| | [ Return to Bugs & Features | Roadmap 2.0 | Post Text | Post File | SVN ⇄ GIT ]
STR #3064
| Application: | FLTK Library |
|---|
| Status: | 5 - New |
|---|
| Priority: | 3 - Moderate, e.g. unable to compile the software |
|---|
| Scope: | 2 - Specific to an operating system |
|---|
| Subsystem: | Unassigned |
|---|
| Summary: | [FLTK2] fltk::gldrawtext always draws in white |
|---|
| Version: | 2.0-current |
|---|
| Created By: | greg.ercolano |
|---|
| Assigned To: | greg.ercolano |
|---|
| Fix Version: | Unassigned |
|---|
| Update Notification: | |
|---|
Trouble Report Files:
[ Post File ]
| |
| #1 | greg.ercolano
12:04 Mar 09, 2014 |
| patch.txt
4k | |
Trouble Report Comments:
[ Post Text ]
| |
| #1 | greg.ercolano
12:03 Mar 09, 2014 |
| Reporting this on behalf of Gonzalo.
This may affect 1.3 as well, which is why I'm handling it.
Gonzalo wrote on fltk.general on Feb 21 2014:
---------------------------------------------------------------------
I have a GLWindow that draws a lot of stuff. I am trying to draw text
using the fltk functions. I am able to draw the text properly,
but it is always drawn in white. It does not respect any glColor3f()
or glsetcolor() function.
My code looks like:
// Turn on Color Buffer and Depth Buffer
glColorMask(true, true, true, true);
// Only write to the Stencil Buffer where 1 is not set
glStencilFunc(GL_NOTEQUAL, 1, 0xFFFFFFFF);
// Keep the content of the Stencil Buffer
glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisable(GL_TEXTURE_2D);
glBegin( GL_BLEND );
// So compositing works properly
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glColor4f( r, g, b, a );
fltk::glsetfont(font(), size() );
fltk::gldrawtext(text().c_str(), pts[0].x, pts[0].y);
I am able to get colors into the font if I add a glBegin(GL_POLYGON) and glEnd() in between the fltk::gl* calls, but then the text is all garbage. I looked into gldrawtext() and glsetfont() for clues and nothing is strange.
---------------------------------------------------------------------
..and followed that up with:
---------------------------------------------------------------------
I tried it on Linux (where I get white letters)
and on Windows (where I get nothing at all ).
[..]
I found the Linux code suffers from the texture generation from
GL_LUMINANCE instead of GL_LUMINANCE_ALPHA.
And the glBlendFunc(GL_ONE) instead of GL_SRC_ALPHA.
The Windows part of the code I am still digging.
--------------------------------------------------------------------- | |
| |
| #2 | greg.ercolano
12:09 Mar 09, 2014 |
| Attached a patch provided by gonzalo that he says:
----
FLTK2.0 patch to make antialiased text in Linux and aliased text
in Windows
----
There are some extraneous mods included in the patch, but worthy
of note are mods to OpenGL/gl_draw.cxx, in particular this mod
caught my eye:
- wglUseFontBitmaps(hdc, base, size, listbase+base);
+
+ bool succeed = false;
+ int MAX_TRIES = 5;
+ for ( int i = 0; i < MAX_TRIES && !succeed; ++i )
+ {
+ succeed = wglUseFontBitmaps(hdc, base, len, listbase+base) == TRUE;
+ }
+ if ( !succeed )
+ {
+ fprintf( stderr, "wglUseFontBitmaps error\n" );
+ }
Suggesting we use fltk::warning() in place of the fprintf(),
and I asked gonzalo about the MAX_TRIES loop around wglUseFontBitmaps:
----
erco writes:
Hmm, can you explain what's up with the for() retry loop..
Does it actually need several retries to work?
gonzalo answers:
Yes, the for loop is needed as the wgl function sometimes fails unexpectedly
(usually after a change in context).
erco follows up:
Thanks -- I see this on the net too, looks like no one seems to know
why it fails, but sometimes it does, so they include the retry loop.
I guess I should make this change in 1.3 as well.
[..]
This is some perhaps relevant info on the issue above.
The MSDN docs for this function:
http://msdn.microsoft.com/en-us/library/windows/desktop/dd374392%28v=vs.85%29.aspx
..includes a "community comment" that sounds like it might be the reason
it fails on the first try, but succeeds on the second try; it reads:
________________________________________________________________________________
_______
wglUseFontBitmaps fails if any GL_ERROR is set before calling this function.
We have to call glGetError() before calling this function.
Example:
// Forcefully setting an error.
// Following code is added to demonstrate the problem
glMatrixMode(GL_TEXTURE_2D); // Set opengl Error since matrix
bool bReturnValue = wglUseFontBitmaps( m_hDC, 0,256, m_nFontDisplayList );
// bReturnValue returns false, glGetError() return GL_NO_ERROR.
Here Font display list is not created, and error status is not provided by wglUseFontBitmaps.
This problem can be solved by calling glGetError() before wglUseFontBitmaps().
// Forcefully setting an error.
// Following code is added to demonstrate the problem
glMatrixMode(GL_TEXTURE_2D);
int nErr = glGetError();
bool bReturnValue = wglUseFontBitmaps( m_hDC, 0,256, m_nFontDisplayList );
bReturnValue is true and bitmap is created.
________________________________________________________________________________
_______
[..] so perhaps doing a glGetError() before the call to wglUseFontBitmaps()
will ensure it works the first time.
---- | |
[ Return to Bugs & Features | Post Text | Post File ]
|
| |
