On 8/16/18 2:42 PM, Maarten Lankhorst wrote:
Op 08-08-18 om 16:30 schreef Dmitry Osipenko:
On Wednesday, 8 August 2018 11:16:09 MSK Russell King - ARM Linux wrote:
On Tue, Aug 07, 2018 at 08:22:01PM +0300, Dmitry Osipenko wrote:
+ * Glossary:
+ *
+ * Destination plane:
+ * Plane to which color keying properties are applied, this planes takes
+ * the effect of color keying operation. The effect is determined by a
+ * given color keying mode.
+ *
+ * Source plane:
+ * Pixels of this plane are the source for color key matching operation.
...
+ /**
+ * @DRM_PLANE_COLORKEY_MODE_TRANSPARENT:
+ *
+ * Destination plane pixels are completely transparent in areas
+ * where pixels of a source plane are matching a given color key
+ * range, in other cases pixels of a destination plane are
unaffected.
+ * In areas where two or more source planes overlap, the topmost
+ * plane takes precedence.
+ */
This seems confusing to me.
What you seem to be saying is that the "destination" plane would be the
one which is (eg0 the graphic plane, and the "source" plane would be the
the plane containing (eg) the video. You seem to be saying that the
colorkey matches the video and determines whether the pixels in the
graphic plane are opaque or transparent.
Your example is correct.
With the "plane_mask" property we can specify any plane as the "source" for
color key, so it can been either a video plane or graphic plane and even both
at the same time.
I'm not sure we should specify plane mask from userspace.
It looks like a quite flexible approach. Do you have any other suggestions?
Can't we make major loops? How do you want to handle those?
It's up to a specific driver to accept the mask or reject it. You could make a
loop if HW allows to do that, I don't see what's the problem.
Surely that is the wrong way round - in video overlay, you want to
colorkey match the contents of the graphic plane to determine which
pixels from the video plane to overlay.
The "transparent" mode makes the color-matched pixels to become transparent,
you want the inversion effect and hence that should be called something like a
"transparent-inverted" mode. Maarten Lankhorst was asking for that mode in his
comment to v3, I'm leaving for somebody else to add that mode later since
there is no real use for it on Tegra right now.
I would like it to be described and included, so I can convert the existing intel_sprite_set_colorkey_ioctl to atomic.
Okay, I can add it. Though probably better to call that mode "opaque" rather
than "transparent-inverted".
Then again, could transparent-inverted also be handled by setting transparent on the primary?
If HW allows to do that, then yes.
So in your case the graphic plane will be the "source" plane (specified via
the colorkey.plane_mask property), video plane will be the "destination" plane
(plane to which the colorkey properties are applied) and the colorkey.mode
will be "transparent-inverted". Pixels of the "source" plane are being matched
and "destination" plane takes the effect of color keying operation, i.e. the
color-matched pixels of graphic plane leave the video plane pixels unaffected
and the unmatched pixels make the video plane pixels transparent.
If it's the other way around (source is the graphic, destination is the
video) it makes less sense to use the "source" and "destination" terms,
I can't see how you could describe a plane that is being overlaid on
top of another plane as a "destination".
Tegra has a bit annoying limitations in regard to a reduced plane blending
functionality when color keying is enabled. I found that the best variant to
work around the limitations is to move the graphic plane on top of the video
plane and to make the graphic plane to match itself. I.e. the matched pixels
of graphic plane become transparent and hence poked by video plane.
I guess the terminology has come from a thought about using a GPU to
physically do the colorkeying when combining two planes - if the GPU
were to write to the "destination" plane, then this would be the wrong
way around. For starters, taking the above example, the video plane
may well be smaller than the graphic plane. If it's the other way
around, that has other problems, like destroying the colorkey in the
graphic plane when writing the video plane's contents to it.
It all depends on a use-case scenario. It won't be easy for userspace to
generalize the usage of color keying, at best the color keying interface could
be generalized and then userspace may choose the best fitting variant based on
available HW capabilities.
There's TEST_ONLY for a reason, though I guess it makes generic color keying slightly more invovled for userspace. :)
It is also quite involved for kernel to present a non-standard feature as
something generic, pleasing everyone in the same time.
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