Can I get the position and size of an axis title?
lazarus / 55-TAChart

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CM630 · 2026-04-01 07:29

I am trying to get the positions (rather borders) of axis titles. The
idea is to use multiple axises.
I have aded a ChartToolset with a ChartToolset1AxisClickTool activated
on left mouse click.
When I click on an axis I get “0;4;4” in the label, which is not the
result I am looking for.
Is there a way to find the position and size of the axis title?

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure T
Form1.ChartToolset1AxisClickTool1Click(ASender:TChartTool;Axis:TChartA
xis;AHitInfo:TChartAxisHitTests);begin  Label1.Caption :=
IntToStr(axis.Margin) + '; ' + IntToStr(axis.Title.Margins.Left) +  ';
' + IntToStr(axis.Title.Margins.Right);end;
A snippet is attached.

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wp · 2026-04-01 12:52

You can query the vertices of the polygon around the title which would
be painted when its Frame.Style is not clear and its Frame.Visible is
true. This is also the polygon which is checked by the
AxisTitleClickTool to decide whether the click is inside the title.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.ChartToolset1AxisClickTool1Click(ASender:TChartTool;  Axis:
TChartAxis; AHitInfo: TChartAxisHitTests);var  s, sp: String;  i:
Integer;begin//  Label1.Caption := IntToStr(axis.Margin) + '; ' +
IntToStr(axis.Title.Margins.Left) +  '; ' +
IntToStr(axis.Title.Margins.Right);  s := '';  for i := 0 to
High(Axis.TitlePolygon) do  begin    sp := Format('%d: (%d;%d)', [i,
Axis.TitlePolygon[i].X, Axis.TitlePolygon[i].Y]);    if i > 0 then   
 s := s + '; ' + sp    else      s := sp;  end;  Label1.Caption :=
'TitlePolygon = [' + s + ']';end;

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CM630 · 2026-04-03 07:50

Thanks!
Meanwhile I found out that there is a property *Scale.Editable, but it
is “Not implemented”.

I added a Tmemo in the main form.
And why trying it, it occurred that when the scale is more than a line
long, is switches from centered to aligned left... sort of (see the
image attached.
Also, if there is an empty line in the caption, it is ignored:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
BottomAxis.Title.Caption = 'Line 1 ' + LineEnding  + LineEnding +
'Line 4';is displayed as:
QuoteLine 1
Line 4

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, Forms,
Controls, Graphics, Dialogs,StdCtrls,TAGraph,TATools, TAChartAxis,
TAChartAxisUtils, LCLType, math; type   { TForm1 }   TForm1 =
class(TForm)    Chart1:TChart;    ChartToolset1:TChartToolset;   
ChartToolset1AxisClickTool1:TAxisClickTool;    Label1:TLabel;   
Memo1:TMemo;    procedure ChartToolset1AxisClickTool1Click(ASender:TCh
artTool;Axis:TChartAxis;AHitInfo:TChartAxisHitTests);    procedure
FormCreate(Sender:TObject);    procedure
Memo1KeyDown(Sender:TObject;var Key:Word;Shift:TShiftState);  private 
   FClickedAxis : TChartAxis;  public   end; var  Form1:
TForm1; implementation {$R *.lfm} { TForm1 } procedure TForm1.ChartToo
lset1AxisClickTool1Click(ASender:TChartTool;Axis:TChartAxis;AHitInfo:T
ChartAxisHitTests);var  s, sp: String;  i: Integer;begin  FClickedAxis
:= Axis;  Memo1.Top :=   Chart1.top +  Axis.TitlePolygon[0].Y; 
Memo1.Height := Axis.TitlePolygon[1].Y - Axis.TitlePolygon[0].Y +1; 
Memo1.left :=  Chart1.ClipRect.Left +   Chart1.Left;  Memo1.Width :=
Chart1.Width - Chart1.ClipRect.Left - Chart1.MarginsExternal.right; 
Memo1.Font := Axis.Title.LabelFont;  memo1.Text :=
 Axis.Title.Caption;  Memo1.Visible := true;  end; procedure
TForm1.FormCreate(Sender:TObject);var  i: integer;begin 
Chart1.Toolset := ChartToolset1;  chart1.AxisList.Add; 
chart1.AxisList.Add;  chart1.AxisList.Add;  chart1.AxisList.Add;  for
i:= 0 to   chart1.AxisList.Count -1 do  begin   
chart1.AxisList[i].Title.Visible  := True;   
chart1.AxisList[i].Title.Caption := 'Axis ' + IntToStr(i);    if i mod
2 = 0 then    begin     
chart1.AxisList[i].Title.LabelFont.Orientation := 900;     
chart1.AxisList[i].Alignment := calLeft;    end    else    begin     
chart1.AxisList[i].Title.LabelFont.Orientation := 0;     
chart1.AxisList[i].Alignment := calbottom;    end;  end; 
chart1.AxisList[3].Title.Caption := chart1.AxisList[2].Title.Caption +
 'abc' + LineEnding + '456';  Memo1.Alignment := taCenter; 
memo1.WordWrap := False;end; function GetMemoLineHeight(AMemo: TMemo):
Integer;var  Bitmap: TBitmap;begin  Bitmap := TBitmap.Create;  try   
Bitmap.Canvas.Font.Assign(AMemo.Font);    // Measure a standard
character    Result := Bitmap.Canvas.TextHeight('Wg');  finally   
Bitmap.Free;  end;end; procedure
TForm1.Memo1KeyDown(Sender:TObject;var
Key:Word;Shift:TShiftState);var  FontHeight : integer = 14;begin 
FontHeight := abs(GetFontData(Memo1.Font.Handle).Height);  if (Key =
VK_ESCAPE) then  begin    Memo1.Visible := false;    Exit;  end;  if
((Key = VK_RETURN) and (ssCtrl in Shift)) then  begin   
FClickedAxis.Title.Caption := Memo1.Text;     Memo1.Visible := false; 
  exit;  end;  if ((key = LCLtype.VK_RETURN) and (shift = [])) then  
begin      Memo1.Height := min (FontHeight*3+8,Memo1.Height +
FontHeight+4); //The first line starts 5 pixels below the top of the
memo (in Windows)      Memo1.top := chart1.top+
FClickedAxis.TitlePolygon[0].Y - Memo1.Height + FontHeight+2;   
end;end; end.

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wp · 2026-04-03 08:25

Quote from: CM630 on April 03, 2026, 09:50:23 amswitches from centered
to aligned left...
There's a property Alignment for the individual lines of the axis
title (and Chart.Title and marks text, as well), you may want to
switch it to taCenter. Another (newly introduced) property Anchor
defines where the overall title is placed along the axis: ctaStart =
where the axis begins, ctaEnd = where the axis ends, ctaCenter =
center of the axis (default).

Quote from: CM630 on April 03, 2026, 09:50:23 amAlso, if there is an
empty line in the caption, it is ignored
This is because an empty line is considered to have zero extent (x:0;
y:0). If you want to include the empty line insert a space character
between the two LineEndings:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
Chart1.BottomAxis.Title.Caption := 'Line 1' + LineEnding + ' ' +
LineEnding + 'Line 2';

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CM630 · 2026-04-03 08:50

Indeed.
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   for i:= 0
to   chart1.AxisList.Count -1 do  begin   
chart1.AxisList[i].Title.Visible  := True;   
chart1.AxisList[i].Title.Caption := 'Axis ' + IntToStr(i);   
chart1.AxisList[i].Title.Alignment := taCenter;   //Here  did the job.

And can I get some position data for the numeric scale (the scale
itself) of the axis?
The scale position itself, or in the perfect case the position/size of
the left/bottommost number and the right/topmost number?

I checked in TChartAxis = class(TChartBasicAxis) ... public... but
nothings sounds similar.

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wp · 2026-04-03 09:40

What do you understand as "numeric scale"?

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CM630 · 2026-04-03 11:34

I want to make the numeric scale editable (to change the extents of
the scale) by the user.
So currently I overlap a text box (named txtExtents) over the
first/last number on the scale when the user clicks there (with green
rectangles on the image attached).

Currently (part of) the code is:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  procedure
*.ctMainAxisClickLeftOnClick(ASender: TChartTool; Axis: TChartAxis;
AHit: TChartAxisHitTests);... txtExtents.Alignment := taLeftJustify; 
   if (ahtAxisStart in aHit) and XScale.Visible then        begin    
    try            txtExtents.Font := Axis.Marks.LabelFont;         
finally          end;          txtExtents.Text :=
FloatToStr(GetExtentsReal(Chart).coords[ExtXmin]);         
AutoSizeEditWidth(txtExtents,True);          txtExtents.Left :=
Chart.Margins.Left + 75;          txtExtents.Top :=
Chart.ClipRect.Bottom + Axis.TickLength + 1;         
txtExtents.Visible := True;          ExtentPosition := epXmin;       
end;...
but I am implementing multiple scales and this solution will not work,
because txtExtents.Left and txtExtents.Top will not be set properly
(most likely Top, Left shall be quite okay).

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wp · 2026-04-04 23:34

Please test the following solution that I just committed to Lazarus
trunk/main:

* TChartAxis has a (public) property Value[index] which lists the
numeric and text value of the axis labels ("scale" in your words)
* TChartAxis.ValueCount is the length of this array.
* I added another element, FPolygon (TPointArray), to the Value record
which contains the polygon surrounding each label. A polygon is used
rather than a TRect because the label frame can have a rather complex
shape. By default, it has the shape of a rectangle, though.
* Unfortunately the first and/or last axis labels are often outside
the axis range so that you must search for the first/last VISIBLE
label yourself.
* In order to draw a green border around the first and last labels on
the axis, I tested the following (quick-and-dirty) code:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses 
Types, TAChartUtils, TADrawUtils, TACustomSource, TATransformations;
 procedure HighlightFirstAndLastAxisLabel(Axis: TChartAxis);var  R:
TRect;  ext: TDoubleRect;  v: Double;  i, idx: Integer;  t:
TChartValueText;  transf: TChartAxisTransformations;  chart:
TChart;begin  Axis.Drawer.SetPenParams(psSolid, clLime); 
Axis.Drawer.SetBrushParams(bsClear, clNone);  chart :=
TChart(Axis.GetChart);  ext := chart.CurrentExtent;  transf :=
TransformByAxis(chart.AxisList, Axis.Index);   // Find first label
which is on the axis  idx := -1;  for i := 0 to Axis.ValueCount - 1
do  begin    t := Axis.Value[i];    v :=
transf.AxisToGraph(t.FValue);    if Axis.IsVertical then    begin    
if (v >= ext.a.y) then      begin        idx := i;        break;     
end;    end else    begin      if (v >= ext.a.x) then      begin     
 idx := i;        break;      end;    end;  end;  if idx = -1 then   
exit;  R.TopLeft := Axis.Value[idx].FPolygon[0];  R.BottomRight :=
Axis.Value[idx].FPolygon[2];  Types.InflateRect(R, 4, 2); 
Axis.Drawer.Rectangle(R);   // Find last label which is on the axis; 
idx := -1;  for i := Axis.ValueCount - 1 downto 0 do  begin    t :=
Axis.Value[i];    v := transf.AxisToGraph(t.FValue);    if
Axis.IsVertical then    begin      if (v <= ext.b.y) then      begin 
     idx := i;        break;      end;    end else    begin      if (v
<= ext.b.x) then      begin        idx := i;        break;      end; 
 end;  end;  if idx = -1 then    exit;  R.TopLeft :=
Axis.Value[idx].FPolygon[0];  R.BottomRight :=
Axis.Value[idx].FPolygon[2];  Types.InflateRect(R, 4, 2); 
Axis.Drawer.Rectangle(R);end;

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wp · 2026-04-05 10:56

Now also added methods GetIndexOfFirst(Last)VisibleMark to TChartAxis.
This way my previous sample code simplifies to

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
HighlightFirstAndLastAxisLabels(Axis: TChartAxis);var  R: TRect;  idx:
Integer;  chart: TChart;begin  Axis.Drawer.SetPenParams(psSolid,
clLime);  Axis.Drawer.SetBrushParams(bsClear, clNone);   // Find first
label which is on the axis  idx := Axis.GetIndexOfFirstVisibleMark; 
if idx > -1 then  begin    R.TopLeft := Axis.Value[idx].FPolygon[0]; 
 R.BottomRight := Axis.Value[idx].FPolygon[2];    Types.InflateRect(R,
4, 2);    Axis.Drawer.Rectangle(R);  end;   // Find last label which
is on the axis;  idx := Axis.GetIndexOfLastVisibleMark;  if idx > -1
then begin    R.TopLeft := Axis.Value[idx].FPolygon[0];   
R.BottomRight := Axis.Value[idx].FPolygon[2];    Types.InflateRect(R,
4, 2);    Axis.Drawer.Rectangle(R);  end;end;
QuoteI want to make the numeric scale editable (to change the extents
of the scale) by the user.
So currently I overlap a text box (named txtExtents) over the
first/last number on the scale when the user clicks there (with green
rectangles on the image attached).I am not sure whether this will
work. Because the first and last visible labels are not necessarily
the values at which the axis starts and ends. You must provide extra
code to make sure that these labels really are positioned at axis
start and end.

If you are interesting in how to provide a GUI for run-time editing of
chart properties you may want to take a look at the "charteditor" in
the demos folder of the TAChart installation.

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CM630 · 2026-04-06 09:42

Thanks!
1. When I try to use HighlightFirstAndLastAxisLabel* in Form.Create
the app crashes
Adding if (axis = nil) then exit; does not prevent the crash.
2. I tried to move it to .OnShow but still the app crashes.
  Neither Chart1.Prepare;  nor   chart1.Invalidate; help.
  I do not intend to use it this way, but maybe this indicates some
problem.

Pretty odd:
  3. The procedure from Reply #7 worked from the first try (named
HighlightFirstAndLastAxisLabel_1 in the attached snippet).
  4. The procedure from Reply #8 did not work (named
HighlightFirstAndLastAxisLabel_2 in the attached snippet) initially.
After I removed a Chart that was not used from the form, it started
working. I have done “clean up and build” before that with no result.
It seemed to find some coordinates, but nothing was drawn.

5. A snippet is attached. Stll no care is taken for inverted axises
(the smaller one is on the right, the higher is on the left).

Quote from: wp on April 05, 2026, 12:56:41 pmQuoteI want to make the
numeric scale editable (to change the extents of the scale) by the
user.
So currently I overlap a text box (named txtExtents) over the
first/last number on the scale when the user clicks there (with green
rectangles on the image attached).I am not sure whether this will
work. Because the first and last visible labels are not necessarily
the values at which the axis starts and ends. You must provide extra
code to make sure that these labels really are positioned at axis
start and end.
Indeed, the user might click on a 5 and get text 8. I am not sure if I
have taken to make sure that these labels really are positioned at
axis start and end, I will find out.


Quote from: wp on April 05, 2026, 12:56:41 pmIf you are interesting in
how to provide a GUI for run-time editing of chart properties you may
want to take a look at the "charteditor" in the demos folder of the
TAChart installation.
I will check that, but if there are questions or issues, I will use
another tread.

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wp · 2026-04-06 15:26

Quote from: CM630 on April 06, 2026, 11:42:15 am1. When I try to use
HighlightFirstAndLastAxisLabel* in Form.Create the app crashes
Adding if (axis = nil) then exit; does not prevent the crash.
2. I tried to move it to .OnShow but still the app crashes.
  Neither Chart1.Prepare;  nor   chart1.Invalidate; help.
  I do not intend to use it this way, but maybe this indicates some
problem.
TAChart does all its sizing and layout adjustments during the Paint
method. Therefore, when your calls are too early, before anything has
been painted, bad things may happen... A good place to invoke
TChartAxis.GetIndexOfFirst(Last)VisibleMarkIndex is the OnAfterPaint
method of the chart; this happens when all painting is finished and
everything is known.

Quote from: CM630 on April 06, 2026, 11:42:15 am5. A snippet is
attached. Stll no care is taken for inverted axises (the smaller one
is on the right, the higher is on the left).
I am attaching a test project for clicking on axis labels after having
added a (read-only) property ClickedLabelIndex to the TAxisClickTool.
Special code to care for inverted axes is not required.

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CM630 · 2026-04-07 11:30

I updated to the latest TChart and your example worked.

What are the ways to have different values on the scales?
For example if I have voltage and current on one waveform, I would
need a scale for -350 V to + 350 V and another one for current, say
from -10 A to + 10 A.
One possible way is TchartAxisTransformations, but can I simply set
the minimum and maximum values for the scale?

Also, in your example I tried

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormCreate(Sender:TObject);begin  Chart1.AxisList.Add; 
Chart1.AxisList[Chart1.AxisList.Count -1].Alignment := calTop; 
Chart1.AxisList.Add;  Chart1.AxisList[Chart1.AxisList.Count
-1].Alignment := calBottom;  Chart1.BottomAxis.Transformations :=
ChartAxisTransformations1; 
TLinearAxisTransform(ChartAxisTransformations1.List[0]).Offset :=0; 
TLinearAxisTransform(ChartAxisTransformations1.List[0]).Scale
:=10;end;
I expected that the BottomAxis (AxisList[1]) would be scaled (from -60
to 120), but actually it remains -6 to 12, and the other two
horizontal axises are scaled 10 times.
Is this the expected behaviour?

Edit: I added a snippet. Things look ever more mysterious.

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wp · 2026-04-07 23:00

For having two (or more) independent vertical axes (or horizontal -
just the same logic...), there is a tutorial: https://wiki.lazarus.fre
epascal.org/TAChart_Tutorial:_Dual_y_axis,_Legend. In essence:
- Add a TChartAxistransformations component per axis, link it to the
Transformations property of the axis.
- Add an AutoScaleAxistransform to the component (rather than a
LinearAxisTransform).
- Every series must set the AxisIndexX and AxisIndexY to the index of
it x and y axis.

For specific axis range:
- Use the Range property of the axis (axis.Range.Min, .Max, .UseMax,
.UseMin) to define the value at which the axis begins (Min) and ends
(Max). But note, when data in the series assigned to this axis will
run out of this range, the range will automatically expand.

For user-entry of axis range:
- My recommendation: Do not use your label-click idea because the
first visible label is not necessarily at the axis start. Suppose you
want the axis to run between 190 and 500. Then TAChart will very
probably put the first label to the value 200. I'd add two edits (or
SpinEdits) to the form close to the axis start/end to define the axis
start/end and let TAChart decide which labels will be displayed.

Inverted axis:
- I don't know whether this is a bug or a feature, but when you have
two vertical axes and set the left axis' Inverted to true, both axes
will flip their direction. It's better to add an additional
LinearAxisTransform ("Linear" is correct now!) and switch its Scale
property to -1 in order to invert the axis direction - the other axis
then is not affected. But note that the LinearAxisTransform must be
listed in the ChartAxisTransformations before the AutoScaleTransform,
otherwise the flipping process will not work. The transformations are
executed in the listed order: at first you must flip the axis
coordinates (TLinearAxisTransform with Scale=-1) and then you must map
the axis coordinates to the interal graph coordinates
(TAutoScaleTransform).

See attached project.

----------------------------------------------------------------------
CM630 · 2026-04-17 13:36

But with inverted axises the mess seems to be even greater.
In the attached example ahtAxisStart and ahtAxisEnd in AHitInfo are
correct for axis 1, which is set to Inverted and is displayed as
inverted.
But for the other X axises (which are displayed as inverted, but their
.Inverted property is false) ahtAxisStart and ahtAxisEnd are wrong.

----------------------------------------------------------------------
wp · 2026-04-17 22:23

The Inverted property cannot be applied to the case of multiple axes
in horizontal or vertical directions. As I showed above you should add
a TLinearAxisTransform with Scale parameter -1 for each individual
axis to be inverted.

----------------------------------------------------------------------
CM630 · 2026-04-21 05:29

Indeed, inversion works with Transformations.
But it occurs that GetIndexOfFirstVisibleMark returns a wrong result
when a transformation with .Scale ≠ |1|.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
...procedure TForm1.Button1Click(Sender:TObject);begin 
ChartAxisTransformations1LinearAxisTransform1.Scale := 1; //Returns 1,
as it should  Chart1.Invalidate;  Application.ProcessMessages; 
ShowMessage (IntToStr(
 Chart1.BottomAxis.GetIndexOfFirstVisibleMark));end; procedure
TForm1.Button2Click(Sender:TObject);begin 
ChartAxisTransformations1LinearAxisTransform1.Scale := 0.1; 
Chart1.Invalidate;  Application.ProcessMessages ;  ShowMessage
(IntToStr(Chart1.BottomAxis.GetIndexOfFirstVisibleMark)); //Returns 6
instead of 1end; ...

----------------------------------------------------------------------
CM630 · 2026-05-11 13:31

Some changes in TAChartAxis seem to make things better:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
TChartAxis.GetIndexOfFirstVisibleMark(aOffset: double = 0; aScale:
double=1): Integer;var  coord: Integer;begin  for Result := 0 to
High(FMarkValues) do begin    coord :=
FHelper.GraphToImage(FMarkValues[Result].FValue*aScale + aOffset);   
if FHelper.IsInClipRange(coord) then      exit;  end;  Result :=
-1;end; function TChartAxis.GetIndexOfLastVisibleMark(aOffset: double
= 0; aScale: double=1): Integer;var  coord: Integer;begin  for Result
:= High(FMarkValues) downto 0 do begin    coord :=
FHelper.GraphToImage(FMarkValues[Result].FValue*aScale + aOffset);   
if FHelper.IsInClipRange(coord) then      exit;  end;  Result :=
-1;end;    
Usage:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  
ShowMessage (IntToStr(Chart1.BottomAxis.GetIndexOfFirstVisibleMark(Cha
rtAxisTransformations1LinearAxisTransform1.Offset,ChartAxisTransformat
ions1LinearAxisTransform1.Scale)));

----------------------------------------------------------------------
CM630 · 2026-05-12 06:38

This should be even better:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
TChartAxis.GetIndexOfFirstVisibleMark: Integer;var  coord: Integer; 
mScale : double = 1;  mOffset : double = 0;  i: integer = 0;begin  if
(FTransformations <> Nil) and (FTransformations.List.Count >0)  then 
begin    for i:=0 to FTransformations.List.Count - 1 do      if
((TObject(Transformations.List.Items[i]) is TLinearAxisTransform)) and
(TLinearAxisTransform(Transformations.List.Items[i]).Enabled = True)
then      begin        mScale := mScale *
TLinearAxisTransform(Transformations.List.Items[i]).Scale;       
mOffset := mOffset *
TLinearAxisTransform(Transformations.List.Items[i]).Scale +
TLinearAxisTransform(Transformations.List.Items[i]).Offset;      end; 
end;   for Result := 0 to High(FMarkValues) do begin    coord :=
FHelper.GraphToImage(FMarkValues[Result].FValue*mScale + mOffset);   
if FHelper.IsInClipRange(coord) then      exit;  end;  Result :=
-1;end; function TChartAxis.GetIndexOfLastVisibleMark: Integer;var 
coord: Integer;  mScale : double = 1;  mOffset : double = 0;  i:
integer = 0;begin  if (FTransformations <> Nil) and
(FTransformations.List.Count >0)  then  begin    for i:=0 to
FTransformations.List.Count - 1 do      if
((TObject(Transformations.List.Items[i]) is TLinearAxisTransform)) and
(TLinearAxisTransform(Transformations.List.Items[i]).Enabled = True)
then      begin        mScale := mScale *
TLinearAxisTransform(Transformations.List.Items[i]).Scale;       
mOffset := mOffset *
TLinearAxisTransform(Transformations.List.Items[i]).Scale +
TLinearAxisTransform(Transformations.List.Items[i]).Offset;      end; 
end;   for Result := High(FMarkValues) downto 0 do begin    coord :=
FHelper.GraphToImage(FMarkValues[Result].FValue * mScale + mOffset); 
 if FHelper.IsInClipRange(coord) then      exit;  end;  Result :=
-1;end;

----------------------------------------------------------------------
wp · 2026-05-12 22:05

Please check out the new version of
TChartAxis.GetIndexOfFirst/LastVisibleAxisMark in the Laz/main
repository. The issue was that the indices were searched by conversion
of the label values from graph to image coordinates, but this is
correct only when no axis transform is involved because label values
always are in axis coordinates - the conversion from axis to graph
coordinates was missing in my old code. The full combination of all
involved axis transformations, in the correct order, can be found from
the GetTransform method of the axis.

In the attachment you can find a small project which combines a
logarithmic and a linear (inverting) axis transformation (it works
correctly only with the new TAChart revision).

----------------------------------------------------------------------
CM630 · 2026-05-13 05:59

Thanks!
The snippet worked fine for me, except that something seemed to be
wrong with the project so I opened the form manually.
I expanded it a little, adding Cumulative something (I doubt that I
will ever use that, maybe someone else will need it, since it is
there), and there is an issue with it, as shown on the image attached.
The extended snippet is also attached.

----------------------------------------------------------------------
wp · 2026-05-13 09:26

TCumulNormDistrAxisTransform is a special transformation for
statistical probability data which expands values from the range 0...1
to the range -INF...+INF in a way to linearize a cumulative normal
distribution. Due to the transformed negative numbers it cannot be
combined with a logarithmic transform. Or, if the log transform would
be executed first, the CumulNormDistrTransform would get values
outside its domain again (e.g. log(0.001) = -3). In any case, these
two transformations cannot be combined in general.

To support the TCumulNormDistrAxisTransform I changed the plotted
function to a sigmoid function y= 1/(1+exp(-x)) which ranges between 0
and 1 as required. This transformation results in a highly non-linear
density of axis labels, and thus I had to adjust the Axis.Intervals
parameters for it.

To see the effect of an AutoScaleTransform I added a second y axis and
assigned the function y=x to it.

Unfortunately there were still some bugs in the index finder, for
example when the suggested label was outside the range of the
transformation. Fixed in new revision.

----------------------------------------------------------------------
CM630 · 2026-05-14 08:16

GetIndexOfLastVisibleMark  returns the mark with the higher value, not
the rightmost/topmost. So when the axis is inverted, it returns the
leftmost value, not the rightmost. The same with
GetIndexOfFirstVisibleMark. I am not sure if this is the intended
behaviour, just to make sure.

I could not understand what you have done in that example, but I
cannot change the parameters of the transformations during runtime.
So here is what I did (maybe rather funny than useful):

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, Forms,
Controls, Graphics, Dialogs,StdCtrls,  Types, math, 
TAGraph,TASeries,TATools,TATransformations, TAChartAxis,
TACustomSource; type   { TForm1 }   TForm1 = class(TForm)   
Button1:TButton;    Chart1:TChart;    Chart1LineSeries1:TLineSeries; 
 Chart1LineSeries2:TLineSeries;   
ChartAxisTransformationsBottom:TChartAxisTransformations;   
AutoBottom:TAutoScaleAxisTransform;   
AutoLeft:TAutoScaleAxisTransform;   
CumuBottom:TCumulNormDistrAxisTransform;   
CumulLeft:TCumulNormDistrAxisTransform;   
LogarithmBottom:TLogarithmAxisTransform;   
LogarithmLeft:TLogarithmAxisTransform;   
LinearBottom:TLinearAxisTransform;   
ChartAxisTransformationsLeft:TChartAxisTransformations;   
LinearLeft:TLinearAxisTransform;    procedure
Button1Click(Sender:TObject);    procedure
FormCreate(Sender:TObject);  private   public   end; var  Form1:
TForm1; implementation {$R *.lfm} { TForm1 }  procedure
HighlightFirstAndLastAxisLabels(Axis: TChartAxis);   procedure
DrawLabelBorder(AIndex: Integer; AColor: TColor);  var    R: TRect;  
vt: TChartValueText;  begin    if AIndex = -1 then      exit;    vt :=
Axis.Value[AIndex];    if Length(vt.FPolygon) = 0 then      exit;   
R.TopLeft := vt.FPolygon[0];    R.BottomRight := vt.FPolygon[2];   
Types.InflateRect(R, 4, 2);     Axis.Drawer.SetPenParams(psSolid,
AColor);    Axis.Drawer.Rectangle(R);  end; begin 
Axis.Drawer.SetBrushParams(bsClear, clNone);  // Find first label
which is on the axis and mark it by a green border 
DrawLabelBorder(Axis.GetIndexOfFirstVisibleMark, clLime);  // Find
last label which is on the axis and mark it by a red border 
DrawLabelBorder(Axis.GetIndexOfLastVisibleMark, clRed);end; procedure
TForm1.FormCreate(Sender: TObject);var  i: Integer;  x, y:
Double;begin  for i := -100 to 100 do  begin    x := i / 10;    y :=
1.0 / (1.0 + exp(-x));    Chart1LineSeries1.AddXY(x, y);   
Chart1LineSeries2.AddXY(x, x);  end;end; procedure
TForm1.Button1Click(Sender:TObject);begin  Randomize; 
LinearLeft.Enabled :=  RandomRange(0, 2) = 1;  LinearBottom.Enabled :=
 RandomRange(0, 2) = 1;  LogarithmLeft.Enabled :=  RandomRange(0, 2) =
1;  LogarithmBottom.Enabled :=  RandomRange(0, 2) = 1; 
AutoLeft.Enabled :=  RandomRange(0, 2) = 1;  AutoBottom.Enabled :=
 RandomRange(0, 2) = 1;  if not LogarithmLeft.Enabled  then   
CumulLeft.Enabled  :=  RandomRange(0, 2) = 1;  if not
LogarithmBottom.Enabled then    CumuBottom.Enabled :=  RandomRange(0,
2) = 1;   LinearLeft.Scale := (Random(2) * 2 - 1) {plus or minus} *
Random * (100 - 0.01) + 0.01;  LinearLeft.Offset := Random * (100 -
0.01) + 0.01;   LinearBottom.Scale := (Random(2) * 2 - 1) {plus or
minus} * Random * (100 - 0.01) + 0.01;  LinearBottom.Offset := Random
* (100 - 0.01) + 0.01;  Chart1.Invalidate; 
Application.ProcessMessages;  HighlightFirstAndLastAxisLabels
(chart1.AxisList[0]);  HighlightFirstAndLastAxisLabels
(chart1.AxisList[1]);end; end.  As I did it gradually, I saw no
issues, except the one I just mentioned.
I will see what will happen when I get to multiple axises...

Also, again, I had to open the .pas file manually, after adding the
project (just FYI).

----------------------------------------------------------------------
wp · 2026-05-14 11:07

Quote from: CM630 on May 14, 2026, 10:16:48
amGetIndexOfLastVisibleMark  returns the mark with the higher value,
not the rightmost/topmost. So when the axis is inverted, it returns
the leftmost value, not the rightmost. The same with
GetIndexOfFirstVisibleMark. I am not sure if this is the intended
behaviour, just to make sure.
Wasn't this your intention in one of the previous posts?

Quote from: CM630 on May 14, 2026, 10:16:48 amAlso, again, I had to
open the .pas file manually, after adding the project (just FYI).
This is because of a recent change in the Laz/main project file, I
should save all projects with the option "Maximize compatibility of
project files (lpi, lps)".

Quote from: CM630 on May 14, 2026, 10:16:48 amCode: Pascal
 [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   if not
LogarithmLeft.Enabled  then    CumulLeft.Enabled  :=  RandomRange(0,
2) = 1;  if not LogarithmBottom.Enabled then    CumuBottom.Enabled :=
 RandomRange(0, 2) = 1; The cumulative normal distribution transform
is very nitpicking on parameters. It only accepts input arguments in
the range 0 ... 1. There normally combinations with any other
transform in which this range is left can fail.

Quote from: CM630 on May 14, 2026, 10:16:48 amCode: Pascal
 [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  
LinearLeft.Scale := (Random(2) * 2 - 1) {plus or minus} * Random *
(100 - 0.01) + 0.01;  LinearLeft.Offset := Random * (100 - 0.01) +
0.01;   LinearBottom.Scale := (Random(2) * 2 - 1) {plus or minus} *
Random * (100 - 0.01) + 0.01;  LinearBottom.Offset := Random * (100 -
0.01) + 0.01; Random linear transformation parameters together with a
log transform? This will not work in general, because the log
transform can only operate on positive numbers

I don't see what you want to prove with these experiments.

----------------------------------------------------------------------
CM630 · 2026-05-14 12:37

Quote from: wp on May 14, 2026, 01:07:10 pmQuote from: CM630 on May
14, 2026, 10:16:48 amGetIndexOfLastVisibleMark  returns the mark with
the higher value, not the rightmost/topmost. So when the axis is
inverted, it returns the leftmost value, not the rightmost. The same
with GetIndexOfFirstVisibleMark. I am not sure if this is the intended
behaviour, just to make sure.
Wasn't this your intention in one of the previous posts?

We started from Inverted was not usable with more than one scale, so
we went to using transformations, but GetIndexOfLast(First)VisibleMark
were not working with transformations. At some place there was some
mess and it if was not possible to tell if GetIndexOFirstVisibleMark
is on the left or on the right and if it is linked to the minimum or
the maximum value.
So let's leave things as they are for now and see when the path will
go to...?

Quote from: wp on May 14, 2026, 01:07:10 pmI don't see what you want
to prove with these experiments.
When scale and offset vary, the number of marks varies too (sometimes
there is one mark only). I just wanted to see if something goes wrong
when the number of marks changes.
Personally I will not use anything except linear and log scale.

----------------------------------------------------------------------
CM630 · 2026-05-22 13:10

Maybe some TRY is needed in TATransformations?

----------------------------------------------------------------------
wp · 2026-05-22 15:48

Can you try to provide a small sample project reproding the issue?
Better than hide it by a silent try-except.

----------------------------------------------------------------------
CM630 · 2026-05-30 09:59

I will try do it next week. The entire project is public anyway, but
it is also absolutely messy.

----------------------------------------------------------------------
CM630 · 2026-06-04 10:39

So this is the code that crashes when the app is closed:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, Forms,
Controls, Graphics,
Dialogs,StdCtrls,TAGraph,TATools,TATransformations; type   { TForm1
}   TForm1 = class(TForm)    procedure FormCreate(Sender:TObject); 
private    Chart1 : TChart;    FAxisTransformations : array of
TChartAxisTransformations;    FLinearAxisTransform : array of
TLinearAxisTransform;    FLogarithmAxisTransform : array of
TLogarithmAxisTransform;  public   end; var  Form1:
TForm1; implementation {$R *.lfm} { TForm1 } procedure
TForm1.FormCreate(Sender:TObject);var  i: integer = 0;begin  Chart1 :=
TChart.Create(Self);  Chart1.Parent := Self;  
SetLength(FAxisTransformations,2); //A TAChart has 2 axises when
created.  SetLength(FLogarithmAxisTransform,2); 
SetLength(FLinearAxisTransform,2);   for i := 0 to
high(FAxisTransformations) do  begin    FAxisTransformations[i] :=
TChartAxisTransformations.Create(self);      FLinearAxisTransform[i]
:= TLinearAxisTransform.Create(FAxisTransformations[i]);     
FLinearAxisTransform[i].Enabled := True;    FLogarithmAxisTransform[i]
:= TLogarithmAxisTransform.Create(FAxisTransformations[i]);     
FLogarithmAxisTransform[i].Enabled := False;    
FAxisTransformations[i].List.Add(FLinearAxisTransform[i]);   
FAxisTransformations[i].List.Add(FLogarithmAxisTransform[i]);  end;
 //for i    FLinearAxisTransform[1].Scale := 0.01;end; end.
But this code does not work anyway (FLinearAxisTransform[1].Scale :=
0.01; is not applied).

On the other hand this code seems to works and so far it does not
crash:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormCreate(Sender:TObject);var  i: integer = 0;begin  Chart1 :=
TChart.Create(Self);  Chart1.Parent := Self;  
SetLength(FAxisTransformations,2); //A TAChart has 2 axises when
created.  SetLength(FLogarithmAxisTransform,2); 
SetLength(FLinearAxisTransform,2);   for i:=0 to high
(FAxisTransformations) do  begin    FAxisTransformations[i]     :=
TChartAxisTransformations.Create(Chart1);      FLinearAxisTransform[i]
  := TLinearAxisTransform.Create(FAxisTransformations[i]);     
FLinearAxisTransform[i].Transformations := FAxisTransformations[i];  
  FLinearAxisTransform[i].Enabled := True;      
FLogarithmAxisTransform[i] :=
TLogarithmAxisTransform.Create(FAxisTransformations[i]);     
FLogarithmAxisTransform[i].Transformations :=
FAxisTransformations[i];      FLogarithmAxisTransform[i].Enabled :=
false;       Chart1.AxisList[i].Transformations :=
FAxisTransformations[i];  end;   FLinearAxisTransform[1].Scale :=
0.01;end; 
So maybe there is no issue here.

EDIT:
This code seems to work, but it crashes:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   for i :=
0 to high(FAxisTransformations) do  begin    FAxisTransformations[i]
:= TChartAxisTransformations.Create(self);     
FLinearAxisTransform[i] :=
TLinearAxisTransform.Create(FAxisTransformations[i]);     
FLinearAxisTransform[i].Enabled := True;    FLogarithmAxisTransform[i]
:= TLogarithmAxisTransform.Create(FAxisTransformations[i]);     
FLogarithmAxisTransform[i].Enabled := False;    
FAxisTransformations[i].List.Add(FLinearAxisTransform[i]);   
FAxisTransformations[i].List.Add(FLogarithmAxisTransform[i]);    
Chart1.AxisList[i].Transformations := FAxisTransformations[i];  end;
 //for i

----------------------------------------------------------------------
wp · 2026-06-04 12:51

Yes, adding elements to collections or collection-like classes in
TAChart is not always intuitive. I remember that I once wrote a wiki
about it some years ago: https://wiki.lazarus.freepascal.org/TAChart_R
untime_FAQ#How_to_add_an_axis_transformation?

I think the problem with
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i    
FAxisTransformations[i].List.Add(FLinearAxisTransform[i]); is that it
does not set the Transformations element of the AxisTransform. This is
done in the setter SetTransformations of TChartAxisTransform:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TAxisTransform.SetTransformations(AValue:
TChartAxisTransformations);begin   if FTransformations = AValue then
exit;  if FTransformations  <> nil then   
FTransformations.List.Remove(Self);  FTransformations := AValue;  if
FTransformations <> nil then    FTransformations.List.Add(Self);end; I
really recommend to use the following code for adding elements to the
ChartTransformations:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i    
FLinearAxisTransform[i].Transformations := FAxisTransformations[i];

----------------------------------------------------------------------
CM630 · 2026-06-10 09:00

I am trying to set the extents using transformations.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
SetAxisMinMax(aAxis: TChartAxis; aBottom_Left : Double; aTop_Right:
Double);var  mExtents: TDoubleRect;  debdo : double = 0;begin 
mExtents := TChart(TChartAxis(aAxis).GetChart).LogicalExtent;   if
(aAxis.Alignment = calTop) or (aAxis.Alignment = calBottom) then 
begin //X axis    mExtents.coords[ord(ExtXmin)] :=
min(aBottom_Left,aTop_Right);    mExtents.coords[ord(ExtXmax)] :=
max(aBottom_Left,aTop_Right);  end  else  begin //Y axis   
mExtents.coords[ord(ExtYmin)] := min(aBottom_Left,aTop_Right);   
mExtents.coords[ord(ExtYmax)] := max(aBottom_Left,aTop_Right); {  
 mExtents.coords[ord(ExtYmin)] := aBottom_Left;   
mExtents.coords[ord(ExtYmax)] := aTop_Right;}  end;  
TChart(TChartAxis(aAxis).GetChart).LogicalExtent := mExtents;   if
(aAxis.Transformations = nil) or (aAxis.Transformations.List.Count =
0)    then exit;  if (aBottom_Left > aTop_Right) then  begin    debdo
:= TLinearAxisTransform(aAxis.Transformations.List[0]).Scale;   
TLinearAxisTransform(aAxis.Transformations.List[0]).Scale := -
abs(TLinearAxisTransform(aAxis.Transformations.List[0]).Scale);   
debdo := TLinearAxisTransform(aAxis.Transformations.List[0]).Scale;  
TLinearAxisTransform(aAxis.Transformations.List[0]).Enabled := true; 
end;  TChart(TChartAxis(aAxis).GetChart).Invalidate; 
TChart(TChartAxis(aAxis).GetChart).Update; 
Application.ProcessMessages;end; 
The first time I execute  SetAxisMinMax(Chart1.LeftAxis,-1,-5); on the
Y (left) scale I get Top= -1; Bottom = 1 (the scales are inverted, but
the values are wrong).
The second time I execute the same I get Top= + 1; Bottom = +5.

I am doing something wrong?