[Mesa-dev] Dmabuf based render buffers!?

[Christian König]

Am 15.01.21 um 11:26 schrieb Michel Dänzer:
> On 2021-01-14 8:02 p.m., Blueroom wrote:
>>
>> Hi Everyone!
>>
>> I have a program that’s using dmabuf’s to create a zero copy 
>> camera->GL texture pipeline and it’s working great on my RPi4.
>>
>> Now as a last step I want to access the pixels that Iv’e processed in 
>> gl with shaders, on the cpu.
>>
>> Iv’e been told that on the Raspberry Pi OpenGL is sharing the same 
>> memory as the cpu so I’m hoping it would be possible to do something 
>> like a dmabuf on the ‘way out’ too?
>>
>> Does anyone have any pointers in how this could work?
>
> I'd recommend using glGetTexImage or other similar GL APIs for getting 
> the data out of the GL texture.
>
> While mmap of a dma-buf file descriptor works in theory, direct CPU 
> reads from GPU accessible memory can be very slow on some platforms.
>

Yeah, agree. Additional to that you don't know the format of the DMA-buf 
of the texture.

The input image is most likely linear, but the output might be tiled.

Christian.