[Mesa-users] Y axis flipped when running OpenGL application over surfaceless EGL without a native window system

[zhigang gong]

I'm trying to create a surfaceless EGL context with drm support on
intel's i965 platform and then run OpenGL on it directly
without a native window system.

Here is my pseudo code:

fd = open("/dev/dri/card0");
eglGetDRMDisplayMESA(fd);
eglInitialize();
ctx = eglCreateContext();
eglMakeCurrent(dp, EGL_NO_SURFACE, EGL_NO_SURFACE, ctx);
eglCreateDRMImageMESA(dp, attribs);
eglExportDRM...  /*Get the image's buffer handle. */
/* Use that handle to create a FB by using drmAddFB. */
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glEGLImageTargetTexture2DOES(GL_TEXTURE_2D, image);

glGenFramebuffersEXT(1, &fb);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fb);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT,
                             GL_COLOR_ATTACHMENT0_EXT,
                             GL_TEXTURE_2D,
                             texture,
                             0);

glViewport(0, 0, (GLsizei) 1366, (GLsizei) 768);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, 1366, 0, 768,  -1.0, 1.0);

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

glClearColor(0.0, 1.0, 0.0, 0.0);
glShadeModel(GL_FLAT);
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(1.0, 0.0, 0.0);
glRectf(0, 0, 16, 16 );
glFlush();
}

I just found that the red rectangle goes to the upper-left corner of
the screen.
But according to OpenGL's standard, it should be at lower-left corner. The
default originl in OpenGL should be at lower left. Right? It shows
that the Y axis is
flipped. Is there any body can give a clue on this issue? Is this somehow a
bug for mesa/EGL or I did something wrong here. Any suggestion is welcome.