Bug 266883

Summary:	You cannot draw with (semi)transparent color, only fill
Product:	[Applications] kolourpaint	Reporter:	Kai Uwe Broulik <KaiUweBroulik2>
Component:	general	Assignee:	kolourpaint-support
Status:	CONFIRMED ---
Severity:	normal	CC:	cfeck, john.kizer, kde, luke-jr+kdebugs, martin, tiposchi, woshilinmanfu+kde
Priority:	NOR
Version First Reported In:	unspecified
Target Milestone:	---
Platform:	Compiled Sources
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:

Description Kai Uwe Broulik 2011-02-22 12:38:58 UTC

Version:           unspecified (using KDE 4.6.0) 
OS:                Linux

Thanks for your awesome work of improving Kolourpaint on KDE 4 :)

I just compiled the most recent trunk version and I noticed that you cannot draw with semitransparent color or the transparent color. You can only fill areas with a color but painting leaves you with the non-transparent full color. The line tool and I think the spray can as well respect the alpha setting but the rubber and pencil and brush don‘t.

Reproducible: Always

Comment 1 Martin Koller 2011-02-23 18:26:03 UTC

Yes, that's correct. Since kolourpaint now supports true transparency, a color with an alpha channel will be blended over the existing pixels.
This also leads to the fact that a complete transparent color is simply not visible and therefore you can not "rub out" pixels by drawing with the full transparent color.
I checked this with gimp and it seems it does it in the same way.

So for now you can only flood-fill areas with full transparent color, handled in a separate way.

Comment 2 Christoph Feck 2011-02-23 20:32:28 UTC

The issue Kai mentions is a different. The alpha value is ignored when using the brush tool, while it works with the line tool.

Comment 3 Martin Koller 2011-02-23 20:42:48 UTC

I see, sorry.
Yes, he's right. I'll have a look.

Comment 4 Christoph Feck 2011-02-23 20:45:08 UTC

Actually, it is more complicated.

If you click once with a large brush, without moving the mouse, you can see that it does respect the alpha channel.

The issue is that KolourPaint draws with the "brush" multiple times, so that when you draw a stroke with it, it saturates the canvas, despite it having transparency.

It probably could cache the drawn shape (QPolygon?), and process it similar to the line tool.

Regarding the issue Martin mentioned in comment #1, it maybe is possible to add a selector for the compositing mode (Source vs. SourceOver).

But I feared that allowing transparency would result in more requests, up to the point where people should rather use Krita instead of KolourPaint. If this issue isn't easy to solve, it might actually really be a "wontfix".

Comment 5 Matthew Forrester 2023-02-27 09:27:45 UTC

Thank you to all the devs who have kindly volunteered their time to make KolourPaint.

This bug is still present in KolourPaint 21.12.3.

I just wanted to change four pixels from grey to transparent but I had to use the flood-fill to do it. Fortunately there were no adjacent pixels of the same colour. But if there had been, I would not have been able to complete this relatively simple task with KolourPaint.

Comment 6 Luke-Jr 2023-11-20 19:48:25 UTC

Confirmed also in 23.04.3

Comment 7 John Kizer 2025-01-21 07:17:16 UTC

*** Bug 498807 has been marked as a duplicate of this bug. ***

Comment 8 John Kizer 2025-01-21 07:19:50 UTC

Moving back to Confirmed status as I don't believe the original work that led to its status moving to Assigned is likely still active.