Re: [FFmpeg-devel] [PATCH v2 1/3] avutil/hwcontext: add a function to get the AVHWDeviceType

["\"zhilizhao(赵志立)\"" <quinkblack@foxmail.com>]

> On Jun 30, 2022, at 7:56 PM, Andreas Rheinhardt <andreas.rheinhardt@outlook.com> wrote:
> 
> "zhilizhao(赵志立)":
>> 
>> 
>>> On Jun 30, 2022, at 4:43 PM, Anton Khirnov <anton@khirnov.net> wrote:
>>> 
>>> Quoting Tong Wu (2022-06-30 04:45:56)
>>>> Add a function to get the corresponding AVHWDeviceType from a given
>>>> hardware pixel format.
>>>> 
>>>> Signed-off-by: Tong Wu <tong1.wu@intel.com>
>>>> ---
>>>> libavutil/hwcontext.c | 12 ++++++++++++
>>>> libavutil/hwcontext.h |  9 +++++++++
>>>> 2 files changed, 21 insertions(+)
>>>> 
>>>> diff --git a/libavutil/hwcontext.c b/libavutil/hwcontext.c
>>>> index ab9ad3703e..3521ed34f4 100644
>>>> --- a/libavutil/hwcontext.c
>>>> +++ b/libavutil/hwcontext.c
>>>> @@ -80,6 +80,18 @@ static const char *const hw_type_names[] = {
>>>>    [AV_HWDEVICE_TYPE_VULKAN] = "vulkan",
>>>> };
>>>> 
>>>> +enum AVHWDeviceType av_hwdevice_get_type_by_pix_fmt(enum AVPixelFormat fmt)
>>>> +{
>>>> +    int i, j;
>>> 
>>> Nit: you can and should declare loop indices in the loop statement
>>> itself
>>> 
>>>> +    for (i = 0; hw_table[i]; i++) {
>>>> +        for (j = 0; hw_table[i]->pix_fmts[j] != AV_PIX_FMT_NONE; j++) {
>>>> +            if (hw_table[i]->pix_fmts[j] == fmt)
>>>> +                return hw_table[i]->type;
>>>> +        }
>>>> +    }
>>>> +    return AV_HWDEVICE_TYPE_NONE;
>>>> +}
>>>> +
>>>> enum AVHWDeviceType av_hwdevice_find_type_by_name(const char *name)
>>>> {
>>>>    int type;
>>>> diff --git a/libavutil/hwcontext.h b/libavutil/hwcontext.h
>>>> index c18b7e1e8b..97f94403e2 100644
>>>> --- a/libavutil/hwcontext.h
>>>> +++ b/libavutil/hwcontext.h
>>>> @@ -229,6 +229,15 @@ typedef struct AVHWFramesContext {
>>>>    int width, height;
>>>> } AVHWFramesContext;
>>>> 
>>>> +/**
>>>> + * Get the device type by a given pixel format.
>>>> + *
>>>> + * @param fmt Pixel format from enum AVPixelFormat.
>>>> + * @return The type from enum AVHWDeviceType, or AV_HWDEVICE_TYPE_NONE if
>>>> + *         not found.
>>>> + */
>>>> +enum AVHWDeviceType av_hwdevice_get_type_by_pix_fmt(enum AVPixelFormat fmt);
>>> 
>>> I wonder if we should consider the possibility of a format being
>>> supported by more than one device type.
>> 
>> For future proof, we can make it clear that there is no guarantee
>> that the device type is unique, e.g.,
>> 
>> "Get any device type which support the given pixel format”
>> 
> 
> Then you'd need to return a list or modify the user accept an iterator.

Iterator should be fine.

However, the use case is unclear: since we only return an AVHWDeviceType
without description like av_pix_fmt_desc_get(), user has little information
to skip to the next one, unless user only wants to get all of the device
types which support a pixel format. 

> 
> - Andreas
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