diff mbox series

[v5,07/13] drm/mediatek: Support alpha blending in display driver

Message ID 20240215101119.12629-8-shawn.sung@mediatek.com
State New
Headers
Series Support IGT in display driver |

Commit Message

Shawn Sung (宋孝謙) Feb. 15, 2024, 10:11 a.m. UTC 
  Support "Pre-multiplied" and "None" blend mode on MediaTek's chips by
adding correct blend mode property when the planes init.
Before this patch, only the "Coverage" mode (default) is supported.

For more information, there are three pixel blend modes in DRM driver:
"None", "Pre-multiplied", and "Coverage".

To understand the difference between these modes, let's take a look at
the following two approaches to do alpha blending:

1. Straight:
dst.RGB = src.RGB * src.A + dst.RGB * (1 - src.A)
This is straightforward and easy to understand, when the source layer is
compositing with the destination layer, it's alpha will affect the
result. This is also known as "post-multiplied", or "Coverage" mode.

2. Pre-multiplied:
dst.RGB = src.RGB + dst.RGB * (1 - src.A)
Since the source RGB have already multiplied its alpha, only destination
RGB need to multiply it. This is the "Pre-multiplied" mode in DRM.

For the "None" blend mode in DRM, it means the pixel alpha is ignored
when compositing the layers, only the constant alpha for the composited
layer will take effects.

Signed-off-by: Hsiao Chien Sung <shawn.sung@mediatek.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
---
 drivers/gpu/drm/mediatek/mtk_drm_plane.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

Comments

AngeloGioacchino Del Regno Feb. 15, 2024, 10:46 a.m. UTC | #1 
Il 15/02/24 11:11, Hsiao Chien Sung ha scritto:
> Support "Pre-multiplied" and "None" blend mode on MediaTek's chips by
> adding correct blend mode property when the planes init.
> Before this patch, only the "Coverage" mode (default) is supported.
> 
> For more information, there are three pixel blend modes in DRM driver:
> "None", "Pre-multiplied", and "Coverage".
> 
> To understand the difference between these modes, let's take a look at
> the following two approaches to do alpha blending:
> 
> 1. Straight:
> dst.RGB = src.RGB * src.A + dst.RGB * (1 - src.A)
> This is straightforward and easy to understand, when the source layer is
> compositing with the destination layer, it's alpha will affect the
> result. This is also known as "post-multiplied", or "Coverage" mode.
> 
> 2. Pre-multiplied:
> dst.RGB = src.RGB + dst.RGB * (1 - src.A)
> Since the source RGB have already multiplied its alpha, only destination
> RGB need to multiply it. This is the "Pre-multiplied" mode in DRM.
> 
> For the "None" blend mode in DRM, it means the pixel alpha is ignored
> when compositing the layers, only the constant alpha for the composited
> layer will take effects.
> 
> Signed-off-by: Hsiao Chien Sung <shawn.sung@mediatek.com>
> Reviewed-by: CK Hu <ck.hu@mediatek.com>

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
diff mbox series

Patch

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_plane.c b/drivers/gpu/drm/mediatek/mtk_drm_plane.c
index 2dc28a79f7603..4e0206c45efd7 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_plane.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_plane.c
@@ -346,6 +346,17 @@  int mtk_plane_init(struct drm_device *dev, struct drm_plane *plane,
 			DRM_INFO("Create rotation property failed\n");
 	}
 
+	err = drm_plane_create_alpha_property(plane);
+	if (err)
+		DRM_ERROR("failed to create property: alpha\n");
+
+	err = drm_plane_create_blend_mode_property(plane,
+						   BIT(DRM_MODE_BLEND_PREMULTI) |
+						   BIT(DRM_MODE_BLEND_COVERAGE) |
+						   BIT(DRM_MODE_BLEND_PIXEL_NONE));
+	if (err)
+		DRM_ERROR("failed to create property: blend_mode\n");
+
 	drm_plane_helper_add(plane, &mtk_plane_helper_funcs);
 
 	return 0;