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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 8th 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.


    Perhaps I've misunderstood the problem you're facing but it looks like what you're trying to do is render to an FBO and then swap the contents of that FBO to the display surface.

    This isn't really what FBOs are for. The EGL surface essentially has its own framebuffer, and when you call glBindFramebuffer(GL_FRAMEBUFFER,0) this is telling the GLES contexrt to render to that.

    When you call glBindFramebuffer(GL_FRAMEBUFFER, framebuffer) the GLES context will start writing to a different surface in memory, and doesn't touch the area of memory which is displayed when you call eglSwapBuffers.

    Usually the reason you would use a frame buffer object in this way is something like:

    GenFramebuffers(1, &framebuffer);

    glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);

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

    // render texture details to frame buffer

    glBindFramebuffer(GL_FRAMEBUFFER, 0)

    // render objects using texture

    eglSwapbuffers(display, surface)



    This allows you to have, for example, a texture showing the scene from a different angle, for if you wanted to have a virtual environment with a screen showing what a camera elsewhere in the scene sees.

    If you don't bind to buffer 0, the rendering done at that point will just go into the texture, and there'll be nothing worth swapping.

    Does that sound like what you're trying to achieve?

    -Stacy
Reply
  • Note: This was originally posted on 8th 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.


    Perhaps I've misunderstood the problem you're facing but it looks like what you're trying to do is render to an FBO and then swap the contents of that FBO to the display surface.

    This isn't really what FBOs are for. The EGL surface essentially has its own framebuffer, and when you call glBindFramebuffer(GL_FRAMEBUFFER,0) this is telling the GLES contexrt to render to that.

    When you call glBindFramebuffer(GL_FRAMEBUFFER, framebuffer) the GLES context will start writing to a different surface in memory, and doesn't touch the area of memory which is displayed when you call eglSwapBuffers.

    Usually the reason you would use a frame buffer object in this way is something like:

    GenFramebuffers(1, &framebuffer);

    glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);

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

    // render texture details to frame buffer

    glBindFramebuffer(GL_FRAMEBUFFER, 0)

    // render objects using texture

    eglSwapbuffers(display, surface)



    This allows you to have, for example, a texture showing the scene from a different angle, for if you wanted to have a virtual environment with a screen showing what a camera elsewhere in the scene sees.

    If you don't bind to buffer 0, the rendering done at that point will just go into the texture, and there'll be nothing worth swapping.

    Does that sound like what you're trying to achieve?

    -Stacy
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