drivers: display_sdl: support transparent screens

doc/releases/release-notes-4.1.rst

@@ -97,6 +97,7 @@ Drivers and Sensors
     signal handling (:github:`81250`)
   * Added ``frame_incomplete`` handling to SDL display driver (:dtcompatible:`zephyr,sdl-dc`)
     (:github:`81250`)
+  * Added transparency support to SDL display driver (:dtcompatible:`zephyr,sdl-dc`) (:github:`81184`)
 
 * Ethernet
 
@@ -292,6 +293,9 @@ LVGL
 Tests and Samples
 *****************
 
+* Fixed incorrect alpha values in :zephyr_file:`samples/drivers/display`. (:github:`81184`)
+* Added :zephyr_file:`samples/modules/lvgl/screen_transparency`. (:github:`81184`)
+
 Issue Related Items
 *******************
 

drivers/display/Kconfig.sdl

@@ -59,4 +59,22 @@ config SDL_DISPLAY_MONO_MSB_FIRST
 	  If selected, set the MSB to represent the first pixel.
 	  This applies when the pixel format is MONO01/MONO10.
 
+config SDL_DISPLAY_TRANSPARENCY_GRID_CELL_SIZE
+	int "Transparency grid cell size"
+	default 8
+	help
+	  The size of the checkerboard pattern squares, in pixels.
+
+config SDL_DISPLAY_TRANSPARENCY_GRID_CELL_COLOR_1
+	hex "Transparency grid cell color 1"
+	default 0xcccccc
+	help
+	  The color of the odd cells in the transparency grid.
+
+config SDL_DISPLAY_TRANSPARENCY_GRID_CELL_COLOR_2
+	hex "Transparency grid cell color 2"
+	default 0xbbbbbb
+	help
+	  The color of the even cells in the transparency grid.
+
 endif # SDL_DISPLAY

drivers/display/display_sdl.c

@@ -33,6 +33,7 @@ struct sdl_display_data {
 	void *mutex;
 	void *texture;
 	void *read_texture;
+	void *background_texture;
 	bool display_on;
 	enum display_pixel_format current_pixel_format;
 	uint8_t *buf;
@@ -80,7 +81,10 @@ static int sdl_display_init(const struct device *dev)
 	int rc = sdl_display_init_bottom(config->height, config->width, sdl_display_zoom_pct,
 					 use_accelerator, &disp_data->window, &disp_data->renderer,
 					 &disp_data->mutex, &disp_data->texture,
-					 &disp_data->read_texture);
+					 &disp_data->read_texture, &disp_data->background_texture,
+					 CONFIG_SDL_DISPLAY_TRANSPARENCY_GRID_CELL_COLOR_1,
+					 CONFIG_SDL_DISPLAY_TRANSPARENCY_GRID_CELL_COLOR_2,
+					 CONFIG_SDL_DISPLAY_TRANSPARENCY_GRID_CELL_SIZE);
 
 	if (rc != 0) {
 		LOG_ERR("Failed to create SDL display");
@@ -119,7 +123,7 @@ static void sdl_display_write_rgb888(uint8_t *disp_buf,
 			pixel = *byte_ptr << 16;
 			pixel |= *(byte_ptr + 1) << 8;
 			pixel |= *(byte_ptr + 2);
-			*((uint32_t *)disp_buf) = pixel;
+			*((uint32_t *)disp_buf) = pixel | 0xFF000000;
 			disp_buf += 4;
 		}
 	}
@@ -145,7 +149,7 @@ static void sdl_display_write_rgb565(uint8_t *disp_buf,
 			pixel = (((rgb565 >> 11) & 0x1F) * 255 / 31) << 16;
 			pixel |= (((rgb565 >> 5) & 0x3F) * 255 / 63) << 8;
 			pixel |= (rgb565 & 0x1F) * 255 / 31;
-			*((uint32_t *)disp_buf) = pixel;
+			*((uint32_t *)disp_buf) = pixel | 0xFF000000;
 			disp_buf += 4;
 		}
 	}
@@ -169,7 +173,7 @@ static void sdl_display_write_bgr565(uint8_t *disp_buf,
 			pixel = (((*pix_ptr >> 11) & 0x1F) * 255 / 31) << 16;
 			pixel |= (((*pix_ptr >> 5) & 0x3F) * 255 / 63) << 8;
 			pixel |= (*pix_ptr & 0x1F) * 255 / 31;
-			*((uint32_t *)disp_buf) = pixel;
+			*((uint32_t *)disp_buf) = pixel | 0xFF000000;
 			disp_buf += 4;
 		}
 	}
@@ -207,9 +211,9 @@ static void sdl_display_write_mono(uint8_t *disp_buf,
 				if ((*byte_ptr & mono_pixel_order(h_idx)) != 0U)  {
 					pixel = one_color;
 				} else {
-					pixel = (~one_color) & 0x00FFFFFF;
+					pixel = ~one_color;
 				}
-				*((uint32_t *)disp_buf) = pixel;
+				*((uint32_t *)disp_buf) = pixel | 0xFF000000;
 				disp_buf += (desc->width * 4U);
 			}
 			disp_buf = disp_buf_start;
@@ -261,7 +265,8 @@ static int sdl_display_write(const struct device *dev, const uint16_t x,
 	}
 
 	sdl_display_write_bottom(desc->height, desc->width, x, y, disp_data->renderer,
-				 disp_data->mutex, disp_data->texture, disp_data->buf,
+				 disp_data->mutex, disp_data->texture,
+				 disp_data->background_texture, disp_data->buf,
 				 disp_data->display_on, desc->frame_incomplete);
 
 	return 0;
@@ -431,7 +436,8 @@ static int sdl_display_blanking_off(const struct device *dev)
 
 	disp_data->display_on = true;
 
-	sdl_display_blanking_off_bottom(disp_data->renderer, disp_data->texture);
+	sdl_display_blanking_off_bottom(disp_data->renderer, disp_data->texture,
+					disp_data->background_texture);
 
 	return 0;
 }
@@ -491,7 +497,8 @@ static int sdl_display_set_pixel_format(const struct device *dev,
 static void sdl_display_cleanup(struct sdl_display_data *disp_data)
 {
 	sdl_display_cleanup_bottom(&disp_data->window, &disp_data->renderer, &disp_data->mutex,
-				   &disp_data->texture, &disp_data->read_texture);
+				   &disp_data->texture, &disp_data->read_texture,
+				   &disp_data->background_texture);
 }
 
 static const struct display_driver_api sdl_display_api = {

drivers/display/display_sdl_bottom.c

@@ -15,7 +15,9 @@
 
 int sdl_display_init_bottom(uint16_t height, uint16_t width, uint16_t zoom_pct,
 			    bool use_accelerator, void **window, void **renderer, void **mutex,
-			    void **texture, void **read_texture)
+			    void **texture, void **read_texture, void **background_texture,
+			    uint32_t transparency_grid_color1, uint32_t transparency_grid_color2,
+			    uint16_t transparency_grid_cell_size)
 {
 	*window = SDL_CreateWindow("Zephyr Display", SDL_WINDOWPOS_UNDEFINED,
 				   SDL_WINDOWPOS_UNDEFINED, width * zoom_pct / 100,
@@ -51,6 +53,7 @@ int sdl_display_init_bottom(uint16_t height, uint16_t width, uint16_t zoom_pct,
 		nsi_print_warning("Failed to create SDL texture: %s", SDL_GetError());
 		return -1;
 	}
+	SDL_SetTextureBlendMode(*texture, SDL_BLENDMODE_BLEND);
 
 	*read_texture = SDL_CreateTexture(*renderer, SDL_PIXELFORMAT_ARGB8888,
 					  SDL_TEXTUREACCESS_TARGET, width, height);
@@ -59,16 +62,50 @@ int sdl_display_init_bottom(uint16_t height, uint16_t width, uint16_t zoom_pct,
 		return -1;
 	}
 
+	*background_texture = SDL_CreateTexture(*renderer, SDL_PIXELFORMAT_ARGB8888,
+						SDL_TEXTUREACCESS_STREAMING, width, height);
+	if (*background_texture == NULL) {
+		nsi_print_warning("Failed to create SDL texture: %s", SDL_GetError());
+		return -1;
+	}
+
+	void *background_data;
+	int background_pitch;
+	int err;
+
+	err = SDL_LockTexture(*background_texture, NULL, &background_data, &background_pitch);
+	if (err != 0) {
+		nsi_print_warning("Failed to lock background texture: %d", err);
+		return -1;
+	}
+	for (int y = 0; y < height; y++) {
+		uint32_t *row = (uint32_t *)((uint8_t *)background_data + background_pitch * y);
+
+		for (int x = 0; x < width; x++) {
+			bool x_cell_even = ((x / transparency_grid_cell_size) % 2) == 0;
+			bool y_cell_even = ((y / transparency_grid_cell_size) % 2) == 0;
+
+			if (x_cell_even == y_cell_even) {
+				row[x] = transparency_grid_color1 | 0xff000000;
+			} else {
+				row[x] = transparency_grid_color2 | 0xff000000;
+			}
+		}
+	}
+	SDL_UnlockTexture(*background_texture);
+
 	SDL_SetRenderDrawColor(*renderer, 0, 0, 0, 0xFF);
 	SDL_RenderClear(*renderer);
+	SDL_RenderCopy(*renderer, *background_texture, NULL, NULL);
 	SDL_RenderPresent(*renderer);
 
 	return 0;
 }
 
 void sdl_display_write_bottom(const uint16_t height, const uint16_t width, const uint16_t x,
 			      const uint16_t y, void *renderer, void *mutex, void *texture,
-			      uint8_t *buf, bool display_on, bool frame_incomplete)
+			      void *background_texture, uint8_t *buf, bool display_on,
+			      bool frame_incomplete)
 {
 	SDL_Rect rect;
 	int err;
@@ -88,6 +125,7 @@ void sdl_display_write_bottom(const uint16_t height, const uint16_t width, const
 
 	if (display_on && !frame_incomplete) {
 		SDL_RenderClear(renderer);
+		SDL_RenderCopy(renderer, background_texture, NULL, NULL);
 		SDL_RenderCopy(renderer, texture, NULL, NULL);
 		SDL_RenderPresent(renderer);
 	}
@@ -127,9 +165,10 @@ int sdl_display_read_bottom(const uint16_t height, const uint16_t width,
 	return err;
 }
 
-void sdl_display_blanking_off_bottom(void *renderer, void *texture)
+void sdl_display_blanking_off_bottom(void *renderer, void *texture, void *background_texture)
 {
 	SDL_RenderClear(renderer);
+	SDL_RenderCopy(renderer, background_texture, NULL, NULL);
 	SDL_RenderCopy(renderer, texture, NULL, NULL);
 	SDL_RenderPresent(renderer);
 }
@@ -141,8 +180,13 @@ void sdl_display_blanking_on_bottom(void *renderer)
 }
 
 void sdl_display_cleanup_bottom(void **window, void **renderer, void **mutex, void **texture,
-				void **read_texture)
+				void **read_texture, void **background_texture)
 {
+	if (*background_texture != NULL) {
+		SDL_DestroyTexture(*background_texture);
+		*background_texture = NULL;
+	}
+
 	if (*read_texture != NULL) {
 		SDL_DestroyTexture(*read_texture);
 		*read_texture = NULL;

drivers/display/display_sdl_bottom.h

@@ -22,17 +22,20 @@ extern "C" {
 
 int sdl_display_init_bottom(uint16_t height, uint16_t width, uint16_t zoom_pct,
 			    bool use_accelerator, void **window, void **renderer, void **mutex,
-			    void **texture, void **read_texture);
+			    void **texture, void **read_texture, void **background_texture,
+			    uint32_t transparency_grid_color1, uint32_t transparency_grid_color2,
+			    uint16_t transparency_grid_cell_size);
 void sdl_display_write_bottom(const uint16_t height, const uint16_t width, const uint16_t x,
 			      const uint16_t y, void *renderer, void *mutex, void *texture,
-			      uint8_t *buf, bool display_on, bool frame_incomplete);
+			      void *background_texture, uint8_t *buf, bool display_on,
+			      bool frame_incomplete);
 int sdl_display_read_bottom(const uint16_t height, const uint16_t width, const uint16_t x,
 			    const uint16_t y, void *renderer, void *buf, uint16_t pitch,
 			    void *mutex, void *texture, void *read_texture);
-void sdl_display_blanking_off_bottom(void *renderer, void *texture);
+void sdl_display_blanking_off_bottom(void *renderer, void *texture, void *background_texture);
 void sdl_display_blanking_on_bottom(void *renderer);
 void sdl_display_cleanup_bottom(void **window, void **renderer, void **mutex, void **texture,
-				void **read_texture);
+				void **read_texture, void **background_texture);
 
 #ifdef __cplusplus
 }

samples/drivers/display/src/main.c

@@ -50,16 +50,16 @@ static void fill_buffer_argb8888(enum corner corner, uint8_t grey, uint8_t *buf,
 
 	switch (corner) {
 	case TOP_LEFT:
-		color = 0x00FF0000u;
+		color = 0xFFFF0000u;
 		break;
 	case TOP_RIGHT:
-		color = 0x0000FF00u;
+		color = 0xFF00FF00u;
 		break;
 	case BOTTOM_RIGHT:
-		color = 0x000000FFu;
+		color = 0xFF0000FFu;
 		break;
 	case BOTTOM_LEFT:
-		color = grey << 16 | grey << 8 | grey;
+		color = 0xFF000000u | grey << 16 | grey << 8 | grey;
 		break;
 	}
 
@@ -239,7 +239,7 @@ int main(void)
 
 	switch (capabilities.current_pixel_format) {
 	case PIXEL_FORMAT_ARGB_8888:
-		bg_color = 0xFFu;
+		bg_color = 0x00u;
 		fill_buffer_fnc = fill_buffer_argb8888;
 		buf_size *= 4;
 		break;

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

@@ -89,7 +89,9 @@ int main(void)
 	display_blanking_off(display_dev);
 
 	while (1) {
-		k_msleep(lv_task_handler());
+		uint32_t sleep_ms = lv_task_handler();
+
+		k_msleep(MIN(sleep_ms, INT32_MAX));
 	}
 
 	return 0;

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

@@ -40,7 +40,9 @@ int main(void)
 	display_blanking_off(display_dev);
 
 	while (1) {
-		k_msleep(lv_task_handler());
+		uint32_t sleep_ms = lv_task_handler();
+
+		k_msleep(MIN(sleep_ms, INT32_MAX));
 	}
 
 	return 0;

samples/modules/lvgl/screen_transparency/CMakeLists.txt

@@ -0,0 +1,9 @@
+# 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

@@ -0,0 +1,4 @@
+# Copyright (c) 2024 Martin Stumpf <[email protected]>
+# SPDX-License-Identifier: Apache-2.0
+
+source "Kconfig.zephyr"

samples/modules/lvgl/screen_transparency/README.rst

@@ -0,0 +1,30 @@
+.. 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

@@ -0,0 +1,9 @@
+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

@@ -0,0 +1,18 @@
+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