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Date:   Tue, 9 Jul 2019 22:54:05 -0300
From:   Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
To:     Daniel Vetter <daniel@ffwll.ch>,
        Haneen Mohammed <hamohammed.sa@gmail.com>,
        David Airlie <airlied@linux.ie>,
        Simon Ser <contact@emersion.fr>,
        Oleg Vasilev <oleg.vasilev@intel.com>,
        Mamta Shukla <mamtashukla555@gmail.com>,
        Harry Wentland <harry.wentland@amd.com>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: [PATCH 2/2] drm/vkms: Use alpha channel for blending cursor with
 primary
Message-ID: <f09271656e9b29cb56e63c0bbf864060e5974cad.1562695974.git.rodrigosiqueiramelo@gmail.com>
References: <cover.1562695974.git.rodrigosiqueiramelo@gmail.com>
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Currently, the blend function overwriting the cursor value into the
primary plane. This patch utilizes the alpha value for a fully
transparent blend of the cursor (vaddr_src) with primary (vaddr_dst)
instead of overwriting it in blend().

Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Cc: Mamta Shukla <mamtashukla555@gmail.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
---
 drivers/gpu/drm/vkms/vkms_composer.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vk=
ms_composer.c
index fb106964d8bf..bb758a5131a4 100644
--- a/drivers/gpu/drm/vkms/vkms_composer.c
+++ b/drivers/gpu/drm/vkms/vkms_composer.c
@@ -26,6 +26,17 @@ static void set_pixel(int x, int y, u8 *buffer,
 	*dst =3D value;
 }
=20
+static u32 apply_alpha(u32 src, u32 dst)
+{
+	u8 alpha;
+	u32 k;
+
+	alpha =3D src >> 24;
+	alpha =3D (alpha + 1) >> 8;
+	k =3D (alpha << 24) - alpha;
+	return (k & src) | (~k & dst);
+}
+
 /**
  * compute_crc - Compute CRC value on output frame
  *
@@ -89,15 +100,19 @@ static void blend(void *vaddr_dst, void *vaddr_src,
 	int y_limit =3D y_src + h_dst;
 	int x_limit =3D x_src + w_dst;
=20
-	u32 pixel_src;
+	u32 pixel_src, pixel_dst, new_pixel;
=20
 	for (y =3D y_src, i_dst =3D y_dst; y < y_limit; ++y) {
 		for (x =3D x_src, j_dst =3D x_dst; x < x_limit; ++x) {
 			pixel_src =3D get_pixel_from_buffer(x, y,
 							  vaddr_src,
 							  src_composer);
-			set_pixel(j_dst, i_dst, vaddr_dst, dest_composer,
-				  pixel_src);
+			pixel_dst =3D get_pixel_from_buffer(j_dst, i_dst,
+							  vaddr_dst,
+							  dst_composer);
+			new_pixel =3D apply_alpha(pixel_src, pixel_dst);
+			set_pixel(j_dst, i_dst, vaddr_dst, dst_composer,
+				  new_pixel);
 			j_dst++;
 		}
 		i_dst++;
--=20
2.21.0

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