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  Problems with setMeter on an Angular meter
Posted by Electron Sheperd on Dec-10-2018 03:09
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I'm having a problem creating a band around a meter, and I'm wondering what I'm doing wrong.  The code to replicate the problem is:

#include <chartdir.h>

int main(int argc, char *argv[])
{
    // Create an AngularMeter object of size 250 x 250 pixels with transparent background
    AngularMeter *m = new AngularMeter(250, 250, Chart::Transparent);

    // Center at (125, 125), scale radius = 111 pixels, scale angle -145 to +145 degrees
    m->setMeter(125, 125, 111, -175, 175);

// Add a red band all the around the meter
m->addZone(0, 100, 95, 111, 0xFF0000);

    // Output the chart
    m->makeChart("roundmeter.png");

    //free up resources
    delete m;

    return 0;
}

This is based on the code for the "Round Meter" sample from the help, with everything that isn't related to the bug removed. When I run this, I get the "Good" image as attached. However, the red band does not go all the way around the meter, since I am passing -175, 175 into the setMeter call. If I change these parameters to be -180, 180 I get the "Bad" image as attached, with the red band just a very thin line at the bottom of the meter.

How can I add a zone that goes all the around the meter?
Good.png
Bad.png

  Re: Problems with setMeter on an Angular meter
Posted by Peter Kwan on Dec-10-2018 21:34
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Hi Electron,

If you want a complete circle, please use AngularMeter.addRing. In the "Round Meter" sample code, you can see the addRing is used to create the grey ring around the meter.

https://www.advsofteng.com/doc/cdcpp.htm#roundmeter.htm

Hope this can help.

Regards
Peter Kwan

  Re: Problems with setMeter on an Angular meter
Posted by Electron Sheperd on Dec-10-2018 23:44
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Peter,

We're using addZone to add a donut-style band around the meter, so the band we add won't always go all the way around. It will only be a full ring when the value is at 100%.

I've seen https://www.chartdir.com/forum/download_thread.php?bn=chartdir_support&pattern=donut&thread=1513164302#N1513189473 and that's the sort of item we're creating, but we also need to add a pointer (to indicate a second value) to the gauge, so I don't think we can use a PieChart.

Some experimentation here indicates that if the gauge goes from 0 - 100, calling addZone(0, 99.99999 ...) works as expected, and if I call setScale(0, 100.000001) and then call addZone(0, 100), it also works as expected, so it looks as if for gauges where the start and end angles define a complete circle, ChartDirector is comparing the value to the maximum, and not drawing the zone if they are the same.

Do I need to detect when the addZone would add a full ring and change the call to addRing, or is there a better way to do it?

  Re: Problems with setMeter on an Angular meter
Posted by Peter Kwan on Dec-11-2018 00:58
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Hi Electron,

If it is easy to detect the full ring condition, I would just check if it is a full ring, and use addRing in such case and addZone in other cases.

If your code will never draw 0% or over 100% (that is, will not create a sector like 20 to 150 where the scale is 0 to 100), you can also try addZone(a, b - 0.000000001). This is visually the same as (a, b) and can avoid the full ring problem.

Regards
Peter Kwan