Can't generate mipmaps with off-screen OpenGL context on Linux - c++

Question

This question is a continuation of the problem I described here .This is one of the weirdest bugs I have ever seen.I have my engine running in 2 modes:display mode and offscreen.The OS is Linux.I generate mipmaps for the textures and in Display mode it all works fine.In that mode I use GLFW3 for context creation.Now,the funny part:in the offscreen mode,context for which I create manually with the code below,the mipmap generation fails OCCASIONALLY!That's on some runs the resulting output looks ok,and in other the missing levels are clearly seen as the frame is full of texture junk data or entirely empty.
At first I though I had my mipmap gen routine wrong which goes like this:
glGenTextures(1, &textureName);
glBindTexture(GL_TEXTURE_2D, textureName);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, imageInfo.Width, imageInfo.Height, 0, imageInfo.Format, imageInfo.Type, imageInfo.Data);
glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 0 );
glGenerateMipmap(GL_TEXTURE_2D);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
I also tried to play with this param:
glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, XXX);
including Max level detection formula:
int numMipmaps = 1 + floor(log2(glm::max(imageInfoOut.width, imageInfoOut.height)));
But all this stuff didn't work consistently.Out of 10-15 runs 3-4 come out with broken Mipmaps.What I then found was that switching to GL_LINEAR solved it.Also in mipmap mode,setting just 1 level worked as well.Finally I started thinking there could a problem on a context level because in screen mode it works!I switched context creation to GLFW3 and it works.So I wonder what's going on here?Do I miss something in Pbuffer setup which breaks mipmaps generation?I doubt it because AFAIK it is done by the driver.
Here is my custom off-screen context creation setup:
int visual_attribs[] = {
GLX_RENDER_TYPE,
GLX_RGBA_BIT,
GLX_RED_SIZE, 8,
GLX_GREEN_SIZE, 8,
GLX_BLUE_SIZE, 8,
GLX_ALPHA_SIZE, 8,
GLX_DEPTH_SIZE, 24,
GLX_STENCIL_SIZE, 8,
None
};
int context_attribs[] = {
GLX_CONTEXT_MAJOR_VERSION_ARB, vmaj,
GLX_CONTEXT_MINOR_VERSION_ARB, vmin,
GLX_CONTEXT_FLAGS_ARB,
GLX_CONTEXT_ROBUST_ACCESS_BIT_ARB
#ifdef DEBUG
| GLX_CONTEXT_DEBUG_BIT_ARB
#endif
,
GLX_CONTEXT_PROFILE_MASK_ARB, GLX_CONTEXT_COMPATIBILITY_PROFILE_BIT_ARB,
None
};
_xdisplay = XOpenDisplay(NULL);
int fbcount = 0;
_fbconfig = NULL;
// _render_context
if (!_xdisplay) {
throw();
}
/* get framebuffer configs, any is usable (might want to add proper attribs) */
if (!(_fbconfig = glXChooseFBConfig(_xdisplay, DefaultScreen(_xdisplay), visual_attribs, &fbcount))) {
throw();
}
/* get the required extensions */
glXCreateContextAttribsARB = (glXCreateContextAttribsARBProc) glXGetProcAddressARB((const GLubyte *) "glXCreateContextAttribsARB");
glXMakeContextCurrentARB = (glXMakeContextCurrentARBProc) glXGetProcAddressARB((const GLubyte *) "glXMakeContextCurrent");
if (!(glXCreateContextAttribsARB && glXMakeContextCurrentARB)) {
XFree(_fbconfig);
throw();
}
/* create a context using glXCreateContextAttribsARB */
if (!(_render_context = glXCreateContextAttribsARB(_xdisplay, _fbconfig[0], 0, True, context_attribs))) {
XFree(_fbconfig);
throw();
}
// GLX_MIPMAP_TEXTURE_EXT
/* create temporary pbuffer */
int pbuffer_attribs[] = {
GLX_PBUFFER_WIDTH, 128,
GLX_PBUFFER_HEIGHT, 128,
None
};
_pbuff = glXCreatePbuffer(_xdisplay, _fbconfig[0], pbuffer_attribs);
XFree(_fbconfig);
XSync(_xdisplay, False);
/* try to make it the current context */
if (!glXMakeContextCurrent(_xdisplay, _pbuff, _pbuff, _render_context)) {
/* some drivers does not support context without default framebuffer, so fallback on
* using the default window.
*/
if (!glXMakeContextCurrent(_xdisplay, DefaultRootWindow(_xdisplay),
DefaultRootWindow(_xdisplay), _render_context)) {
throw();
}
}
Almost forgot:My system and hardware:
Kubuntu 13.04 64bit. GPU: NVidia Geforce GTX 680 . The engine uses OpenGL 4.2 API
Full OpenGL info:
**OpenGL vendor string: NVIDIA Corporation
OpenGL renderer string: GeForce GTX 680/PCIe/SSE2
OpenGL version string: 4.4.0 NVIDIA 331.49
OpenGL shading language version string: 4.40 NVIDIA via Cg compiler**
Btw,I used also older drivers and it doesn't matter.
UPDATE:
Seems like my assumption regarding GLFW was wrong.When I compile the engine and run it from the terminal the same is happening.BUT - if I run the engine from IDE (debug or release )there are no issues with the mipmaps.Is it possible the standalone app works against different SOs?
To make it clear,I dont't use Pbuffers to render into.I render into custom Frame buffers.
UPDATE1:
I have read that non-power of 2 textures can be tricky to auto generate mipmaps.And that in case OpenGL fails to generate all the levels it turns of texture usage.Is it possible that's what I am experiencing here?Because once the mipmapped texture goes wrong the rest of textures (non mipmapped) disappear too.But if this is the case then why this behavior is inconsistent?

Answer 1

Uh, why are you using PBuffers in the first place? PBuffers have just too many caveats as that there was only one valid reason to use them in a new project?
You want offscreen rendering? Then use Framebuffer Objects (FBOs).
You need a purely off-screen context? Then create a normal window which you simply don't show and create an FBO on it.