Can I get the position and size of an axis title?

[CM630]

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

Code: Pascal  [Select][+][-]

1. ...
2. procedure TForm1.Button1Click(Sender:TObject);
3. begin
4.   ChartAxisTransformations1LinearAxisTransform1.Scale := 1; //Returns 1, as it should
5.   Chart1.Invalidate;
6.   Application.ProcessMessages;
7.   ShowMessage (IntToStr(  Chart1.BottomAxis.GetIndexOfFirstVisibleMark));
8. end;
9.  
10. procedure TForm1.Button2Click(Sender:TObject);
11. begin
12.   ChartAxisTransformations1LinearAxisTransform1.Scale := 0.1;
13.   Chart1.Invalidate;
14.   Application.ProcessMessages ;
15.   ShowMessage (IntToStr(Chart1.BottomAxis.GetIndexOfFirstVisibleMark)); //Returns 6 instead of 1
16. end;
17.  
18. ...
19.  
20.  

[CM630]

Some changes in TAChartAxis seem to make things better:

Code: Pascal  [Select][+][-]

1. function TChartAxis.GetIndexOfFirstVisibleMark(aOffset: double = 0; aScale: double=1): Integer;
2. var
3.   coord: Integer;
4. begin
5.   for Result := 0 to High(FMarkValues) do begin
6.     coord := FHelper.GraphToImage(FMarkValues[Result].FValue*aScale + aOffset);
7.     if FHelper.IsInClipRange(coord) then
8.       exit;
9.   end;
10.   Result := -1;
11. end;
12.  
13. function TChartAxis.GetIndexOfLastVisibleMark(aOffset: double = 0; aScale: double=1): Integer;
14. var
15.   coord: Integer;
16. begin
17.   for Result := High(FMarkValues) downto 0 do begin
18.     coord := FHelper.GraphToImage(FMarkValues[Result].FValue*aScale + aOffset);
19.     if FHelper.IsInClipRange(coord) then
20.       exit;
21.   end;
22.   Result := -1;
23. end;    

Usage:

Code: Pascal  [Select][+][-]

1.   ShowMessage (IntToStr(Chart1.BottomAxis.GetIndexOfFirstVisibleMark(ChartAxisTransformations1LinearAxisTransform1.Offset,ChartAxisTransformations1LinearAxisTransform1.Scale)));

[CM630]

This should be even better:

Code: Pascal  [Select][+][-]

1. function TChartAxis.GetIndexOfFirstVisibleMark: Integer;
2. var
3.   coord: Integer;
4.   mScale : double = 1;
5.   mOffset : double = 0;
6.   i: integer = 0;
7. begin
8.   if (FTransformations <> Nil) and (FTransformations.List.Count >0)  then
9.   begin
10.     for i:=0 to FTransformations.List.Count - 1 do
11.       if ((TObject(Transformations.List.Items[i]) is TLinearAxisTransform)) and (TLinearAxisTransform(Transformations.List.Items[i]).Enabled = True) then
12.       begin
13.         mScale := mScale * TLinearAxisTransform(Transformations.List.Items[i]).Scale;
14.         mOffset := mOffset * TLinearAxisTransform(Transformations.List.Items[i]).Scale + TLinearAxisTransform(Transformations.List.Items[i]).Offset;
15.       end;
16.   end;
17.  
18.   for Result := 0 to High(FMarkValues) do begin
19.     coord := FHelper.GraphToImage(FMarkValues[Result].FValue*mScale + mOffset);
20.     if FHelper.IsInClipRange(coord) then
21.       exit;
22.   end;
23.   Result := -1;
24. end;
25.  
26. function TChartAxis.GetIndexOfLastVisibleMark: Integer;
27. var
28.   coord: Integer;
29.   mScale : double = 1;
30.   mOffset : double = 0;
31.   i: integer = 0;
32. begin
33.   if (FTransformations <> Nil) and (FTransformations.List.Count >0)  then
34.   begin
35.     for i:=0 to FTransformations.List.Count - 1 do
36.       if ((TObject(Transformations.List.Items[i]) is TLinearAxisTransform)) and (TLinearAxisTransform(Transformations.List.Items[i]).Enabled = True) then
37.       begin
38.         mScale := mScale * TLinearAxisTransform(Transformations.List.Items[i]).Scale;
39.         mOffset := mOffset * TLinearAxisTransform(Transformations.List.Items[i]).Scale + TLinearAxisTransform(Transformations.List.Items[i]).Offset;
40.       end;
41.   end;
42.  
43.   for Result := High(FMarkValues) downto 0 do begin
44.     coord := FHelper.GraphToImage(FMarkValues[Result].FValue * mScale + mOffset);
45.     if FHelper.IsInClipRange(coord) then
46.       exit;
47.   end;
48.   Result := -1;
49. end;  

[wp]

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).