plotting with Canvas - many issues
lazarus / 11-Options

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endik · 2007-05-24 10:24

I started next plot in my application and will have several questions:

1/ I want to draw points at some coordinates, it can be done by means
of:
Canvas.Pixels[x,y]. Unfortunately points are very small almost
unvisible. How to draw bigger points?

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antonio · 2007-05-24 16:17

You can draw little rectangles by Canvas.Rectangle(X1, Y1, X2, Y2).

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endik · 2007-05-28 19:42

that works, another solution is to use .Ellipse which can draw a
circle also

2/ next issue touches displaying of any figure, when a figure is drawn
and I click on TComboBox or switch between desktops or open terminal
or do many other things (I guess), a figure disappears so I need to
create it again.
How can I freeze my figure?

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antonio · 2007-05-28 19:59

You must save your figure on a bitmap, make changes on it if
necessary, and draw it again at each time you need it.

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endik · 2007-05-28 20:17

I draw my figure on a Tshape and could not find the option for Bitmap
saving

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antonio · 2007-05-28 20:20

You must create and handle it by yourself by TBitmap.Create, etc. It's
a back buffer.

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theo · 2007-05-28 21:26

Paint in the OnPaint EventHandler

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Zomis · 2007-05-29 07:48

Quote from: "endik"that works, another solution is to use .Ellipse
which can draw a circle also

2/ next issue touches displaying of any figure, when a figure is drawn
and I click on TComboBox or switch between desktops or open terminal
or do many other things (I guess), a figure disappears so I need to
create it again.
How can I freeze my figure?Seems related to the problem I had just a
few days ago, maybe it can help: http://www.lazarus.freepascal.org/ind
ex.php?name=PNphpBB2&file=viewtopic&t=3831
Today I use a paintbox, a couple of shapes moving inside the paintbox
(but with Form1 as Parent, since TPaintbox is not a descendant of
TWinControl), and the Paintbox.OnPaint event draws circles and stuff
in the paintbox sometimes. Works great.

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endik · 2007-05-30 08:00

4/ I had this problem with TChart and it was one of the reson I
decided to make my figure on Canvas:
How can I put some text vertically? I want to label my Y axis and now
am doing with .Canvas.TextOut but I have not found option concerning
angle or rotation or so.

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antonio · 2007-06-01 17:40

If you want text written vertically, you can Textout it for each
character changing only "y" coordinate for each character.

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endik · 2007-06-01 18:01

I mean rotated, sorry if you got confused

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antonio · 2007-06-01 18:28

If it's for Windows only, I guess there's something on Windows API.
Anyway, you can rotate by yourself by googleing some rotation
algorithm.