Problems with extent Ymax < Ymin
lazarus / 55-TAChart

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CM630 · 2012-10-25 07:25

Here are some cases:
If Chart1.extent.Ymax= -5 and Chart1.extent.Ymin= 5 (UseYmax and
UseYmin are true) and exception is generated, but I see no reason for
that.

Here is the other case- if logicalextent [2]:= +5 and logicalextent
[4]:=-5 instead of displaying the curve upside down, it is not
displayed at all.

I have not tested what will happen with Xmax and Ymax.

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wp · 2012-10-25 07:58

The max must always be greater than the min. Use the property
"Inverted" of the axis if you want to have min and max interchanged.

@Ask: When working with the extent of a chart I sometimes get the same
message reported here by Paskal. I am not quite sure, when it happens.
But I am thinking of a situation that I change the extent when it is
already set. Suppose the extent is set to go from 5 to 10. Now I want
to change it to a range from -10 to -5. Since I can only set the
limits one at a time I have to decide which one to change first -- in
this example it would be the Minimum; if I'd start with altering the
Max I'd get that error. If, on the other hand, the range would be from
-10 to -5 at first and I want to change to 5 to 10 I have to set the
maximum first to avoid the error. The situation gets even more complex
if one of the limits is not "used".

In essence, there is always a large number of cases to check when
using the Extent feature. I think it would be better to have an
additional fail-safe procedure like Delphi's SetMaxMin which find out
the right oder by itself or temporarily ignors such errors.

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Ask · 2012-10-25 11:47

At run-time, you can call TChartExtent.FixTo procedure to
simultaneously set and turn on all four limits.
I can add more helpers based on well-founded suggestions

The design-time error is another case -- it is ignorable (i.e. you can
click "OK" without a risk for destabilizing IDE), and is intended to
warn user about a possible mistake.
It can certainly be annoying in the cases you outlined, although it is
IMHO rather minor annoyance.

I see several solutions:
1) Add Warnings property which will collect non-fatal errors in chart
parameters
(other examples are non-compatible axises in the same axis group,
non-default pen parameters for invisible pens etc...)
The problem with this solution is that IDE currently lacks a mechanism
to display such warnings in a convenient fashion.
2) Add specialized property editor for TChartExtent.
Incidentally, it is a first item on the current roadmap,
although of course the position there does not indicate priority.
The only obstacle here is a lack of time.

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CM630 · 2012-10-25 13:13

Why not simply remove this limitation:
Quote from: wp on October 25, 2012, 09:58:34 amThe max must always be
greater than the min.If the reason for having it is Delphi
compatibility, there might be a settable workaround (i.e. Delphi mode
or Lazarus mode).
If the reason is that such behaviour is hard to implement, then it is
another issue.
Now we get exceptions if Ymax<Imin, but we get no exception if 
logicalextent [4] < logicalextent [2]. First the curve is not
displayed without a warning, exception or warning, and second- this is
somehow inconsistent.

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wp · 2012-10-25 14:07

Quotecall TChartExtent.FixTo procedure to simultaneously set and turn
on all four limits
That's exactly what I wanted, thanks for the hint. I don't care about
the designtime error because I know where it comes from.

QuoteWhy not simply remove this limitationI'd vote against that - it
will create an never-ending series of issues because it is one of the
most fundamental decisions which cannot be reverted easily.

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Ask · 2012-10-25 14:37

QuoteWhy not simply remove this limitationI agree with wp -- there are
quite a few places which assume correct orientation of logical extent.
It is would be easy to normalize passed rectangle (i.e. auto-sort
limits),
but since mis-ordered limits might be an indication of user error, I
prefer to fail early.

QuoteNow we get exceptions if Ymax<Imin, but we get no exception if 
logicalextent [4] < logicalextent [2]. First the curve is not
displayed without a warning, exception or warning, and second- this is
somehow inconsistent.
The reason is that YMax/YMin is settable at design-time, while
LogicalExtent is not.
I do agree that some inconsistency is present, see my previous post
for suggestions to improve the situation. What is your opinion on
them?

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CM630 · 2012-10-26 06:32

Still I am not sure that I understand what the Extent property
actually does, while CurrentExtent and LogicalExtent are clear.
Wiki says only: Fixed extent -- determined by TChart.Extent property.
May override full extent calculation partially or fully.

What I am trying to do is:
When I click on the upper or the lower displayed value in a chart to
have a text box exactly on the text value a text box to appear over
the value. When I write the value, the LogicalExtent shall change to
the given value (the same shall be done for the X axes, too).
Here are some of the issues to be solved:
1. I shall forbid the chart to autosize. Probably I shall
   Code: [Select]  Chart1.LeftAxis.LogicalExtent [4]:= NewYmax; //This
line won't work directly, it is just for example
  Chart1.Extent.Ymax:= NewYmax; //Probably I shall use this to prevent
auto scale, when I drag or zoom only horizontally ???
  Chart1.Extent.UseYmax:= True;
    Regarding this clause, I got to the point with the Ymax < Ymin
issue, so I posted here.
  In fact, there is a problem, that sometimes when I use
Chart1.LeftAxis.LogicalExtent [4]:= NewYmax; the absolute value that
is really used is higher.
  I have not yet found the exact reason for that behaviour, but here
is the case:
      When I have one LineSeries on the chart everything is fine.
      If I have more then one LineSeries (currently I use cursors as
separate line series, each
      lineseries containing one point only, though I intent to switch
to one series, with several
      points). The indexes of the cursors are before the index of the
actual curve.
      So when I have a cursor if the value of the cursor is positive,
when I do
      Chart1.LeftAxis.LogicalExtent [4]:= 5000; the actually displayed
axis value is higher,
      i.e. 6231,2576546.
      In the same time there is not problem with
Chart1.LeftAxis.LogicalExtent [2]:= -5000;
      but if the cursor has a negative value, then I star having the
same problem with
      LogicalExtent [2]. So far I cannot post the code, but maybe this
sounds you familiar.
      I have to mention that I have set all margins to 0;
2. I have no idea where the upper and the lower values are located on
the screen.
3. I have to handle the cases when Ymax < Ymin. Probably that is the
time, where I could have some more questions or proposals.

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wp · 2012-10-26 07:25

QuoteI am not sure that I understand what the Extent property actually
doIt freezes the axis range. If fixed the axis minimum and maximum are
no longer updated when the data range changes, i.e. it
prevents/enables autoscaling. I think that is exactly what you want to
achieve: If you enter a number in the upper edit box set
chart.Extent.YMax to that value und set UseYMax to true. I think most
of your problems come from the "illegal" use of LogicalExtent.

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CM630 · 2012-10-26 07:31

What do you mean by „illegal use of LogicalExtent“?
LogicalExtent.Ymax < LogicalExtent.Ymin is something that I tried on a
later stage, the problem with actual LogicalExtent and the given one
occurred earlier.
If you mean something else, this could lead me to a solution.

Maybe in half an hour I can test some things, including „which one has
higher priority- .Extent of .LogicalExtent“ but I think that it would
be better if this information is given in the wiki.

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wp · 2012-10-26 08:13

Sorry, "illegal" is certainly not the correct word. But my strategy
has always been:
- Use Chart.Extent to force certain axis limits
- Use the zoom/pan tools to modify the LogicalExtent; I never change
the LogicalExtent by code.

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CM630 · 2012-10-26 08:16

I tried to find out which one has a higher priority. Well, still I
have no answer. Here is the code:

Code: [Select]procedure TForm1.Button1Click(Sender: TObject);
  var
    LogicalExtent: TDoubleRect;
  begin
    Chart1.Extent.yMax:= 10000;
    Chart1.Extent.yMin:= -10000;
    chart1.Extent.UseyMax:= True;
    chart1.Extent.UseyMin:= True;

    LogicalExtent.coords[1]:= Chart1.LogicalExtent.coords [1];
    LogicalExtent.coords[3]:= Chart1.LogicalExtent.coords [3];
    LogicalExtent.coords[2]:= -12000;
    LogicalExtent.coords[4]:= 12000;
    Chart1.LogicalExtent:= LogicalExtent;
end; 
Here is what happens:
When I press the button the Y extents are -12000 to +12000.
When I press it once again they become -10000 to +10000.
When I go on pressing the button these extents keep changing.
I think uploading the project is not necessary?

Quote- Use the zoom/pan tools to modify the LogicalExtent; I never
change the LogicalExtent by code.You mean that using the zoom/pan tool
I can set Ymax/min and Xmax/min by supplying a numeric value to them,
not only by mouse actions, etc?
I have only ZoomByDrag, ZoomByClick and ZoomByMouseWheel.
Maybe you do not get my idea- I want when I click on the clickarea (as
displayed on the screenshot) a text field to appear, and when I write
3450 the LogicalExtent to become 3450.

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wp · 2012-10-26 08:41

QuoteYou mean that using the zoom/pan tool I can set Ymax/min and
Xmax/min by supplying a numeric value to them, not only by mouse
actions, etc?No, I use the tools for mouse actions etc.

QuoteI want when I click on the clickarea (as displayed on the
screenshot) a text field to appear, and when I write 3450 the
LogicalExtent to become 3450.I do understand that, but why do you want
to edit the LogicalExtent, not the "normal" Extent which is designed
for overriding the axis limits? Maybe the LogicalExtent should be a
readonly property -- it is not, but as I said I never write into the
LogicalExtent because I don't know about the sideeffects.

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CM630 · 2012-10-26 08:57

Wiki says:
LogicalExtent -- the extent requested by user to be seen on chart
image. Writing to this property if the official way to change chart
extent by the external code.

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Ask · 2012-10-26 09:06

Quote from: paskalwhich one has a higher priorityAs written in the
documentation,
Extent property modifies the fixed extent, i.e. the value
which will be written to LogicalExtent when you call ZoomFull
procedure or
reset the extent with the zoom tool.
It does not in itself limit the values which may be assigned to the
LogicalExtent,
but merely sets the default.

There are various ways to limit LogicalExtent -- Chart.ExtentSizeLimit
property, TBasicPanTool.LimitToExtent property, etc.
These ways may be extended, for example by recently suggested
ZoomTool.LimitToExtent property.

Quote from: paskalWhen I go on pressing the button these extents keep
changing.This is actually a bug.
Unfortunately, it is caused by a workaround for another bug,
and so is not easy to fix without causing another regression.
I'll think about it.
Fortunately, it is easy to work around -- either do not set chart
extent and logical extent in the same handler, or write
Code: [Select]  ChartColorMap.LogicalExtent:= EmptyExtent;
  ChartColorMap.LogicalExtent:= LogicalExtent;

Quote from: wp I never write into the LogicalExtent because I don't
know about the sideeffectsYou should -- as said in the docs linked
above, writing to LogicalExtent is an "official" method to change
viewport from the code.
Any unwanted side effects will be considered bugs, as the one above.

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Ask · 2012-10-26 10:43

More answers to earlier questions:

QuoteWhen I click on the upper or the lower displayed value in a chart
to have a text box exactly on the text value a text box to appear over
the value.As discussed in corresponding topics, the ideal way to
implement this is to add specialized axis tools. While I did not do
that yet, I have already added some helpers which should make custom
solutions easier.

QuoteI shall forbid the chart to autosize.This is exactly what setting
Extent does. Note that auto-sizing is triggered by ZoomFull procedure,
while assigning to LogicalExtent is considered "manual" sizing and
thus not subject to Extent property.

Quotewhen I use Chart1.LeftAxis.LogicalExtent [4]:= NewYmax; the
absolute value that is really used is higher.This is the difference
between logical and current extent. Current extent includes various
margins, in your case it is probably margins reserved for mark labels.
You can try to avoid them by setting Marks.Visible = false for all
series and
MarginsForMarks = false for all axises.

QuoteI have no idea where the upper and the lower values are located
on the screen.Use GraphToImage (and AxisToGraph, if you use
transformations) to find out.

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wp · 2012-10-26 11:15

QuoteQuoteI never write into the LogicalExtent because I don't know
about the sideeffectsYou should

You are right - I also use it in the extent history. Where was my head
when writing that?

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CM630 · 2012-10-29 08:41

Quote from: Ask on October 26, 2012, 12:43:37 pmQuoteWhen I click on
the upper or the lower displayed value in a chart to have a text box
exactly on the text value a text box to appear over the value.As
discussed in corresponding topics, the ideal way to implement this is
to add specialized axis tools. While I did not do that yet, I have
already added some helpers which should make custom solutions easier.
If you are working on this, there is a functionality, that I've seen-
if on the positive side of the Y axis you have -1000; -500; 0; 500;
1000 and you click on 500 and set the value to 1000, then then values
would become -2000; -1000; 0; 500; 1000.
I would never use this functionality, but obviously someone found
something interesting in it.

Quote from: Ask on October 26, 2012, 12:43:37 pmQuotewhen I use
Chart1.LeftAxis.LogicalExtent [4]:= NewYmax; the absolute value that
is really used is higher.This is the difference between logical and
current extent. Current extent includes various margins, in your case
it is probably margins reserved for mark labels.
You can try to avoid them by setting Marks.Visible = false for all
series and
MarginsForMarks = false for all axises.
I tried Chart1.LeftAxis.Marks.Visible:= False and
Chart1.LeftAxis.Marks.Visible:= False with no success.
Anyway, I am convinced that this is not the case. As I said, if I have
no cursor everything works okay. Besides, when I write 5000, I get
6015,453. This is more than 20% difference, IMHO it cannot be
explained by marks, etc.
Besides, to make sure- I put showmessage (...logicalextent.coords[4] +
'   ' + currentextent.coords[4] ) and both values are the same.
I will keep on trying to find out what (or where) exactly causes this
behaviour. I still do not want to show the source, since we will get
the position of someone debugging my code, which is not quite right.

Quote from: Ask on October 26, 2012, 12:43:37 pmQuoteI have no idea
where the upper and the lower values are located on the screen.Use
GraphToImage (and AxisToGraph, if you use transformations) to find
out.
I do not use transformations.
I did not find info about GraphToImage but from the examples I got the
idea that it gives the position of the mouse over the Chart?
What I need to know is where are written the topmost and lowermost
values of the Y or X scales (shown as "Click area" on the
screeenshot). I already did the event handling by mousedown.

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Ask · 2012-10-29 09:19

Quotethere is a functionality, that I've seenYou mean there is some
application or library which works like that? What is it?

Quote from: AskYou can try to avoid them by setting Marks.Visible =
false for all seriesQuote from: paskalI tried
Chart1.LeftAxis.Marks.Visible:= False and
Chart1.LeftAxis.Marks.Visible:= False with no success.Note that I
recommended to turn off series marks, not axis marks.

QuoteI did not find info about GraphToImage but from the examples I
got the idea that it gives the position of the mouse over the
Chart?No, it is a function that converts graph coordinates to image
coordinates.

QuoteWhat I need to know is where are written the topmost and
lowermost values of the Y or X scalesUse GraphToImage functions to
convert axis values to screen coordinates.
For example, YGraphToImage(1000) would return Y position of a "1000"
mark.

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CM630 · 2012-10-29 09:47

Quote from: Ask on October 29, 2012, 10:19:44 amQuotethere is a
functionality, that I've seenYou mean there is some application or
library which works like that? What is it?
It is a propitiatory software for handling oscillograms. If you are
interested to know- PM.

Quote from: Ask on October 29, 2012, 10:19:44 amQuote from: AskYou can
try to avoid them by setting Marks.Visible = false for all seriesQuote
from: paskalI tried Chart1.LeftAxis.Marks.Visible:= False and
Chart1.LeftAxis.Marks.Visible:= False with no success.Note that I
recommended to turn off series marks, not axis marks.
Well, I did. Indeed, now what I write is what I get! But I need the
series marks, how am I to get out of this situation? I cannot write
CurrentExtents. I tried extensions only but with the same result. And
absolutely cannot understand what the series.marks (and series at all)
have to do with the extents. Relation with axis margins is clear, but
that... If there is some explanation, I would like to read it.
Perhaps, I should set series marks.visible:= False, to change the
extents and to set them back to visible again?

Quote from: Ask on October 29, 2012, 10:19:44 amQuoteI did not find
info about GraphToImage but from the examples I got the idea that it
gives the position of the mouse over the Chart?No, it is a function
that converts graph coordinates to image coordinates.

QuoteWhat I need to know is where are written the topmost and
lowermost values of the Y or X scalesUse GraphToImage functions to
convert axis values to screen coordinates.
For example, YGraphToImage(1000) would return Y position of a "1000"
mark.

I do not know what graph and image coordinates are, probably I should
read somewhere.
So if I get you right I have to find out how many marks I have, or at
least which are the topmost and lowermost.
If order to do that, there shall be some array with the marks, which I
could use to get these values.
I sought LeftAxis.Marks but I found no such property there.
Yet this is not all- marks themselves are the short lines, but they
may or may not have  labels (right?). So in this case I need the
topmost and lowermost markers which have labels.

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Ask · 2012-10-29 11:23

Quotecannot understand what the series.marks (and series at all) have
to do with the extentsMargins are reserved to guarantee that all marks
labels fit into the viewport.
As for series themselves -- they are a primary source of chart full
extent,
which is, by definition, an extent designed to cover all series data.

QuotePerhaps, I should set series marks.visible:= False, to change the
extents and to set them back to visible again?No, this will not help,
as the chart extent will be recalculated automatically.
The solution is to improve control over series margins.
I can see several independent options:
1) Add Chart.CombineMargins property with values of (cmMax, cmMin,
cmSum, cmNone), which would control algorithm of TChart.GetMargins
function.
2) Add MarginsForMarks property to series, which could be either a
boolean or enumeration like the above.

What do you think?

QuoteI do not know what graph and image coordinates are, probably I
should read somewhere.I suggest documentation.

Quotearray with the marks, which I could use to get these values.
I sought LeftAxis.Marks but I found no such property there.Did you
miss Value and ValueCount properties?

Quotemarks themselves are the short lines, but they may or may not
have  labels (right?)That depends on chart settings. Usually, if
OverlapPolicy=opIgnore and labels are visible, all marks will have
labels.

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CM630 · 2012-10-29 12:18

Quote from: Ask on October 29, 2012, 12:23:33 pmQuotecannot understand
what the series.marks (and series at all) have to do with the
extentsMargins are reserved to guarantee that all marks labels fit
into the viewport.
As for series themselves -- they are a primary source of chart full
extent,
which is, by definition, an extent designed to cover all series data.
I absolutely agree that full extent must take care to show series
marks.
But full extent is one thing, and extents and logicalextents seem a
completely different thing to me. If I choose to change them manually,
then I am supposed to know what I want to have on the screen?
IMHO, the current behaviour is somehow unpascalish.
In Pascal when I write showmessage (i) I get an error message, just
because i is an integer, and Pascal is not sure how I want to convert
it. But when I set the extents TChart decides instead of me what the
real extents shall be.
Indeed, I have very limited experience with Pascal, probably I have
much more to see.

Quote from: Ask on October 29, 2012, 12:23:33 pmQuotePerhaps, I should
set series marks.visible:= False, to change the extents and to set
them back to visible again?No, this will not help, as the chart extent
will be recalculated automatically.
Indeed, I tried this, too. If I switch off series marks- scales are
fine. But if switch them back to visible again- the same result as
before. Probably I should make marks visible in another handler, but I
use TEdit- there is no handler after EditingDone. The only thing, that
occurs to me is to use a timer, which will make marks visible after
some delay

Quote from: Ask on October 29, 2012, 12:23:33 pmThe solution is to
improve control over series margins.
I can see several independent options:
1) Add Chart.CombineMargins property with values of (cmMax, cmMin,
cmSum, cmNone), which would control algorithm of TChart.GetMargins
function.
2) Add MarginsForMarks property to series, which could be either a
boolean or enumeration like the above.

What do you think?
I just tried and found that TChart does not have a GetMargins
property? Unfortunately I could not understand what is the idea of
your first proposal.
As far as your second idea is concerned- do you mean that if
MarginsForMarks= False (cmNone) then logicalextent= 5000 will result
in extent 5000, because the margins around the labels will be
neglected? It seems fine to me, since both those who share your
understanding and mine will be content.
As I mentioned maybe cmMax, cmMin, cmSum, cmNone are nice (usually the
more options, the better, providing that implementing them won't hurt
something else), but still I do not understand their conception.

Quote from: Ask on October 29, 2012, 12:23:33 pmQuotemarks themselves
are the short lines, but they may or may not have labels (right?)That
depends on chart settings. Usually, if OverlapPolicy=opIgnore and
labels are visible, all marks will have labels.
In some other tread I asked how to make sure that labels are displayed
for the firsts (min) and the last (max) displayed values.
I will search it, but as far as I remember, there was not an easy
solution.
Anyway I could place an area of another colour (better at mouseover),
so the user will know where the click area is.

@ask, since you are an moderator, could I ask you to put the item into
another tread?

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Ask · 2012-10-29 14:58

QuoteI absolutely agree that full extent must take care to show series
marks.
But full extent is one thing, and extents and logicalextents seem a
completely different thing to me. If I choose to change them manually,
then I am supposed to know what I want to have on the screen?
IMHO, the current behaviour is somehow unpascalish.That is debatable.
Currently, TAChart design leans in the direction of "works
automatically by default, have advanced switches for manual control".
I can see a merit of "does only what explicitly requested, even if
inconvenient in the default case". However, I do not want to go this
way -- for each advanced user like you who wants manual control, there
are ten casual users who just want simple chart with minimal effort.

QuoteTChart does not have a GetMargins property?Note I said
"function", not "property".

Implemented TChartMarks.AutoMargins property in r39187 -- try setting
it to false.

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CM630 · 2012-10-30 09:12

Quote from: Ask on October 29, 2012, 03:58:42 pm...there are ten
casual users who just want simple chart with minimal effort.
Er, I think I want the same thing 

Quote from: Ask on October 29, 2012, 03:58:42 pmImplemented
TChartMarks.AutoMargins property in r39187 -- try setting it to false.

While waiting for a new build- shall I use it as
Chart1.AutoMargins:=false ;
Chart1.LeftAxis.Marks.AutoMargins:=false ;
Chart1.Series.Marks.AutoMargins:=false or in some other way?

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Ask · 2012-10-30 11:01

Something like Chart1.LineSeries1.Marks.AutoMargins := false
This property is available from Object Inspector, so you can just set
it at design-time.

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CM630 · 2012-10-31 09:11

Lazarus snapshots for Win32 have not been updated in the last two
weeks, I will try to copy the data from the source to
....\lazarus\components\tachart\.
Meanwhile, I did a simple function, which could be very useful.
TChart calculates the autoextents in a very unpleasant way, so the
values are something like for example Ymax:=3456,5693974573245098 and
Ymin:=-2543,048109302.
This function makes things somehow better:
Code: [Select]function NiceRound (const aExtended: extended; const
PercentAddition: Byte=10 ): Extended;
var
  FirstDigit: Single;
  Exponent: Integer;
  Negative: Boolean= false;
  TempVar: Extended;
begin
  if aExtended< 0 then
  begin //if
    Negative:=True;
    TempVar:= abs(aExtended);
  end
  else
    TempVar:= aExtended;
  Exponent:=  StrToInt (MidBStr(FloatToStrF(TempVar*(1+(PercentAdditio
n/100)),ffExponent,1,1),5,5))-1;
  FirstDigit:=  StrToFloat(LeftStr (FloatToStrF
(TempVar*(1+(PercentAddition/100)),ffExponent,1,1),3))*10;
  if Negative = True
  then
     Result:= -1*StrToFloat (FloatToStr(FirstDigit) +'E'+IntToStr
(Exponent))
  else
     Result:= StrToFloat (FloatToStr(FirstDigit) +'E'+IntToStr
(Exponent));
end;  
I did it heavily relaying on number <-> string convertion, maybe it
can be done in a more mathematical way, but what do you think about
its functionality?
BTW, I found a similar function here.

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Ask · 2012-10-31 09:42

Quotewhat do you think about its functionality?I do not know what you
question is exactly so I'll try to answer all possible questions --
hopefully yours is one of them.

Q: Can a specific user (you) use NiceRound function in his own
application?
A: Of course, although I would remove PercentAddition argument, since
one function should do one thing, in this case round floating point
value.

Q: Is NiceRound function a useful addition to a standard FPC library?
A: No, because it is essentially equivalent to Format('%.2e',
[aExtended])

Q: Is it useful for TAChart to automatically adjust extent boundaries
using NiceRound function?
A: No, it will cause total breakage in some cases.

Q: Is it useful for TAChart to automatically adjust extent boundaries
to shorten their decimal representation, while retaining the same
chart image?
A: I am not sure. Similar adjustment for axis marks is already present
and is controlled by Marks.Tolerance property. However, extent
boundaries are never printed by the chart, so what is the point of
rounding them?

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CM630 · 2012-10-31 11:02

Quote from: Ask on October 31, 2012, 10:42:34 amQ: Is it useful for
TAChart to automatically adjust extent boundaries using NiceRound
function?
A: No, it will cause total breakage in some cases.
I rather mean a function with a similar effect, but explaining what it
should do is harder, than making it do it.

Quote from: Ask on October 31, 2012, 10:42:34 am...extent boundaries
are never printed by the chart...
That is exactly the problem that I am trying to solve, so some nicer
values could be helpful, thought indeed the total number of marks per
axis shall be considered.

Even disregarding that
Quote from: Ask on October 31, 2012, 10:42:34 am...However, extent
boundaries are never printed by the chart, so what is the point of
rounding them?
You mentioned (or at least I understood so) that you were working on a
functionality, that would allow users to change maximum/ minimum
extents of the axis. So when the axis value is set automatically to a
long trail float number, when you click to change it you would get a
number, which is not very pleasant to deal with.
If I misunderstood you about this functionality- than it is not worth
discussing.

As far as PercentAddition is concerned, you can see on the screenshot,
that the curve is exactly fitting into the Y range. It is a question
of taste, but according to mine, it would look nicer if there was some
empty space under and over it.

----------------------------------------------------------------------
CM630 · 2012-11-09 07:02

Finally a new snapshot of Lazarus was uploaded, so I could try
Chart1.LineSeries1.Marks.AutoMargins := false;
LogicaExtents seem to work just fine- I say 5000, it understands 5000.

But Extents work as before- I say 5000, it hears whatever it wants.
So a problem that remains is that when I zoom only horizontally the
Graph autoscales at the Y axis.

Case1: If this is how things were meant to be (AutoMargins to be
considered for LogicalExtents only)- I can force Y scale by using
LogicalExtents after each zoom operation.
Case 2: If this is a bug, I hope that it will be fixed.

I would like to ask @Ask which is the case, so I would know if I shall
proceed with implementing forced Y scale?

----------------------------------------------------------------------
Ask · 2012-11-09 11:59

QuoteBut Extents work as before- I say 5000, it hears whatever it
wants.I can not reproduce. Try this:
1) Open "extents" demo
2) Set Chart1.Margins to all zeroes
3) Set MargingForMarks = false for both axises
3) Run
=>
Note that the current extent exactly follows fixed extent.

----------------------------------------------------------------------
CM630 · 2012-11-09 14:26

Thanks! Now everything seems to work fine, probably next week I could
try to spend some more time to see how exactly I have reached this odd
result, in case there is something more to be fixed.

----------------------------------------------------------------------
CM630 · 2013-05-07 13:27

I will examine this further, probably tomorrow, but it just occured to
me that usings Extent.FixTo prevents panning in  TChartToolset  from
working, while ZOOMing continues to work fine. Is it supposed to work
this way?

----------------------------------------------------------------------
wp · 2013-05-07 15:15

I don't see this here. Maybe you have set the LimitToExtent options of
the panning tool?

----------------------------------------------------------------------
CM630 · 2013-05-08 06:04

Indeed, that is the case. I had LimitTo left and right extents. When I
removed it, panning started working!
Yet this did not solve my problem, since now I can pan outside the
data area of the X scale.
I got the impression, that Extent.FixTo is to be used for setting
LogicalExtents, but it occurs that it sets simply Extents.

I tried to replace chart.Extent.FixTo(Extents); with
chart.LogicalExtent:= Extents;
but unfortunately it does not work properly (i.e. I set Ymax
(coords[4]):= 1000, it sets it to 863,9213749832943), although all my
margins are set to 0.
The only idea I have is to enable/disable LimitTo left and right if
panning goes outside the values of the X scale or to force them back
within the values area. This is quite a clumsy solution.

Here is my procedure:

Code: [Select]procedure SetLogicalExtent (var Chart:  TChart;const 
Value: double;const Index: byte);
var
  Extents: tDoubleRect;
  TempCoord:double;
  PlusMinus:integer=+1;
begin
  Extents:=Chart.LogicalExtent;
  if Index<3 then PlusMinus:=+1 else PlusMinus:=-1;
  if ((Index<3) and (Value<Extents.coords [Index+2])) or ((Index>2)
and (Value>Extents.coords [Index-2]))
  then
  begin //Max > Min
     Extents.coords [Index]:= Value;
     if (Index= 1) or (Index=3) then chart.BottomAxis.Inverted:=False;
     if (Index= 2) or (Index=4) then chart.LeftAxis.Inverted:=False;
  end
  else
  begin //Min < Max
    TempCoord:=Extents.coords[Index+PlusMinus*2];
    Extents.coords[Index+PlusMinus*2]:=Value;
    Extents.coords[Index]:=TempCoord;
    if (Index=1) or (Index=3) then chart.BottomAxis.Inverted:=True;
    if (Index=2) or (Index=4) then chart.LeftAxis.Inverted:=True;
  end;
  chart.Extent.FixTo(Extents);  //Works fine this way
  //chart.LogicalExtent:= Extents; //Does not work this way
end;

----------------------------------------------------------------------
wp · 2013-05-08 15:54

I don't exactly understand what you want to achieve: Zoom and pan, but
when zoomed you only want to pan vertically? The panning tools have a
property Direction to restrict the panning. Did you try that?

----------------------------------------------------------------------
CM630 · 2013-05-13 06:49

When I pan/zoom horizonatlly, TAChart autoscales vertically.
This causes several issue:
1. Sometimes I do not want the contents to be autoscaled vertically,
but TAChart does not have an option to disable, so I have to set
extents.
2. Sometimes I want to autoscale vertically, but  TAChart does it in
an unpleasant way, so I have to use my procedures.

I have uploaded a video in Youtube, for some reason it is extremely
ugly, but I hope that you can get the idea.

----------------------------------------------------------------------
CM630 · 2015-02-23 14:45

Houston, we have a serious problem.
Here is the source:
Code: [Select]procedure TForm1.FormCreate(Sender: TObject);
var
  TempExtents: TDoubleRect;
begin
  Chart1.Margins.Bottom:=0;
  Chart1.Margins.Left:=0;
  Chart1.Margins.Right:=0;
  Chart1.Margins.Top:=0;
  Chart1LineSeries1.AddXY (2, 3);
  Chart1LineSeries1.Pointer.Visible:=True;
  Chart1LineSeries1.Marks.Visible:=True;
  Chart1LineSeries1.ShowPoints:=True;
  Chart1LineSeries1.Marks.Style:=smsLabel;  //This causes problems
  Chart1LineSeries1.SetText(0,'aaaa');
  TempExtents.coords[1]:=-10;
  TempExtents.coords[2]:=-15;
  TempExtents.coords[3]:=+20;
  TempExtents.coords[4]:=+25;
  Chart1.Extent.FixTo   (TempExtents);
end;                                   If line
Chart1LineSeries1.Marks.Style:=smsLabel; is commented everything is
fine and FixTo works properly.
But, when I enable it,  FixTo does not work properly for the vertical
scale. I set -15 to +25, but actual values are -15 to 31,...
If I have a negative point, the -15 will become -16 or something like
this.
Is this a bug of if it is a feature, how am I to override it?

----------------------------------------------------------------------
wp · 2015-02-23 14:50

Please put your code into a compilable demo which I can test
immediately - it makes my life easier... Put pas, lfm, lpi and lpr
files of the demo into a single zip file which you can upload here, no
other files please, in particular no exe and no ppu.

Anyway, your code is pretty much self-contained and it was easy to
create a project...

I see the issue. Yes this is caused by the labels attached to the data
points.The problem is that the labels are drawn ABOVE the data points.
This chart does not take care of the positions where the data points
are, it just makes additonal space for the labels. While this behavior
makes sense in an auto-scaled chart it is unexpected for a chart with
frozen extent. Therefore, I'll look into the sources of TAChart to
find the issue.

----------------------------------------------------------------------
wp · 2015-02-23 15:13

Ah - nothing to do, it's already there: Series.Marks.AutoMargins =
false

----------------------------------------------------------------------
CM630 · 2015-02-24 08:21

Thanks, it works!
Now I am trying to handle with the problems caused by that:
 Quote from: wp on October 25, 2012, 09:58:34 amThe max must always be
greater than the min. Use the property "Inverted" of the axis if you
want to have min and max interchanged.

----------------------------------------------------------------------
wp · 2015-02-24 09:46

No, as is says: the max must ALWAYS be greater than the min.
"Inverted" is intended to invert the drawing direction of an axis,
there's nothing else to be done for this purpose. Never exchange max
and min to invert the axis.

----------------------------------------------------------------------
CM630 · 2015-02-26 07:09

I added some info in the wiki, hopefully it contains no mistakes.


Quote from: wp on February 24, 2015, 10:46:26 am
No, as is says: the max must ALWAYS be greater than the min...
Yes, I understand how it works, I am just beating my head how to
overcome the troubles that this behaviours creates   .


EDIT: Which exactly extents does FixTo set? I thought it sets
LogicalExtents, but odd results occur?

----------------------------------------------------------------------
wp · 2015-02-26 11:01

Quote from: CM630Which exactly extents does FixTo set? I thought it
sets LogicalExtents, but odd results occur?The extent you apply it to:
For the chart you can only call FixTo for the Chart.Extent which
corresponds to the unzoomed window. When you zoom into the chart you
modify the LogicalExtent, Or you can assign a DoubleRect to the
LogicalExtent. And there is a CurrentExtent which is equal to the
LogicalExtent plus the chart's margins translated to graph
coordinates. A bit confusing...

Please have a look at the attached demo which plays with various ways
to modify the extents and shows their effect.

----------------------------------------------------------------------
CM630 · 2015-02-26 14:22

I kind of solved my problems by adding an additional storage for the
extents.
I use an additional function, which sets the extents, and if necessary
swaps them and inverts the scales, but does not touch the additional
storage. Still my control happens to crash, but I will dig more trough
it.
I will check you demo, but if I understand you right, I'd better use
LogicalExtents[1..4]:=something instead of FixToo.
But the odd thing is that I use FixTo, my minimum X scale is i.e. 1,
but both LogicalExtemt.coords[1] and  CurrentExtemt.coords[1] return
i.e. 3,xyz which in not even close neither to 1, nor to the other
border  I have no zoom, my chart margins are zeroes, I have no
captions on the plot... I am not sure if I had a plot at all.
The bad things is that code is too big, to reproduce it in a simple
way.
So as I mentioned I added an additional buffer for the coordinates and
stopped reading logical exents, except when an OnChangeExtents event
occurs.

----------------------------------------------------------------------
wp · 2015-02-26 15:33

I am pretty sure that you are doing something wrong.

The entire extent thing I must confess is a bit tricky because all the
calculations are done during the painting procedure. So, if you
initiate an extent change at the wrong place I could be overridden by
the original calculation - just a feeling. This could explain why your
LogicalExtent returns non-sense results.

Please try to create a simple application which shows the issue.

----------------------------------------------------------------------
CM630 · 2015-02-27 08:22

These two functions shall provide the solution. I have made some
standalone tests and they seem to be okay, I will report after some
more usage:
Code: [Select]uses
...TAChartUtils...
const
   ExtXmin=1;
   ExtYmin=2;
   ExtXmax=3;
   ExtYmax=4;
...

function  GetExtentsReal (var aChart: TChart): TDoubleRect;
var
  OutputExtents: TDoubleRect;
  SwapExtent: Double;
begin
   OutputExtents:= aChart.LogicalExtent;
   if aChart.BottomAxis.Inverted then
   begin
      SwapExtent:= OutputExtents.coords[ExtXmin];
      OutputExtents.coords[ExtXmin]:= OutputExtents.coords[ExtXmax];
      OutputExtents.coords[ExtXmax]:= SwapExtent;
   end;
   if aChart.LeftAxis.Inverted then
   begin
      SwapExtent:= OutputExtents.coords[ExtYmin];
      OutputExtents.coords[ExtYmin]:= OutputExtents.coords[ExtYmax];
      OutputExtents.coords[ExtYmax]:= SwapExtent;
   end;
   Result:= OutputExtents;
end;

function  SetExtentsReal (var aChart: TChart; aPosition: Integer;
Value: Double): Boolean;
var
  OutputExtents: TDoubleRect;
  SwapExtent: Double;
begin
   Result:=False;
   OutputExtents:= GetExtentsReal(aChart);
   OutputExtents.coords[aPosition]:=Value;
   if (OutputExtents.coords[ExtXmin]= OutputExtents.coords[ExtXmax])
or (OutputExtents.coords[ExtYmin]= OutputExtents.coords[ExtYmax])
         then Exit;  //Function does nothing and returns False if
equal extents exist.

   if (aPosition=ExtXmin) or (aPosition=ExtXmax) then
     if OutputExtents.coords[ExtXmin]> OutputExtents.coords[ExtXmax]
then
        begin
          SwapExtent:= OutputExtents.coords[ExtXmin];
          OutputExtents.coords[ExtXmin]:=
OutputExtents.coords[ExtXmax];
          OutputExtents.coords[ExtXmax]:= SwapExtent;
          aChart.BottomAxis.Inverted:=True;
        end
     else
        aChart.BottomAxis.Inverted:=False;

   if (aPosition=ExtYmin) or (aPosition=ExtYmax) then
     if OutputExtents.coords[ExtYmin]> OutputExtents.coords[ExtYmax]
then
        begin
          SwapExtent:= OutputExtents.coords[ExtYmin];
          OutputExtents.coords[ExtYmin]:=
OutputExtents.coords[ExtYmax];
          OutputExtents.coords[ExtYmax]:= SwapExtent;
          aChart.LeftAxis.Inverted:=True;
        end
     else
        aChart.LeftAxis.Inverted:=False;

   aChart.LogicalExtent:= OutputExtents;
   Result:=True;
end;
             
What I noticed is that when a Chart is put on a form, logical and
current extents return nonsense if invoked in the procedure FormCreate
procedure.
Should it be this way?
I get no exception, so the Chart is created. Probably some default
values for the logical and current extents  are not set?

----------------------------------------------------------------------
wp · 2015-02-27 10:19

QuoteWhat I noticed is that when a Chart is put on a form, logical and
current extents return nonsense if invoked in the procedure FormCreate
procedure.This reminds of what I forgot to write yesterday: As I saw
recently it may help to call Chart.Prepare before manipulating
extents. As I wrote above the extents of data ranges are calculated
during painting; Prepare does this immediately.