The best way to have lineseries with snapping cursors (pointers)?
lazarus / 55-TAChart

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CM630 · 2012-09-19 06:26

Here is the goal:
I want to have one (probably more) series (graphic). I will need let's
say 10 cursors (pointers) on it. According to the needs, these cursors
might need to snap to the graphic, i.e. when I move them (left and
right) their Y value shall be the same as the one of the graphic (they
will snap).
I intend to use the Data Point Drag tool.
First I intended to use separate series for each cursor, but maybe I
will use one series with disabled line, still I have not checked if it
can be detected which exactly point of the curve is dragged.
Here is the major question:
I do not expect such a feature to exist, but since I have already
reimplemented something existing before (horizontal sync) this time I
am asking, if there is some ready solution for snapping cursors?
If there is not such a feature, I intend to use something like:
Code: [Select]ondrag (or on mouseup- it will look worse, but might be
faster) if cursor.snap=true then cursor.Y= graphic.Y
But in order to do that, I need to know which value of graphic is
closer to the X of the cursor. Shall I use getnearestpoint or
something else. I searched the demos, but there is not a single
occurrence of getnearestpoint there.

Any proposal is welcome. I noticed, that Data Point Drag is not moving
very smoothly so speed might be important.

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Ask · 2012-09-19 10:00

I recommend you to create your own descendant of TLineSeries and
override
MovePoint procedure, including "snapping" logic into it.
To find a point to snap to, you should indeed use GetNearestPoint
procedure,
it should also work for function series.
All your pointers can indeed be contained in a single series.

At this moment, I am not sure if this is general enough feature to
merit inclusion in TAChart, however parallel discussion about
functional series and discontinuity pointers makes me this it might
be.

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CM630 · 2012-09-19 11:16

I attached a demo to illustrate exactly what I need. It seems to be
working properly, but is absolutely not optimized.
I couldn't find info how to use GetNearestPoint, I would appreciate
some help with it.
Edit: I just read in the other thread
(http://lazarus.freepascal.org/index.php/topic,18257.0.html), that
@ask mentioned adding a property OnIsSeriesAffected. It would be nice
to know exactly which series was affected (as written in one of the
TODOs).

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Ask · 2012-09-19 14:20

Yes, the demo is a good way to explain what you want.

I recommend:
1) Set Chart1.DoubleBuffered := true
2) Set MarkPositions := lmpPositive for both "cursors"
3) Remove Cursor1DrawPointer, it does nothing (although it actually
exposed a minor bug in TAChart, fixed in r38754)
4) Remove SnapCursor and GetClosestToX procedures
5) Replace ChartToolset1DataPointDragTool1AfterMouseMove with the
following:
Code: [Select]procedure
TForm1.ChartToolset1DataPointDragTool1AfterMouseMove(
  ATool: TChartTool; APoint: TPoint);
var
  p: TNearestPointParams;
  r: TNearestPointResults;
  dt: TDataPointDragTool;
begin
  p.FDistFunc := @PointDist;
  p.FPoint := APoint;
  p.FRadius := 15;
  if Wavedata.GetNearestPoint(p, r) then begin
    dt := ATool as TDataPointDragTool;
    if dt.Series = nil then exit;
    with dt.Series as TLineSeries do begin
      SetXValue(0, r.FValue.X);
      SetYValue(0, r.FValue.Y);
      SetText(0, Format('U=%3.3f V', [r.FValue.Y]));
    end;
  end;
end;
6) Replace the constant "1000" in GenSin function by 100 or lower.
Note that you are currently drawing more then 10 data points per
pixel(!). Which is, of course, slow.
7) If you really want to draw a function (as opposed to some
measurement data, with function only for demonstration purposes), use
TFuncSeries.

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Ask · 2012-09-20 14:04

Since r38765, you can write even simpler code:
Code: [Select]procedure TForm1.ChartToolset1DataPointDragTool1Drag(
  ASender: TDataPointDragTool; var APoint: TPoint);
var
  p: TNearestPointParams;
  r: TNearestPointResults;
begin
  p.FDistFunc := @PointDist;
  p.FPoint := APoint;
  p.FRadius := 15;
  if Wavedata.GetNearestPoint(p, r) then
    APoint := r.FImg;
end;

and set Marks.Format := 'U=%0:3.3f V'

Also, there is no need to set properties of "cursors" at run-time, you
can set them all in the designer.

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CM630 · 2012-09-21 06:49

Quote from: Ask on September 19, 2012, 04:20:05 pmI recommend:
1) Set Chart1.DoubleBuffered := true
I found no documentation about this, but if I get it right, it will
speed up work with the chart?

Quote from: Ask on September 19, 2012, 04:20:05 pm2) Set MarkPositions
:= lmpPositive for both "cursors"
I have already seen this property outside is usually better, when you
have longer duration and respectively more sinusoids in the screen-
the oscillogram will look rather like a black bar.
You can try this in the demo, by changing SinData:=GenSin(10,50,15);
to SinData:=GenSin(10,50,300);

Quote from: Ask on September 19, 2012, 04:20:05 pm5) Replace
ChartToolset1DataPointDragTool1AfterMouseMove with the following:
Here is a question. Usually all the higher speed oscillograms will
have the same distance between the points. For example, if 1 second
contains 10 000 points, I can easily calculate that 0,35 seconds will
correspond to point №0,35.10 000-1=3 499. I might just check one point
on the left and one on the right.
I do not know which method uses GetNearestPoint (probably some numeric
method), but in you opinion, which solution will be faster in this
particular case?

Quote from: Ask on September 19, 2012, 04:20:05 pm6) Replace the
constant "1000" in GenSin function by 100 or lower. Note that you are
currently drawing more then 10 data points per pixel(!). Which is, of
course, slow.
In real cases I will have between 200 and 400 point per period, but
with a much longer duration (say 10 seconds). I hope that this won't
be a big problem.

Quote from: Ask on September 19, 2012, 04:20:05 pm7) If you really
want to draw a function (as opposed to some measurement data, with
function only for demonstration purposes), use TFuncSeries.
I'll search some info about it, if it can generate sinusoids (or
y:=sin(x)) it might be useful.

For now this is not a higher priority for me, and I could not find how
to use it, but at least I found a bug. Here is how it happened. I
added "Function series" to a chart.  I started editing parameters in
the object inspector. While editing it I clicked in the Series editor
„Remove" and I got "Invalid type cast...." error. I tried several
other cases- it occurs, that this message is displayed while editing
"AxisIndexX" and "AxisIndexY", in some other cases (properties) there
is no problem.


Quote from: Ask on September 20, 2012, 04:04:50 pmAlso, there is no
need to set properties of "cursors" at run-time, you can set them all
in the designer.
If you mean colour, crosshair shape, etc. I have several reasons to do
it at run-time:
1. The number of the charts will vary, so they themselves will be
generated.
2. Maybe the number of the cursor will vary.
3. It will be nice to adjust properties during program settings.
Or maybe you mean something else?

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Ask · 2012-09-21 18:03

QuoteQuote from: AskSet Chart1.DoubleBuffered := trueI found no
documentation about this, but if I get it right, it will speed up work
with the chart?
It is not a TAChart-specific feature, but a property of TWinControl.
If set, it will actually slow down chart drawing a little, but reduce
flickering.
Google "double buffering" for more info.

Quote I started editing parameters in the object inspector. While
editing it I clicked in the Series editor „Remove" and I got "Invalid
type cast...." error.Hm, it seems that some incompatible changes were
made to designer code,
and I did not know about them.
Should be fixed in r38792 -- please test.

QuoteIf you mean colour, crosshair shape, etc. I have several reasons
to do it at run-timeSure, these are perfectly good reasons -- I just
mentioned it in case it was accidental decision.

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CM630 · 2012-09-27 08:27

To no surprise, when writing your code I got:
Identifier not found: PointDist;
I suppose I should have a function with the same name, too?

You did not answer my previous question, so I'd ask again, I hope it
is not too hard to answer:
QuoteUsually all the higher speed oscillograms will have the same
distance between the points. For example, if 1 second contains 10 000
points, I can easily calculate that 0,35 seconds will correspond to
point №0,35.10 000-1=3 499. I might just check one point on the left
and one on the right.
I do not know which method uses GetNearestPoint (probably some numeric
method), but in you opinion, which solution will be faster in this
particular case?

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Ask · 2012-09-27 12:24

QuoteIdentifier not found: PointDist;
Add TAGeometry unit to the uses clause.

QuoteI do not know which method uses GetNearestPoint (probably some
numeric method), but in you opinion, which solution will be faster in
this particular case?
GetNearestPoint basically uses a simple loop, because it must work
with an arbitrary distance function. In r38853 I have added some
optimization for the case when the distance function is superlinear of
X coordinate. Note that the source must be sorted to get the full
effect.

However, the extreme optimization you propose (only consider two point
nearest by X) is only correct for the case of PointDistX function,
which ignores Y coordinate entirely. You can easily see the problem on
the example your provided -- with your original code, the pointer
jumped up and down near the steep slopes of the function, while with
GetNearestPoint it snaps to the actual nearest point.

Also, the main source of slowness with extremely large number of
points is probably not the distance calculation, but chart redrawing.
You can test that by adding a crosshair tool, which on Windows does
not require full chart redraw to move. Note that switching
CrossHairTool.DrawingMode between tdmNormal and tdmXor significantly
affects performance in this case.

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CM630 · 2012-09-28 08:26

Quote from: Ask on September 27, 2012, 02:24:37 pmGetNearestPoint
basically uses a simple loop, because it must work with an arbitrary
distance function. In r38853 I have added some optimization for the
case when the distance function is superlinear of X coordinate. Note
that the source must be sorted to get the full effect.I will install
r38853 and check, because with my current version  GetNearestPoint
seems to work even slower than mine simple loop.
I thought that GetNearestPoint uses Newton- Raphson or something
similar.

Quote from: Ask on September 27, 2012, 02:24:37 pmHowever, the extreme
optimization you propose (only consider two point nearest by X) is
only correct for the case of PointDistX function, which ignores Y
coordinate entirely.
Google gave me nothing about PointDistX , but I was thinking, that
really data about the X scale is quite useless, I just need correct
display of the scale. I'll check if I can add only Y values to series
and then maybe I could use the transformation tool.

Quote from: Ask on September 27, 2012, 02:24:37 pmAlso, the main
source of slowness with extremely large number of points is probably
not the distance calculation, but chart redrawing.
Shall I understand, that when I move only the cursors, all other
series are redrawn, including the one with the many points?

Quote from: Ask on September 27, 2012, 02:24:37 pmYou can test that by
adding a crosshair tool, which on Windows does not require full chart
redraw to move. Note that switching CrossHairTool.DrawingMode between
tdmNormal and tdmXor significantly affects performance in this case.
I'll test these, as soon as I get somewhere with some other issues,
that occurred recently.

A question, that is bothering me is if there are 10 000 points on a
200 pixels wide chart- how many points are actually drawn on the
chart? Are they 200 or all the 10 000? If only the 200 are displayed,
won't this increase performance, since the other 9 800 are useless
(until a zoom in)?

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wp · 2012-09-28 10:18

Quotehow many points are actually drawn on the chart? As many as there
are in the ChartSource, so I fear it's the full 10 000.

QuoteIf only the 200 are displayed, won't this increase performance,
since the other 9 800 are useless (until a zoom in)?Certainly. You
could draw only every, say, 10th data point, and the speed increase
will we dramatic. If you plot data from a UserDefined ChartSource, you
could do something like this:

Code: [Select]procedure
TForm1.UserDefinedChartSource1GetChartDataItem(
  ASource:TUserDefinedChartSource; AIndex:Integer; var
AItem:TChartDataItem);
begin
  AIndex := Min(AIndex*10, High(DataArray);
  AItem.X := DataArray[AIndex].x;
  AItem.Y := DataArray[AIndex].y;
end;

and set the UserDefinedChartSource's PointsNumber to Length(DataArray)
div 10.

But you must be aware that very narrow features in your data curve
will be lost or distorted.

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CM630 · 2012-09-28 11:05

Quote from: wp on September 28, 2012, 12:18:52 pmBut you must be aware
that very narrow features in your data curve will be lost or
distorted.
I was thinking about this solution, but this way when I will have to
resend the draw data when zooming. If would be much nicer, if TChard
did this automatically (if this could improve performance, of course).
Also, the idea is that the Chart should know, that the point exists,
even if it is not displayed, so I could find it, when I search it.

Yet I have another question. Here is an event for the point drag tool:
Quoteprocedure TForm1.ChartToolset1DataPointDragTool1Drag(ASender:
TDataPointDragTool; var APoint: TPoint); So I have ASender:
TDataPointDragTool and var APoint: TPoint.
How am I to detect which is the series, to which the dragged point
belongs and what is it's index in the series?
In fact, the Toolset is used for several charts, but I detect the
chart from MouseDown.


Yet, another issue arise, which seems more important to me.
I have a Chart, the chart has let's say 5 line series.
But when I try to adress them as Chart.Series[0] they are addressed as
TBasicChartSeries, so I cannot do Chart.Series[0].GetXValue(0). Is
there a way out?

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wp · 2012-09-28 11:49

QuoteHow am I to detect which is the series, to which the dragged
point belongs and what is it's index in the series?The datapoint drag
tool has properties "Series" and "PointIndex". There is no need for a
separate treatment of MouseDown by you because all that is handled by
the tool.

BTW: in your source code, hold the CTRL key down while clicking on any
identifier. Lazarus will open the unit where this identifier is
implemented and jump to its definition. In this way you will be guided
to the corresponding source units where you can see all properties of
the class.

QuoteI have a Chart, the chart has let's say 5 line series.
But when I try to adress them as Chart.Series[0] they are addressed as
TBasicChartSeries, so I cannot do Chart.Series[0].GetXValue(0). Is
there a way out?Type-cast the series to TChartSeries -- this is the
common ancestor of all series types that provide GetXValue, i.e. do
Code: [Select]TChartSeries(Chart.Series[0]).GetXValue(0)

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CM630 · 2012-09-28 12:15

Just a remark, before I go on making out rthe other stuff: you
probably did not mean TChartSeries(Chart.Series[0]).GetXValue(0), but 
TLineSeries(Chart.Series[0]).GetXValue(0)

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wp · 2012-09-28 12:22

No - TLineSeries inherits from TChartSeries, i.e. all published and
public properties of TChartSeries are also available for TLineSeries.
Using TChartSeries is  more general than using TLineSeries. If you
once would decide to use a TAreaSeries (which inherits from
TChartSeries as well) instead of a TLineSeries the expression with the
TChartSeries would still compile while that with TLineSeries won't.

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CM630 · 2012-09-28 12:56

Hm, my Lazarus does not know TChartSeries, it only knows
TChartSeriesList.
On the other hand, TlineSeries seems to work fine (so far)...

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wp · 2012-09-28 13:09

QuoteHm, my Lazarus does not know TChartSeries
Lazarus definitely knows, just add
Code: [Select]uses
  TACustomSeries;

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Ask · 2012-09-28 17:08

Quote from: paskalI thought that GetNearestPoint uses Newton- Raphson
or something similar.
I do not see how Newton-Raphson method is applicable to the nearest-
point problem
(except perhaps for a quite specific case of monotonic function
series).

Quote from: wpCertainly. You could draw only every, say, 10th data
point, and the speed increase will we dramatic.Quote from: paskalI was
thinking about this solution, but this way when I will have to resend
the draw data when zooming. If would be much nicer, if TChart did this
automatically (if this could improve performance, of course). Also,
the idea is that the Chart should know, that the point exists, even if
it is not displayed, so I could find it, when I search it.First, note
that you do not have to write extra code to resend data on redraw,
chart series request their sources for data as needed.

I did consider automatic adjustment of series details depending in the
scale, but there are some issues to be solved:
1) While working on "fast line" series optimization, I have already
tried to eliminate sequential points with the same X coordinate during
the drawing. It turned out to decrease speed, at least on Windows,
presumably because system code performs similar optimization while
drawing polylines, and is more efficient than is possible to achieve
in Pascal. At the same time, axis and graph transformation still
needed to be performed for every point.

2) So, I see two viable ways:
2.1) Pre-select points without actually accessing them all
(essentially what wp suggested). To do this in general case, we need:
2.1.1) a method of of density estimation (simply selecting with a
fixed step might fail for non-uniformly distributed series)
2.1.2) as wp already noted, a method of local extent estimation (so as
not to lose local peaks)
2.1.3) either a method to change source values based on the current
extent, which is contrary to the current source/series architecture,
or a decision to implement this for each series separately.
If we are willing to ignore all the above issues, the it is quite
simple to add TSparseChartSource with Origin and IndexStep properties.
However, as we have seen, the same effect can already be easily
achieved with user-defined source. So, in order to have a feature
worth building, we need to answer the above questions.

2.2) Caching. This is a big topic -- caching may be performed on
various levels -- source points, source totals and extents, graph-
converted points, image-converted points, raster images, etc. Each of
these levels might bring benefits for speed of certain operations.
However, they come with the price of substantial code complexity.
Some basic caching is already implemented in various sources and
series (see, for example, TListSource.Extent and corresponding code in
SetXValue/SetYValue to update it efficiently).
Nevertheless, I do plan to add more caches in the future.
Currently, the main obstacle for this is a too simplistic notification
system used in TAChart. I hoped to improve it based on Observer
pattern support which was recently added to FPC, but the follow-up
discussion seems to indicate that it may be insufficient for my
goals...

3) There is another solution, which, while not "automatic", may be
appropriate for your case:
3.1) Create several sources with your data averaged over different
windows.
3.2) Create a separate line series for each source
3.3) Display only one of series depending on the current scale
3.4) [Optionally] search only the full-data series to the drag tool
Besides the optimization, this solution will also look much better for
the small zoom levels. The downside is that it requires some coding at
the application level. If you like it, I shall see how I can make it
easier from the TAChart side.

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CM630 · 2012-09-29 05:55

I'll think about your ideas on a later stage.
Meanwhile I found something, that I'm maybe right, maybe- not.
If I use LineSeries.SetYValue(0,5); in an OnDrag event, SetYValue
won't work- the point will stay on the position of the mouse pointer.
Meanwhile LineSeries.GetYValue returns the previously set result, i.e.
5.
I have attached a lightly modified version of the previous tool.
If the point of the series does not move during SetYvalues, then
GetYValue shall return the actual value of the point.
And if the Y value should be programically  changed while dragging-
this is question of view point- which one should have higher priority-
user (mouse) or program. Maybe the best decisions (as always) is to
have this property adjustable?

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Ask · 2012-09-29 06:36

OnDrag event has AGraphPoint parameter which you should change to
modify the position of the dragged point.

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CM630 · 2012-09-29 07:56

I found no AGraphPoint parameter, I only found APoint, so I started
examining your code again, and I just understood what you meant by
that:

Quote from: Ask on September 27, 2012, 02:24:37 pmYou can easily see
the problem on the example your provided -- with your original code,
the pointer jumped up and down near the steep slopes of the function,
while with GetNearestPoint it snaps to the actual nearest point.My
code works exactly as I want-  the point moves on the curve, ignoring
the Y value of the drag (mouse) pointer. Your code searches a point in
the vicinity, having the same Y as the mouse pointer, but I do not
want that (though I might use it, i.e. for snapping on the zero
values).

As far as AGraphPoint is it the same as APoint?

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Ask · 2012-09-29 10:37

QuoteAs far as AGraphPoint is it the same as APoint?Not quite. I have
changed the definition of OnDrag event slightly since my previous
post. It now accepts a point in graph, rather then image, coordinates.

Quotethe point moves on the curve, ignoring the Y value of the drag
(mouse) pointerUse PointDistX instead of PointDist function.

The handler should now read:

Code: [Select]procedure TForm1.ChartToolset1DataPointDragTool1Drag(
  ASender: TDataPointDragTool; var AGraphPoint: TDoublePoint);
var
  p: TNearestPointParams;
  r: TNearestPointResults;
begin
  p.FDistFunc := @PointDistX;
  p.FOptimizeX := true;
  p.FPoint := Chart1.GraphToImage(AGraphPoint);
  p.FRadius := 15;
  if Wavedata.GetNearestPoint(p, r) then
    AGraphPoint := Chart1.ImageToGraph(r.FImg);
end;

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CM630 · 2012-09-29 12:13

Error: identifier idents no member "FOptimizeX"
I need later Lazarus (I'm currently with the latests available
snapshot) or Uses something?
I have no idea what "FOptimizeX"does, so I removed it, but without it
sometimes the cursor is not located on the sine curve, but at some
distance away from it.
BTW, can I remove the crosshair (the four arrows)?

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Ask · 2012-09-29 14:39

QuoteError: identifier idents no member "FOptimizeX"
I need later Lazarus (I'm currently with the latests available
snapshot) or Uses something?Yes, update your Lazarus. Make sure you
are using trunk, not fixes branch.

Quotethe cursor is not located on the sine curve, but at some distance
away from it.Can't reproduce. Does it happen for you in the demo
project you posted?

Quotecan I remove the crosshair (the four arrows)?You mean how to
change cursor shape? Set ActiveCursor property.

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CM630 · 2012-10-02 05:49

There are still no later win32 builds for Lazarus.
If FOptimizeX is not related, I have attached the source and some
snapshots to show the problem, that @ask cannot reproduce.

ActiveCursor:=0 is exactly what I need, thanks!

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Ask · 2012-10-02 06:35

QuoteI have attached the source and some snapshots to show the
problem,That's very helpful, thanks. The key point you did to mention
in the previous reports is the fact that the "inexact" snapping is
visible only after zooming in.

This is caused simply by rounding error -- if you look at the code,
you may notice that that it performs conversion from graph to image
coordinates.
You can replace the last line of handler with
Code: [Select]    AGraphPoint := Wavedata.AxisToGraph(r.FValue);

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CM630 · 2012-10-04 06:12

Now it looks fine, besides cursors move very smoothly.

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CM630 · 2012-10-12 08:58

I think that it won't be bad if I remind something, because IMHo the
issue still is open:

I wrote:
Quote from: paskal on September 29, 2012, 07:55:37 amIf I use
LineSeries.SetYValue(0,5); in an OnDrag event, SetYValue won't work-
the point will stay on the position of the mouse pointer.
Meanwhile LineSeries.GetYValue returns the previously set result, i.e.
5.

And I got this answer:
Quote from: Ask on September 29, 2012, 08:36:19 amOnDrag event has
AGraphPoint parameter which you should change to modify the position
of the dragged point.
Anyway, if SetYValue does not change the Y values, the result given by
LineSeries.GetYValue shall not change, too? Is this a bug or there is
some purpose?

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Ask · 2012-10-12 09:42

Point coordinates are changed by the drag tool immediately after a
call to the OnDrag event. Perhaps AGraphPoint parameter should be
renamed to ANewGraphPoint for clarity?

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CM630 · 2012-10-12 10:24

It seems that we cannot understand each other, so I try again.
So when I do LineSeries.SetYValue(0,5); the point is not moved to Y=5.
I suppose that the reason for that is the fact that after that the
point from dragging is taken (i.e. after running
LineSeries.SetYValue(0,5); the point gets moved by the mouse to let's
say Y=4. Whatever the reason is, after all is done, when I run
LineSeries.GetYValue the result should be 4, but it is 5 instead.
I could try to find an app to take a video, if necessary?

P.S. Currently I do not use LineSeries.SetYValue(0,5);, I use
aGraphPoint, but I think that the issue remained open.

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Ask · 2012-10-12 12:43

I do understand you. You are trying to call SetYValue from the inside
of OnDrag event handler. It does work (if you call GetYValue
immediately, you will see the effect).
However, just after return from the handler, point position is moved
to the value determined by AGraphPoint.

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CM630 · 2012-10-12 13:03

So right after return from the handler, point position is moved to the
value determined by AGraphPoint and this is okay.
But shouldn't GetYValue return the value, set by AGraphPoint?
I'll check again on Monday, if it really behaves so, maybe I got
confused by the synchronization.

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Ask · 2012-10-12 13:43

Quoteshouldn't GetYValue return the value, set by AGraphPoint?Yes, it
should, but (1) you should check it after the handler, not inside of
it and (2) if you active have axis transformations, they will of
course affect the Y value.

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CM630 · 2012-10-15 06:23

So here it is:

Code: [Select]procedure TForm1.ChartToolset1DataPointDragTool1Drag(
ASender: TDataPointDragTool; var AGraphPoint: TDoublePoint);
var
  p: TNearestPointParams;
  r: TNearestPointResults;
begin
  p.FDistFunc := @PointDistX;
  p.FOptimizeX := true;
  p.FPoint := Chart1.GraphToImage(AGraphPoint);
  p.FRadius := 15;
  Cursor1.SetYValue(0,7);
  if Wavedata.GetNearestPoint(p, r) then AGraphPoint :=
Wavedata.AxisToGraph(r.FValue);
  Cursor1.SetText(0,'U='+
FloatToStrF(Cursor1.GetYValue(0),ffFixed,3,3) + ' V') ; //Comment this
line, if you are using Lazarus build less than  38732.
  Label2.Caption:= FloatToStrf(Cursor1.GetYValue(0),ffFixed,3,3) + ' 
  ' + FloatToStrf(Cursor2.GetYValue(0),ffFixed,3,3);
end;
If the code is run this way, both label2.caption and the cursor
caption show „7“.
But if I do Cursor1.GetYValue(0) in a procedure run after procedure
TForm1.ChartToolset1DataPointDragTool1Drag( ASender:
TDataPointDragTool; var AGraphPoint: TDoublePoint); then I get the
exact Y value.
If I get you right, the idea is that the behaviour shall be exactly
this?
Couldn't and shouldn't running AGraphPoint :=
Wavedata.AxisToGraph(r.FValue); change the result of GetYValue
immediately, instead of waiting the whole procedure to finish? Or
probably the concept is that with the current implementation the
designer will know both the values in the beginning and during the
execution process (current value) of the procedure. It is sure, that
breaking compatibility with Delphi is unwanted.

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Ask · 2012-10-15 07:08

QuoteIf I get you right, the idea is that the behaviour shall be
exactly this?Yes.

QuoteCouldn't and shouldn't running AGraphPoint :=
Wavedata.AxisToGraph(r.FValue); change the result of GetYValue
immediately, instead of waiting the whole procedure to finish?That is
a simple variable assignment, it can not immediately change value of
another variable.
Also, note the point I made in the previous post about axis
transformation -- AGraphPoint is in graph coordinates, but GetYValue
returns axis coordinates.