Re: [PATCH RFC v5 02/10] drm: Introduce solid fill DRM plane property

[Jessica Zhang <quic_jesszhan@quicinc.com>]

On 8/8/2023 3:57 PM, Jessica Zhang wrote:
> 
> 
> On 8/7/2023 6:07 PM, Dmitry Baryshkov wrote:
>>
>>
>> On 8 August 2023 00:41:07 GMT+03:00, Jessica Zhang 
>> <quic_jesszhan@quicinc.com> wrote:
>>>
>>>
>>> On 8/4/2023 6:27 AM, Dmitry Baryshkov wrote:
>>>> On Fri, 28 Jul 2023 at 20:03, Jessica Zhang 
>>>> <quic_jesszhan@quicinc.com> wrote:
>>>>>
>>>>> Document and add support for solid_fill property to drm_plane. In
>>>>> addition, add support for setting and getting the values for 
>>>>> solid_fill.
>>>>>
>>>>> To enable solid fill planes, userspace must assign a property blob to
>>>>> the "solid_fill" plane property containing the following information:
>>>>>
>>>>> struct drm_mode_solid_fill {
>>>>>           u32 version;
>>>>>           u32 r, g, b;
>>>>> };
>>>>>
>>>>> Signed-off-by: Jessica Zhang <quic_jesszhan@quicinc.com>
>>>>> ---
>>>>>    drivers/gpu/drm/drm_atomic_state_helper.c |  9 +++++
>>>>>    drivers/gpu/drm/drm_atomic_uapi.c         | 55 
>>>>> +++++++++++++++++++++++++++++++
>>>>>    drivers/gpu/drm/drm_blend.c               | 30 +++++++++++++++++
>>>>>    include/drm/drm_blend.h                   |  1 +
>>>>>    include/drm/drm_plane.h                   | 35 ++++++++++++++++++++
>>>>>    include/uapi/drm/drm_mode.h               | 24 ++++++++++++++
>>>>>    6 files changed, 154 insertions(+)
>>>>>
>>>>
>>>> [skipped most of the patch]
>>>>
>>>>> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
>>>>> index 43691058d28f..53c8efa5ad7f 100644
>>>>> --- a/include/uapi/drm/drm_mode.h
>>>>> +++ b/include/uapi/drm/drm_mode.h
>>>>> @@ -259,6 +259,30 @@ struct drm_mode_modeinfo {
>>>>>           char name[DRM_DISPLAY_MODE_LEN];
>>>>>    };
>>>>>
>>>>> +/**
>>>>> + * struct drm_mode_solid_fill - User info for solid fill planes
>>>>> + *
>>>>> + * This is the userspace API solid fill information structure.
>>>>> + *
>>>>> + * Userspace can enable solid fill planes by assigning the plane 
>>>>> "solid_fill"
>>>>> + * property to a blob containing a single drm_mode_solid_fill 
>>>>> struct populated with an RGB323232
>>>>> + * color and setting the pixel source to "SOLID_FILL".
>>>>> + *
>>>>> + * For information on the plane property, see 
>>>>> drm_plane_create_solid_fill_property()
>>>>> + *
>>>>> + * @version: Version of the blob. Currently, there is only support 
>>>>> for version == 1
>>>>> + * @r: Red color value of single pixel
>>>>> + * @g: Green color value of single pixel
>>>>> + * @b: Blue color value of single pixel
>>>>> + */
>>>>> +struct drm_mode_solid_fill {
>>>>> +       __u32 version;
>>>>> +       __u32 r;
>>>>> +       __u32 g;
>>>>> +       __u32 b;
>>>>
>>>> Another thought about the drm_mode_solid_fill uABI. I still think we
>>>> should add alpha here. The reason is the following:
>>>>
>>>> It is true that we have  drm_plane_state::alpha and the plane's
>>>> "alpha" property. However it is documented as "the plane-wide opacity
>>>> [...] It can be combined with pixel alpha. The pixel values in the
>>>> framebuffers are expected to not be pre-multiplied by the global alpha
>>>> associated to the plane.".
>>>>
>>>> I can imagine a use case, when a user might want to enable plane-wide
>>>> opacity, set "pixel blend mode" to "Coverage" and then switch between
>>>> partially opaque framebuffer and partially opaque solid-fill without
>>>> touching the plane's alpha value.
>>>
>>> Hi Dmitry,
>>>
>>> I don't really agree that adding a solid fill alpha would be a good 
>>> idea. Since the intent behind solid fill is to have a single color 
>>> for the entire plane, I think it makes more sense to have solid fill 
>>> rely on the global plane alpha.
>>>
>>> As stated in earlier discussions, I think having both a 
>>> solid_fill.alpha and a plane_state.alpha would be redundant and serve 
>>> to confuse the user as to which one to set.
>>
>> That depends on the blending mode: in Coverage mode one has 
>> independent plane and contents alpha values. And I consider alpha 
>> value to be a part of the colour in the rgba/bgra modes.
> 
> Acked -- taking Sebastian's concern into consideration, I think I'll 
> have "PIXEL_SOURCE_SOLID_FILL_RGB" and add a separate 
> "PIXEL_SOURCE_SOLID_FILL_RGBA".

Hi Dmitry,

Since it looks like there's still some ongoing discussion with Pekka 
about whether to support an RGBA solid fill source, I'll just leave a 
note to add an RGBA source in the future.

Thanks,

Jessica Zhang

> 
> Thanks,
> 
> Jessica Zhang
> 
>>
>>
>>>
>>> Thanks,
>>>
>>> Jessica Zhang
>>>
>>>>
>>>> -- 
>>>> With best wishes
>>>> Dmitry
>>
>> -- 
>> With best wishes
>> Dmitry