Using LAMW objects, how to DrawBitmap() using only a PART of a Bitmap?
lazarus / 43-Android

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Manlio · 2019-07-30 08:42

When I need to draw on the screen from a bitmap, I use something like
this:

    jDrawingView1.DrawBitmap(jBitmap1.GetImage(), TargetRect.Left,
TargetRect.Top, TargetRect.Right, TargetRect.Bottom); 

This works well, and it even automatically stretches the image to fit
into the destination coordinates, which is very useful.

However, with the above method, I can only draw the entire source
bitmap. Now I would like to be able to select only a portion of the
source bitmap.

For example, if the source bitmap is 100x100 pixels, I would like to
be able to select, say, a 30x30 rectangle at (10,10,40,10), and draw
only that portion on the jDrawingView.

I could not find a method that allows to specify only a portion of the
source bitmap, and I also am not sure of what should be an efficient
way of doing that, and what object should I use.

For example, should I create another temporary jBitmap object at
runtime, somehow (how?) copy into it the portion of the source bitmap
that I want to use, and then use the temp object to call DrawBitmap()?

Or is there a function that I didn't discover yet that I can use?

Or should I use some other objects instead of jBitmap?

As I have to draw many such partial bitmaps to the screen, I'd like to
know what's an efficient solution -- which method and objects would
you recommend to use?

And best of all would be a couple of lines of code that show exactly
how to do that...

Many thanks in advance to anyone who can help us in this regard.

All the best!

Manlio

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jmpessoa · 2019-08-03 04:36

Done!!!

Added method  "DrawCroppedBitmap" to jDrawingView component!

Thank you!!!