add image_load_from_memory helper

[XuhuiSun95]

Hello,

I am recently working on GPU jpeg encoding and this library offered me some great tools to accomplish my goal.
With some sort of digging on the source code, I realized there is no helper method that load image already in the memory. I would like to contribute my code to help encode raw data that already in the memory.
Notes that my method modified based on gpu_image_load_from_file, however, some of the parameters are not working exactly the same as load_from_file. But this should provide a similar way to load data into CUDA host buffer. I have tested this method on my own code and it works as I desired.
Please let me know if there is anything need to improve on this pull request, and I would like to hear your feedback.

Best,
Xuhui

[MartinPulec]

Hi Xuhui,

I am not sure what is the advantage of that function. I mean, why just don't call gpujpeg_encoder_input_set_image with the buffer? Actually I think that the only advantage is that after the gpujpeg_encoder_input_set_image call, the input buffer can be released. Is this the aim?

However, I don't think that for effective usage of the library, cudaMallocHost should not be called for every image, because the function is quite costy. If you need to make a copies of the buffers, I'd allocate the pinned-buffer memory (allocated with cudaMallocHost) once and then reuse that repeatedly. If the use is just one-shot, it shall be sufficient to use gpujpeg_image_load_from_memory directly (it does the same, copies the buffer to a pinned memory, see here).

Regards,
Martin

[XuhuiSun95]

Hi Martin,

I think you are right. Because I am only starting to using CUDA, I am not so familiar with all the differences between cudaMalloc and when should I use which. Thanks for bringing up some reference and I will close the request.

Best,
Xuhui

[MartinPulec]

Hi Xuhul,

actually you correctly pointed out that it is not quite clear in the GPUJPEG API. The "official" functions are those gpujpeg_encoder_input_*. The load_from_file function is rather an utility function used by the command-line application.

Martin