drivers: display_sdl: support transparent screens #81184

Finomnis · 2024-11-10T08:30:07Z

The display_sdl already supports ARGB8888 colors, but does not display them correctly.

This PR performs the following things:

Add a gray checkerboard as background to the display_sdl driver
Add the sample samples/modules/lvgl/screen_transparency that demonstrates its functionality
Adjust samples/drivers/display in ARGB8888 mode to have a transparent background
Bug fixes

screen_transparency sample before adding transparency support to display_sdl:

with transparency support in display_sdl:

NOTE: The artifacts around the letters are a bug in LVGL. That bug is fixed in LVGL 9, but in 8.4, this is what it really looks like, this is not a mistake in the display_sdl driver.

This is the updated samples/drivers/display in ARGB8888 mode:

kartben · 2024-11-10T09:20:23Z

@Finomnis very nice! Could you share a screenshot of how https://github.com/zephyrproject-rtos/zephyr/tree/main/samples%2Fdrivers%2Fdisplay?
I like the idea of the checkerboard but it feels like it would be nice if the background was customizable, i.e maybe a choice of WHITE/BLACK/GREEN/MAGENTA/CHECKER? And maybe white should still be the default?

Finomnis · 2024-11-10T09:24:05Z

I like the idea of the checkerboard but it feels like it would be nice if the background was customizable, i.e maybe a choice of WHITE/BLACK/GREEN/MAGENTA/CHECKER? And maybe white should still be the default?

Should we make it configurable via Kconfig?

Finomnis · 2024-11-10T09:29:22Z

Could you share a screenshot of how https://github.com/zephyrproject-rtos/zephyr/tree/main/samples%2Fdrivers%2Fdisplay?

@kartben Would you mind explaining? The colors are 0x00ff0000 and so on, so in my opinion it's correct that they are 100% transparent. Is this a bug in the sample?

Finomnis · 2024-11-10T09:33:09Z

@kartben I'm very confused. Is the Alpha value 'transparent' in Zephyr defined as 0xff? Because that's the complete opposite of what it usually is.

LVGL also does "transparent" as 0x00, and so does the rest of the world.

Finomnis · 2024-11-10T09:39:14Z

@kartben I can't find the definition of ARGB8888. Can you help me with that?

The entire display_sdl driver uses it like 0xrrggbb => 0x00rrggbb. Although in my opinion it should be 0xffrrggbb everywhere.

This is very confusing and a little bit infuriating. What's going on?

Finomnis · 2024-11-10T10:11:00Z

@kartben Made grid size and color Kconfig values.

kartben · 2024-11-10T10:23:47Z

@kartben I'm very confused. Is the Alpha value 'transparent' in Zephyr defined as 0xff? Because that's the complete opposite of what it usually is.

LVGL also does "transparent" as 0x00, and so does the rest of the world.

Yes that looks like a bug, they should be 0xff..... indeed

Finomnis · 2024-11-10T10:34:56Z

@kartben Fixed alpha handling in samples/drivers/display and added an alpha test patch. Now looks like this:

Finomnis · 2024-11-17T00:11:29Z

@kartben should I create an issue that gets fixed by this change or is it OK if this change exists on its own?

kartben · 2024-11-17T00:39:59Z

@kartben should I create an issue that gets fixed by this change or is it OK if this change exists on its own?

The latter is fine!

Finomnis · 2024-11-17T19:01:37Z

The latter is fine!

@kartben In that case, is there any way to bump priority?

It's currently really hard to develop apps with screen transparency :/

kartben · 2024-11-17T19:08:05Z

The latter is fine!

@kartben In that case, is there any way to bump priority?

It's currently really hard to develop apps with screen transparency :/

PR has been open for only a week, right as everyone was pretty busy getting 4.0 ready. Please allow some time for reviewers to have a look at it, likely next week, I would say :)

Finomnis · 2024-11-17T19:23:34Z

PR has been open for only a week, right as everyone was pretty busy getting 4.0 ready. Please allow some time for reviewers to have a look at it, likely next week, I would say :)

Oh, I did not realize it's only been open for a week :D guess I'm being too impatient.

Thanks for the response :)

samples/drivers/display/src/main.c

drivers/display/Kconfig.sdl

drivers/display/display_sdl_bottom.c

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

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]>

`lv_task_handler()` returns a `uint32_t`, but `k_msleep` takes a `int32_t`. If no timer exists, `lv_task_handler()` returns `UINT32_MAX` to indicate that we should wait forever. However, this gets auto-cast to `-1`, indicating to `k_msleep` to not wait at all, creating a busy loop. Hence, a clamping to `[0, INT32_MAX]` is required. Signed-off-by: Martin Stumpf <[email protected]>

While the driver was already capable of processing `ARGB8888` data, it did not actually show the alpha value in any way. This change adds a checkerboard background that shows transparent regions. Signed-off-by: Martin Stumpf <[email protected]>

Non-alpha colors were converted to colors with `0x00` alpha, which makes them fully transparent. The correct way would be to add a `0xff` alpha, which this change does. Signed-off-by: Martin Stumpf <[email protected]>

ARGB8888 values all had alpha '0x00' (=transparent). Changed them to '0xFF' and added a transparency test patch in the middle of the screen. Signed-off-by: Martin Stumpf <[email protected]>

Added release notes for PR zephyrproject-rtos#81184. Signed-off-by: Martin Stumpf <[email protected]>

Finomnis · 2024-11-18T13:29:15Z

@kartben Thanks for the review and your time :)

Finomnis force-pushed the alpha_screen_main branch 6 times, most recently from e7b40ee to c691c6c Compare November 10, 2024 09:07

Finomnis marked this pull request as ready for review November 10, 2024 09:09

zephyrbot added area: Samples Samples area: Display labels Nov 10, 2024

zephyrbot requested review from danieldegrasse, jfischer-no, kartben and nashif November 10, 2024 09:10

zephyrbot assigned kartben Nov 10, 2024

Finomnis force-pushed the alpha_screen_main branch 3 times, most recently from e9e89d3 to fda6257 Compare November 10, 2024 09:18

Finomnis force-pushed the alpha_screen_main branch 3 times, most recently from 420b1df to 97d91dd Compare November 10, 2024 10:10

Finomnis force-pushed the alpha_screen_main branch 2 times, most recently from 79e0977 to cf80afd Compare November 10, 2024 10:54

Finomnis force-pushed the alpha_screen_main branch from b4164a3 to 01a9191 Compare November 17, 2024 18:59

kartben requested changes Nov 18, 2024

View reviewed changes

Finomnis added 4 commits November 18, 2024 12:33

samples: modules: lvgl: add screen_transparency sample

7b53686

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]>

drivers: display_sdl: add alpha support

1330b1b

While the driver was already capable of processing `ARGB8888` data, it did not actually show the alpha value in any way. This change adds a checkerboard background that shows transparent regions. Signed-off-by: Martin Stumpf <[email protected]>

drivers: display_sdl: fix incorrect color conversion

3c66212

Non-alpha colors were converted to colors with `0x00` alpha, which makes them fully transparent. The correct way would be to add a `0xff` alpha, which this change does. Signed-off-by: Martin Stumpf <[email protected]>

mstumpf-vected force-pushed the alpha_screen_main branch from 9b3ad00 to 4cf8488 Compare November 18, 2024 11:33

samples: drivers: display: adjust alpha handling

70c0951

ARGB8888 values all had alpha '0x00' (=transparent). Changed them to '0xFF' and added a transparency test patch in the middle of the screen. Signed-off-by: Martin Stumpf <[email protected]>

mstumpf-vected force-pushed the alpha_screen_main branch from 4cf8488 to 625084f Compare November 18, 2024 11:41

docs: add release notes for zephyrproject-rtos#81184

32e982d

Added release notes for PR zephyrproject-rtos#81184. Signed-off-by: Martin Stumpf <[email protected]>

mstumpf-vected force-pushed the alpha_screen_main branch from 625084f to 32e982d Compare November 18, 2024 11:46

Finomnis requested a review from kartben November 18, 2024 13:11

kartben approved these changes Nov 18, 2024

View reviewed changes

danieldegrasse approved these changes Nov 18, 2024

View reviewed changes

nashif merged commit 5d4f4ac into zephyrproject-rtos:main Nov 18, 2024
24 checks passed

Finomnis deleted the alpha_screen_main branch November 18, 2024 18:18

Finomnis mentioned this pull request Nov 18, 2024

Update LVGL module to 9.2.0 #68168

Merged

8 tasks

PetervdPerk-NXP mentioned this pull request Mar 24, 2025

[native_sim] Zephyr 4.1 breaks GPIO_EMUL_SDL and INPUT_SDL_TOUCH #87519

Closed

soburi mentioned this pull request Apr 16, 2025

Fails tests/drivers/display/display_read_write on SDL display driver #88714

Open

kartben mentioned this pull request Jul 15, 2025

subsys: display: cfb: tests: tests fail #92860

Open

1 task

drivers: display_sdl: support transparent screens #81184

drivers: display_sdl: support transparent screens #81184

Uh oh!

Conversation

Finomnis commented Nov 10, 2024 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

kartben commented Nov 10, 2024

Uh oh!

Finomnis commented Nov 10, 2024

Uh oh!

Finomnis commented Nov 10, 2024 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Finomnis commented Nov 10, 2024 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Finomnis commented Nov 10, 2024 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Finomnis commented Nov 10, 2024

Uh oh!

kartben commented Nov 10, 2024

Uh oh!

Finomnis commented Nov 10, 2024

Uh oh!

Finomnis commented Nov 17, 2024

Uh oh!

kartben commented Nov 17, 2024

Uh oh!

Finomnis commented Nov 17, 2024

Uh oh!

kartben commented Nov 17, 2024

Uh oh!

Finomnis commented Nov 17, 2024

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Finomnis commented Nov 18, 2024

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

Finomnis commented Nov 10, 2024 •

edited

Loading

Finomnis commented Nov 10, 2024 •

edited

Loading

Finomnis commented Nov 10, 2024 •

edited

Loading

Finomnis commented Nov 10, 2024 •

edited

Loading