[FFmpeg-devel] [PATCH V3 3/5] libavutil/hwcontext_vulkan: Allocate vkFrame in one memory

[Lynne]

29 Nov 2021, 05:07 by wenbin.chen at intel.com:

>> 26 Nov 2021, 03:54 by wenbin.chen at intel.com:
>>
>> > The vaapi can import external frame, but the planes of the external
>> > frames should be in the same drm object. A new option
>> "contiguous_planes"
>> > is added to device. This flag tells device to allocate places in one
>> > memory. When device is derived from vaapi this flag will be enabled.
>> > A new flag frame_flag is also added to AVVulkanFramesContext. User
>> > can use this flag to force enable or disable this behaviour.
>> > A new variable "offset "is added to AVVKFrame. It describe describe the
>> > offset from the memory currently bound to the VkImage.
>> >
>> > Signed-off-by: Wenbin Chen <wenbin.chen at intel.com>
>> >
>>
>> Why is a new offset variable needed?
>> vkGetImageSubresourceLayout is valid for DRM tiled images.
>> According to the specs,
>> "If the image’s tiling is VK_IMAGE_TILING_DRM_FORMAT_MODIFIER_EXT,
>> then vkGetImageSubresourceLayout describes one memory plane of the
>> image. If the image’s tiling is
>> VK_IMAGE_TILING_DRM_FORMAT_MODIFIER_EXT and the image is non-
>> linear, then the returned layout has an implementation-dependent meaning;
>> the vendor of the image’s DRM format modifier may provide documentation
>> that explains how to interpret the returned layout.".
>>
>> Isn't this what you already have in the offset field?
>>
>
> The offset we get from vkGetImageSubresourceLayout is from the start of the image or plane.
> The offset drm_object need is from the start of the memory, and vkGetImageSubresourceLayout
> cannot get this information. I add a new offset variable because I allocate all planes in one memory 
> not because I use VK_IMAGE_TILING_DRM_FORMAT_MODIFIER_EXT.
>

What do you mean, from the start of the plane? I don't recall it
being a thing.
The spec says it's driver-dependent, so wouldn't it make sense for
the driver to return the offset from the start of the memory?