Still pounding head against wall over glReadPixels => external buffer

> 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.
>

> 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.
>>
>
> Confused. ExternalHandle is...?

> 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
>
>

> 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@0 extent:100@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
>>
>>
>
>

>
> 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
>>
>>
>
>
>

> Lawson English wrote:
>> ogl                     "read pixels into my buffer"
>>    glReadPixels: 0
>>    with:  -100
>>    with: 100
>>    with: 100
>>    with: ogl imagePixelFormat32
>>    with: ogl imagePixelType32
>>    with: xData.
>
> Reading from -100? That would be offscreen. Try replacing the -100
> with 0 and you'll get a lot further.
>
> Cheers,
>   - Andreas
>
>>
>>>
>>>     with: ogl extent y - rect bottom
>>>

> Lawson English wrote:
>>
>>
>> So,  I can now draw using squeak opengl calls and they are now accessible in another process.
>>
>
> Benchmark:
>
> Time millisecondsToRun: [1000 timesRepeat: [
> ogl                     "read pixels into my buffer"
>   glReadPixels: 0
>   with:  0
>   with: 1000
>   with: 1000
>   with: ogl imagePixelFormat32
>   with: ogl imagePixelType32
>   with: xData.
> ]]   => 5930
>
>
> :-)
>
>
> Lawson
>

> Very cool, nice work!
>
> If it turns out that you need more CPU cycles, you might try using PBOs to asynchronously read the pixels... when you call glReadPixels(), the function does not return until the pixels have been completely read, and while you're waiting for the pixels to cross the PCI-E bus, Squeak isn't doing any processing.  If you're reading back 30fps at 5ms per frame (according to your measurements below), you're sitting idle about 15% of the time.
>
> Search for "Asynchronous glReadPixels:" in the PBO extension spec (http://www.opengl.org/registry/specs/ARB/pixel_buffer_object.txt).  Google will turn up many more tutorials.
>
> It probably won't be your top priority right now, but I wanted to ensure that you're aware of the option.
>
> Cheers,
> Josh
>
>  

>
> On Feb 11, 2010, at 1:54 PM, Lawson English wrote:
>
>  
>> Lawson English wrote:
>>    
>>> So,  I can now draw using squeak opengl calls and they are now accessible in another process.
>>>
>>>      
>> Benchmark:
>>
>> Time millisecondsToRun: [1000 timesRepeat: [
>> ogl                     "read pixels into my buffer"
>>   glReadPixels: 0
>>   with:  0
>>   with: 1000
>>   with: 1000
>>   with: ogl imagePixelFormat32
>>   with: ogl imagePixelType32
>>   with: xData.
>> ]]   => 5930
>>
>>
>> :-)
>>
>>
>> Lawson
>>
>>    
>
>
>  

> Josh Gargus wrote:
>> Very cool, nice work!
>>
>> If it turns out that you need more CPU cycles, you might try using
>> PBOs to asynchronously read the pixels... when you call
>> glReadPixels(), the function does not return until the pixels have
>> been completely read, and while you're waiting for the pixels to
>> cross the PCI-E bus, Squeak isn't doing any processing.  If you're
>> reading back 30fps at 5ms per frame (according to your measurements
>> below), you're sitting idle about 15% of the time.
>>
>> Search for "Asynchronous glReadPixels:" in the PBO extension spec
>> (http://www.opengl.org/registry/specs/ARB/pixel_buffer_object.txt).  
>> Google will turn up many more tutorials.
>>
>> It probably won't be your top priority right now, but I wanted to
>> ensure that you're aware of the option.
>>
>> Cheers,
>> Josh
>>
>>  
>
> Thanks. I was aware of PBOs and the like but didn't want to get into
> them until I got something simple working. Am I misunderstanding
> 1000x1000x1000x4/6?
>
> I get more like 160fps x 1megapixel raw blitting speed which sounds
> fast until one realizes that not much else is going on period.

> Lawson English wrote:
>> Josh Gargus wrote:
>>> Very cool, nice work!
>>>
>>> If it turns out that you need more CPU cycles, you might try using PBOs to asynchronously read the pixels... when you call glReadPixels(), the function does not return until the pixels have been completely read, and while you're waiting for the pixels to cross the PCI-E bus, Squeak isn't doing any processing.  If you're reading back 30fps at 5ms per frame (according to your measurements below), you're sitting idle about 15% of the time.
>>>
>>> Search for "Asynchronous glReadPixels:" in the PBO extension spec (http://www.opengl.org/registry/specs/ARB/pixel_buffer_object.txt).  Google will turn up many more tutorials.
>>>
>>> It probably won't be your top priority right now, but I wanted to ensure that you're aware of the option.
>>>
>>> Cheers,
>>> Josh
>>>
>>>  
>>
>> Thanks. I was aware of PBOs and the like but didn't want to get into them until I got something simple working.