Translucent form and opaque roundrect
lazarus / 39-Graphics

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xinyiman · 2019-06-14 06:57

Hi guys, I want to understand how to draw an opaque roundrect on a
translucent form. I did some tests, but by making the form translucent
even the roundrect that I draw in the form2 paint event becomes
translucent. Try my test and press the button on the first form. You
will understand what I mean.

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Pascal · 2019-06-14 08:57

On windows you can use:
SetLayeredWindowAttributes(Handle, clFuchsia, 180, LWA_COLORKEY or
LWA_ALPHA);

See attached project.

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xinyiman · 2019-06-14 09:03

Quote from: Pascal on June 14, 2019, 10:57:36 amOn windows you can
use:
SetLayeredWindowAttributes(Handle, clFuchsia, 180, LWA_COLORKEY or
LWA_ALPHA);

See attached project.

Thanks but your solution isn't cross-platform. Run only windows
system.

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Pascal · 2019-06-14 09:21

Yes, right.

Mybe someone can add a ColorKey property to TForm and uses system
specific functions to set it.

There should be a Unix/OSX pendant.

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xinyiman · 2019-06-14 09:52

sorry but don't understand

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Pascal · 2019-06-14 10:15

We need a new property for TForm like AlphaBlend and AlphaBlendValue:
ColorKey.

AlphaBlend and AlphaBlendValue are set in the Windows widgetset by
SetLayeredWindowAttributes.
SetLayeredWindowAttributes can also set the ColorKey. So for Windows
widgetset there is a solution.

For other widgetsets there must be an equivalent function to set the
ColorKey.

If we know them we can add ColorKey property to TForm and will have a
cross platform solution!

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xinyiman · 2019-06-14 10:24

AlphaBlend and AlphaBlendValue run correctly on mac but all form and
components get transparent value. For me necessity is important form
with transparency and component (like a button or image) not.

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Pascal · 2019-06-14 11:37

So my solution doesn't work either.

Have a look here:
https://stackoverflow.com/questions/4928215/changing-alpha-of-window-
background-not-the-whole-window

But LCL can't set alpha value of window background color.