{"id":200,"date":"2011-09-24T15:21:30","date_gmt":"2011-09-24T15:21:30","guid":{"rendered":"http:\/\/www.drmop.com\/?p=200"},"modified":"2011-09-27T19:28:47","modified_gmt":"2011-09-27T19:28:47","slug":"marmalade-sdk-tutorial-touch-and-multi-touch","status":"publish","type":"post","link":"http:\/\/www.drmop.com\/index.php\/2011\/09\/24\/marmalade-sdk-tutorial-touch-and-multi-touch\/","title":{"rendered":"Marmalade SDK Tutorial – Touch and Multi-touch"},"content":{"rendered":"

This tutorial is part of the Marmalade SDK tutorials collection. To see the tutorials index\u00a0click here<\/a><\/p>\n

<\/a>A little rushed this weekend but I did kind of commit myself to producing another tutorial this weekend, so here goes.<\/p>\n

This tutorial is going to cover handling touch and multi-touch pointer events using the Marmalade SDK. Thankfully the Marmalade SDK makes this pretty simple as you will soon see.<\/p>\n

As usual if you just want the code then grab it from here<\/a>. if you want the details then read on. If you just want the details on how to use the CInput class then jump straight to the \u201cUsing CInput\u201d section<\/p>\n

Oh its worth noting that week by week I am going to keep updating the original Iw2D DrawSprite example with the systems that we put together. This week for example, I have added a new CInput class. I like to try and keep code for separate systems in their own neat little classes because a) it makes the code easier to understand b) you can strip out the code and use it as-is with no modification c) its good programming practice. I would ordinarily create systems such as CInput using a singleton, but for the sake of readability and so that you don\u2019t have to run off finding out about the likes of singletons, I have simply declared the concrete version of CInput as a global (slap on the wrist for me, but whatever makes the code easier to understand)<\/p>\n

Marmalade Events and Callbacks<\/h2>\n

The Marmalade pointer system handles screen touches using an event system. This means that when something happens to the pointer (the users finger or a stylus touches the phone or tablets screen for example) the system calls a function to handle it. The Marmalade SDK uses what are called Callbacks<\/strong> to implement this type of event notification system. A call back is basically a function that we define that gets called back by the Marmalade system when the event occurs. The system usually passes some parameters to the call back function to let us know what the heck it wants. Here’s a quick example:<\/p>\n

\r\n
\r\n\r\n\/\/\r\n\/\/ HandleSingleTouchButtonCB - The system will call this callback when the user moves their finger on the screen\r\n\/\/<\/span>\r\nvoid HandleSingleTouchButtonCB(s3ePointerEvent* event)\r\n{\r\n    \/\/ Please add code to do something about this important event<\/span>\r\n}<\/blockquote>\r\n<\/pre>\n
In this example HandleSingleTouchButtonCB gets called by the system when the user touches the screen. Behold, the system has also provided us with some data about the event by way of a pointer to the s3ePointerEvent data type. We can now query this data to find out what the system wants to tell us.<\/p>\n
Taking a quick look at the s3ePointerEvent data type we discover that there is some pretty interesting stuff in there that we can use:<\/p>\n
\r\n
\r\n\r\ntypedef <\/span>struct <\/span>s3ePointerTouchEvent<\/span>\r\n{\r\n    \/**\r\n     * ID of the touch. The ID given to a touch is equal to the number\r\n     * of simultaneous touches active at the time the touch began. This ID\r\n     * can be between 0 and S3E_POINTER_TOUCH_MAX-1 inclusive\r\n     *\/<\/span>\r\n    uint32 m_TouchID;\r\n    \/**  Whether the touch started (1) or ended (0).*\/<\/span>\r\n    uint32 m_Pressed;\r\n    \/** Position X. *\/<\/span>\r\n    int32  m_x;\r\n    \/** Position Y. *\/<\/span>\r\n    int32  m_y;\r\n} s3ePointerTouchEvent<\/span>;<\/blockquote>\r\n<\/pre>\n
Ok, so some of you may be thinking, how do I tell the Marmalade SDK to use my callback when such an event does occur? Because call backs are so useful the Marmalade SDK has lots of function for registering a callback with the system. The one we are interested in for the pointer is called:<\/p>\n
S3E_API s3eResult s3ePointerRegister(s3ePointerCallback cbid, s3eCallback fn<\/strong>, void* userData);<\/pre>\n