LV_COLOR_DEPTH 1 results in segmentation fault

smallscreen · November 5, 2021, 8:03pm

Hello All,

I am brand new to lvgl and got the simulator running with SDL2.
I am trying to simulate a small screen 240x400 with a color depth of 8 bits.
So I edited the lv_sim_vscode_sdl/ui/simulator/inc/lv_conf.h to this:

#define LV_COLOR_DEPTH 1

However that results in a segmentation fault.

rm -f ./build/bin/demo && make clean && make -j8 && ./build/bin/demo
[Warn]	(0.000, +0)	 lv_init: Memory integrity checks are enabled via LV_USE_ASSERT_MEM_INTEGRITY which makes LVGL much slower 	(in lv_obj.c line #138)
[Warn]	(0.000, +0)	 lv_init: Object sanity checks are enabled via LV_USE_ASSERT_OBJ which makes LVGL much slower 	(in lv_obj.c line #142)
Segmentation fault (core dumped)

The code is otherwise the same as the git repo:

Any help is appreciated.
Thanks,

Copland

water · March 26, 2023, 9:28am

Did you manage to find a fix for this? I’m on simulator 8.0.0 for VS Code and running into the same problem.

robekras · March 26, 2023, 9:34am

I think, when having a color depth of 8 bits per pixel, the correct setting would be
#define LV_COLOR_DEPTH 8

water · March 26, 2023, 9:39am

I agree, the OP may have made a mistake. But setting color depth to 1 (which is my intention with the simulator for prototyping a monochrome display GUI) still causes a segfault, specifically here:

github.com

lvgl/lvgl/blob/release/v8.0/src/draw/lv_draw_rect.c#L153


      
           *It is always the same or inside `fill_area`*/
          lv_area_t draw_area;
          bool is_common;
          is_common = _lv_area_intersect(&draw_area, &coords_bg, clip);
          if(is_common == false) return;
          
          
const lv_area_t * disp_area = &draw_buf->area;
          
          
/*Now `draw_area` has absolute coordinates.
           *Make it relative to `disp_area` to simplify draw to `disp_buf`*/
          draw_area.x1 -= disp_area->x1;
          draw_area.y1 -= disp_area->y1;
          draw_area.x2 -= disp_area->x1;
          draw_area.y2 -= disp_area->y1;
          
          

          
lv_grad_dir_t grad_dir = dsc->bg_grad_dir;
          if(dsc->bg_color.full == dsc->bg_grad_color.full) grad_dir = LV_GRAD_DIR_NONE;
          
          
uint16_t other_mask_cnt = lv_draw_mask_get_cnt();
          bool simple_mode = true;

robekras · March 26, 2023, 9:52am

Hmm, seems to be writing into a wrong memory location.
A mismatch of buffer sizes? As far as I can see, a color depth of 1 also needs one byte per pixel on lvgl side

water · March 26, 2023, 10:21am

Is there something else that needs modification for the LVGL simulator to run properly with 1-bit color depth? The same problem occurs when I try to set color depth to 8. I’m running the simulator on Ubuntu 22.04. The only changes I have made to the original repo are:

Changed LV_COLOR_DEPTH to 1 in lv_conf.h
Changed LV_BUILD_EXAMPLES to 0 in lv_conf.h
Commented out lv_demo_widgets() from main.c
Added a “Hello world” label in main.c to be displayed

water · March 27, 2023, 7:59am

This was indeed a buffer problem. The hal init function in main doesn’t account for color depth selection when setting the draw buffer, so any color depth value besides 32 results in a segfault. I can open a PR with a proposed fix, but I don’t know if this was intentionally left as-is and would prefer to not embarrass myself on GitHub if that’s the case.