Copying buffers when using DIRECT and double buffering. about lvgl HOT 5 OPEN

buf 1 flushing to display
as buf 1 is being written to the display copy the invalid areas from the buffer to buf 2
buf 2 gets updated by LVGL
hold program until buf 1 is fully flushed.
write buf 2 to the display

I assume that you are using a display with RGB interface. If so one step is missing from here: when do you switch the frame buffers buffers? With #6120 it will work like this:

1. buf1 flushing to screen: the flashing is fast as LVGL already rendered everything to the correct place, and we just need to wat for VSYNC. At this point still buf2 is shown.
2. LVGL wants to render to buf2, but it need to wait for VSYNC to not draw to the active buffer
3. Buffers are swapped, now buf1 is on the screen, buf2 can be used for rendedring
4. Sync buf2 from buf1
5. Draw to buf2
6. Flush buf2, same as 1)

If you are using an SPI/parallel based display with a display controller PARTIAL mode should be better choice.

from lvgl.

I am testing this using SDL locally but the same thing is being seen wen running an actual MCU with a display that has and RGB connection

I am not able to wrap my head around the order in which things are being done. It looks like the copying of the buffer is being done before the invalidated areas are rendered but the notes in the file say otherwise.

Are the notes incorrect?

I feel like there is a stall in the code that is causing a wait until the buffer gets emptied before doing anything. Even when removing that one wait that is in the code I still end up with a 15 millisecond hang when calling lv_task_handler. That seems like a very large amount of time for rendering 2 sliders. While I know the pixel count is high at 800 x 480 having that kind of a stall seems to be pretty excessive. This is also running on a PC and not a micro controller so the stall would be even longer on a microcontroller.

from lvgl.

This is what a user is running as a test...

scrn = lv.screen_active()
lslider = lv.slider(scrn)
lslider.set_style_size(225, 480, lv.PART.MAIN)
lslider.align(lv.ALIGN.TOP_LEFT, 0, 0)
rslider = lv.slider(scrn)
rslider.set_style_size(225, 480, lv.PART.MAIN)
rslider.align(lv.ALIGN.TOP_RIGHT, 0, 0)


slider_1_inc = 1
slider_2_inc = -1
slider_1_value = 0
slider_2_value = 100

while True:
    time.sleep_ms(10)
    lslider.set_value(slider_1_value, lv.ANIM.OFF)

    slider_1_value += slider_1_inc
    if slider_1_value in (0, 100):
        slider_1_inc = -slider_1_inc

    rslider.set_value(slider_2_value, lv.ANIM.OFF)

    slider_2_value += slider_2_inc
    if slider_2_value in (0, 100):
        slider_2_inc = -slider_2_inc

    start_time = time.ticks_ms()
    lv.refr_now(lv.display_get_default())
    stop_time = time.ticks_ms()
    print('refr time:', time.tick_diff(stop_time, start_time))
    print()
    lv.tick_inc(10)

This test is only testing how long it takes for lv_refr_now to run after updating the 2 slider widgets

This is what I am getting for output

refr time: 185
refr time: 186
refr time: 186

Now change the code so a refresh is done after each widget has it's value changed

scrn = lv.screen_active()
lslider = lv.slider(scrn)
lslider.set_style_size(225, 480, lv.PART.MAIN)
lslider.align(lv.ALIGN.TOP_LEFT, 0, 0)
rslider = lv.slider(scrn)
rslider.set_style_size(225, 480, lv.PART.MAIN)
rslider.align(lv.ALIGN.TOP_RIGHT, 0, 0)


slider_1_inc = 1
slider_2_inc = -1
slider_1_value = 0
slider_2_value = 100

while True:
    time.sleep_ms(10)
    lslider.set_value(slider_1_value, lv.ANIM.OFF)
    lv.refr_now(lv.display_get_default())

    slider_1_value += slider_1_inc
    if slider_1_value in (0, 100):
        slider_1_inc = -slider_1_inc

    rslider.set_value(slider_2_value, lv.ANIM.OFF)

    slider_2_value += slider_2_inc
    if slider_2_value in (0, 100):
        slider_2_inc = -slider_2_inc

    start_time = time.ticks_ms()
    lv.refr_now(lv.display_get_default())
    stop_time = time.ticks_ms()
    print('refr time:', time.tick_diff(stop_time, start_time))
    print()
    lv.tick_inc(10)

so now I am only doing a refresh of one of the sliders and this is the output

refr time: 98
refr time: 98
refr time: 98
refr time: 98

The flickering and tearing is also reduced by 95%

98 milliseconds seems like a really long time for the refresh to run for. This is an RGB565 display that is 800 x 480 connected using an RGB bus with double buffering.

from lvgl.

forgot to mention that is running on an ESP32-S3

from lvgl.