ndg/lib/lvgl/examples/widgets/chart/lv_example_chart_8.c

#include "../../lv_examples.h"
#if LV_USE_CHART && LV_DRAW_COMPLEX && LV_BUILD_EXAMPLES

/*  A struct is used to keep track of the series list because later we need to draw to the series in the reverse order to which they were initialised. */
typedef struct {
    lv_obj_t * obj;
    lv_chart_series_t * series_list[3];
} stacked_area_chart_t;

static stacked_area_chart_t stacked_area_chart;

/**
 * Callback which draws the blocks of colour under the lines
 **/
static void draw_event_cb(lv_event_t * e)
{
    lv_obj_t * obj = lv_event_get_target(e);

    /*Add the faded area before the lines are drawn*/
    lv_obj_draw_part_dsc_t * dsc = lv_event_get_draw_part_dsc(e);
    if(dsc->part == LV_PART_ITEMS) {
        if(!dsc->p1 || !dsc->p2)
            return;

        /*Add a line mask that keeps the area below the line*/
        lv_draw_mask_line_param_t line_mask_param;
        lv_draw_mask_line_points_init(&line_mask_param, dsc->p1->x, dsc->p1->y, dsc->p2->x, dsc->p2->y,
                                      LV_DRAW_MASK_LINE_SIDE_BOTTOM);
        int16_t line_mask_id = lv_draw_mask_add(&line_mask_param, NULL);

        /*Draw a rectangle that will be affected by the mask*/
        lv_draw_rect_dsc_t draw_rect_dsc;
        lv_draw_rect_dsc_init(&draw_rect_dsc);
        draw_rect_dsc.bg_opa = LV_OPA_COVER;
        draw_rect_dsc.bg_color = dsc->line_dsc->color;

        lv_area_t a;
        a.x1 = dsc->p1->x;
        a.x2 = dsc->p2->x;
        a.y1 = LV_MIN(dsc->p1->y, dsc->p2->y);
        a.y2 = obj->coords.y2 -
               13; /* -13 cuts off where the rectangle draws over the chart margin. Without this an area of 0 doesn't look like 0 */
        lv_draw_rect(dsc->draw_ctx, &draw_rect_dsc, &a);

        /*Remove the mask*/
        lv_draw_mask_free_param(&line_mask_param);
        lv_draw_mask_remove_id(line_mask_id);
    }
}

/**
 * Helper function to round a fixed point number
 **/
static int32_t round_fixed_point(int32_t n, int8_t shift)
{
    /* Create a bitmask to isolates the decimal part of the fixed point number */
    int32_t mask = 1;
    for(int32_t bit_pos = 0; bit_pos < shift; bit_pos++) {
        mask = (mask << 1) + 1;
    }

    int32_t decimal_part = n & mask;

    /* Get 0.5 as fixed point */
    int32_t rounding_boundary = 1 << (shift - 1);

    /* Return either the integer part of n or the integer part + 1 */
    return (decimal_part < rounding_boundary) ? (n & ~mask) : ((n >> shift) + 1) << shift;
}

/**
 * Stacked area chart
 */
void lv_example_chart_8(void)
{
    /*Create a stacked_area_chart.obj*/
    stacked_area_chart.obj = lv_chart_create(lv_scr_act());
    lv_obj_set_size(stacked_area_chart.obj, 200, 150);
    lv_obj_center(stacked_area_chart.obj);
    lv_chart_set_type(stacked_area_chart.obj, LV_CHART_TYPE_LINE);
    lv_chart_set_div_line_count(stacked_area_chart.obj, 5, 7);
    lv_obj_add_event_cb(stacked_area_chart.obj, draw_event_cb, LV_EVENT_DRAW_PART_BEGIN, NULL);

    /* Set range to 0 to 100 for percentages. Draw ticks */
    lv_chart_set_range(stacked_area_chart.obj, LV_CHART_AXIS_PRIMARY_Y, 0, 100);
    lv_chart_set_axis_tick(stacked_area_chart.obj, LV_CHART_AXIS_PRIMARY_Y, 3, 0, 5, 1, true, 30);

    /*Set point size to 0 so the lines are smooth */
    lv_obj_set_style_size(stacked_area_chart.obj, 0, LV_PART_INDICATOR);

    /*Add some data series*/
    stacked_area_chart.series_list[0] = lv_chart_add_series(stacked_area_chart.obj, lv_palette_main(LV_PALETTE_RED),
                                                            LV_CHART_AXIS_PRIMARY_Y);
    stacked_area_chart.series_list[1] = lv_chart_add_series(stacked_area_chart.obj, lv_palette_main(LV_PALETTE_BLUE),
                                                            LV_CHART_AXIS_PRIMARY_Y);
    stacked_area_chart.series_list[2] = lv_chart_add_series(stacked_area_chart.obj, lv_palette_main(LV_PALETTE_GREEN),
                                                            LV_CHART_AXIS_PRIMARY_Y);

    for(int point = 0; point < 10; point++) {
        /* Make some random data */
        uint32_t vals[3] = {lv_rand(10, 20), lv_rand(20, 30), lv_rand(20, 30)};

        int8_t fixed_point_shift = 5;
        uint32_t total = vals[0] + vals[1] + vals[2];
        uint32_t draw_heights[3];
        uint32_t int_sum = 0;
        uint32_t decimal_sum = 0;

        /* Fixed point cascade rounding ensures percentages add to 100 */
        for(int32_t series_index = 0; series_index < 3; series_index++) {
            decimal_sum += (((vals[series_index] * 100) << fixed_point_shift) / total);
            int_sum += (vals[series_index] * 100) / total;

            int32_t modifier = (round_fixed_point(decimal_sum, fixed_point_shift) >> fixed_point_shift) - int_sum;

            /*  The draw heights are equal to the percentage of the total each value is + the cumulative sum of the previous percentages.
                The accumulation is how the values get "stacked" */
            draw_heights[series_index] = int_sum + modifier;

            /*  Draw to the series in the reverse order to which they were initialised.
                Without this the higher values will draw on top of the lower ones.
                This is because the Z-height of a series matches the order it was initialised */
            lv_chart_set_next_value(stacked_area_chart.obj, stacked_area_chart.series_list[3 - series_index - 1],
                                    draw_heights[series_index]);
        }
    }

    lv_chart_refresh(stacked_area_chart.obj);
}

#endif