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  drawing horizontal lines that stop at start
Posted by dave on Jan-10-2023 11:18
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hi Peter,
Hopefully this question makes sense. I have a finance chart. I need to draw a horizontal line across the premarket high and low, but only for a given day.

When a new day starts, a different line needs to be drawn. I can't quite get it figured out.

I know I can use mainChart.yAxis().addMark(...) but that draws a line across the entire chart.

Attached is what I want to draw. The lines I want to add are in blue (I'll want different colors, but drew them in blue, so you know what I'm trying to do).

Thanks!
premarket_lines.png

  Re: drawing horizontal lines that stop at start
Posted by dave on Jan-10-2023 21:55
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btw, I know the X & Y data values. I tried plotting them using .addLine() (I think that was the method I used, but I tried so many things, they are getting blurry), but, it didn't work. (lines didn't show up).

So, I'm guessing there is a difference between data values and the underlying xy cords (makes sense).

I just don't know how to translate accordingly.
premarket_lines2.png

  Re: drawing horizontal lines that stop at start
Posted by dave on Jan-10-2023 22:55
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I think I may have this resolved. I'm testing using .addLineLayer(...) and I'm really close.

I'll let you know if I still need help.

Thanks!

  Re: drawing horizontal lines that stop at start
Posted by Peter Kwan on Jan-11-2023 02:36
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Hi Dave,

Sorry for the late reply.

The line you need can be drawn by using Axis.addMark and use an x-zone color as the line color. The following is an example using an x-zone color:

https://www.advsofteng.com/doc/cdnet.htm#xzonecolor.htm

Basically, an x-zone color is color that changes based whether the pixel is on the left or right side of a given x-data value. If you set an mark line with the red color on the left side, and transparent color on the right side, you can get a line that stops at the middle.

It is also possible to cascade x-zone color. For example, an x-zone color can be the red color on the left side, and on the right side, it is another x-zone color. In this way, you can create a line that is visible two values x1 and x2, like:

// Line color is 0x333399 beteween 10 and 20
int myLineColor = c.xZoneColor(10, Chart.Transparent, c.xZoneColor(20, 0x333399, Chart.Transparent)

Note that the x-coordinate for a FinanceChart is the trading session count 0, 1, 2, 3, 4, ...  The first visible candlestick is x=0, the second visible candlestick is x=1, etc.. (The x=0, 1, 2, ... refers to the center position of the candlestick.) You can use fractional x values if you want the line to stop at the gap between two candlesticks. For example, c.xZoneColor(-1, 0xff0000, 3.5) will start from the left side, and ends at the middle point between the 4th and 5th candlesticks.

Best Regards
Peter Kwan

  Re: drawing horizontal lines that stop at start
Posted by dave on Jan-11-2023 04:33
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wow. Thanks!

  Re: drawing horizontal lines that stop at start
Posted by Peter Kwan on Jan-11-2023 14:13
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Hi dave,

There is a mistake in the last paragraph of my previous post. The xZoneColor should be:

// red color starts from the left, and stops at the middle of the gap between the
// 4th and 5th candlesticks.
int myLineColor = c.xZoneColor(3.5, 0xff0000, Chart.Transparent);

Best Regards
Peter Kwan