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Wed, 8 Jun 2022 04:17:18 -0400 (EDT) Date: Wed, 8 Jun 2022 10:17:15 +0200 From: Maxime Ripard To: Roman Stratiienko Cc: Jernej =?utf-8?Q?=C5=A0krabec?= , wens@csie.org, airlied@linux.ie, Daniel Vetter , Samuel Holland , dri-devel@lists.freedesktop.org, linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev, linux-kernel@vger.kernel.org, megi@xff.cz Subject: Re: [PATCH v2] drm/sun4i: Enable output signal premultiplication for DE2/DE3 Message-ID: <20220608081715.cblotjle6benihal@houat> References: <20220605094018.9782-1-r.stratiienko@gmail.com> <5826286.lOV4Wx5bFT@jernej-laptop> MIME-Version: 1.0 In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220608_011728_696574_DE4CC1BB X-CRM114-Status: GOOD ( 16.76 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: multipart/mixed; boundary="===============9194568463616964996==" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org --===============9194568463616964996== Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="zp6iwgscfyq77x44" Content-Disposition: inline --zp6iwgscfyq77x44 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Jun 06, 2022 at 01:16:06PM +0300, Roman Stratiienko wrote: > =D0=B2=D1=81, 5 =D0=B8=D1=8E=D0=BD. 2022 =D0=B3. =D0=B2 23:23, Jernej =C5= =A0krabec : > > > > Dne nedelja, 05. junij 2022 ob 11:40:18 CEST je Roman Stratiienko napis= al(a): > > > Otherwise alpha value is discarded, resulting incorrect pixel > > > apperance on the display. > > > > > > This also fixes missing transparency for the most bottom layer. > > > > Can you explain that a bit more? >=20 > Well... I would recommend reading Bartosz Ciechanowski's blog > https://ciechanow.ski/alpha-compositing/ or the Porter-Duff's 1984 > whitepaper itself. >=20 > HINT: That magic numbers from sun8i_mixer.h ( 0x03010301 ) corresponds > to SOURCE OVER mode. >=20 > As you can see from the blending equation it outputs both pixel value > and alpha value (non-premultiplied data mode). >=20 > Also single-layer non-premultiplied buffers may have for example > (R255,G255,B255,A2) pixel value, which should be sent as {R2, G2, B2} > through the physical display interface. >=20 > When OUTCTL.PREMULTI disabled pixel, the RGB values passes as is, and > even 100% transparent data {R255, G255, B255, A0} will appear as 100% > opaque white. Without going into the full explanation about what alpha is, your commit log must describe what the bug is exactly, and most importantly how do you trigger it. Maxime --zp6iwgscfyq77x44 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQRcEzekXsqa64kGDp7j7w1vZxhRxQUCYqBbCwAKCRDj7w1vZxhR xSPVAP9WCuEJOeR5feptswaFZEGtKBmQmfsH0V6aZNlGCKQWXAD/RNZOTXFU59/5 B4sP7l0sbDznzHweIEM2DwDCKh/7FQs= =6Jim -----END PGP SIGNATURE----- --zp6iwgscfyq77x44-- --===============9194568463616964996== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel --===============9194568463616964996==--