samples: lvgl: Refactor screen_transparency sample

The LVGL screen_transparency sample was refactored in two ways:

- Remove old obsolete display initialization code. LVGL does not even
  react to this code because LVGL color format is determined during LVGL
  initialization, which comes before main().
  Further, the way it is written right now is incompatible with `AL_88`
  color.
- Add some RGB color text for demonstration purposes.

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

Author: Finomnis

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

@@ -27,36 +27,32 @@ static void initialize_gui(void)
 	/* Create a label, set its text and align it to the center */
 	label = lv_label_create(lv_screen_active());
 	lv_label_set_text(label, "Hello, world!");
-	lv_obj_set_style_text_color(lv_screen_active(), lv_color_hex(0xff00ff), LV_PART_MAIN);
-	lv_obj_align(label, LV_ALIGN_CENTER, 0, 0);
+	lv_obj_set_style_text_color(label, lv_color_hex(0xff00ff), LV_PART_MAIN);
+	lv_obj_align(label, LV_ALIGN_CENTER, 0, -20);
+	label = lv_label_create(lv_screen_active());
+	lv_label_set_text(label, "RED");
+	lv_obj_set_style_text_color(label, lv_color_hex(0xff0000), LV_PART_MAIN);
+	lv_obj_align(label, LV_ALIGN_CENTER, -70, 20);
+	label = lv_label_create(lv_screen_active());
+	lv_label_set_text(label, "GREEN");
+	lv_obj_set_style_text_color(label, lv_color_hex(0x00ff00), LV_PART_MAIN);
+	lv_obj_align(label, LV_ALIGN_CENTER, 0, 20);
+	label = lv_label_create(lv_screen_active());
+	lv_label_set_text(label, "BLUE");
+	lv_obj_set_style_text_color(label, lv_color_hex(0x0000ff), LV_PART_MAIN);
+	lv_obj_align(label, LV_ALIGN_CENTER, 70, 20);
 }
 
 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_timer_handler();