display: add PIXEL_FORMAT_AL_88

When rendering an overlay on top of something like a video stream on a
monochrome display, the only way to achieve this right now is by using
ARGB8888 and discarding two of the colors, which is not ideal.

This introduces the new AL_88 pixel format, which is much more efficient
for this usecase.

This change is somewhat inspired by LVGL, which also supports AL_88
natively.

Signed-off-by: Martin Stumpf <[email protected]>

Author: Finomnis

doc/releases/release-notes-4.3.rst

@@ -85,6 +85,10 @@ New APIs and options
 
     * :c:struct:`bt_audio_codec_cfg` now contains a target_latency and a target_phy option
 
+* Display
+
+  * Added new pixel format :c:enum:`PIXEL_FORMAT_AL_88`
+
 * Logging:
 
   * Added rate-limited logging macros to prevent log flooding when messages are generated frequently.

include/zephyr/drivers/display.h

@@ -68,6 +68,7 @@ enum display_pixel_format {
 	PIXEL_FORMAT_BGR_565		= BIT(5),
 	PIXEL_FORMAT_L_8		= BIT(6), /**< 8-bit Grayscale/Luminance, equivalent to */
 						  /**< GRAY, GREY, GRAY8, Y8, R8, etc...        */
+	PIXEL_FORMAT_AL_88		= BIT(7), /**< 8-bit Grayscale/Luminance with alpha */
 };
 
 /**
@@ -84,7 +85,8 @@ enum display_pixel_format {
 	(((fmt & PIXEL_FORMAT_ARGB_8888) >> 3) * 32U) +				\
 	(((fmt & PIXEL_FORMAT_RGB_565) >> 4) * 16U) +				\
 	(((fmt & PIXEL_FORMAT_BGR_565) >> 5) * 16U) +				\
-	(((fmt & PIXEL_FORMAT_L_8) >> 6) * 8U))
+	(((fmt & PIXEL_FORMAT_L_8) >> 6) * 8U) +				\
+	(((fmt & PIXEL_FORMAT_AL_88) >> 7) * 16U))
 
 /**
  * @brief Display screen information

include/zephyr/dt-bindings/display/panel.h

@@ -30,6 +30,7 @@
 #define PANEL_PIXEL_FORMAT_RGB_565   (0x1 << 4)
 #define PANEL_PIXEL_FORMAT_BGR_565   (0x1 << 5)
 #define PANEL_PIXEL_FORMAT_L_8       (0x1 << 6)
+#define PANEL_PIXEL_FORMAT_AL_88     (0x1 << 7)
 
 /**
  * @}