Using the mouse scrollwheel in GLUT

不问归期 提交于 2019-12-17 09:31:01

问题


I want to use the mouse scrollwheel in my OpenGL GLUT program to zoom in and out of a scene? How do I do that?


回答1:


Freeglut's glutMouseWheelFunc callback is version dependant and not reliable in X. Use standard mouse function and test for buttons 3 and 4.

The OpenGlut notes on glutMouseWheelFunc state:

Due to lack of information about the mouse, it is impossible to implement this correctly on X at this time. Use of this function limits the portability of your application. (This feature does work on X, just not reliably.) You are encouraged to use the standard, reliable mouse-button reporting, rather than wheel events.

Using standard GLUT mouse reporting:

#include <GL/glut.h>

<snip...>

void mouse(int button, int state, int x, int y)
{
   // Wheel reports as button 3(scroll up) and button 4(scroll down)
   if ((button == 3) || (button == 4)) // It's a wheel event
   {
       // Each wheel event reports like a button click, GLUT_DOWN then GLUT_UP
       if (state == GLUT_UP) return; // Disregard redundant GLUT_UP events
       printf("Scroll %s At %d %d\n", (button == 3) ? "Up" : "Down", x, y);
   }else{  // normal button event
       printf("Button %s At %d %d\n", (state == GLUT_DOWN) ? "Down" : "Up", x, y);
   }
}

<snip...>

glutMouseFunc(mouse);

As the OP stated, it is "dead simple". He was just wrong.




回答2:


Note that venerable Nate Robin's GLUT library doesn't support the scrollwheel. But, later implementations of GLUT like FreeGLUT do.

Using the scroll wheel in FreeGLUT is dead simple. Here is how:

Declare a callback function that shall be called whenever the scroll wheel is scrolled. This is the prototype:

void mouseWheel(int, int, int, int);

Register the callback with the (Free)GLUT function glutMouseWheelFunc().

glutMouseWheelFunc(mouseWheel);

Define the callback function. The second parameter gives the direction of the scroll. Values of +1 is forward, -1 is backward.

void mouseWheel(int button, int dir, int x, int y)
{
    if (dir > 0)
    {
        // Zoom in
    }
    else
    {
        // Zoom out
    }

    return;
}

That's it!




回答3:


observe case 3 and 4 in the switch statement below in the mouseClick callback

glutMouseFunc(mouseClick);

...

void mouseClick(int btn, int state, int x, int y) {
  if (state == GLUT_DOWN) {
    switch(btn) {
    case GLUT_LEFT_BUTTON:
      std::cout << "left click at: (" << x << ", " << y << ")\n";
      break;
    case GLUT_RIGHT_BUTTON:
      std::cout << "right click at: (" << x << ", " << y << ")\n";
      break;
    case GLUT_MIDDLE_BUTTON:
      std::cout << "middle click at: (" << x << ", " << y << ")\n";
      break;
    case 3:  //mouse wheel scrolls
      std::cout << "mouse wheel scroll up\n";
      break;
    case 4:
      std::cout << "mouse wheel scroll down\n";
      break;
    default:
      break;
    }
  }
  glutPostRedisplay();
}


来源:https://stackoverflow.com/questions/14378/using-the-mouse-scrollwheel-in-glut

易学教程内所有资源均来自网络或用户发布的内容,如有违反法律规定的内容欢迎反馈
该文章没有解决你所遇到的问题?点击提问,说说你的问题,让更多的人一起探讨吧!