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04.15.2008 at 09:25PM PDT, ID: 23325979

	[x] Attachment Details

OpenGL texture mapping problem

Asked by lzha022 in OpenGL Graphics & Game Programming

Tags: OpenGL

Hello experts,
I do not know much about OpenGL, but i need to fix this bug (code written by someone else).
When two canvas windows opened at the same time, the image display does not work properly. Sometimes, the whole canvas becomes black or green or red...
I think might be related to the call glGenTextures(1, &textureID) - the main windows mixed the textureID in the two cavas windows. But the code related to this part is like this
if(!glIsTexture(textureId))
glGenTextures(1,&textureId);
Looks like the above code will make sure the textureID be unique, is it?
Any other idea why this problem happens?

Thanks.
AlisonStart Free Trial

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04.16.2008 at 09:55PM PDT, ID: 21374268

ikework:

hey lzha022.

if you have two opengl windows, then you need two opengl-contexts. two contexts cant share the same texture-id.you have to generate one textureid for each gl-context.

ike

04.16.2008 at 09:58PM PDT, ID: 21374279

lzha022:

Hi Ikework,
Thanks for your reply. But how do i use two openGL-contextx? As both the two windows share the same canvas class.

04.16.2008 at 10:11PM PDT, ID: 21374321

ikework:

>> As both the two windows share the same canvas class.

are you talking about Qt-canvas?

04.17.2008 at 01:33PM PDT, ID: 21381070

lzha022:

>>are you talking about Qt-canvas?

Yes, Qt canvas.
I checked the code again, one openGL window has 4 canvases (same canvas class), another openGL window has one canvas (different cavas class). If i open the two openGL at the same time, the images will not display properly, but each window itself works fine.
thanks
Alison

04.17.2008 at 09:48PM PDT, ID: 21383374

ikework:

ok, each of the opengl-windows has to generate its own texture ids. you might have to use QGLWidget::makeCurrent when you generate the texture-ids. have a look at:

http://stuff.mit.edu/afs/athena/software/qt-dynamic_v4.2.1/www/qglwidget.html#makeCurrent

Accepted Solution

04.17.2008 at 09:51PM PDT, ID: 21383384

lzha022:

Thanks ikework.
It is time to go home, i will have a look next Monday.
Have a good weekend!

04.17.2008 at 09:58PM PDT, ID: 21383406

ikework:

thanks alison .. to you too :)

04.20.2008 at 04:32PM PDT, ID: 21397984

lzha022:

Hi ikework,
I made some changes to the code. I can not call makeCurrrent immediately before i generate the texture ids as the code below will show you
void TwoDCanvas::paintGL()
{
this->makeCurrent();
implement->paintGL();
}/* void TwoDCanvas::paintGL() */
The actual drawing part is in implement->paintGL(). implement is just a normal c++ class.
The image disply looks better but still does not work correctly.
Have you got any other idea?
thanks
Alison

04.21.2008 at 11:48AM PDT, ID: 21404767

ikework:

just create the texture-ids in the initialize function of the OpenGL-widget

>> but still does not work correctly.

can you explain what is wrong?

04.21.2008 at 02:59PM PDT, ID: 21406472

lzha022:

Hi ikework,
I have cines to display, so creating texture-ids in the initialize function will not work.

>>can you explain what is wrong?
The images do not display propery as before but a bit better - maybe because of the makeCurrent call before implement->paintGL();

04.21.2008 at 11:31PM PDT, ID: 21408489

ikework:

what are cines? there is a virtual function QGLWidget::initializeGL() what i mean is this:

class YourClass : public QGLWidget
{
public:
virtual void initializeGL ();

....

private:
GLuint texture_id;
};

void YourClass::initializeGL ()
{
// load your texturefile ..
....

// generate the texture-id
glGenTextures( 1, &texture_id );
glBindTexture( GL_TEXTURE_2D, texture_id );

glTexImage2D( GL_TEXTURE_2D, ..

}

>> The images do not display propery as before but a bit better

can you upload the texture and a screenshot of your application?

04.21.2008 at 11:34PM PDT, ID: 21408506

ikework:

have a look at this for more details:

http://doc.trolltech.com/4.3/qglwidget.html#details

04.22.2008 at 01:42PM PDT, ID: 21415379

lzha022:

Hi ikework,
cines are movies in our project - sorry about this. There are lots of images in one movie, so it is not possible to generate all texture_ids in initializeGL.
All the texture_ids are generated in renderCanvas() in my code.
Thanks
Alison

04.22.2008 at 02:17PM PDT, ID: 21415717

lzha022:

Hi ikework,
Here is a screenshot. The yellow images should look like the other image. but they turn yellow, sometimes some images are white or red.

image.bmp (2.0 MB) (File Type Details)

error

04.22.2008 at 10:58PM PDT, ID: 21418026

ikework:

can you show the code of your QGLWidget, especially initializeGL() and paintGL()

04.22.2008 at 11:30PM PDT, ID: 21418146

ikework:

1) what is rendered in the second gl-window. the movie as well? if it has static-textures at least you can generate them in its initializeGL() functions

2) are you sure you have to use opengl to render the movie, seems to be overkill to me. better convert it to a common movie-format and use a plugin to render it

04.23.2008 at 02:24PM PDT, ID: 21425574

lzha022:

some code:

QGLWidget
void MyCanvas::initializeGL()
{
initialiseCoords();
implement->initializeGL();
}
void MyCanvas::paintGL()
{
this->makeCurrent(); //i added this line of code
implement->paintGL();
}
implement is class MyCanvasImpl
void MyCanvasImpl::initializeGL()
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
glEnable(GL_TEXTURE_2D);
glShadeModel(GL_FLAT);
// Initialize the "OpenGL Extension Wrangler" library
glewInit();
glEnable(GL_COLOR_TABLE);
initialised = true;
}
void myCanvasImpl::paintGL()
{
renderCanvas();
}
void myCanvasImpl::renderCanvas(void)
{
if (initialised)
{
setCoords();
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
drawImage();
...
}

image will be updated by calling setImage() from outside for showing movies
myCanvasImpl::drawImage()
{
...
for(int i=0;i<imageSize*imageSize;i++)
{
short filteredValue = (short)(contrast*(image[i] - brightness) + 127.5f);
if (filteredValue > 255)
{
filteredValue = 255;
}
else if (filteredValue < 0)
{
filteredValue = 0;
}
imageData[i] = (unsigned char)filteredValue;
}
glPixelStorei(GL_UNPACK_ALIGNMENT,1);
if(!glIsTexture(textureId))
glGenTextures(1,&textureId);
glBindTexture(GL_TEXTURE_2D,textureId);
...
}
I am not quite familiar with openGl, and the code has been there for a long time. Maybe my unclear discription confused you.
Thanks

04.26.2008 at 01:47AM PDT, ID: 21444933

ikework:

you never delete "textureid" before reusing it.

add this to initializeGL:

void MyCanvasImpl::initializeGL()
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
glEnable(GL_TEXTURE_2D);
glShadeModel(GL_FLAT);
// Initialize the "OpenGL Extension Wrangler" library
glewInit();
glEnable(GL_COLOR_TABLE);
initialised = true;
textureId = 0; // <<<<<<<<<<<<<<<<<<< init textureid to zero
}

and before you call glGenTextures, you must delete it, before reusing it:

myCanvasImpl::drawImage()
{
...
for(int i=0;i<imageSize*imageSize;i++)
{
short filteredValue = (short)(contrast*(image[i] - brightness) + 127.5f);
if (filteredValue > 255)
{
filteredValue = 255;
}
else if (filteredValue < 0)
{
filteredValue = 0;
}
imageData[i] = (unsigned char)filteredValue;
}
glPixelStorei(GL_UNPACK_ALIGNMENT,1);

// add this if-block to delete the textureid, before reusing it
if( 0 != textureId )
{
glDeleteTextures( 1, &textureId )
textureid=0;
}
glGenTextures(1,&textureId);
glBindTexture(GL_TEXTURE_2D,textureId);
...
}

can you answer the 2 questions from my previous post anyway ;)

04.27.2008 at 09:07PM PDT, ID: 21451550

lzha022:

Hi ikework,
the program works the same after i changed the code as above.
>1) what is rendered in the second gl-window. the movie as well? if it has static-textures at least you >can generate them in its initializeGL() functions
Yes, the other window also display movie as well, but the code looks better as all textureIds generated in InitializeGL()
void myThreeDCanvasImpl::initializeGL()
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glPixelStorei(GL_UNPACK_ALIGNMENT,1);
glGenTextures(numImages, textureId); //GLuint *textureId;
...
}

2) are you sure you have to use opengl to render the movie, seems to be overkill to me. better convert it to a common movie-format and use a plugin to render it.
I think so, the movie is just help users to view all images in a consecutive way, the users need to put some points on each image.

05.09.2008 at 01:21AM PDT, ID: 21531083

ikework:

>> better convert it to a common movie-format and use a plugin to render it.
after some thinking about it i guess the problem remains the same. there are some things you have to ntake care of. each line hab to be alogned on 4 bytes.
if you dont mind ploease upload the project. i would be interest in helping you, since the matter is very interesting to me too :)

ike

20080716-EE-VQP-32 / EE_QW_2_20070628

OpenGL texture mapping problem

Asked by lzha022 in OpenGL Graphics & Game Programming

Tags: OpenGL

About this solution