update lvgl simulator on ubuntu

lv_sim_linux/README.md

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+# LVGL on top of Linux graphics stack
+
+Example project to use LVGL on top of Linux graphics stack.
+Currently supported backends are either legacy framebuffer
+(fbdev), modern DRM/KMS, or SDL2.
+
+By default, legacy framebuffer backend uses `/dev/fb0` device node,
+DRM/KMS backend uses '/dev/dri/card0' card node, SDL2 uses window
+resolution of 800x480.
+
+Check out this blog post for a step by step tutorial:
+https://blog.lvgl.io/2018-01-03/linux_fb
+
+## Clone the project
+
+Clone the LVGL Framebuffer Demo project and its related sub modules.
+
+```
+git clone https://github.com/lvgl/lv_port_linux.git
+cd lv_port_linux/
+git submodule update --init --recursive
+```
+
+## Select graphics backend (optional)
+
+To use legacy framebuffer (fbdev) support, adjust `lv_conf.h` as follows:
+```
+#define LV_USE_LINUX_FBDEV	1
+#define LV_USE_LINUX_DRM	0
+#define LV_USE_SDL		0
+```
+
+To use modern DRM/KMS support, adjust `lv_conf.h` as follows:
+```
+#define LV_USE_LINUX_FBDEV	0
+#define LV_USE_LINUX_DRM	1
+#define LV_USE_SDL		0
+```
+
+To use SDL2 support, adjust `lv_conf.h` as follows:
+```
+#define LV_USE_LINUX_FBDEV	0
+#define LV_USE_LINUX_DRM	0
+#define LV_USE_SDL		1
+```
+
+## Build the project (cmake or Makefile)
+
+### cmake
+
+```
+mkdir build
+cd build 
+cmake ..
+make -j
+```
+
+### Makefile
+
+```
+make -j
+```
+
+## Environment variables
+
+Environment variables can be set to modify behavior of the demo.
+The following variables are supported.
+
+### Legacy framebuffer (fbdev)
+
+- `LV_LINUX_FBDEV_DEVICE` - override default (`/dev/fb0`) framebuffer device node.
+
+### DRM/KMS
+
+- `LV_LINUX_DRM_CARD` - override default (`/dev/dri/card0`) card.
+
+### SDL2
+
+- `LV_SDL_VIDEO_WIDTH` - width of SDL2 surface (default `800`).
+- `LV_SDL_VIDEO_HEIGHT` - height of SDL2 surface (default `480`).
+
+## Run the demo application
+
+### As root
+
+Normal users don't have access to `/dev/fb0` so use `sudo` (or see below) : 
+
+cmake:
+```
+cd ../bin
+sudo main
+```
+
+Makefile:
+```
+cd build/bin/
+sudo main
+```
+
+### Userland
+
+You can give a normal user access to the framebuffer by adding them to the `video` group : 
+
+
+cmake:
+```
+sudo adduser $USER video
+newgrp video
+cd ../bin
+./main
+```
+
+Makefile:
+```
+sudo adduser $USER video
+newgrp video
+cd build/bin/
+./main
+```