rotate cube with mouse - opengl

[nickm687]

Hi there,

I have the following code and when ran a cube is shown and using the mouse and holding the left mouse button you can rotate it. The problem is that you can rotate the cube whether you click on the cube or the background.

What i would like to do is rotate the cube only when the mouse pointer is clicked onto the cube. Reading up i have read that i would need to implement picking/selection techniques.

Can anyone help me as i am haveing some trouble? I would then like to be able to move(drag) the cube with the mouse around the screen.

Kind Regards
Nick

 
#include <gl/glut.h>
 
bool fullscreen = false;
bool mouseDown = false;
 
float xrot = 0.0f;
float yrot = 0.0f;
 
float xdiff = 0.0f;
float ydiff = 0.0f;
 
void drawBox()
{
glBegin(GL_QUADS);
 
glColor3f(1.0f, 0.0f, 0.0f);
// FRONT
glVertex3f(-0.5f, -0.5f, 0.5f);
glVertex3f( 0.5f, -0.5f, 0.5f);
glVertex3f( 0.5f, 0.5f, 0.5f);
glVertex3f(-0.5f, 0.5f, 0.5f);
// BACK
glVertex3f(-0.5f, -0.5f, -0.5f);
glVertex3f(-0.5f, 0.5f, -0.5f);
glVertex3f( 0.5f, 0.5f, -0.5f);
glVertex3f( 0.5f, -0.5f, -0.5f);
 
glColor3f(0.0f, 1.0f, 0.0f);
// LEFT
glVertex3f(-0.5f, -0.5f, 0.5f);
glVertex3f(-0.5f, 0.5f, 0.5f);
glVertex3f(-0.5f, 0.5f, -0.5f);
glVertex3f(-0.5f, -0.5f, -0.5f);
// RIGHT
glVertex3f( 0.5f, -0.5f, -0.5f);
glVertex3f( 0.5f, 0.5f, -0.5f);
glVertex3f( 0.5f, 0.5f, 0.5f);
glVertex3f( 0.5f, -0.5f, 0.5f);
 
glColor3f(0.0f, 0.0f, 1.0f);
// TOP
glVertex3f(-0.5f, 0.5f, 0.5f);
glVertex3f( 0.5f, 0.5f, 0.5f);
glVertex3f( 0.5f, 0.5f, -0.5f);
glVertex3f(-0.5f, 0.5f, -0.5f);
// BOTTOM
glVertex3f(-0.5f, -0.5f, 0.5f);
glVertex3f(-0.5f, -0.5f, -0.5f);
glVertex3f( 0.5f, -0.5f, -0.5f);
glVertex3f( 0.5f, -0.5f, 0.5f);
glEnd();
}
 
bool init()
{
glClearColor(0.93f, 0.93f, 0.93f, 0.0f);
 
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);
glClearDepth(1.0f);
 
return true;
}
 
void display()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
 
gluLookAt(
0.0f, 0.0f, 3.0f,
0.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f);
 
glRotatef(xrot, 1.0f, 0.0f, 0.0f);
glRotatef(yrot, 0.0f, 1.0f, 0.0f);
 
drawBox();
 
glFlush();
glutSwapBuffers();
}
 
void resize(int w, int h)
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
 
glViewport(0, 0, w, h);
 
gluPerspective(45.0f, 1.0f * w / h, 1.0f, 100.0f);
 
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
 
void idle()
{
if (!mouseDown)
{
xrot += 0.3f;
yrot += 0.4f;
}
 
glutPostRedisplay();
}
 
void keyboard(unsigned char key, int x, int y)
{
switch(key)
{
case 27 : 
exit(1); break;
}
}
 
void specialKeyboard(int key, int x, int y)
{
if (key == GLUT_KEY_F1)
{
fullscreen = !fullscreen;
 
if (fullscreen)
glutFullScreen();
else
{
glutReshapeWindow(500, 500);
glutPositionWindow(50, 50);
}
}
}
 
void mouse(int button, int state, int x, int y)
{
if (button == GLUT_LEFT_BUTTON &amp;&amp; state == GLUT_DOWN)
{
mouseDown = true;
 
xdiff = x - yrot;
ydiff = -y + xrot;
}
else
mouseDown = false;
}
 
void mouseMotion(int x, int y)
{
if (mouseDown)
{
yrot = x - xdiff;
xrot = y + ydiff;
 
glutPostRedisplay();
}
}
 
int main(int argc, char *argv[])
{
glutInit(&amp;argc, argv);
 
glutInitWindowPosition(50, 50);
glutInitWindowSize(500, 500);
 
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
 
glutCreateWindow("13 - Solid Shapes");
 
glutDisplayFunc(display);
glutKeyboardFunc(keyboard);
glutSpecialFunc(specialKeyboard);
glutMouseFunc(mouse);
glutMotionFunc(mouseMotion);
glutReshapeFunc(resize);
//glutIdleFunc(idle);
 
if (!init())
return 1;
 
glutMainLoop();
 
return 0;
}

[juglarx]

take a look at this tutorial
http://nehe.gamedev.net/data/lessons....asp?lesson=32

[Ali S. Alfaraj]

Thanks for the sharing your code.

One question If i may ask, what is the purpose of the idle function:

void idle()
{
if (!mouseDown)
{
xrot += 0.3f;
yrot += 0.4f;
}

Isn't the cube rotation is already implemented in the mouseMotion function?

Thanks again

[Savalia]

ALi
It looks like idle() tests if one of the buttons on the mouse is being held down, if it is NOT (held down) then idle() will put a slow rotation on the object in both the positive x and y directions. If that's not what you need, you could always rewrite this idle() function to reset your cube to the original state, when the window first opened. Just add your cube's original coordinates, move it to that position, and then zero out all the rotation values.

[Vineet]

Hello,
I also have the same question as Nick has (in the first post).
I want to rotate or move a cube only when we click somewhere ON it, and not if we click in the background.
Can someone please help me with this. Any pointers would be really really appreciated.
Thanks and Regards,
Vineet

[Alfonse Reinheart]

Let me make sure I understand this.

You felt the need to unearth a post from 6 months ago, which itself was a reply to a post from 3 years before it. All to ask a question that the second post in the thread answers.

[Xi Yang]

Actually, what you want is a picking test. If you want to know whether an location is inside an object, you have to cope with picking mode, name stack. Have a look at functions: glRenderMode, glInitNames, glSelectBuffer, glPushName, glPopName, glLoadName...