Linear horizontal transparent gradient

How-to
1

Hello,
I would like to achieve a linear horizontal transparent gradient effect like in this picture:
image

I was not able to achieve it using gradients functions.
Anyone has suggestions on how to do it?
Thanks

2

What have you tried so far?

3

After trying unsuccesfully the solutions proposed here:

The solution proposed uses animations that applies to the whole object.
I was able to make it using a simple linear gradient that melts with the background color, i was complicating things too much trying to make the gradient transparent.

static void apply_gradient_in(lv_obj_t *obj)
{
    lv_obj_set_style_bg_color(obj, <bg_color>, 0);
    lv_obj_set_style_bg_grad_color(obj, <obj_color>, 0);
    lv_obj_set_style_bg_grad_dir(obj, LV_GRAD_DIR_HOR, 0);
}

static void apply_gradient_out(lv_obj_t *obj)
{
    lv_obj_set_style_bg_color(obj, <obj_color>, 0);
    lv_obj_set_style_bg_grad_color(obj, <bg_color>, 0);
    lv_obj_set_style_bg_grad_dir(obj, LV_GRAD_DIR_HOR, 0);
}

<bg_color> is backgroung color;
<obj_color> is the color of the static object to fade in/out;

4

Complex gradients can be achieved using images and bars

5

as far as I understand in lvgl v9 this effect could be realized with bg_grad_opa & bg-main-opa

6 
//While executing this method, I am sending object which I want to give gradient (ptrObj); GradientStopInfo which is struct type which contains color, fraction & opacity; gradientDirection which can be horizontal or vertical; and gradientStopCount which contains total number of gradient stops. 
_declspec(dllexport) void Set_ObjectBackColor_Gradient(lv_obj_t* ptrObj, struct GradientStopInfo* gradientStopInfo, int gradientDirection, int gradientStopCount) 
{
    if (ptrObj != NULL)
    {
        //Reset Opacity
        lv_obj_set_style_bg_opa(ptrObj, 255, LV_PART_MAIN); //setting whole object opacity as 255 mean "No transparent".
        lv_grad_dsc_t* grad_dsc = lv_malloc_zeroed(sizeof(lv_grad_dsc_t)); // used lv_malloc_zeroed to apply changes to selected object only.
        grad_dsc->dir = gradientDirection;
        grad_dsc->stops_count = gradientStopCount;

        for (int i = 0; i < gradientStopCount; i++) //fill grad_dsc using available colors in gradientStopInfo
        {
            grad_dsc->stops[i].color = lv_color_hex(((UINT32)gradientStopInfo[i].color)); //color
            grad_dsc->stops[i].frac = gradientStopInfo[i].fraction * 255; //gradient stop location
            grad_dsc->stops[i].opa = gradientStopInfo[i].opacity; //in place of 255 just pass 0 as an opacity for your last few colors of 'stops' array to make it transparent.
        }

        lv_obj_set_style_bg_grad(ptrObj, grad_dsc, LV_PART_MAIN); //applying changes (grad_dsc) to selected object only (ptrObj).
    }
}

I think that this my implemented code may help you. Currently, I have not applied transparent option to each stop. Please, refer my screenshot for more references.
ImageHGradient