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

Thanks,

Jessica Zhang

>
> --
> With best wishes
> Dmitry

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