Re: [platform-swt-dev] no background on GTK

[Steve_Northover@xxxxxxx]

Yes.  The windows behind do not draw through because they are clipped against
their siblings.

Right now, transparent widgets are not supported in SWT.  As far as I know, they are
not supported on X.  Feel free to enter a feature request.

Steve

"Bob Foster" <bob@xxxxxxxxxx> Sent by: platform-swt-dev-admin@xxxxxxxxxxx 04/05/02 04:11 PM Please respond to platform-swt-dev

To:        <platform-swt-dev@xxxxxxxxxxx>         cc:                 Subject:        Re: [platform-swt-dev] no background on GTK

This explanation says to me that transparent canvases should work, in the sense that whatever is drawn behind them in the same window should show through. But they don't. Is this because the drawing area of the canvas is "subtracted" from that of the widgets before them in the drawing order, so they are not drawn?
 
I need a drawing surface that "draws over" widgets behind it. How can this be accomplished? Thanks.
 
Bob
Object Factory Inc.
----- Original Message ----- 
From: Steve_Northover@xxxxxxx 
To: platform-swt-dev@xxxxxxxxxxx 
Sent: Friday, April 05, 2002 11:04 AM
Subject: Re: [platform-swt-dev] no background on GTK


SWT.NO_BACKGROUND stops the control from automatically being 
filled with the background color.  The idea is that application code can 
get rid of flashing by painting the whole window once instead of erasing 
and then painting. 

On Windows, we makeWM_ERASEBKGND do nothing. 
On X, we convince the server not to fill the X window. 

On GTK ... we call gdk_window_set_back_pixmap()which is spec'd 
to behave the same as X but this doesn't seem to work. 

Steve

"Bob Foster" <bob@xxxxxxxxxx> Sent by: platform-swt-dev-admin@xxxxxxxxxxx 04/04/02 05:53 PM Please respond to platform-swt-dev

To:        <platform-swt-dev@xxxxxxxxxxx>        cc:                Subject:        Re: [platform-swt-dev] no background on GTK

This raises the question: What is SWT.NO_BACKGROUND is supposed to do? Let's
say you set up a Canvas with no background that is "in front of" another
widget (drawn last). Shouldn't the other widget show through the canvas?
Instead, it appears that the widget in back is not drawn at all, which means
that nothing is drawn and the desktop shows through the window.

I need a transparent canvas for my application. Why doesn't
SWT.NO_BACKGROUND give me that?

Bob
Object Factory Inc.

----- Original Message -----
From: <Silenio_Quarti@xxxxxxx>
To: <platform-swt-dev@xxxxxxxxxxx>
Sent: Thursday, April 04, 2002 3:24 PM
Subject: [platform-swt-dev] no background on GTK


> Havoc,
>
> We are trying to implement the SWT.NO_BACKGROUND style. This
> style determines with a widget will fill the background when
> an expose event happens.
>
> On X, it is possible to do this by setting the background
> pixmap of a Window to None.
>
> On GTK, the equivalent API is gdk_window_set_back_pixmap().
>
> If you run the test below, you will see that the shell
> will fill its background even though the test is setting
> the back pixmap to NULL.
>
> It seems that the background is not filled by X, but it is
> been filled by GTK. Havoc is there a away of avoiding this?
>
> Silenio
>
>
> Here is some code that shows the problem:
>
> public class NoBackgroundTest {
>
> public static void main (String [] args) throws Exception {
>         OS.gtk_init_check (new int [] {0}, null);
>
>         int shellHandle = OS.gtk_window_new (OS.GTK_WINDOW_TOPLEVEL);
>
>         OS.gtk_widget_realize(shellHandle);
>
>         int window = OS.GTK_WIDGET_WINDOW(shellHandle);
>         OS.gdk_window_set_back_pixmap(window, 0, false);
>
>         OS.gtk_widget_show(shellHandle);
>
>         while (OS.gtk_main_iteration() != 0);
> }
> }
> _______________________________________________
> platform-swt-dev mailing list
> platform-swt-dev@xxxxxxxxxxx
> http://dev.eclipse.org/mailman/listinfo/platform-swt-dev
>

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