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OpenGL How to update just one part of a gl texture?

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I'm developing a 3D Painting tool that uses OpenGL as hardware rendering. Since the texture changes with every brush stroke, I'm using glTexture2D to apply the texture to the mesh that is being painted. Everything works fine with small textures ( 512 x 512 ), but with larger textures ( 2048 x 2048 ) the frame rate decreases, affecting the painting performance (creating more linear brush strokes). My question is... Is there a way to update just part of a texture? I'd like to use glGenTextures and glBindTexture to upload the texture to the video card memory, and then just update the damaged rectangular zones of the texture (where the brush stroke was painted). This is the source code I'm using right now: http://sceneengine.svn.sourceforge.net/viewvc/sceneengine/trunk/CrackArt/src/Core/viewport_entities.cpp?revision=1154&view=markup line 1878 : ViewportMesh::SetMaterial http://sceneengine.svn.sourceforge.net/viewvc/sceneengine/trunk/CrackArt/src/Plugins/TexPaint/PaintMaterialGUI.cpp?revision=1156&view=markup line 960 : PaintMaterialGUI::GetViewMaterial line 1016 : PaintMaterialGUI::UpdateViewBitmap ps. I still consider myself a beginner with OpenGL. Please don't hesitate to tell me if you think there is an easier way to do this. Thank you for your help, Diego A. Castano

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I don't have time right now to go into details (or look through your code, sorry!), but it seems like you're looking for glTexSubImage2D. If you're already using it, then I've completely misunderstood and you'll need to do something algorithmically if things aren't going fast enough for you. However, it's a definite step in the right direction if not.

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Hello jouley,

Thank you for your tip. Indeed this seems the way to update the texture in video memory.

I found a tutorial (Nehe 35) that uses glTexSubImage2D, but the workflow is different to what I need.

I've been trying to load the texture in video memory using glGenTextures, glBindTexture and glTexImage2D, and then update it using glTexSubImage2D, but the texture never gets updated.

I suspect it has something to do with the method I'm using to select the texture (glBindTexture).

This is the source code I'm using:

Note.
For simplicity the subregion send with glTexSubImage2D is the whole image.

if ( tex )
{
if ( tex->m_gl_id == UNDEFINED_INDEX )
{
// Load the texture to video memory...

glGenTextures( 1, &tex->m_gl_id );
glBindTexture( GL_TEXTURE_2D, tex->m_gl_id );
glTexParameteri( GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri( GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
glTexImage2D( GL_TEXTURE_2D, 0, tex->m_bpp, tex->m_width, tex->m_height, 0, tex->m_type, GL_UNSIGNED_BYTE, tex->m_image_data);
}

// Bind loaded texture...

glBindTexture( GL_TEXTURE_2D, tex->m_gl_id );

if ( tex->m_gl_id && tex->m_image_data )
{
glTexSubImage2D( GL_TEXTURE_2D, 0, 0, 0, tex->m_width, tex->m_height, tex->m_type, GL_UNSIGNED_BYTE, tex->m_image_data );
}

glTexParameteri( GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri( GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
glEnable( GL_TEXTURE_2D );
}

tex is an instance of a class that holds the texture data.

I'm I doing something wrong? Do I need to enable or disable something to update texture regions?

Thank you again,
Diego A. Castano

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Do not call the second set of glTexParameteri(). You just need to set them once when you first create the texture.

Also, I see why you're keeping it all in one place. But I'd suggest breaking into two different functions, one that creates your texture, and one that updates it, just to prevent any issues there.

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Thank you guys...

I created a clean application and it works with the code that I posted in my previous reply (sans second call to parameters), the texture gets updated just as I need.

Now my problem is that this is not working on the 3D application I'm developing (CrackArt).

Both applications use wxWidgets' wxGLCanvas, but I suspect that there is a wrong parameter or an error in CrackArt that it's preventing glTexSubImage2D to work. In fact a few months ago I tried to implement multitexturing (with alpha blending) in CrackArt and it didn't work, although it was working on a wxGLCanvas test application.

In short, my new questions are... Is there any GL parameter that deactivates GL functionality? Or what kind of error can prevent multitexturing and glTexSubImage2D to work?

Thanks for your help!
Diego

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Quote:
Original post by ScEngMan
Thank you guys...
Both applications use wxWidgets' wxGLCanvas, but I suspect that there is a wrong parameter or an error in CrackArt that it's preventing glTexSubImage2D to work. In fact a few months ago I tried to implement multitexturing (with alpha blending) in CrackArt and it didn't work, although it was working on a wxGLCanvas test application.

In short, my new questions are... Is there any GL parameter that deactivates GL functionality? Or what kind of error can prevent multitexturing and glTexSubImage2D to work?

For error checking, you should already be using glGetError()... if, though, you haven't been, now's the time to start [wink].

Given no errors, I'd make sure that all the setup you have in your test application is also present in CrackArt, and that you aren't undoing it anywhere. Make sure you've enabled GL_TEXTURE_2D without disabling it before you need it. This can be done several times a frame, it just has to be on/off at the correct times. Then check that you're binding the right textures correctly. It'd also be helpful to strip down CrackArt until things work, then put pieces back in to narrow it down to a smaller problem chunk of code.

That said, I'm only passingly familiar with wxWidgets and can't offer any input on that front.

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Thank you jouley,

I checked my code in CrackArt and I found a call to glTexImage2D right before my textures were loaded or updated...

glTexImage2D(GL_TEXTURE_2D,0,3,0,0,0,GL_RGB,GL_UNSIGNED_BYTE,0);

Just by commenting that line, glTexSubImage2D started working.

Thank you for your help!
Diego

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