Lawson, I have not been following this thread closely so I'm probably
wrong but should you be using "xData byteAt:..."? xHandle doesn't make
sense to me.

On 11/02/2010 15:45, Lawson English wrote:
> Hi Andreas. Even if I use a normally allocated bit of memory, I can't
> get it to work:
> 
> 
> xHandle := ExternalAddress  allocate: 100 * 100 * 4.  "create external
> buffer handle"
> xData := ExternalData fromHandle: xHandle type: ExternalType void
> asPointerType. "convert for use with glReadPixels"
> 
> ogl := OpenGL newIn: (0 at 0 extent:100 at 100).    "create ogl context"
> 
> 
> 
> ogl glClearColor(0.2, 0.9, 0.7, 0.5).   "set clear color"
> 
> ogl glClear(16r4000).      "clear backbuffer"
> 
> ogl swapBuffers.    "draw to screen"
> 
> ogl                     "read pixels into my buffer"
>    glReadPixels: 0
>    with:  -100
>    with: 100
>    with: 100
>    with: ogl imagePixelFormat32
>    with: ogl imagePixelType32
>    with: xData.
> 
> xHandle byteAt: 1000=> 0   "print byte value in my buffer???"
> xHandle byteAt: 1000 put: 10   "manually set byte value in my buffer"
> xHandle byteAt: 1000  =>  10  "print byte value in my buffer???????"
> 
> 
> 
> 
> 
> 
> Andreas Raab wrote:
>> Lawson English wrote:
>>> I'm still having problems with my external shared memory thingie. I
>>> can evoke the unix shm* calls and obtain a reference to a shared
>>> memory buffer and attach it to squeak's heap. I can write into it and
>>> read back. I can even attach the same shared memory to two different
>>> instances of squeak and write to the buffer in one and read it with
>>> the other. What I still cannot figure out is how to take that
>>> external buffer and direct the OpenGL>>glReadPixels call to it so
>>> that I can draw using squeak and have it become a bitmap for a
>>> different application.
>>
>> Post your code. Using glReadPixels is straightforward, so there must
>> be something simple in your code that goes wrong. Simply speaking the
>> following should work fine:
>>
>> "Allocate or obtain shared memory buffer"
>> xHandle := ExternalHandle allocate: rect width * rect height * 4.
>>
>> "Convert it to ExternalData"
>> xData := ExternalData fromHandle: xHandle type: ExternalType void
>> asPointerType.
>>
>> "Call glReadPixels"
>> ogl
>>     glReadPixels: rect left
>>     with: ogl extent y - rect bottom
>>     with: rect width
>>     with: rect height
>>     with: ogl imagePixelFormat32
>>     with: ogl imagePixelType32
>>     with: xData.
>>
>> This should be all there is to it.
>>
>> Cheers,
>>   - Andreas
>>
>>
> 
>