Difference between revisions of "Tutorial - Picking"

Picking the mesh under the mouse cursor

Picking an object within the scene is a common problem. Supposing you want to select the object using a mouse the following sample will show you how you get the NodeHandle for the object under the mouse cursor.

Based on the knight example in the Horde3D SDK we will first remove the mouseMoveListener. To enable the mouse cursor again we have to remove the
glfwDisable( GLFW_MOUSE_CURSOR ); and glfwEnable( GLFW_MOUSE_CURSOR ); statements, too.

Then we define a mouseButtonListener in the main.cpp:

void GLFWCALL mouseButtonListener( int button, int action )
{
   // If left mouse button has been pressed...
   if( button == GLFW_MOUSE_BUTTON_LEFT && action == GLFW_PRESS)
   {
       int x, y;
       int width, height;
       // get mouse position
       glfwGetMousePos(&x, &y);
       // get window size for normalization
       glfwGetWindowSize(&width, &height);
       // pick the node under the normalized mouse position
       app->pick( x / float( width ), (height - y) / float( height ) );
   }
}

To activate that listener we have to add the following code to the setupWindow method:

glfwSetMouseButtonCallback( mouseButtonListener );

For the use of Horde3DUtils::pickNode we have to normalize the window coordinates received by glfwGetMousePos. That's why we need to call glfwGetWindowSize additionally. Another conversion has to be made, since GLFW has it's origin in the upper left corner while Horde3D requires the origin to be in the lower left corner.

Then in the app.cpp we implement a call to the h3dutPickNode utility function.

void Application::pick( float dX, float dY )
{
   H3DNode node = h3dutPickNode(_cam, dX, dY);
}