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
// enable vertex and color arrays
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
// set vertex and color pointers
glVertexPointer(3, GL_FLOAT, sizeof(Vertex), &verts[0].x );
glColorPointer(4, GL_UNSIGNED_BYTE, sizeof(Vertex), &verts[0].r );
// draw verts array
glDrawArrays(GL_TRIANGLES, 0, verts.size() );
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_COLOR_ARRAY);
glFlush();
glutSwapBuffers();
}
void reshape(int w, int h)
{
glViewport(0, 0, w, h);
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE);
glutInitWindowSize(800,600);
glutCreateWindow("Demo");
glutDisplayFunc(display);
glutReshapeFunc(reshape);
init();
glutMainLoop();
return 0;
}