This one lab really demonstrates three concepts: using the WTDrop object to merge 2D information with a 3D scene, using transparency with bitmaps, and mouse handling. Click and drag in the window and you'll see a rubber-banding rectangle. It doesn't do any picking here, but it demonstrates how you can add a drop object to your camera to create an image that overlays the rendering scene.
Three drops are used in this scene: a "backdrop" is placed behind it, and two "frontdrops" are grouped together and placed in front of the scene. The backdrop is displaying a 2D logo image, and one frontdrop is used to display the rubber-banding rectangle while the other displays screen coordinates. Note that the rectangle appears behind the text but in front of everything else.
Drops are created based on WTBitmap objects, and any drawing operations performed on the bitmap are reflected in the scene. Creating the bitmap with the same dimensions as the camera's viewing rectangle ensures that the drop covers the entire view. The bitmap is made transparent by setting its color (WTBitmap::setColor() method) to be the same as its transparent color (setColorKey() method). Then, using other colors, set with the setDrawColor() method, you can draw 2D primitives, like lines, pixels, or text, to the bitmap, and erase them by redrawing with the transparent color.
WTCamera::addDrop, WTBitmap::drawLine, WTBitmap::setColorKey, WTBitmap::setDrawColor, WTBitmap::setTextColor, WTBitmap::setTextBkColor, WTBitmap::drawText, WTEvent::getType, WTEvent::getWTX, WTEvent::getWTY