overlapping images
lazarus / 39-Graphics

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xinyiman · 2016-08-04 12:19

Hello guys, who tells me how to get two overlapping images and the one
that remains the front can move? Let me give an example, we shall have
to draw a line on a TImage and this line must be able to move after it
is drawn. How can I do? Are there examples? Thank you

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Handoko · 2016-08-04 12:43

It depends on what graphics engine you want to use.

If you just want to use the default Lazarus components, you can make
use the onDraw (or sometimes it called as onPaint) event. Store all
the objects' data in a list (array of object or TFPObjectList or your
own create class). And paint them using the z-order you like on the
onDraw event. You can move and animate each one or all of them any way
you like.

Default Lazarus components aren't optimized for animation nor graphics
performance. Usually, you will notice the performance issue if the
total objects reaches about 10 or more. I suggest you to learn OpenGL.
It's maybe the hardest but probably the fastest. I tested animation
with hundreds of random moving object, it still run smoothly.

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xinyiman · 2016-08-04 12:54

Ok, we assume that you have an X-ray in a TImage, the line to be drawn
on the radiograph the drawings in another TImage (with transparent
background) and the other image positions?

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Handoko · 2016-08-04 12:59

Sorry, my English is limited. Please explain more clearly.

Do you know Z-order?
https://en.wikipedia.org/wiki/Z-order

Make use Z-order properly, there should be no problem, the transparent
things will overlap correctly.