Re: Overlapping viewports

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Scott McMillan (scott++at++ht.com)
Mon, 19 Aug 1996 11:00:12 -0400 (EDT)

> Subject: Time: 2:39 PM
> OFFICE MEMO Overlapping viewports Date: 8/16/96
>
> Greetings:
>
> My objective is to create a HUD overlay for the main channel, which contains
> an Earth/Sky and other objects. I have accomplished this by creating 2
> channels with overlapping viewports, using the share mask to control which
> attributes are shared, and using a draw callback function for the HUD
> channel. This approach works fine when applied only to a Performer
> application. The problem occurs when I try to apply this approach with a
> mixed Performer and Motif application; in which Motif is forked off. In this
> case, the HUD viewport appears to be behind (is blocked from view by) the
> main channel viewport. I would greatly appreciate any help with this one.
>
> Thanks in Advance, Gary Adair

This seems like overkill to me. We just draw text and graphics to the
framebuffer/window of the main channel in a post-pfDraw function. It works
for us in OpenGL. This has come up a number of times, so I have included
code that also loads in fonts too.

Here's the second half of the draw function:

   // ========= DRAW =========
   // invoke Performer draw-processing for this frame
   pfDraw();

   // ======= POST DRAW ======
   // set up ortho viewing
   glDepthFunc(GL_ALWAYS);
   glDepthMask(GL_FALSE);

   pfPushState();
   pfBasicState();

   static pfMatrix tempmat;
   glGetFloatv(GL_PROJECTION_MATRIX, (GLfloat *)tempmat.mat);
   glMatrixMode(GL_PROJECTION);
   glLoadMatrixf((GLfloat *)pfIdentMat.mat);
   glOrtho(0.0f, 1.0f, 0.0f, 1.0f, 1.0, -1.0);
   glMatrixMode(GL_MODELVIEW);

   pfPushIdentMatrix();

   // ALL ORTHO2 DRAW ROUTINES GO HERE

   // output heads-up display information
   if (G_shared->HUD_flag)
   {
      displayHUD();
   }

   // RESTORE GRAPHICS STATE
   pfPopMatrix();
   glMatrixMode(GL_PROJECTION);
   glLoadMatrixf((GLfloat *)tempmat.mat);
   glMatrixMode(GL_MODELVIEW);
   pfPopState();

   glDepthMask(GL_TRUE);
   glDepthFunc(GL_LESS);

Here's what the displayHUD() function looks like:

//----------------------------------------------------------------------
// Function: displayHUD
// Summary: output the heads-up (overlay) display to GUI
// Parameters: none
// Returns: none
//----------------------------------------------------------------------
void displayHUD()
{
   // DRAW THE CROSSHAIRS
   float linelen = .05f;
   float linesep = 0.01;

   glColor3ub(55,168,255);
   glBegin(GL_LINES);
      // the cross hairs
      glVertex2f(0.5-linelen-linesep, 0.5);
      glVertex2f(0.5-linesep, 0.5);
      glVertex2f(0.5+linelen+linesep, 0.5);
      glVertex2f(0.5+linesep, 0.5);
      glVertex2f(0.5, 0.5-linelen-linesep);
      glVertex2f(0.5, 0.5-linesep);
      glVertex2f(0.5, 0.5+linelen+linesep);
      glVertex2f(0.5, 0.5+linesep);
   glEnd();

   // Print text (graphically) to screen
   glColor3ub(44, 106, 249);

   // current time
   char text[100];
   sprintf(text, "Time: %5.2f sec.", G_shared->time);
   glRasterPos2f(0.02, 0.02);
   drawXFontString(fontDLHandleS, text);
}

Doing fonts was not exactly straight forward (credit goes to Paul Sherman for
working this stuff out). Here are some of the things that need to be added:

Variables:

static char fontNameS[] = "-*-courier-medium-r-*-*-13-*-*-*-*-*-iso8859-*";
static XFontStruct *fontInfoS;
int fontDLHandleS;
#define FIRSTGLYPH 32
#define LASTGLYPH 128

Loading fonts during initialization I was told that this should be executed the
first time through the draw process, however I have had success in calling it
after the pw->open() (pfPipeWindow) function in the function
(openPipeWindow for example) specified by

   pw->setConfigFunc(openPipeWindow);

that is called when pw->config() is executed:

    fontInfoS = XLoadQueryFont(xdisplay, fontNameS);
    if(fontInfoS == NULL){
        pfNotify(PFNFY_FATAL,PFNFY_USAGE,
                                "loadXFont: Couldn't load Small X font\n");
                exit(1);
    }

    // Create GL display lists for fonts
    fontDLHandleS = glGenLists((GLuint) LASTGLYPH + 1);
    if(fontDLHandleS == 0)
    {
        pfNotify(PFNFY_FATAL, PFNFY_USAGE, "loadXFont: Couldn't get %d "
            "display lists for Small Font\n", LASTGLYPH + 1);
        exit(1);
    }
    glXUseXFont(fontInfoS->fid, FIRSTGLYPH, LASTGLYPH - FIRSTGLYPH + 1,
        fontDLHandleS + FIRSTGLYPH);

Drawing fonts on screen

//----------------------------------------------------------------------------
// Function:
// Summary:
// Parameters:
// Returns:
//----------------------------------------------------------------------------
void drawXFontString(int fontDLHandle, char *s)
{
    glPushAttrib(GL_LIST_BIT);
    glListBase(fontDLHandle);
    glCallLists(strlen(s), GL_UNSIGNED_BYTE, (GLubyte *)s);
    glPopAttrib();
}

Hope this helps,
scott

-- 
  Scott McMillan  |      HT Medical, Inc.      | Developing virtual environ-
   scott++at++ht.com   |     http://www.ht.com      | ment medical and surgical
 Ph: 301-984-3706 | 6001 Montrose Rd., St. 902 | simulations and surgery
Fax: 301-984-2104 |    Rockville, MD 20852     | simulation creation tools.


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