Canvas Origin
lazarus / 39-Graphics

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JimKueneman · 2017-05-06 17:06

Is there the concept of the viewport origin in TCanvas that I an
change the definition of what 0, 0 means to the drawing functions?  I
have a large viewport of rectangles and would like to move them around
in the client window by changing the origin of the canvas, that way I
can always draw the rectangle to the point that I have defined its
upper left corner to be.

Thanks,
Jim

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taazz · 2017-05-06 18:50

Quote from: JimKueneman on May 06, 2017, 07:06:21 pmIs there the
concept of the viewport origin in TCanvas that I an change the
definition of what 0, 0 means to the drawing functions?  I have a
large viewport of rectangles and would like to move them around in the
client window by changing the origin of the canvas, that way I can
always draw the rectangle to the point that I have defined its upper
left corner to be.
Not to my knowledge. I have a custom canvas that supports something
similar in my simplegraph's port to lcl at
https://sourceforge.net/projects/evssimplegraph/ it has two properties
offsetx, offsety which are used internally to offset the coordinates
of the canvas drawing methods only. I do not know how useful this
would be to you (not much I assume) at least you'll have a starting
point.

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User137 · 2017-05-07 11:07

You can make a temporary TBitmap size it to the viewport. Draw
graphics in it and finally draw the bitmap on the main canvas. Any
graphics that you draw that go over boundaries of the bitmap are
clipped out.

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Thaddy · 2017-05-07 11:27

Maybe you can move a TPaintbox around in your case, given left-top.
[edit] Just tested that. Works pretty good...