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