true isometric projection with opengl

Question

I am a newbie in OpenGL programming with C++ and not very good at mathematics. Is there a simple way to have isometric projection?

I mean the true isometric projecti

Answer 1

If you do not want to use GLU, here is bare bones using glOrtho

void gl_enter_2_5d_mode (void)
{
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();

    glLoadIdentity();

    double scale = 50;
    glOrtho(-scale,
            scale,
            -scale * 0.7,
            scale * 0.7,
            -scale,
            scale);

    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();

    glLoadIdentity();

    glRotatef(35.264f, 1.0f, 0.0f, 0.0f);
    glRotatef(-45.0f, 0.0f, 1.0f, 0.0f);
}

void gl_leave_2_5d_mode (void)
{
    glMatrixMode(GL_MODELVIEW);
    glPopMatrix();

    glMatrixMode(GL_PROJECTION);
    glPopMatrix();
}

then draw a cube in it

void cube (double size)
{
    glBegin(GL_QUADS);

    glVertex3f(size,size,size);
    glVertex3f(-size,size,size);
    glVertex3f(-size,-size,size);
    glVertex3f(size,-size,size);

    glVertex3f(size,size,-size);
    glVertex3f(-size,size,-size);
    glVertex3f(-size,-size,-size);
    glVertex3f(size,-size,-size);

    glVertex3f(size,size,size);
    glVertex3f(size,-size,size);
    glVertex3f(size,-size,-size);
    glVertex3f(size,size,-size);

    glVertex3f(-size,size,size);
    glVertex3f(-size,-size,size);
    glVertex3f(-size,-size,-size);
    glVertex3f(-size,size,-size);

    glVertex3f(size,size,size);
    glVertex3f(-size,size,size);
    glVertex3f(-size,size,-size);
    glVertex3f(size,size,-size);

    glVertex3f(size,-size,size);
    glVertex3f(-size,-size,size);
    glVertex3f(-size,-size,-size);
    glVertex3f(size,-size,-size);

    glEnd();
}

void test (void)
{
    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
    glBindTexture(GL_TEXTURE_2D, 0);
    cube(1.0);
    glPolygonMode(GL_FRONT_AND_BACK,GL_FILL);
}

and call something like this

gl_enter_2_5d_mode()
test()
gl_leave_2_5d_mode()

should you want to toggle between 2d and 2.5d (so you can draw your UI) then I have similar functions to enter and leave 2d mode e.g.

void gl_init_2d_mode (void)
{
    /*
     * Enable Texture Mapping
     */
    glEnable(GL_TEXTURE_2D);

    /*
     * Enable alpha blending for sprites
     */
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    /*
     * Setup our viewport
     */
    glViewport(0, 0, game.video_pix_width,
               game.video_pix_height);

    /*
     * Make sure we're changing the model view and not the projection
     */
    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();

    /*
     * Reset the view
     */
    glLoadIdentity();

    gl_init_fbo();
}

void gl_enter_2d_mode (void)
{
    /*
     * Change to the projection matrix and set our viewing volume.
     */
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();

    /*
     * Reset the view
     */
    glLoadIdentity();

    /*
     * 2D projection
     */
    glOrtho(0,
             game.video_gl_width, game.video_gl_height,
             0, -1200.0, 1200.0);

    /*
     * Make sure we're changing the model view and not the projection
     */
    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();

    /*
     * Reset the view
     */
    glLoadIdentity();
}