Greetings all, I been redoing some of my code where I use quads and redone it using triangles. Although, my sides are not always made in the counter-clockwise winding. For instance, when I set glPolygonMode(GL_FRONT, GL_LINE), some sides of the cube have clockwise winding and others do not. Here is some code of a partial cube made out of triangle_strips. Maybe it is just bad implementation. Constructive criticism is encouraged. Thanks in advance.

[code] int RenderScene()//Does all the OpenGL drawing { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); // glTranslatef(0,0,-45); glRotatef(xRot, 1, 0, 0); glRotatef(yRot, 0, 1, 0); // glColor3f(1,0,0); glBegin(GL_TRIANGLE_STRIP); //front glColor3f(1,0,0); glVertex3f(25, 25, 25); glVertex3f(-25, 25, 25); glVertex3f(25,-25, 25); glColor3f(1,0,1); glVertex3f(-25,-25,25); //back glColor3f(0,1,0); glVertex3f(25, 25, -25);//tr glVertex3f(-25, 25, -25);//tl glVertex3f(25,-25, -25);//br glColor3f(0,1,1); glVertex3f(-25,-25,-25);//bl //left glColor3f(0,0,1); glVertex3f(-25, 25, -25); glVertex3f(-25, 25, 25); glVertex3f(-25,-25, -25); glColor3f(0,0,1); glVertex3f(-25,-25,25); glEnd(); glPopMatrix(); return 0; } [/code]

----------------------------- "There are ones that say they can and there are those who actually do." "...u can not learn programming in a class, you have to learn it on your own." Edited by - cMADsc on March 5, 2002 6:23:36 PM

Ok, I have seemed to of figured it out. Not a complete cube yet but I am getting there. Trial and error....., don't you just love it. Not certain though, any suggestion still appreciated.

source]
glBegin(GL_TRIANGLE_STRIP);
//front
glColor3f(1,0,0);
glVertex3f(25, 25, 25);//tr
glVertex3f(-25, 25, 25);//tl
glVertex3f(25,-25, 25);//br
glColor3f(1,0,1);
glVertex3f(-25,-25,25);//b/

glColor3f(0,0,1);
glVertex3f(-25,-25,-25);
glVertex3f(-25,25,-25);
glColor3f(0.5,1,0);
glVertex3f(25, -25, -25);
glVertex3f(25, 25, -25);
glVertex3f(25, 25, 25);
glColor3f(1,1,0);
glVertex3f(-25, 25, 25);
glVertex3f(25, -25, 25);
glVertex3f(-25, -25, 25);
//glVertex3f(25, -25, 25);


glEnd();
glPopMatrix();
return 0;
}


[/source]


-----------------------------
"There are ones that say they can and there are those who actually do."

"...u can not learn programming in a class, you have to learn it on your own."



Edited by - cMADsc on March 5, 2002 7:41:47 PM

For one thing, you might try putting all the vertices in an array and using OpenGL's vertex array capability (or at least glVertex3fv(boxcorner[1]); rather than glVertex3f(float, float, float)) The code is shorter that way and a lot easier to read, so you don't need to worry that maybe your code is 99.9% right but you missed the sign on one of the floats or something.

[edited] here I had written a paragraph on why it isn't possible to make a cube out of a single triangle strip and as soon as I saw it posted I realized what I had done wrong I'll post the complete code shortly.

Edited by - Chromebender on March 5, 2002 9:50:53 PM

OK, I finally managed to tesselate the cube into a triangle strip. Flattened, the cube would look like this:
(each X represents a face of the cube, the slashes are half-faces)
X\-----
-X-----
-X-----
-X-----
-\X----

Here are the relevant code snippets (I used Nehe Lesson 7 as the base code):
Basically, looking at the cube from above, the vertices of the top face in clockwise order, starting at the upper-left are 0,1,2,3. If the top face were removed, the corners of the bottom face in clockwise order from the upper-let would be 4,5,6,7.

GLfloat boxcoords[8][3] = { -1.0, 1.0, 1.0, 1.0, 1.0, 1.0,
1.0, -1.0, 1.0, -1.0,-1.0, 1.0,
-1.0, 1.0,-1.0, 1.0, 1.0,-1.0,
1.0,-1.0,-1.0, -1.0,-1.0,-1.0 };

The actual triangle strip drawing code (with texture support)
glBegin(GL_TRIANGLE_STRIP);
// Top Face
glNormal3f( 0.0f, 0.0f, 1.0f);
glTexCoord2f(0.0f, 1.0f); glVertex3fv(boxcoords[0]);
glTexCoord2f(1.0f, 1.0f); glVertex3fv(boxcoords[1]);
glTexCoord2f(0.0f, 0.0f); glVertex3fv(boxcoords[3]);
glTexCoord2f(1.0f, 0.0f); glVertex3fv(boxcoords[2]);
// Front upper-right half face
glNormal3f( 0.0f, -1.0f, 0.0f);
glTexCoord2f(1.0f, 1.0f); glVertex3fv(boxcoords[6]);
// Right Face
glNormal3f( 1.0f, 0.0f, 0.0f);
glTexCoord2f(0.0f, 0.0f); glVertex3fv(boxcoords[1]);
glTexCoord2f(0.0f, 1.0f); glVertex3fv(boxcoords[5]);
// Rear Face
glNormal3f( 0.0f, 1.0f, 0.0f);
glTexCoord2f(1.0f, 0.0f); glVertex3fv(boxcoords[0]);
glTexCoord2f(1.0f, 1.0f); glVertex3fv(boxcoords[4]);
// Left Face
glNormal3f( -1.0f, 0.0f, 0.0f);
glTexCoord2f(0.0f, 0.0f); glVertex3fv(boxcoords[3]);
glTexCoord2f(0.0f, 1.0f); glVertex3fv(boxcoords[7]);
// Front lower-left half face
glNormal3f( 0.0f, -1.0f, 0.0f);
glTexCoord2f(1.0f, 1.0f); glVertex3fv(boxcoords[6]);
//Bottom face
glNormal3f( 0.0f, 0.0f, -1.0f);
glTexCoord2f(0.0f, 0.0f); glVertex3fv(boxcoords[4]);
glTexCoord2f(1.0f, 0.0f); glVertex3fv(boxcoords[5]);
glEnd();

In fact the texture coordinates could be put into an array and loaded along with the vertex array with only a few OpenGL calls, but I leave that as an exercise for the reader