Discussion:
GDI32 drawing over OpenGL - How to get rid of the flickering.
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R.Wieser
2015-09-06 11:37:55 UTC
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Hello All,

In the paint event, directly after the wglSwapBuffers and before the event
ends I'm overlaying some information using DrawText, which sometimes
flickers (showing the OpenGL drawing behind it). How can I stop that
flickering ?

I've tried a GdiFlush, but that didn't help.

Regards,
Rudy Wieser

P.s.
I know that I can also create a 2D overlay in OpenGL itself. I would still
like to know how to combine OpenGL and GDI.
Jean-Christophe
2015-09-06 12:49:35 UTC
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"R.Wieser"
In the paint event, directly after the wglSwapBuffers
I guess that you shouldn't call any
OpenGL functions after wglSwapBuffers.
R.Wieser
2015-09-06 15:00:10 UTC
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Jean-Christophe,
Post by Jean-Christophe
I guess that you shouldn't call any
OpenGL functions after wglSwapBuffers.
Shucks. Although I hinted at it in the subjectline, I forgot to
explicitily name the DrawText function that I call after the wglSwapBuffers
as being from GDI32. Sorry.

Regards
Rudy Wieser
Post by Jean-Christophe
"R.Wieser"
In the paint event, directly after the wglSwapBuffers
I guess that you shouldn't call any
OpenGL functions after wglSwapBuffers.
Jean-Christophe
2015-09-06 15:50:31 UTC
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"Jean-Christophe"
I guess that you shouldn't call any
OpenGL functions after wglSwapBuffers.
"R.Wieser"
Shucks. Although I hinted at it in the subjectline ...
Sure, I read too fast - sorry about that !
Jean-Christophe
2015-09-06 16:21:42 UTC
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Post by R.Wieser
In the paint event, directly after the wglSwapBuffers and before the event
ends I'm overlaying some information using DrawText, which sometimes
flickers (showing the OpenGL drawing behind it). How can I stop that
flickering ? I've tried a GdiFlush, but that didn't help.
Overlayed: is this text GDI-drawn inside the OpenGL viewport area itself ?
Post by R.Wieser
I know that I can also create a 2D overlay in OpenGL itself.
That's what I do to write 'flat' ( XY fixed ) text into an OpenGL view,
when I don't want 3D translations and/or rotations to affect the text.
Loading Image...
Post by R.Wieser
I would still like to know how to combine OpenGL and GDI.
Is there any reason why you absolutely need to
somehow mix GDI and OpenGL instead of just writing
all the text at the OpenGL level before swapping buffers ?
Jean-Christophe
2015-09-06 16:44:24 UTC
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Post by R.Wieser
In the paint event, directly after the wglSwapBuffers and before the
event ends I'm overlaying some information using DrawText
MSDN excerpt (applies to 'DrawText' since it's a graphic function) says :
" OpenGL and GDI graphics cannot be mixed in a double-buffered window. "

Full text :
https://msdn.microsoft.com/en-us/library/windows/desktop/dd374250%28v=vs.85%29.aspx

---
Post by R.Wieser
Post by R.Wieser
In the paint event, directly after the wglSwapBuffers and before the event
ends I'm overlaying some information using DrawText, which sometimes
flickers (showing the OpenGL drawing behind it). How can I stop that
flickering ? I've tried a GdiFlush, but that didn't help.
"Jean-Christophe"
Overlayed: is this text GDI-drawn inside the OpenGL viewport area itself ?
Post by R.Wieser
I know that I can also create a 2D overlay in OpenGL itself.
That's what I do to write 'flat' ( XY fixed ) text into an OpenGL view,
when I don't want 3D translations and/or rotations to affect the text.
http://www.cjoint.com/data/EIgqfmYuONh_0.jpg
Post by R.Wieser
I would still like to know how to combine OpenGL and GDI.
Is there any reason why you absolutely need to
somehow mix GDI and OpenGL instead of just writing
all the text at the OpenGL level before swapping buffers ?
R.Wieser
2015-09-06 19:58:10 UTC
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Jean-Christophe,
Post by Jean-Christophe
Overlayed: is this text GDI-drawn inside the OpenGL viewport
area itself ?
Yes. Currently its just the camera's position and horizintal and vertical
angles, but could be used for other info too.
Post by Jean-Christophe
Post by R.Wieser
I know that I can also create a 2D overlay in OpenGL itself.
That's what I do to write 'flat' ( XY fixed ) text into an OpenGL
view, when I don't want 3D translations and/or rotations to affect
the text.
I wrote some test code for it, and there is quite a bit to manage. From
continuously setting up and switching between 3D and 2D mode, you also need
to take care that stuff like fog and lighting do not interfere. A GDI32
kind of overlay is than a lot simpler.
Post by Jean-Christophe
MSDN excerpt (applies to 'DrawText' since it's a graphic
function) says : "OpenGL and GDI graphics cannot be mixed
in a double-buffered window."
Whoops ...

Oh well. That I've got to live with OpenGLs overlay method I guess (and use
the GDI32 overlay method for "debugging" purposes only).
Post by Jean-Christophe
Is there any reason why you absolutely need to
somehow mix GDI and OpenGL instead of just writing
all the text at the OpenGL level before swapping buffers ?
Nope, there is no absolute need to do it with GDI. Its just that I was
curious if it could be done that way, as it seemed simpler to use. And,
apart from the flickering, it definitily works. :-)

Thanks for the help,
Rudy Wieser.
Post by Jean-Christophe
Post by R.Wieser
In the paint event, directly after the wglSwapBuffers and before the event
ends I'm overlaying some information using DrawText, which sometimes
flickers (showing the OpenGL drawing behind it). How can I stop that
flickering ? I've tried a GdiFlush, but that didn't help.
Overlayed: is this text GDI-drawn inside the OpenGL viewport area itself ?
Post by R.Wieser
I know that I can also create a 2D overlay in OpenGL itself.
That's what I do to write 'flat' ( XY fixed ) text into an OpenGL view,
when I don't want 3D translations and/or rotations to affect the text.
http://www.cjoint.com/data/EIgqfmYuONh_0.jpg
Post by R.Wieser
I would still like to know how to combine OpenGL and GDI.
Is there any reason why you absolutely need to
somehow mix GDI and OpenGL instead of just writing
all the text at the OpenGL level before swapping buffers ?
Jean-Christophe
2015-09-06 21:44:13 UTC
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... write 'flat' (XY fixed) text into an OpenGL view, when I don't
want 3D translations and/or rotations to affect the text.
I wrote some test code for it, and there is quite a bit to manage.
From continuously setting up and switching between 3D and 2D mode,
you also need to take care that stuff like fog and lighting do not
interfere.
Well, you don't need to switch all those things off and on if you
implement the 2D text display after the complete drawing of the 3D
scene and just before swapping buffers - when you don't need any
OpenGL calls anymore - just first disable all 'featurettes' and that's it.
Plus, the text background can be transparent if you want it to.
Loading Image...

The tiny drawback is that all the information you need to display
shall be available at the time you finally call the text display function,
you know that already since you implemented DrawText after swapping
buffers, so you just need to "OpenGL-ise" it before swapping buffers ...
Nope, there is no absolute need to do it with GDI. Its just that I was
curious if it could be done that way, as it seemed simpler to use.
Well, if you _really_ want it to use it that bad, then you've
got to say good-bye to the marvels of double-buffering !
And, apart from the flickering, it definitily works. :-)
... apart from the flickering :-)

Rudy, here's an excerpt of the code I wrote for this,
to be used after the drawing of the whole OpenGL scene
and just before swapping thy OpenGL buffers ... HTH.


// disable all stuff I don't need anymore (add you own)
glDisable(GL_DEPTH_TEST);
glShadeModel(GL_FLAT);
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
glOrtho(winRect.left, winRect.right, winRect.bottom, winRect.top, -1, 1);
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();
glDisable(GL_BLEND);
glColor3ubv( (GLbyte*)&cColor[COL_WHITE] ); // text color

// display 2D 'flat' text
glListBase(INDEX_LIST_TEXT); // use display lists for the glyphs
/// insert here the display of all strings
glRasterPos2i(x,y); // screen coordinates text location
glCallLists( strlen(s), GL_UNSIGNED_BYTE, s ); // string 's'
... // display other text at other location
/// ending of the display of all strings

// restore (don't really need to - except for PopMatrixes)
glMatrixMode(GL_MODELVIEW);
glPopMatrix();
glMatrixMode(GL_PROJECTION);
glPopMatrix();
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective( stP.fovy, stP.aspect, stP.zNear, stP.zFar );
glMatrixMode(GL_MODELVIEW);
glEnable(GL_DEPTH_TEST);

// ends
R.Wieser
2015-09-07 10:05:33 UTC
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Jean-Christophe,
Post by Jean-Christophe
Plus, the text background can be transparent if you want it to.
Lol. I removed my own remark in that direction from a previous post, as I
did not want to muddy my question with it.

Yes, thats something plain GDI (as opposed to GDI+ ) does not seem to be
able to do (I asked in another newsgroup about it).
Post by Jean-Christophe
when you don't need any OpenGL calls anymore - just
first disable all 'featurettes' and that's it.
Next to setting ortho mode, yes. But there seem to be quite a few of those
'featurettes' that need to be switched on and off again. Z-Buffer,
lighting and fog to name a few to start with.
Post by Jean-Christophe
Well, if you _really_ want it to use it that bad, then you've
got to say good-bye to the marvels of double-buffering !
You know, thats something I do not quite understand. I took it that when
the glSwapBuffers is executed the backbuffer gets swapped with the front one
(probably just copied to the DC), so where is the flickering coming from ?
Is there some kind of delay involved causing the actual "swapping" to take
place some time later ?

And by the way, I saw the same kind of flickering when I had a control
placed ontop of the OpenGL canvas, so its not just my GDI drawing thats
bothered by it.
Post by Jean-Christophe
And, apart from the flickering, it definitily works. :-)
... apart from the flickering :-)
Well, that just a minor issue, isn't it ? :-p
Post by Jean-Christophe
Rudy, here's an excerpt of the code I wrote for this,
to be used after the drawing of the whole OpenGL
scene and just before swapping thy OpenGL buffers
... HTH.
Thats pretty-much the same as what I have (in the test code I spoke of
before), save for not pushing anything* and having the projection part as
the first thing.

## start frame
-- Set perspective mode
-- Set features
-- Set camera
draw 3D environment
-- Set ortho mode
-- Reset features
draw 2D environment
## end frame

*By setting the the perspective mode as the first thing when drawing a frame
there is no need to push anything. And to me thats important, as I do not
have full control over whats done in the "draw 3D environment" and "draw 2D
environment" phases.

A remark though: In the "restore" phase you switch to and than pop the
projection matrix, only to directly overwrite it by using glPerspective.
Does that combination do something I'm not (yet) aware of ?

Regards,
Rudy Wieser
Post by Jean-Christophe
... write 'flat' (XY fixed) text into an OpenGL view, when I don't
want 3D translations and/or rotations to affect the text.
I wrote some test code for it, and there is quite a bit to manage.
From continuously setting up and switching between 3D and 2D mode,
you also need to take care that stuff like fog and lighting do not
interfere.
Well, you don't need to switch all those things off and on if you
implement the 2D text display after the complete drawing of the 3D
scene and just before swapping buffers - when you don't need any
OpenGL calls anymore - just first disable all 'featurettes' and that's it.
Plus, the text background can be transparent if you want it to.
http://www.cjoint.com/data/EIgun1ZTXch_0.jpg
The tiny drawback is that all the information you need to display
shall be available at the time you finally call the text display function,
you know that already since you implemented DrawText after swapping
buffers, so you just need to "OpenGL-ise" it before swapping buffers ...
Nope, there is no absolute need to do it with GDI. Its just that I was
curious if it could be done that way, as it seemed simpler to use.
Well, if you _really_ want it to use it that bad, then you've
got to say good-bye to the marvels of double-buffering !
And, apart from the flickering, it definitily works. :-)
... apart from the flickering :-)
Rudy, here's an excerpt of the code I wrote for this,
to be used after the drawing of the whole OpenGL scene
and just before swapping thy OpenGL buffers ... HTH.
// disable all stuff I don't need anymore (add you own)
glDisable(GL_DEPTH_TEST);
glShadeModel(GL_FLAT);
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
glOrtho(winRect.left, winRect.right, winRect.bottom, winRect.top, -1, 1);
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();
glDisable(GL_BLEND);
glColor3ubv( (GLbyte*)&cColor[COL_WHITE] ); // text color
// display 2D 'flat' text
glListBase(INDEX_LIST_TEXT); // use display lists for the glyphs
/// insert here the display of all strings
glRasterPos2i(x,y); // screen coordinates text location
glCallLists( strlen(s), GL_UNSIGNED_BYTE, s ); // string 's'
... // display other text at other location
/// ending of the display of all strings
// restore (don't really need to - except for PopMatrixes)
glMatrixMode(GL_MODELVIEW);
glPopMatrix();
glMatrixMode(GL_PROJECTION);
glPopMatrix();
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective( stP.fovy, stP.aspect, stP.zNear, stP.zFar );
glMatrixMode(GL_MODELVIEW);
glEnable(GL_DEPTH_TEST);
// ends
Jean-Christophe
2015-09-07 16:38:23 UTC
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"Jean-Christophe"
Plus, the text background can be transparent if you want it to.
"R.Wieser"
Lol. I removed my own remark in that direction from a previous
post, as I did not want to muddy my question with it.
Yes, thats something plain GDI (as opposed to GDI+ ) does not
seem to be able to do (I asked in another newsgroup about it).
I used to GDI-draw transparent background text this way :

SetBkMode(hdc,TRANSPARENT);
SetTextColor( hdc, value );
DrawText( hdc, str, -1, &rect, DT_CENTER );
I took it that when the glSwapBuffers is executed
the backbuffer gets swapped with the front one
That's how I understand it too : complete flush, then swapped.
( each time I had a funny display, it was because of a bug in my
own code, or a misunderstanding on how to use OpenGL :-)
(probably just copied to the DC), so where is the flickering coming from ?
Is there some kind of delay involved causing the actual "swapping" to take
place some time later ?
Dunno, just a guess :
I suppose that using both GDI and OpenGL on the same area rises
some conflict (?) and not the same one wins every time, so the flickering.

I know that, when catching WM_PAINT msg, one can't mess too much
between BeginPaint() and EndPaint(). I tried several different approches,
like calling the whole OpenGL scene drawing from inside a thread loop,
or like this :

//// main window message loop
for( ok=1; ok; )
{ if( PeekMessage(&msg,NULL,0,0,PM_REMOVE) ) // got some
{ TranslateMessage(&msg); // process
DispatchMessage(&msg);
if( msg.message == WM_QUIT ) ok=0; // leave loop
}
else // no win msg to process
{ fDrawOpenGLscene(); // OpenGL scene
}
}
// ...

//// inside WndProc()
case WM_PAINT:
fDrawOpenGLscene(); // OpenGL scene
return 0;
And by the way, I saw the same kind of flickering when I had a control
placed ontop of the OpenGL canvas, so its not just my GDI drawing thats
bothered by it.
What kind of "control" ?
A windows dialog box or something ?
A remark though: In the "restore" phase you switch to and than pop the
projection matrix, only to directly overwrite it by using glPerspective.
Does that combination do something I'm not (yet) aware of ?
No :-)
I don't call anymore OpenGL functions after "restore".

This 'restore' phase is a remaining of the time when this function was
still called from inside the middle of the drawing scene ... later I moved
it after total scene completion, and never took time to clean-up the code !
So don't bother too much about how bad it looks :-)
R.Wieser
2015-09-08 08:34:17 UTC
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Jean-Christophe,
[Snip]

Whoops. I was referring to the transparency of the big black-ish box the
text is drawn ontop of ( in your example image:
http://www.cjoint.com/data/EIgun1ZTXch_0.jpg ).

I used CreateDIBSection to create a 32-bit DIB to draw on using GDI
commands, which I than converted into a texture using glTextImage2D. Color
me surprised when the OpenGL cube I used the texture on disappeared from the
scene ....

The cause was/is that any GDI drawing will zero the high byte (alpha
channel) of all pixels touched by the command(s), causing full transparency.
:-\
Post by Jean-Christophe
I suppose that using both GDI and OpenGL on the same area rises
some conflict (?) and not the same one wins every time, so the flickering.
Hmmm... I assumed that after the swapping the OpenGL scene effectivily
becomes a 2D GDI image (otherwise Windows can't handle it). And as the GDI
command comes later in the code that the OpenGL swapping one it *should* be
placed ontop of it.

There is one thing I realized a bit later though: Its possible that the
actual OpenGL "swapping" is done, unsynchronized, from within another
thread. That might cause a race condition (with the curent thread)
resulting in the flickering.
Post by Jean-Christophe
What kind of "control" ?
A windows dialog box or something ?
Nope. It was/is a listbox, used as a debugging/status output window. My
first atempt (based on a tutorial) used the whole dialog as an OpenGL
canvas. This meant that any control placed on the dialog was always
overlapping the OpenGL output.
Post by Jean-Christophe
later I moved it after total scene completion, and never
took time to clean-up the code !
So don't bother too much about how bad it looks :-)
:-) Don't worry about it, I know the problem. It regulary happens to me
that I have to rewrite a program from scratch again, because the current one
has been "tested to death" (with all kinds of orphan testcode still embedded
everywhere).


One quick question (yeah, even I do not believe that anymore :-) ) : I just
tried to create a textbox (alike the one in that example image of yours) for
which I used a glSetViewport (so the text coordinates would be relative to
the current "box", not to the 3D scene's window). I than did draw text into
the box using wglUseFontBitmaps (initilisation) and glCallLists. What I did
not expect is that that text "spilled over" the sides (top and right) of the
Viewport (not clipped against it). Should it ? A 2D quad I also did draw
was, unlike the text, indeed clipped ...

Regards,
Rudy Wieser
Post by Jean-Christophe
"Jean-Christophe"
Plus, the text background can be transparent if you want it to.
"R.Wieser"
Lol. I removed my own remark in that direction from a previous
post, as I did not want to muddy my question with it.
Yes, thats something plain GDI (as opposed to GDI+ ) does not
seem to be able to do (I asked in another newsgroup about it).
SetBkMode(hdc,TRANSPARENT);
SetTextColor( hdc, value );
DrawText( hdc, str, -1, &rect, DT_CENTER );
I took it that when the glSwapBuffers is executed
the backbuffer gets swapped with the front one
That's how I understand it too : complete flush, then swapped.
( each time I had a funny display, it was because of a bug in my
own code, or a misunderstanding on how to use OpenGL :-)
(probably just copied to the DC), so where is the flickering coming from ?
Is there some kind of delay involved causing the actual "swapping" to take
place some time later ?
I suppose that using both GDI and OpenGL on the same area rises
some conflict (?) and not the same one wins every time, so the flickering.
I know that, when catching WM_PAINT msg, one can't mess too much
between BeginPaint() and EndPaint(). I tried several different approches,
like calling the whole OpenGL scene drawing from inside a thread loop,
//// main window message loop
for( ok=1; ok; )
{ if( PeekMessage(&msg,NULL,0,0,PM_REMOVE) ) // got some
{ TranslateMessage(&msg); // process
DispatchMessage(&msg);
if( msg.message == WM_QUIT ) ok=0; // leave loop
}
else // no win msg to process
{ fDrawOpenGLscene(); // OpenGL scene
}
}
// ...
//// inside WndProc()
fDrawOpenGLscene(); // OpenGL scene
return 0;
And by the way, I saw the same kind of flickering when I had a control
placed ontop of the OpenGL canvas, so its not just my GDI drawing thats
bothered by it.
What kind of "control" ?
A windows dialog box or something ?
A remark though: In the "restore" phase you switch to and than pop the
projection matrix, only to directly overwrite it by using glPerspective.
Does that combination do something I'm not (yet) aware of ?
No :-)
I don't call anymore OpenGL functions after "restore".
This 'restore' phase is a remaining of the time when this function was
still called from inside the middle of the drawing scene ... later I moved
it after total scene completion, and never took time to clean-up the code !
So don't bother too much about how bad it looks :-)
Jean-Christophe
2015-09-08 17:56:04 UTC
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Raw Message
Rudy,
Post by R.Wieser
[Snip]
Whoops. I was referring to the transparency of the big black-ish
http://www.cjoint.com/data/EIgun1ZTXch_0.jpg ).
The bgnd looks black because there's no image under the text ... when
there's an image under then you see it thru the text's transparent bgnd.
(actually I set the bgnd _partially_ transparent to materialize the 2D box)
Loading Image...

Anyway it's OpenGL, not GDI, but I _used_ transparent bgnd
GDI DrawText and it works well, like for instance the screen
of this scope with the transparent-bgnd text (yellow, top right)
Loading Image...
Post by R.Wieser
I used CreateDIBSection to create a 32-bit DIB to draw on using GDI
commands, which I than converted into a texture using glTextImage2D.
Color me surprised when the OpenGL cube I used the texture on
disappeared from the scene .... The cause was/is that any GDI drawing
will zero the high byte (alpha channel) of all pixels touched by the
command(s), causing full transparency. :-\
The delicate complexity of the OpenGL machine :-8
http://www.cjoint.com/data/EIirHtyFVKh_-openglm.pdf

Personnally I won't mix GDI & OpenGL together as it sounds
to me like "looking for trouble" -- honestly, once one started
to write a program already using OpenGL, who needs GDI ?
( except for the launch of sharp technical threads on usenet :-)
Post by R.Wieser
Post by Jean-Christophe
I suppose that using both GDI and OpenGL on the same area rises
some conflict (?) and not the same one wins every time, so the flickering.
Hmmm... I assumed that after the swapping the OpenGL scene
effectivily becomes a 2D GDI image (otherwise Windows can't
handle it). And as the GDI command comes later in the code
that the OpenGL swapping one it *should* be placed ontop of it.
Yeah, but you know how it is with software programing, look at it
the other way : a user is thinking « oh I see, it should work this way,
therefore if I do *this* then it should do *that* ... » next thing you
know, your phone is ringin' and he complains that it didn't work ;-)
Post by R.Wieser
There is one thing I realized a bit later though: Its possible that the
actual OpenGL "swapping" is done, unsynchronized, from within
another thread. That might cause a race condition
(with the curent thread) resulting in the flickering.
I seriously doubt that Windows and OpenGL will really conflict
... as long as we're not messing (too much) with the rules.
(but it's always interresting to check and try unusual things)
Post by R.Wieser
Post by Jean-Christophe
... don't bother too much about how bad it looks :-)
It regulary happens to me that I have to rewrite a program from
scratch again, because the current one has been "tested to death"
(with all kinds of orphan testcode still embedded everywhere).
Usually I use several couples of { #ifdef | #endif } with an identifier
like 'ISDEBUG' to avoid the need to comment out the code everywhere,
then I just comment out { #define ISDEBUG }, recompile, and that's it.
( unless I feel lazy, or bored, or out of time, or all of the above,
which appends more and more frequently as I get older )
Post by R.Wieser
I just tried to create a textbox (alike the one in that example image
of yours) for which I used a glSetViewport (so the text coordinates
would be relative to the current "box", not to the 3D scene's window).
I than did draw text into the box using wglUseFontBitmaps
(initilisation) and glCallLists. What I did not expect is that that
text "spilled over" the sides (top and right) of the Viewport
(not clipped against it). Should it ?
It think it shouldn't since you explicitely set the wiewport,
but, as you already guessed, I'm not an OpenGL expert.
(there ARE some experts roaming around in this newsgroup)

However :-) my 2DFlatTextBox bypasses this problem :
Loading Image...

Best Regards.
R.Wieser
2015-09-08 21:20:03 UTC
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Raw Message
Jean-Christophe,
Post by Jean-Christophe
Anyway it's OpenGL, not GDI, but I _used_ transparent
bgnd GDI DrawText and it works well,
Yeah, it certainly does (have used it myself, with that DrawText this thread
started with).

But I didn't mean the text itself, but the box its drawn on. When using
OpenGL you can make the box itself transparent. Straight GDI on the other
hand isn't able to do transparency when drawing such a rectangle.
Post by Jean-Christophe
The delicate complexity of the OpenGL machine :-8
It didn't have anything to do with OpenGL. I could alter the raw RGBA
pixel data directly in memory (before converting it to an OpenGL texture),
and get the expected results (with transparency as I set it). Its just that
any GDI drawing sets the alpha of the affected pixels to Zero, making them
invisible.
Post by Jean-Christophe
Personnally I won't mix GDI & OpenGL together as it
sounds to me like "looking for trouble" -- honestly, once
one started to write a program already using OpenGL,
who needs GDI ?
I could definitily use it. Because drawing an overlay using GDI is quite a
bit simpler than the equivalent in OpenGL. Both in terms of lines of code,
as well as not having to manage, in OpenGL, switching between 3D and 2D
modes as well as enabeling and disabeling other stuff (an enabled depth-test
caused the lower part of some drawn text to disappear, depending on the
height my camera was on).
Post by Jean-Christophe
I seriously doubt that Windows and OpenGL will really
conflict ...
But it *does* "conflict". Hence the flickering.
Post by Jean-Christophe
as long as we're not messing (too much) with the rules.
:-) That sounds like making up "don't do that" rules as a result of "hey,
this doesn't work" experiences. I myself are currently wondering why
glFlush and/or glFinish (or something similar) cannot be used to wait for
that wglSwapBuffers to complete ...
Post by Jean-Christophe
Usually I use several couples of { #ifdef | #endif } with an
identifier like 'ISDEBUG' to avoid the need to comment out
the code everywhere,
Same here. But I've just been tinkering around with some code to create a
textbox much like yours, and now have multiple bits of code all doing it
their own way. If I would continue with this program It would probably
contain quite a few bits of orphaned code.
Post by Jean-Christophe
It think it shouldn't since you explicitely set the wiewport,
Thats what I thought too.
Post by Jean-Christophe
but, as you already guessed, I'm not an OpenGL expert.
:-) Well, it looks like you know more about it than I do, so I thought it
smart to ask.
And *how* does it do that ?

I myself have added a clipping box to the viewport (both placed around the
textbox), which gives an acceptable result. Still, text drawin before the
viewport as well as with a baseline (just) below the viewport disappears
entirely. :-\

Regards,
Rudy Wieser
Post by Jean-Christophe
Rudy,
Post by R.Wieser
[Snip]
Whoops. I was referring to the transparency of the big black-ish
http://www.cjoint.com/data/EIgun1ZTXch_0.jpg ).
The bgnd looks black because there's no image under the text ... when
there's an image under then you see it thru the text's transparent bgnd.
(actually I set the bgnd _partially_ transparent to materialize the 2D box)
http://www.cjoint.com/data/EIip02dxhoh_0.jpg
Anyway it's OpenGL, not GDI, but I _used_ transparent bgnd
GDI DrawText and it works well, like for instance the screen
of this scope with the transparent-bgnd text (yellow, top right)
http://www.cjoint.com/data/EIirk07676h_0.jpg
Post by R.Wieser
I used CreateDIBSection to create a 32-bit DIB to draw on using GDI
commands, which I than converted into a texture using glTextImage2D.
Color me surprised when the OpenGL cube I used the texture on
disappeared from the scene .... The cause was/is that any GDI drawing
will zero the high byte (alpha channel) of all pixels touched by the
command(s), causing full transparency. :-\
The delicate complexity of the OpenGL machine :-8
http://www.cjoint.com/data/EIirHtyFVKh_-openglm.pdf
Personnally I won't mix GDI & OpenGL together as it sounds
to me like "looking for trouble" -- honestly, once one started
to write a program already using OpenGL, who needs GDI ?
( except for the launch of sharp technical threads on usenet :-)
Post by R.Wieser
Post by Jean-Christophe
I suppose that using both GDI and OpenGL on the same area rises
some conflict (?) and not the same one wins every time, so the flickering.
Hmmm... I assumed that after the swapping the OpenGL scene
effectivily becomes a 2D GDI image (otherwise Windows can't
handle it). And as the GDI command comes later in the code
that the OpenGL swapping one it *should* be placed ontop of it.
Yeah, but you know how it is with software programing, look at it
the other way : a user is thinking « oh I see, it should work this way,
therefore if I do *this* then it should do *that* ... » next thing you
know, your phone is ringin' and he complains that it didn't work ;-)
Post by R.Wieser
There is one thing I realized a bit later though: Its possible that the
actual OpenGL "swapping" is done, unsynchronized, from within
another thread. That might cause a race condition
(with the curent thread) resulting in the flickering.
I seriously doubt that Windows and OpenGL will really conflict
... as long as we're not messing (too much) with the rules.
(but it's always interresting to check and try unusual things)
Post by R.Wieser
Post by Jean-Christophe
... don't bother too much about how bad it looks :-)
It regulary happens to me that I have to rewrite a program from
scratch again, because the current one has been "tested to death"
(with all kinds of orphan testcode still embedded everywhere).
Usually I use several couples of { #ifdef | #endif } with an identifier
like 'ISDEBUG' to avoid the need to comment out the code everywhere,
then I just comment out { #define ISDEBUG }, recompile, and that's it.
( unless I feel lazy, or bored, or out of time, or all of the above,
which appends more and more frequently as I get older )
Post by R.Wieser
I just tried to create a textbox (alike the one in that example image
of yours) for which I used a glSetViewport (so the text coordinates
would be relative to the current "box", not to the 3D scene's window).
I than did draw text into the box using wglUseFontBitmaps
(initilisation) and glCallLists. What I did not expect is that that
text "spilled over" the sides (top and right) of the Viewport
(not clipped against it). Should it ?
It think it shouldn't since you explicitely set the wiewport,
but, as you already guessed, I'm not an OpenGL expert.
(there ARE some experts roaming around in this newsgroup)
http://www.cjoint.com/data/EIiqQXEYaTh_0.jpg
Best Regards.
Jean-Christophe
2015-09-09 17:45:27 UTC
Permalink
Raw Message
Rudy,
(...) drawing an overlay using GDI is quite a bit simpler
than the equivalent in OpenGL. Both in terms of lines of code,
I don't agree ... you just need to write your own fct2DFlatText()
To me, if 'it works' and _never_ shows any funny behavior, it's done.
I re-used the same code on several OpenGL softs w/ just a copy/paste
of the code, the only tuning was to sprintf the strings to display.
( plus ... now I know what problems I escaped by not using GDI :-)
as well as not having to manage, in OpenGL, switching between 3D
and 2D modes as well as enabeling and disabeling other stuff
You won't need this heavy load anymore if you disable all 'features'
at the very start of your fct2DFlatText() function, and call it after
your OpenGL scene is completed and before the final buffer swap.
an enabled depth-test caused the lower part of some drawn text
to disappear, depending on the height my camera was on
Wait, I never experienced that, wherever near or far the camera is.
(no surprise, since all features have already been disabled before)

Or, it may be because glOrtho( r.left, r.right, r.bottom, r.top, -1.0, 1.0 )
with 'r' being the whole window rectangle ...

BTW, I used something quite close to insert 2D-flat-text into the 3D
scene itself with the possibility to locate text in 3D(x,y,z) while always
keep oriented straight in front of the viewer, whatever the rotations.
( like 'XYZ' text to identify the three axis of a 3D system coordinates )
And *how* does it do that ?
With the very same code I already posted here before.
I myself have added a clipping box to the viewport (both placed around
the textbox), which gives an acceptable result. Still, text drawin before
the viewport as well as with a baseline (just) below the viewport
disappears entirely. :-\
Uh ... never had that, but I don't clip the box at all.

Regards
R.Wieser
2015-09-09 19:37:49 UTC
Permalink
Raw Message
Jean-Christophe,
Post by Jean-Christophe
I don't agree ... you just need to write your own fct2DFlatText()
Lol. And how many lines would that procedure contain ?

With GDI32 I can just use the DLL function like TextOut directly. Nothing
to switch, nothing that needs to be set and cleared the whole time.
Ofcourse, disabeling the texts own background does make it look a bit
better. So, two calls all-in all.

With OpenGL on the other hand I have had quite a few troubles. It also
needs me to set up 3D and 2D modes in every frame, as well as switching
quite a few things related to those off and on the whole time.

And pardon me, but the OpenGL way isn't really what you call simple *or* too
well documented. I've just posted a problem where switching to Ortho causes
me to loose pixel row and column Zero, causing an offset. ...Which I only
noticed when I tried to match-up ortho coordinates with the ones that I
supplied to glScissor.

Nope, I've now spend a few days *just* to get Ortho to work, and to keep
working when I desire a bit more ffrom it than just overlay the whole canvas
and draw a line or two text on it somewhere.
Post by Jean-Christophe
You won't need this heavy load anymore if you disable all
'features' at the very start of your fct2DFlatText() function
Yeah, thats exactly the "switching on and off" I referred too. Because when
I disable them at the start of some orthographic drawing I need to re-enable
them again when a new frame is started and the 3D mode is initialized. Right
?
Post by Jean-Christophe
Wait, I never experienced that, wherever near or far the camera is.
Well, I think it *might* have something to do with the fact that I did not
clear the z-buffer after switching to ortho mode (which you normally give
a -1.0f to +1.0f range), and my 3D ViewNear was set to a rather high 1.0f
value. After I disabled the depth-test that problem disappeared.
Post by Jean-Christophe
BTW, I used something quite close to insert 2D-flat-text into
the 3D scene itself with the possibility to locate text in 3D(x,y,z)
while always keep oriented straight in front of the viewer, whatever
the rotations.
I will probably try to do the same/similar, as I would like to place some
"name tags" onto certain 3D locations (like when displaying a game world).
Post by Jean-Christophe
Post by R.Wieser
And *how* does it do that ?
With the very same code I already posted here before.
Ah. Sorry, I thought it would do a bit more than that. Your image and
function name hinted at a true textbox*, something which I also aimed to
make (already wrote it using GDI, but now needed to recreate it in OpenGL).

*One where the textbox top-left would be the origin to the drawn text, and
which would not allow any drawn text to spill outof/over the box. Possibly
even including CR,LF awareness.
Post by Jean-Christophe
Uh ... never had that, but I don't clip the box at all.
:-) Thats what I referred to a few messages back: You know how long your
text will be(come) at its maximum, and just draw a big enough rectangle that
the text will always stay "inside" of it.

My approach is a bit different: I have no idea how long the text might
become, so I somehow need to clip it against the box. Hence my experiments
with placing the box inside a small viewport -- and subsequently bumping
into the problem that glDrawLists does not play nice with it (still spilling
over it as well as not drawing text which does not origionate inside the
viewport).

I think I've found another way though, using glScissor (but, as already
mentioned in the above, that approach came with its own problems ...).

Thanks for the help though, I appreciate it.

Regards,
Rudy Wieser


-- Origional message.
Post by Jean-Christophe
Rudy,
Post by R.Wieser
(...) drawing an overlay using GDI is quite a bit simpler
than the equivalent in OpenGL. Both in terms of lines of code,
I don't agree ... you just need to write your own fct2DFlatText()
To me, if 'it works' and _never_ shows any funny behavior, it's done.
I re-used the same code on several OpenGL softs w/ just a copy/paste
of the code, the only tuning was to sprintf the strings to display.
( plus ... now I know what problems I escaped by not using GDI :-)
Post by R.Wieser
as well as not having to manage, in OpenGL, switching between 3D
and 2D modes as well as enabeling and disabeling other stuff
You won't need this heavy load anymore if you disable all 'features'
at the very start of your fct2DFlatText() function, and call it after
your OpenGL scene is completed and before the final buffer swap.
Post by R.Wieser
an enabled depth-test caused the lower part of some drawn text
to disappear, depending on the height my camera was on
Wait, I never experienced that, wherever near or far the camera is.
(no surprise, since all features have already been disabled before)
Or, it may be because glOrtho( r.left, r.right, r.bottom, r.top, -1.0, 1.0 )
with 'r' being the whole window rectangle ...
BTW, I used something quite close to insert 2D-flat-text into the 3D
scene itself with the possibility to locate text in 3D(x,y,z) while always
keep oriented straight in front of the viewer, whatever the rotations.
( like 'XYZ' text to identify the three axis of a 3D system coordinates )
Post by R.Wieser
And *how* does it do that ?
With the very same code I already posted here before.
Post by R.Wieser
I myself have added a clipping box to the viewport (both placed around
the textbox), which gives an acceptable result. Still, text drawin before
the viewport as well as with a baseline (just) below the viewport
disappears entirely. :-\
Uh ... never had that, but I don't clip the box at all.
Regards
Jean-Christophe
2015-09-10 18:20:26 UTC
Permalink
Raw Message
Rudy,
Post by R.Wieser
Post by R.Wieser
Jean-Christophe,
I don't agree ... you just need to write your own fct2DFlatText()
Lol. And how many lines would that procedure contain ?
And how many lines will this thread contain ?

Sorry, I can't see where the fun is ... maybe because the
number of lines isn't exactly my metric for code quality,
mine is : 'it does exactly what I want' ... I'm a simple man !
Post by R.Wieser
With GDI32 I can just use the DLL function like TextOut directly.
Nothing to switch, nothing that needs to be set and cleared the whole
time.
Ofcourse, disabeling the texts own background does make it look a bit
better. So, two calls all-in all.
Fine - except it doesn't work like you wanted it - hence this thread,
and me trying to help while getting back unexpected comments :-|
Post by R.Wieser
With OpenGL on the other hand I have had quite a few troubles. It also
needs me to set up 3D and 2D modes in every frame, as well as switching
quite a few things related to those off and on the whole time.
And pardon me, but the OpenGL way isn't really what you call simple *or* too
well documented. I've just posted a problem where switching to Ortho causes
me to loose pixel row and column Zero, causing an offset. ...Which I only
noticed when I tried to match-up ortho coordinates with the ones that I
supplied to glScissor.
Nope, I've now spend a few days *just* to get Ortho to work
Well, I guess that, all in all, total you wrote more lines than I did,
with the result that yours gives you trouble while mine works.
( now I start to see where the fun is ... no seriously, come on :-)
Post by R.Wieser
Post by R.Wieser
You won't need this heavy load anymore if you disable all
'features' at the very start of your fct2DFlatText() function
Yeah, thats exactly the "switching on and off" I referred too. Because
when
I disable them at the start of some orthographic drawing I need to re-enable
them again when a new frame is started and the 3D mode is initialized.
Right ?
Sure, being the programmer, you're the master,
you can't expect OpenGL to guess and do it four you.

You want flat 2D text, fine; then after your 3D scene is done you disable
3D 'features' and enable 2D text drawing, draw text, then swap buffers,
and that's it; next frame will process your already written 3D scene.
Sounds quite logical to me and I still can't see where the problem is.
Mix GDI rised problems leading to complain about OpenGL ?
Post by R.Wieser
Post by R.Wieser
BTW, I used something quite close to insert 2D-flat-text into
the 3D scene itself with the possibility to locate text in 3D(x,y,z)
while always keep oriented straight in front of the viewer, whatever
the rotations.
I will probably try to do the same/similar, as I would like to place some
"name tags" onto certain 3D locations (like when displaying a game world).
Yes, that's it exactly.

Works fine unless you want better-looking, 'sexy', 3D fonts.
I used to use a BMP with nice alphabet and numbers and map
string characters into it to display textured 3D floating messages.
Looks better ... unless you demand to count number of code lines :op
Post by R.Wieser
Post by R.Wieser
Post by R.Wieser
And *how* does it do that ?
With the very same code I already posted here before.
Ah. Sorry, I thought it would do a bit more than that.
Sorry I didn't post what you expected.
Post by R.Wieser
Your image and function name hinted at a true textbox*, something
which I also aimed to make (already wrote it using GDI, but now
needed to recreate it in OpenGL).
*One where the textbox top-left would be the origin to the drawn text, and
which would not allow any drawn text to spill outof/over the box.
Possibly
even including CR,LF awareness.
I did this in the past, by parsing the string to detect CRLFs,
split the string, skip one character_height down (+Y)
and restart at the left of the box (X)
I don't use it anymore since I just display numeric values,
where strings are sprintf'ed at the time the box is drawn.
Post by R.Wieser
Post by R.Wieser
Uh ... never had that, but I don't clip the box at all.
:-) Thats what I referred to a few messages back: You know how long your
text will be(come) at its maximum, and just draw a big enough rectangle that
the text will always stay "inside" of it.
Yes, that is true.

Another way is to dynamically resize the rectangle of the box
to make it fit by itself to the longest string ( strlen * charwidth )
Implied : use of non-proportional font like ANSI 'Courier' or else.
Works fine too.
I don't use it there since I fixed the longest string length.
Post by R.Wieser
Thanks for the help though, I appreciate it.
You're welcome, Rudy.
R.Wieser
2015-09-10 21:31:54 UTC
Permalink
Raw Message
Jean-Christophe,
Post by Jean-Christophe
And how many lines will this thread contain ?
Sorry, I can't see where the fun is ...
My apologies. At the moment I wrote that you where referring to a function I
knew nothing about. It could have possibly held several thousands of lines.
Which you did, quite offhandidly, offer it as a/the solution to me. That
combination was funny to me.
Post by Jean-Christophe
Fine - except it doesn't work like you wanted it - hence this thread,
True.

But please do not tell me that the OpenGL method is easy. Which is all I
tried to say there.
Post by Jean-Christophe
Well, I guess that, all in all, total you wrote more lines than I did,
You can say that again. If only to try to get different approaches to work.
Post by Jean-Christophe
with the result that yours gives you trouble while mine works.
:-) If all I wanted to make would have been a copy of what you've got I
would probably have had it in less than an hour after it became clear that
GDI wouldn't do. No, as I've been mentioning thruout our conversation, my
textbox was intended to do a bit more than yours.

Next to that, your approach to it is quite different than mine. Where you
are content with having it "look good" I have the deep-rooted urge to figure
out the reason why some things do not want to work as expected -- like that
rectangle and its border coordinates mismatch -- and often learn a thing or
two in the process (just as I did here).
Post by Jean-Christophe
( now I start to see where the fun is ... no seriously, come on :-)
:-) I think I see what you think is funny.
Post by Jean-Christophe
you can't expect OpenGL to guess and do it four you.
No. But I did try a fully different approach which would not have needed
all of that, and thus would make overlaying text quite a bit easier (and
also most likely speed the whole thing up a bit).
Post by Jean-Christophe
Sorry I didn't post what you expected.
Nothing to be sorry about. You posted code you thought would be helpfull
(and it was), it was just me thinking it was in reference to what I had
been talking about at that moment (viewports, text-on-textbox, clipping).
Post by Jean-Christophe
I don't use it anymore since I just display numeric values,
where strings are sprintf'ed at the time the box is drawn.
Other than you, my textbox isn't geared to a specific goal. I think that
being able to display a multi-line string on its own (much like GDI's
ExtTextOut does) could come in handy.
Post by Jean-Christophe
Another way is to dynamically resize the rectangle of the box
to make it fit by itself to the longest string ( strlen * charwidth )
A kind of "messagebox" approach. Yep, that would be another solution.

Regards,
Rudy Wieser
Post by Jean-Christophe
Rudy,
Post by R.Wieser
Post by R.Wieser
Jean-Christophe,
I don't agree ... you just need to write your own fct2DFlatText()
Lol. And how many lines would that procedure contain ?
And how many lines will this thread contain ?
Sorry, I can't see where the fun is ... maybe because the
number of lines isn't exactly my metric for code quality,
mine is : 'it does exactly what I want' ... I'm a simple man !
Post by R.Wieser
With GDI32 I can just use the DLL function like TextOut directly.
Nothing to switch, nothing that needs to be set and cleared the whole
time.
Ofcourse, disabeling the texts own background does make it look a bit
better. So, two calls all-in all.
Fine - except it doesn't work like you wanted it - hence this thread,
and me trying to help while getting back unexpected comments :-|
Post by R.Wieser
With OpenGL on the other hand I have had quite a few troubles. It also
needs me to set up 3D and 2D modes in every frame, as well as switching
quite a few things related to those off and on the whole time.
And pardon me, but the OpenGL way isn't really what you call simple *or* too
well documented. I've just posted a problem where switching to Ortho causes
me to loose pixel row and column Zero, causing an offset. ...Which I only
noticed when I tried to match-up ortho coordinates with the ones that I
supplied to glScissor.
Nope, I've now spend a few days *just* to get Ortho to work
Well, I guess that, all in all, total you wrote more lines than I did,
with the result that yours gives you trouble while mine works.
( now I start to see where the fun is ... no seriously, come on :-)
Post by R.Wieser
Post by R.Wieser
You won't need this heavy load anymore if you disable all
'features' at the very start of your fct2DFlatText() function
Yeah, thats exactly the "switching on and off" I referred too. Because
when
I disable them at the start of some orthographic drawing I need to re-enable
them again when a new frame is started and the 3D mode is initialized.
Right ?
Sure, being the programmer, you're the master,
you can't expect OpenGL to guess and do it four you.
You want flat 2D text, fine; then after your 3D scene is done you disable
3D 'features' and enable 2D text drawing, draw text, then swap buffers,
and that's it; next frame will process your already written 3D scene.
Sounds quite logical to me and I still can't see where the problem is.
Mix GDI rised problems leading to complain about OpenGL ?
Post by R.Wieser
Post by R.Wieser
BTW, I used something quite close to insert 2D-flat-text into
the 3D scene itself with the possibility to locate text in 3D(x,y,z)
while always keep oriented straight in front of the viewer, whatever
the rotations.
I will probably try to do the same/similar, as I would like to place some
"name tags" onto certain 3D locations (like when displaying a game world).
Yes, that's it exactly.
Works fine unless you want better-looking, 'sexy', 3D fonts.
I used to use a BMP with nice alphabet and numbers and map
string characters into it to display textured 3D floating messages.
Looks better ... unless you demand to count number of code lines :op
Post by R.Wieser
Post by R.Wieser
Post by R.Wieser
And *how* does it do that ?
With the very same code I already posted here before.
Ah. Sorry, I thought it would do a bit more than that.
Sorry I didn't post what you expected.
Post by R.Wieser
Your image and function name hinted at a true textbox*, something
which I also aimed to make (already wrote it using GDI, but now
needed to recreate it in OpenGL).
*One where the textbox top-left would be the origin to the drawn text, and
which would not allow any drawn text to spill outof/over the box.
Possibly
even including CR,LF awareness.
I did this in the past, by parsing the string to detect CRLFs,
split the string, skip one character_height down (+Y)
and restart at the left of the box (X)
I don't use it anymore since I just display numeric values,
where strings are sprintf'ed at the time the box is drawn.
Post by R.Wieser
Post by R.Wieser
Uh ... never had that, but I don't clip the box at all.
:-) Thats what I referred to a few messages back: You know how long your
text will be(come) at its maximum, and just draw a big enough rectangle that
the text will always stay "inside" of it.
Yes, that is true.
Another way is to dynamically resize the rectangle of the box
to make it fit by itself to the longest string ( strlen * charwidth )
Implied : use of non-proportional font like ANSI 'Courier' or else.
Works fine too.
I don't use it there since I fixed the longest string length.
Post by R.Wieser
Thanks for the help though, I appreciate it.
You're welcome, Rudy.
\

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