samples: modules: lvgl: add screen_transparency sample

Adds a sample that renders the simple `hello world` LVGL demo
with a transparent background, to demonstrate ARGB8888 framebuffer
capabilities.

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

Author: Finomnis

samples/modules/lvgl/screen_transparency/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(screen_transparency)
+
+FILE(GLOB app_sources src/*.c)
+target_sources(app PRIVATE ${app_sources})

samples/modules/lvgl/screen_transparency/Kconfig

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+# Copyright (c) 2024 Martin Stumpf <[email protected]>
+# SPDX-License-Identifier: Apache-2.0
+
+source "Kconfig.zephyr"

samples/modules/lvgl/screen_transparency/README.rst

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+.. zephyr:code-sample:: lvgl-screen-transparency
+   :name: LVGL screen transparency
+   :relevant-api: display_interface
+
+   Rendering to screens with transparency support using LVGL.
+
+Overview
+********
+
+A sample application that demonstrates how to use LVGL to render to
+screens that support transparency, like OSD overlays.
+
+Requirements
+************
+
+* A board with a display that supports ``ARGB8888`` color.
+
+.. _lvgl_screen_transparency_building_and_running:
+
+Building and Running
+********************
+
+The demo can be built as follows:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/modules/lvgl/screen_transparency
+   :host-os: unix
+   :board: native_sim
+   :goals: run
+   :compact:

samples/modules/lvgl/screen_transparency/prj.conf

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+CONFIG_MAIN_STACK_SIZE=4096
+CONFIG_LOG=y
+
+CONFIG_LVGL=y
+CONFIG_LV_Z_MEM_POOL_SIZE=16384
+CONFIG_LV_COLOR_DEPTH_32=y
+CONFIG_LV_COLOR_SCREEN_TRANSP=y
+
+CONFIG_DISPLAY=y

samples/modules/lvgl/screen_transparency/sample.yaml

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+sample:
+  description: Demonstrating Screen Transparency using LVGL
+  name: LVGL screen transparency
+tests:
+  sample.modules.lvgl.screen_transparency:
+    filter: dt_chosen_enabled("zephyr,display")
+    min_flash: 250
+    min_ram: 32
+    harness: none
+    tags:
+      - samples
+      - display
+      - gui
+      - lvgl
+    modules:
+      - lvgl
+    integration_platforms:
+      - native_sim/native/64

samples/modules/lvgl/screen_transparency/src/main.c

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+/*
+ * Copyright (c) 2024 Martin Stumpf <[email protected]>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/device.h>
+#include <zephyr/devicetree.h>
+#include <zephyr/drivers/display.h>
+
+#include <lvgl.h>
+#include <stdio.h>
+#include <string.h>
+#include <zephyr/kernel.h>
+
+#include <zephyr/logging/log.h>
+LOG_MODULE_REGISTER(app, CONFIG_LOG_DEFAULT_LEVEL);
+
+static void initialize_gui(void)
+{
+	lv_obj_t *label;
+
+	/* Configure screen and background for transparency */
+	lv_obj_set_style_bg_opa(lv_scr_act(), LV_OPA_TRANSP, LV_PART_MAIN);
+	lv_disp_set_bg_opa(NULL, LV_OPA_TRANSP);
+	lv_obj_set_style_bg_color(lv_scr_act(), lv_color_hex(0x000000), LV_PART_MAIN);
+
+	/* Create a label, set its text and align it to the center */
+	label = lv_label_create(lv_scr_act());
+	lv_label_set_text(label, "Hello, world!");
+	lv_obj_set_style_text_color(lv_scr_act(), lv_color_hex(0xff00ff), LV_PART_MAIN);
+	lv_obj_align(label, LV_ALIGN_CENTER, 0, 0);
+}
+
+int main(void)
+{
+	int err;
+	const struct device *display_dev;
+	struct display_capabilities display_caps;
+
+	display_dev = DEVICE_DT_GET(DT_CHOSEN(zephyr_display));
+	if (!device_is_ready(display_dev)) {
+		LOG_ERR("Device not ready, aborting test");
+		return -ENODEV;
+	}
+
+	display_get_capabilities(display_dev, &display_caps);
+	if (!(display_caps.supported_pixel_formats | PIXEL_FORMAT_ARGB_8888)) {
+		LOG_ERR("Display does not support ARGB8888 mode");
+		return -ENOTSUP;
+	}
+
+	if (PIXEL_FORMAT_ARGB_8888 != display_caps.current_pixel_format) {
+		err = display_set_pixel_format(display_dev, PIXEL_FORMAT_ARGB_8888);
+		if (err != 0) {
+			LOG_ERR("Failed to set ARGB8888 pixel format");
+			return err;
+		}
+	}
+
+	initialize_gui();
+
+	lv_task_handler();
+	display_blanking_off(display_dev);
+
+	while (1) {
+		uint32_t sleep_ms = lv_task_handler();
+
+		k_msleep(MIN(sleep_ms, INT32_MAX));
+	}
+
+	return 0;
+}