ZZ coordinates not Matching

Question

I have this code in c++ that basically creates a series of cubes using GlutSolidCube(1).

I do a rescale to have cubes that have 8 in width and 5 in height constant whatever elements. The ZZ value serves to draw different kinds of things.

The problem is that the distances between the Cubes don't make sense: if I draw a cube with 2 units in ZZ it makes sense that the next cube starts in 2 ZZ, right? Why is the result different?

Here is the Code :

#include "stdafx.h"
#include "glut.h"

void reshape(int w, int h) {
    float xmin = -10., xmax = 10., ymin = -2., ymax = 10.;
    float ratio = (xmax - xmin) / (ymax - ymin);
    float aspect = (float)w / h;
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glOrtho(xmin, xmax, ymin, ymax,-2,30); 
    if (ratio < aspect)
        glScalef(ratio / aspect, 1., 1.);
    else
        glScalef(1., aspect / ratio, 1.);
}

void myDisplay(void)
{
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0f, 1.0f, 1.0f);


    glMatrixMode(GL_MODELVIEW);

    //Margem 1
    glPushMatrix();
    glColor3f(0.0f, 0.4f, 0.0f);
    glRotatef(90.0, 1.0, 0.0, 0.0);
    glScalef(8.0, 5.0, 2.0);
    glTranslatef(0.0, 0.0, 0.0);
    glutSolidCube(1);
    glPopMatrix();

    //Estrada
    glPushMatrix();
    glColor3f(1.0f, 1.0f, 1.0f);
    glRotatef(90.0, 1.0, 0.0, 0.0);
    glScalef(8.0, 5.0, 3.0);
    glTranslatef(0.0, 0.0, -1.);
    glutSolidCube(1);
    glPopMatrix();

    glFlush();
}

void main (int argc,char** argv) {
    glutInit(&argc,argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(400, 400);
    glutInitWindowPosition(-1, -1);
    glutCreateWindow("Teste");
    glutDisplayFunc(myDisplay);
    glutReshapeFunc(reshape);
    glutMainLoop();
}

Resulting image:

Answer 1

The image is OK, given your GL calls. By default, the OpenGL camera is looking down the negative Z axis (i.e. the Z axis points towards it). You draw the green box by first rotating around the X axis by 90deg., which makes Z point downwards and Y towards the camera. Then, you scale Z (the up-down axis now) by 2.0, and finally draw the cube. The Z size of the cube is 1 (from glutSolidCube()) multiplied by 2.0 (the scale) for 2 units total.

For the white cube, you start by the same rotation, scale Z by 3.0, and the translate by 1.0 along the negative scaled Z axis. This is equivalent to 3 unscaled units upwards, and the cube will also have a Z dimension of 3 (1 from glutSolidCube() times 3.0 scale). So it's bigger and above the green one.

It is unclear to me what you want to achieve, so I cannot suggest the appropriate operations.

---

As a side note, you should probably use glOrtho to set up the projection matrix, not the modelview one.