color registers are all the same value making the objects effectively "invisible", the intersections of objects will still register collisions. This is useful for making hidden or secret objects and walls. Obscured intersections will also register collisions. If a Player object priority is behind a Playfield color register and another Player object priority is higher (foreground) than the Playfield, and the foreground Player pixels obscure both the Playfield and the Player object behind the Playfield, then the collision between the Playfield and both the background and foreground Player objects will register along with the collision between the foreground and background Player objects. Note that there is no Missile to Missile collision. Player/Missile collisions can only occur when Player/Missile object pixels occur within the visible portions of the display. Player/Missile objects are not rendered during the horizontal blank or the vertical blank. The range of visible color clocks is 34 to 221, and the visible scan lines range from line 8 through line 247. Player/Missile data outside of these coordinates are not rendered and will not register collisions. An object can be partially within the horizontal blank. The objects' pixels that fall outside of the horizontal blank are within the visible portion of the display and can still register collisions. To remove a Player/Missile object from the visible display area horizontal positions (left) 0 and (right) 222 (or greater) will insure no pixels are rendered regardless of the size of the Player/Missile object and so no unintentional collisions can be flagged. Finally, Player, Missile, and Playfield objects collision detection is real-time, registering a collision as the image pixels are merged and output for display. Checking an object's collision bits before the object has been rendered by CTIA/GTIA will show no collision. Once set, collisions remain in effect until cleared by writing to the HITCLR register. Effective collision response routines should occur after the targeted objects have been displayed, or at the end of a frame or during the Vertical Blank to react to the collisions and clear collisions before the next frame begins. Because collisions are only a single bit, collisions are quite obviously not additive. No matter how many times and different locations a collision between pixels occurs within one frame there is only 1 bit to indicate there was a collision. A set collision bit informs a program that it can examine the related objects to identify collision locations