Octane fog problem

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Mark Davey (mkd@medphys.ucl.ac.uk)
Thu, 02 Mar 2000 14:16:01 -0800

Hi.. I have now sorted out my dithering problems on our new Octane (by
reducing the resolution to 1024x768, which makes the screen look a
little horrid since we have a nice 21 inch flat screen monitor and so
now text looks very pixelated indeed... Never mind...)
However, I now have a new problem ( is it just me that has so many
problems? ) As part of my current application, I use glFog as a means of
improving depth perception. Development has taken place on an Onyx2.
Since we received our new Octane I have tried running our application on
this platform. Everything goes well (after I fixed the dithering
problem) EXCEPT for the GL fog. It appears that maybe lookup tables are
not working on the Octane when fog is enabled.

As an example I am including a revised Draw function to replace that
found in voglMain.cxx

If the demo program

voglBasic CT.Head.Small.char.tif -sc 1 1 3.2

is then run on our Onyx2 then I get a nice fog enhanced volume rendered
image. If however I run the same code on the Octane then I simply get a
black screen. Am I defining my fog incorrectly? Or is there some problem
with the Octane? Or is Volumizer doing something strange if fog is
enabled (seems unlikely)

Anyway here is the code segment. I replace the usual glFrustum command
with one of my own to help me set the fog up correctly.

Regards
Mark

void
Draw(Widget widget)
{

    glEnable(GL_DEPTH_TEST);
    glClearColor(0.0, 0.0, 0.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    float m[4][4];
    build_rotmatrix(m, cumulativeQuaternion);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

// Temporary changes to show fog

      glMatrixMode(GL_PROJECTION);
      glLoadIdentity();
      glFrustum(
        -0.0025, 0.0025, -0.0025, 0.0025, 0.01, my_Data.modelSize[2]*4);

      glMatrixMode(GL_MODELVIEW);
      glTranslatef(0, 0, -my_Data.modelSize[2]*3);
      glEnable(GL_FOG);
      GLfloat fogColor[4] = {0.0,0.0,0.0,0.0};
      glFogi(GL_FOG_MODE,GL_LINEAR);
      glFogfv(GL_FOG_COLOR,fogColor);
      glFogf(GL_FOG_DENSITY,0.01);
      glFogf(GL_FOG_START,my_Data.modelSize[2]*2.0);
      glFogf(GL_FOG_END,my_Data.modelSize[2]*3);

// End of changes

    glMultMatrixf(&(m[0][0]));
    glRotatef(180, 0, 1, 0); // initial rotations
    glRotatef( 90, 1, 0, 0); // initial rotations

    glScalef(
      my_Data.modelScale[0], my_Data.modelScale[1],
my_Data.modelScale[2]);
    glTranslatef(
      -my_Data.modelCentroid[0],
      -my_Data.modelCentroid[1],
      -my_Data.modelCentroid[2]);

    my_DrawVolume(my_Data.aTetraSet, my_Data.aVolume);

    GLwDrawingAreaSwapBuffers(widget);

}

--
From: Mark Davey
Dept. of Medical Physics, UCL.


TEL: +44 (0)171 915 1673.
FAX: +44 (0)171 837 9279.


Institute of Laryngology and Otology,
330 Gray's Inn Road,
London.
WC1X 8GE.

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