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    <p>Well, where do you read the image back from your GPU? </p> <p>You allocate your input image with the flag <code>CL_MEM_COPY_HOST_PTR</code></p> <blockquote> <p>This flag is valid only if host_ptr is not NULL. If specified, it indicates that the application wants the OpenCL implementation to allocate memory for the memory object and copy the data from memory referenced by host_ptr. </p> </blockquote> <p>and your output image with <code>CL_MEM_USE_HOST_PTR</code></p> <blockquote> <p>This flag is valid only if host_ptr is not NULL. If specified, it indicates that the application wants the OpenCL implementation to use memory referenced by host_ptr as the storage bits for the memory object.</p> <p>OpenCL implementations are allowed to cache the buffer contents pointed to by host_ptr in device memory. This cached copy can be used when kernels are executed on a device.</p> <p>The result of OpenCL commands that operate on multiple buffer objects created with the same host_ptr or overlapping host regions is considered to be undefined.</p> </blockquote> <p>there is nothing wrong with your allocation, however you never tell the OpenCL implementation to write the memory to the used device and to read that memory back into hosts main memory. This may work for CPUs because the memory is already in their device memory (the main memory) but fails for GPUs.</p> <p>The OpenCL c++ binding offers <code>cl::enqueueWriteImage(/*params*/);</code> and <code>cl::enqueueReadImage(/*params*/);</code> to write and read image buffers to/from a device. </p>
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    1. POOpenCL program works on the CPU but outputs empty image when run on the GPU
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    1. USMichael Haidl
    1. USMichael Haidl
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    1. COWhen using integrated gpu's, a copy is needed like this?
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      1. UShuseyin tugrul buyukisik
    2. COA copy is always needed. However under some conditions, it is a NOP because the source and destiny is the same (CPU->CPU).
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      1. USDarkZeros
    3. COVery good point. The way I interpreted the API was that specifying `CL_MEM_COPY_HOST_PTR` or `CL_MEM_USE_HOST_PTR` when creating the image would perform the write or reads automatically and that simply calling `cl::finish()` would force the synchronization. It's not the case and adding the proper writes and reads now works correctly on the CPU and returns a fully black (as opposed to transparent before) image when run on the GPU. http://stackoverflow.com/questions/11866942/enqueuewriteimage-fail-on-gpu leads me to suspect a driver bug. I'll report back when I find the cause.
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      1. USAnthony Vallée-Dubois
 

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