User Input - Marmalade SDK Mobile Game Development Essentials - page 76

{
// Left mouse button or touch screen released
}
}
return 0;
}
// We use this to register the callback function…
s3ePointerRegister(S3E_POINTER_BUTTON_EVENT,
(s3eCallback) ButtonEventCallback, NULL);
// …and this to cancel notifications
s3ePointerUnRegister(S3E_POINTER_BUTTON_EVENT,
(s3eCallback) ButtonEventCallback);
The button event callback's first parameter is a pointer to an s3ePointerEvent
structure that contains four members. The button that was pressed is stored in a
member called m_Button that is of the type s3ePointerButton (see the table in
the Detecting single touch input using polling section earlier in this chapter for more
details on this enumerated type).
The m_Pressed member will be 0 if the button was released and 1 if it was
pressed. You might expect this to be of type bool rather than an integer but it
isn't, because this is a C-based API, not C++-based and bool is not a part of the
standard C language.
We can also discover the screen position where the event occurred by using the
structure's m_x and m_y members.
It is also possible to register a callback that will inform us when the user
has performed a pointer motion. We again use the s3ePointerRegister /
s3ePointerUnRegister functions, but this time use S3E_POINTER_MOTION_EVENT
as the callback type.
The callback function we register will be passed a pointer to an
s3ePointerMotionEvent structure that consists of just m_x and m_y members
containing the screen coordinate that is now being pointed at.
Detecting multi-touch input
A multi-touch capable display allows us to detect more than one touched point on
the screen at a time. Every time the screen is touched, the device's OS will assign
that touch point an ID number. As the user moves their finger around the screen, the
coordinates associated with that ID number will be updated until the user removes
their finger from the screen, whereupon that touch will become inactive and the ID
number becomes invalid.