Several bugs when Gantt start is in different timezone because of daylight savings time

[mCharbonneauCortex]

Several bugs happen when a shift in daylight savings time happened between the start of the Gantt and a Gantt rectangle. For example, if there's a switch from UTC-4 to UTC-5, times that are calculated using the gantt_start time as reference will gain 1 hour, since the 00:00 AM at UTC-4 is an hour later than 00:00 AM at UTC-5. My bet is that the reverse situation can also happen.

• gantt rectangles will be slightly shifted by 1 hour all across the board
• If, for example, the user set the end date on the 28-11-2018, the real end time returned by the Gantt should be the 28-11-2018 at 11:59 PM. However, with this bug, the end time will be the 29-11-2018 at 00:59 AM. Checking only the date without checking if this bug happened will get you the day after the day the user intended.

[samlogan]

+1

[jcjobin]

Hey, I had this issue as well. The problem lies in "compute_start_end_date()" of Bar.js. They are finding the start date based off of the views start date and the x position of the bar. So, if the gantt start date is in Daylight savings and the bar start date is in standard, then the times will be off by 1 hour. The way I fixed this was by extending the Bar class in a custom Bar class, overwriting "compute_start_end_date()" with:

export class CustomBar extends Bar {
    compute_start_end_date() {
        const bar = this.$bar;
        const x_in_units = bar.getX() / this.gantt.options.column_width;
        let new_start_date = date_utils.add(
            this.gantt.gantt_start,
            x_in_units * this.gantt.options.step,
            'hour'
        );
        const start_offset = this.gantt.gantt_start.getTimezoneOffset() - new_start_date.getTimezoneOffset();
        if (start_offset !== 0) {
            new_start_date = date_utils.add(
                new_start_date,
                start_offset,
                'minute'
            );
        }
        const width_in_units = bar.getWidth() / this.gantt.options.column_width;
        const new_end_date = date_utils.add(
            new_start_date,
            width_in_units * this.gantt.options.step,
            'hour'
        );

        return { new_start_date, new_end_date };
    }
}

The key here is adding the timezone offset difference between the gantt start and the bar start.

[cepauskas]

@jcjobin Hi ! Could you give a hint how to extend and use your example "CustomBar" without modifying original source of gantt lib?

[kpetrow]

Thanks for the snippet. In theoretical terms what is supposed to be displayed on the timeline during repeating or missing hours? Should there be a skipped 2am and a double 2am?