tchart legend & pointers
lazarus / 55-TAChart

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mmab · 2010-09-25 02:39

Hi,
I've noticed an unusual behavior of tchart legend.
A line series with a pointer is not properly drawn in the legend
field. I can only obtain the line color not the pointer. I guess this
is a missing part. I tried to check it if it is still missing at the
daily snapshot but looks like http://www.hu.freepascal.org/lazarus/ is
not responding.
I also would like to see a bunch of different pointers such as
triangle, left/right triangle.

But, I'd like to congratulate for the efforts to Tchart. I hope 3D
plotting will be added in near future. (I can share some info such as
Z-buffer on this topic)

Thanks.
MMAB

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Ask · 2010-09-26 01:51

Quote from: mmab on September 25, 2010, 04:39:00 amHi,
I've noticed an unusual behavior of tchart legend.
A line series with a pointer is not properly drawn in the legend
field. I can only obtain the line color not the pointer. I guess this
is a missing part. I tried to check it if it is still missing at the
daily snapshot but looks like http://www.hu.freepascal.org/lazarus/ is
not responding.

You are right, this was a TODO item, (you can see a list of them on
the wiki).
Implemented in r27461-27462, should be available in the next snapshot.

Quote from: mmab on September 25, 2010, 04:39:00 amI also would like
to see a bunch of different pointers such as triangle, left/right
triangle.

Added those in r27463. Note that you can create custom pointers via
OnShowPointer event.

Quote from: mmab on September 25, 2010, 04:39:00 amI hope 3D plotting
will be added in near future.

Which kind of 3D plot do you need?
TAChart already has support for 3D versions of line, bar and area
series.

Quote from: mmab on September 25, 2010, 04:39:00 amI can share some
info such as Z-buffer on this topic

Chart drawing is a typical application of painter's algorithm, so
Z-buffer in not needed.
On the other hand, moving to full OpenGL implementation would be
interesting,
but require nearly total rewrite, so is not likely to happen soon.

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mmab · 2010-09-26 23:10

Thanks for the reply.
The 3D I mean is a line, a bar or a surface as in

http://www.google.com/imgres?imgurl=http://www.cyber-
wit.com/images/gallery/surface1_b.png&imgrefurl=http://www.cyber-wit.c
om/gallery_surface.html&h=320&w=450&sz=98&tbnid=81r-jLT-
x2h_QM:&tbnh=90&tbnw=127&prev=/images%3Fq%3D3d%2Bsurface&zoom=1&q=3d+s
urface&usg=__sycNZSK_Fgr2XCzp1-Dmj-1EXjY=&sa=X&ei=m-
mfTJagKYLGlQfMos3ZCQ&ved=0CB8Q9QEwAw

Regards,
MMAB

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Ask · 2010-09-27 03:13

Quote from: mmab on September 27, 2010, 01:10:08 amThe 3D I mean is a
line, a bar or a surface

Lines and bars already work, see demo/3d.
Surface, on the other hand, is not even planned yet.

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mmab · 2010-09-27 03:43

Thanks for the info.
I've downloaded the latest trunk version and I've noticed that you've
solved the legend issue.

I've developed a basic project with two charts on the same form, I've
selected animate option at zoom for both. Whenever I zoom to one of
charts, I no longer zoom in at the other chart. Is this a bug? What do
you think?

I knew the 3d look demo. I am not mentioning the 3d look, actual 3d
plot, for example: a line that describes a helix

x=3cos 3t
y=3sin 3t
z=t
0<t<pi

I do have a 3d example for a wire surface, (which is basically plot of
lines) including azimuth, elevation implementation. I can provide it
if you need.

Thanks.
MMAB

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Ask · 2010-09-28 20:50

Quote from: mmab on September 27, 2010, 05:43:20 amI've developed a
basic project with two charts on the same form, I've selected animate
option at zoom for both. Whenever I zoom to one of charts, I no longer
zoom in at the other chart. Is this a bug?

Probably yes, but I can not easily reproduce it.
Can you please create a bug report and attach a demo project to it?

Quote from: mmab on September 27, 2010, 05:43:20 amI knew the 3d look
demo. I am not mentioning the 3d look, actual 3d plot, for example: a
line that describes a helix
x=3cos 3t
y=3sin 3t
z=t
0<t<pi
I do have a 3d example for a wire surface, (which is basically plot of
lines) including azimuth, elevation implementation. I can provide it
if you need.

Hm, so you want parametrically defined surfaces?
This is even more complex than functional surfaces you requested
in the previous message :-)

You can add a feature request for that, but I do not promise it will
be implemented soon.
To speed it up, what I need is not the sample of wireframe drawing
code --
this is the easy part. The complex question is how should it interact
with
other series and chart properties, in particular with axis
transformations etc.
If course, an actual patch may things speed up even more :-)

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mmab · 2010-09-29 02:41

Here it is : http://mantis.freepascal.org/view.php?id=17507


I guess the complex question is how to draw the 3D surface. I'm not an
expert on this, but it seems to me it'd be better to use two canvas
(or a 2d matrix if you like), one is to keep info of the distance to
camera or viewscene of the pixels, the other one is for actual visible
plot.

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mmab · 2010-09-30 00:29

I'd like to add a request for the pointers:
 for a huge amount of data (10000-50000 data points) the chart becomes
so crowded due to the pointers since every data point has a pointer
assigned, it would be nice to have a pointer draw frequency. i.e
instead of drawing the pointer for all data, plotting only the
pointers with multiple of a frequency assigned by user :

Code: [Select]begin
  i:=0;
   repeat
    Drawpointer_for_data(...);
    i:=i+frequency;
  until i>=length(data);
end;


thanks
MMAB

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Ask · 2010-09-30 09:35

Quotea huge amount of data (10000-50000 data points)
You do realize that this is about 10-100 data points *per pixel*?
Such chart would be totally incomprehensible except for extreme zoom-
in levels.
And if you zoom in enough, pointers became less overlapped too.

So, can you describe the problem more completely -- what are you
trying to achieve by building such a chart?
Maybe what you really need is a more general "overview mode",
where too-dense series are automatically (or manually) replaced by
a coarse-grained versions to allow user to select an appropriate area
to zoom into?

In other words, I think the feature you propose is too niche and
suggest
you think of a more general feature instead ;-)

That said, you can already do exactly what you asked for:
1) Set ShowPoints=true, Pointer.Style=psNone
2) In OnDrawPointer pointer event, draw a pointer only if
  AIndex mod FYourFrequency = 0

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mmab · 2010-09-30 19:04

I tried to draw 100k points but the application cannot respond, I
first thought of the pointer drawing is the bottle neck of the code.
So you

QuoteSo, can you describe the problem more completely -- what are you
trying to achieve by building such a chart?
Maybe what you really need is a more general "overview mode",
where too-dense series are automatically (or manually) replaced by
a coarse-grained versions to allow user to select an appropriate area
to zoom into?
I wanted to mention this to bring out the development of fast drawing
series, i.e if a couple of x values corresponds to a same pixel column
then, take min and max of the data (to identify max and min y pixels
to draw) for that couple and use it for pixel drawing.

Thanks.
MMAB

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Ask · 2010-10-04 11:48

I fixed zooming bug, please test and close the issue if ok.

Quote from: mmab on September 30, 2010, 09:04:19 pmI tried to draw
100k points but the application cannot respond, I first thought of the
pointer drawing is the bottle neck of the code.

That's right, very long series should not display pointers for fast
drawing.

Quote from: mmab on September 30, 2010, 09:04:19 pmI wanted to mention
this to bring out the development of fast drawing series, i.e if a
couple of x values corresponds to a same pixel column then, take min
and max of the data (to identify max and min y pixels to draw) for
that couple and use it for pixel drawing.

Line drawing is already optimized for the simple cases, and should be
quite fast.
See linedemo for a timed example.

I tried the optimization you suggested, but did not achieve any speed-
up.
I guess that polyline drawing already joins successive horizontal and
vertical segments.