使用OpenGL围绕枢轴点旋转

Question

I am trying to rotate an object about one of its side and already tried the common approach as found on the forums:

translate(-P);
rotate();
translate(P);

In OpenGL (reversing the order of translations/rotations), I used the following code:

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPushMatrix();
    glTranslatef(-50, 50, 0);
        glRotatef(rotationCoord, 0, 1, 0);
    glTranslatef(50, -50, 0);
    glBegin(GL_QUADS); 
        glVertex3f(-50.0, 50.0, 0);
        glVertex3f(50.0, 50.0, 0);
        glVertex3f(50.0, -50.0, 0);
        glVertex3f(-50.0, -50.0, 0);
    glEnd();
glPopMatrix();

However, the rectangle that I am drawing doesn't seem to be rotating around one side as pivot. (trying to set the left side as the pivot point and rotate around it). I made a screen capture vid to show what kind of rotation I am getting right now. Here's the video:

http://youtu.be/VgEZ_rsG3xU

How do I set the pivot for this object so that it rotated around that point?

Answer 1

The problem comes from the

glTranslatef(0, 0, -10.0);

you're calling after the rotation. That means the (0,0,-10) is applied to the object coordinates (+-50,+-50,0) before they are transformed by anything else, so the quad is offset before it's being rotated.

Here's the code I used for testing, maybe you get something out of it:

#include <glm/glm.hpp>
#include <glm/ext.hpp>
using namespace glm;

void display(void)
{
  glClearColor(0,0,0,0);
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  GLfloat aspect = (float)g_Width / g_Height;
  mat4 eyeToCamera = perspective(45.f, aspect, g_nearPlane, g_farPlane); // projection
  mat4 cameraToWorld = lookAt(vec3(0, 0, -150), vec3(), vec3(0, 1, 0)); // view

  vec3 pivot(50, -50, 0);
  mat4 worldToObject = translate(pivot)
    * rotate(rotationAngle, vec3(0, 1, 0))
    * translate(-pivot); // model
  glLoadMatrixf(value_ptr(eyeToCamera * cameraToWorld * worldToObject));
  glBegin(GL_QUADS);
    glVertex3f(-50.0, 50.0, 0);
    glVertex3f(50.0, 50.0, 0);
    glVertex3f(50.0, -50.0, 0);
    glVertex3f(-50.0, -50.0, 0);
  glEnd();

  glutSwapBuffers();
}

Note that I don't use any matrix stack functions, and I only set the GL_MODELVIEW matrix.