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

[Dmitry Baryshkov]

On 8 August 2023 00:41:07 GMT+03:00, Jessica Zhang <quic_jesszhan@xxxxxxxxxxx> wrote:
>
>
>On 8/4/2023 6:27 AM, Dmitry Baryshkov wrote:
>> On Fri, 28 Jul 2023 at 20:03, Jessica Zhang <quic_jesszhan@xxxxxxxxxxx> 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@xxxxxxxxxxx>
>>> ---
>>>   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.


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

-- 
With best wishes
Dmitry