Round Number for the Marks

[AmirNA]

Hi all,

I have problem with marks interval setting. Is there any option to limit the minimum interval between the marks. I do not want to have interval less than 1 in the axis. For example for the attached image,  I want to have only 0,1 and 2 on the left axis.

[wp]

This is not possible with the built-in labeller. As a replacement you can add a TListChartSource to the form and populate it with the y values at which you want to see a label. When you assign this chartsource to the Source property of the chart's LeftAxis.Marks.Source it will replace the built-in labels - see attached demo.

But be aware that when you zoom into such a chart you very easily will be lost with no labels being displayed any more.

[AmirNA]

Thanks a lot.

[wp]

Just committed a new version of TAChart to Laz/main which has a new option "aipInteger" for Axis.Intervals.Options. It forces the labeling algorithm to select only integer labels. Thus, the original issue of this post can be solved easier now: Simply add aipInteger to the Chart.BottomAxis.Intervals.Options. See attached project.

The new code is in the main branch of the Lazarus repository. But I think it is not difficult to add this also to older versions:

• Make a backup copy of the files TACustomSource.pas and TAIntervalSources.pas in folder components/tachart of your Lazarus installation.
• Open the file TACustomSource.pas, find the declaration of the type TAxisIntervalParamOption (near the top) and add "aipInteger" to the list. The declaration should look like this finally:

Code: Pascal  [Select][+][-]

1. type
2.   TAxisIntervalParamOption = (
3.     aipGraphCoords,
4.     aipUseCount, aipUseMaxLength, aipUseMinLength, aipUseNiceSteps,
5.     aipInteger);  

• Open the file TAIntervalSources and find the procedure TIntervalChartSource.CalculateIntervals. Replace the body of the procedure by the following code (or add the highlighted lines):

Code: Pascal  [Select][+][-]

1. procedure TIntervalChartSource.CalculateIntervals(
2.   AParams: TValuesInRangeParams; out ABestStart, ABestStep: Double);
3. [...]
4. begin
5.   CalcMinMaxCount(minCount, maxCount);
6.   bestCount := 0;
7.   if aipInteger in Params.Options then begin
8.     ABestStart := Int(AParams.FMin);
9.     ABestStep := 1.0;
10.     bestCount := Round(AParams.FMax) - round(ABestStart);
11.     if bestCount <= maxCount then
12.       exit;
13.   end;
14.   if aipUseNiceSteps in Params.Options then begin
15.     s := AParams.CountToStep(minCount)  * 10;
16.     while s >= Max(AParams.CountToStep(maxCount), AParams.FMinStep) do begin
17.       for sv in Params.StepValues do
18.         TryStep(s * sv, bestCount);
19.       // We are not required to pick the best count, so any one will do.
20.       if not (aipUseCount in Params.Options) and (bestCount > 0) then break;
21.       s *= 0.1;
22.     end;
23.   end;
24.   if (aipInteger in Params.Options) and (bestCount > maxCount) then
25.     bestCount := 0;
26.   if bestCount > 0 then
27.     exit;
28.   // Either nice steps were not required, or we failed to find one.
29.   if aipUseCount in Params.Options then
30.     bestCount := EnsureRange(Params.Count, minCount, maxCount)
31.   else
32.     bestCount := minCount;
33.   ABestStep := (AParams.FMax - AParams.FMin) / bestCount;
34.   ABestStart := AParams.FMin - ABestStep;
35. end;

• Rebuild the IDE: "Tools" > "Build Lazarus with profile...". After a while, when Lazarus restarts, you can use the new feature.