Controlling Games with the Keyboard and Mouse - Tracking the Mouse
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When you move the mouse, a series of events is set off that is very similar to those set off by the keyboard. In fact, the Win32 API includes a series of mouse messages that are used to convey mouse events, similar to how keyboard messages convey keyboard events. In the previous section, you learned that the Win32 keyboard messages aren't up to the task of providing efficient input for games. Fortunately, the same cannot be said of the mouse messages. It turns out that the built-in Win32 approach to handling mouse events via messages works out just fine for games. The following are the mouse messages used to notify Windows programs of mouse events:
WM_MOUSEMOVE—Any mouse movement
WM_LBUTTONDOWN—Left mouse button pressed
WM_LBUTTONUP—Left mouse button released
WM_RBUTTONDOWN—Right mouse button pressed
WM_RBUTTONUP—Right mouse button released
WM_MBUTTONDOWN—Middle mouse button pressed
WM_MBUTTONUP—Middle mouse button released
The first mouse message, WM_MOUSEMOVE, lets you know whenever the mouse has been moved. The remaining messages relay mouse button clicks for the left, right, and middle buttons, respectively. Keep in mind that a mouse button click consists of a button press followed by a button release; you can implement a mouse dragging feature by keeping track of when a mouse button is pressed and released and watching for mouse movement in between.
Note - A WM_MOUSEWHEEL message is also sent whenever the user rotates the wheel that is located on the top of some mouse devices. Although the mouse wheel could certainly prove useful in some game scenarios, I opted to focus on the core mouse input messages in this discussion. By all means, explore adding support for the WM_MOUSEWHEEL message to the game engine if you have a game in mind that would benefit from it.
Regardless of whether you're interested in mouse movement or a mouse button click, the important factor regarding the mouse is where the mouse cursor is located. Fortunately, the mouse cursor position is provided with all the previously mentioned mouse messages. It's packed into the lParam argument that gets sent to the GameEngine::HandleEvent() method. The following is the prototype for this method, just in case you forgot:
LRESULT GameEngine::HandleEvent(HWND hWindow, UINT msg, WPARAM wParam,
LPARAM lParam);
If you recall, the wParam and lParam arguments are sent along with every Windows message and contain message-specific information. In the case of the mouse messages, lParam contains the XY position of the mouse cursor packed into its low and high words. The following is an example of a code snippet that extracts the mouse position from the lParam argument in a WM_MOUSEMOVE message handler:
case WM_MOUSEMOVE:
WORD x = LOWORD(lParam);
WORD y = HIWORD(lParam);
return 0;
The wParam argument for the mouse messages includes information about the mouse button states, as well as some keyboard information. More specifically, wParam lets you know if any of the three mouse buttons are down, as well as whether the Shift or Control keys on the keyboard are being pressed. In case you don't see it, the wParam argument—used in conjunction with WM_MOUSEMOVE— provides you with enough information to implement your own Doom strafing feature! The following are the constants used with the mouse messages to interpret the value of the wParam argument:
MK_LBUTTON—Left mouse button is down
MK_RBUTTON—Right mouse button is down
MK_MBUTTON—Middle mouse button is down
MK_SHIFT—Shift key is down
MK_CONTROL—Control key is down
You can check for any of these mouse constants to see if a button or key is being pressed during the mouse move. The constants are actually flags, which means that they can be combined together in the wParam argument. To check for the presence of an individual flag, you must use the bitwise AND operator (&) to see if the flag is present. The following is an example of checking wParam to see if the right mouse button is down:
if (wParam & MK_RBUTTON)
// Yep, the right mouse button is down!
This code shows how to use the bitwise AND operator (&) to check for individual flags. This is a technique you use in Chapter 7 to check the state of a joystick.
 This chapter is from Beginning Game Programming, by Michael Morrison (Sams, ISBN: 0672326590). Check it out at your favorite bookstore today.
Buy this book now. |
Next: Revamping the Game Engine for Input >>
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