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Screen Dark working with FBOs

enzo sacchi
Note: This was originally posted on 7th November 2010 at http://forums.arm.com

Hi Guys,

Trying to port an akready well running Sw from Fedora PC to the Mali400 on ST7108 chip, with GLES-2.0, I got a problem working with Framebuffer Objects.
Everything is ok, debugging ok, framebuffer objects completes, no errors, but the screen remains completely dark.
My environment on Mali/ST7108 is OK, other applications can run nicely.

But I think to have not completely understood (or better: not understood at all) how to set display and surfaces while working woth FBOs (maybe the problem could be also found somewhere else)

Basic setting is more or less as below, where I have put only the relevant setting and call for Display and Surfaces.

In does seem that the eglSwapBuffers does't work at all while working with FBOs
(even a monocolor screen cannot be seen...).
In contrast, while working out of FBOs, everything seems to be ok.

After binding with glBindFramebuffer(GL_FRAMEBUFFER,0), then everything is working and can be displayed.

In contrast, after glBindFramebuffer(GL_FRAMEBUFFER, framebuffer), I cannot see anything after he eglSwapBuffers, even if the debug seems to be ok.

Could someone pls help me in giving me suggestions on how to properly set Display and Surfaces?
Does there is a running examples while using FBOs on ST7108 chip?
Thanks a lot in advance for this
(here below I have just put a rough skeleton of the used code)

"
EGLDisplay eglDisplay = 0;
EGLSurface eglSurface = 0;
EGLint major, minor, num_configs;

..........
eglDisplay = eglGetDisplay(EGL_DEFAULT_DISPLAY));

eglInitialize(eglDisplay, &major, &minor);
eglBindAPI(EGL_OPENGL_ES_API);

eglChooseConfig(eglDisplay, configAttribs, &eglConfig, 1, &num_configs);

eglSurface = eglCreateWindowSurface(eglDisplay, eglConfig, NULL, NULL);
eglContext = eglCreateContext(eglDisplay, eglConfig, NULL, contextAttribs)));
eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext);
...........
...........


egl_setup(&eglDisplay,&eglSurface);


GLuint framebuffer;
GLuint depthRenderbuffer;
GLuint texture;

.....

glGenFramebuffers(1, &framebuffer);
glGenRenderbuffers(1, &depthRenderbuffer);
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, texWidth, texHeight, 0, GL_RGB, GL_UNSIGNED_SHORT_5_6_5, NULL);


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

glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, texWidth, texHeight);

glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);

glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);

glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);

Switch (glCheckFramebufferStatus(GL_FRAMEBUFFER))
{
case GL_FRAMEBUFFER_COMPLETE:
fprintf(stdout, "\n o Framebuffer Complete");
break;
......
}


GLCheckError(glClearColor(1.0f, 0.0f, 0.0f, 1.0f));
.....
eglSwapBuffers(eglDisplay, eglSurface);


// glBindFramebuffer(GL_FRAMEBUFFER,0);
.........

eglSwapBuffers(eglDisplay, eglSurface);
""


Many Thanks
Parents
  • Note: This was originally posted on 13th September 2011 at http://forums.arm.com


    Hi there. I'm having a similar issue.

    Like the original poster, I create the FBO, bind it to a texture, check the status to make sure it's framebuffer complete, then set it to the rendering buffer, call drawelements, and I get GL_INVALID_FRAMEBUFFER_OPERATION error. Bit of a mystery since I check the completeness status on the line immediately prior to the draw call.

    Without knowing more about what you're trying to do or what hardware you're using it's hard to really answer this. It sounds like you might be using the texture in the scene with the FBO still bound, so it's trying to write to the framebuffer using content from the frame buffer. Is that what you're doing?


    Do the settings on the texture object matter, e.g. repeat/linear/reflect. Does Mali require me to specify a depth or stencil buffer? Does it require an alpha channel?

    It doesn't require a depth or stencil buffer but if you want to use depth or stencil features you'll need to have one bound.


    This code works on Tegra2 and Adreno 205. Not sure why Mali doesn't like it.

    I've also noticed that this graphics unit seems to have trouble with the first texture write to the display. I'll have to go into that in detail in another thread when I'm ready to deal with it.

    There are certain actions with frame buffers  (such as binding an FBO to a texture and renderbuffer simultaneously, which it sounds like you might be doing) which have undefined or poorly defined behaviours in the spec. Depending on your GPU (or more specifically how strict the drivers are) some things will error, others will fail silently and simply have that texture appear messed up.

    I can't really give a more specific answer without details of what you're doing...

    -Stacy
Reply
  • Note: This was originally posted on 13th September 2011 at http://forums.arm.com


    Hi there. I'm having a similar issue.

    Like the original poster, I create the FBO, bind it to a texture, check the status to make sure it's framebuffer complete, then set it to the rendering buffer, call drawelements, and I get GL_INVALID_FRAMEBUFFER_OPERATION error. Bit of a mystery since I check the completeness status on the line immediately prior to the draw call.

    Without knowing more about what you're trying to do or what hardware you're using it's hard to really answer this. It sounds like you might be using the texture in the scene with the FBO still bound, so it's trying to write to the framebuffer using content from the frame buffer. Is that what you're doing?


    Do the settings on the texture object matter, e.g. repeat/linear/reflect. Does Mali require me to specify a depth or stencil buffer? Does it require an alpha channel?

    It doesn't require a depth or stencil buffer but if you want to use depth or stencil features you'll need to have one bound.


    This code works on Tegra2 and Adreno 205. Not sure why Mali doesn't like it.

    I've also noticed that this graphics unit seems to have trouble with the first texture write to the display. I'll have to go into that in detail in another thread when I'm ready to deal with it.

    There are certain actions with frame buffers  (such as binding an FBO to a texture and renderbuffer simultaneously, which it sounds like you might be doing) which have undefined or poorly defined behaviours in the spec. Depending on your GPU (or more specifically how strict the drivers are) some things will error, others will fail silently and simply have that texture appear messed up.

    I can't really give a more specific answer without details of what you're doing...

    -Stacy
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