3 Replies Latest reply: Nov 21, 2011 3:37 AM by Dario Pelella RSS

    Can't use memory allocated in C to write then read BitmapData in AS

    mark_aok Community Member

      Hi all,

      I've been attempting to use Alchemy to allocate a chunk of memory in C, and then write a bitmap to the memory (via getPixels) which is I would then be able to modify using my super fast C image processing functions.  I've been following the "Memory allocation in C with direct access in Actionscript (FAST!!)" section from here.


      The problem is that when I allocate the memory in C, then try to display the image using setImage, all I see is a black box on the screen.  The code below shows how I use getPixels to fill the C memory region with my bitmap data, then use setPixels to fill the BitmapData object which is displayed on the screen.  Does anyone know what I'm doing wrong here?  I've been really stuck on this




      ActionScript variables, and event function which runs after my Bitmap is loaded


              private var _dataPosition:uint;
              private var displayedImage:Image;
              private var bmp:Bitmap;


      public function loaded(e:Event):void {

                  bmp = e.target.content as Bitmap;
                  // A setImage at the beggining of this function properly displays my image
                  var loader:CLibInit = new CLibInit();
                  var lib:Object = loader.init();
                  var ns:Namespace = new Namespace("cmodule.alchemyrgr");
                  var byteArray:ByteArray = (ns::gstate).ds; //point to memory
                  var tmpByteArray:ByteArray = new ByteArray();
                  var imgSize:int = bmp.width * bmp.height * 4;
                  _dataPosition = lib.initByteArray(imgSize); //This is the position of the data in memory           
                  var bounds:Rectangle = new Rectangle(0, 0, bmp.width, bmp.height);
                  tmpByteArray = bmp.bitmapData.getPixels(bounds);
                  byteArray.readBytes(tmpByteArray, 0, imgSize);
                  byteArray.position = _dataPosition;
                  bmp.bitmapData.setPixels(bounds, byteArray);
                  //lib.clearByteArray(); //Free the bytearray


      C memory allocation function

      static AS3_Val initByteArray(void* self, AS3_Val args)

          AS3_ArrayValue(args, "IntType", &bufferSize);

          //Allocate buffer of size "bufferSize"
          buffer = (unsigned char*)malloc(bufferSize*sizeof(char));

          //return pointer to the location in memory
          return AS3_Int((int)buffer);


      Thanks in advance!



        • 1. Re: Can't use memory allocated in C to write then read BitmapData in AS
          DigitalArchitectCanada Community Member

          Hi Mark,


          I too attempted to use a method similar to yours to no avail. I posted my solution for passing bytearray data to/from alchemy here:




          There is full flash code and C++ code so you should be able to answer all your questions just by reading my post. However, one thing I see about how you're passing your pointer back to flash is:


              //return pointer to the location in memory
              return AS3_Int((int)buffer);


          I think should be:


              //return pointer to the location in memory
              return AS3_Ptr(buffer);


          You shouldn't be casting your char array as an int and returning it, just use AS3_Ptr(buffer) and that will return the actual memory address as an int to flash. I'm not 100% sure but I think this could be an issue. I use this method also in my code you can find in the link above so you can see the full implementation there. Hope that helps.

          • 2. Re: Can't use memory allocated in C to write then read BitmapData in AS
            audioMirror Community Member

            I see a bug in your code:


            byteArray.readBytes(tmpByteArray, 0, imgSize);


            You must have the


            byteArray.position = _dataPosition;


            line before this, as well as after.  You read the tmpByteArray into some junk alchemy memory, not where you expected.

            • 3. Re: Can't use memory allocated in C to write then read BitmapData in AS
              Dario Pelella



              simply after the

                          tmpByteArray = bmp.bitmapData.getPixels(bounds);


                          tmpByteArray.position = 0;

              then use the tmpByteArray for reading.


              it seems that the getPixels returns the bytearray but forget to set the position to 0 and leave it (i suppose) to the end...

              so your code start to read from a wrong position...


              but in debug mode flash (fdb at least) should throw an error of " ... End of file ..".


              hope this helps


              PS: i see that the bytearray returned from getPixels is big endian... no good for alchemy.