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

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

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

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