Mouse Selection

Introduction

Mouse picking is an often used, intuitive operation to interact with 3D scenes in a variety of 3D graphics applications. CHAI3D provides some basic capabilities to detect if an object has been selected. The mouse selection procedure requires first setting up a collision recorder and the desired collision settings. The following listing illustrate a basic example.

using namespace chai3d;

cCollisionRecorder recorder;
cCollisionSettings settings;

// detect for any collision between mouse and scene
bool hit = camera->select(x, y, windowWidth, windowHeight, recorder, settings);

The collision recorder is empty at first and accumulates the selected objects located underneath the mouse pointer. The information returned for each collision event is stored in a cCollisionEvent structure. Such structure will contain a pointer to the object, 3D position information of the mouse click, selected triangle (cMesh), and surface normal.

Collision settings can be setup to filter certain types of data or to speed up the procedure.

Example

Example 07-mouse-select: The operator can select and move an object with the mouse.

In the following listing extracted from example 12-polygon, a mouse click callback is programmed. If a triangle from a mesh object is selected, its vertices a painted in red.

using namespace chai3d;

void mouseClick(int button, int state, int x, int y)
{
    // mouse button down
    if (state == GLUT_DOWN)
    {
        cCollisionRecorder recorder;
        cCollisionSettings settings;

        // detect for any collision between mouse and scene
        bool hit = camera->select(x, y, windowW, windowH, recorder, settings);
        if (hit)
        {
            // set color to red
            cColorf color;
            color.setRed();

            // retrieve triangle selected by mouse
            cTriangle* triangle = recorder.m_nearestCollision.m_triangle;
            if (triangle != NULL)
            {
                // paint each vertex with the selected color
                triangle->getVertex0()->setColor(color);
                triangle->getVertex1()->setColor(color);
                triangle->getVertex2()->setColor(color);
            }
        }
    }
}