Re: Setting up Pipes/Windows/Channels...

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Dick Rous (dick++at++demeern.sgi.com)
Thu, 03 Dec 1998 10:30:53 +0100

First, what is the geometry of your screen? Is it cylindrical or
spherical, or just 3 flat screens put at an angle?
To adjust the projection system to a curved screen, you need some
3D model of a section of a sphere built from horizontal and vertical
lines.
Then you have to position your eyepoint in the centre of this sphere
and adjust the keystone of the projectors in such a way that all
horizontal and vertical lines are parallel and colinear. With a
small radius of the screen, some projectors have difficulty to
achieve this. Examples in the good sense are Barco Seos and Sony.
In the case of a curved screen, you also have to account for some
form of edge-blending between the projectors. Most projector
suppliers have this as an option.
To do the setup, an example way is to use perfly with the following
options:

perfly -c 3 \ # 3 channels
       -g 0 \ # no gui
       -H 40,30,36 \ # hor FOV 40, vert FOV 30, offset 36 degrees
                     # this gives a 4 degree edge-blending area
       -l 0 \ # no lighting
       -p 0,0,0 \ # position the eyepoint at 0,0,0
       -R 0 \ # do not optimize the mesh
       <your model of a sphere>

I include a little c-program that generates 180 degree meshes in
Inventor ascii format using the following options:

mesh [shere|cylinder] rows columns radius offset

It draws markers at the viewing offsets / 2, to facilitate the
adjustment of the edge-blending.
It writes to stdout, so just rederict output to a file with
extension .iv and use this file in perfly.

Hope this helps,

regards,

Dick.

-- 
__________________________________________________________________
Dick Rous              Senior Systems Engineer Graphics Technology
                       European Technical Support
phone: +31-30-6696868  fax: +31-35-6423162     voicemail: 955-6868
__________________________________________________________________


#include <stdlib.h>
#include <stdio.h>
#include <math.h>


#define MAXROWS (100)
#define MAXCOLS (180)
#define DEGREES   0.017453292


float    vertices[MAXCOLS * MAXROWS][3];
int      cylinder;
    
void genHorizontalLines (int rows, int cols, 
                         float radius, float r, float g, float b);
void genVerticalLines (int rows, int cols, 
                       float radius, float r, float g, float b, float offset);
void genDiagonalLines (int rows, int cols, 
                       float radius, float r, float g, float b);


void
main (int argc,  char **argv)
{
    float    radius, offset;
    int      i, rows, cols;
    
    if (argc < 6)
    {
	printf ("Usage: %s <cylinder | sphere> <rows> <columns> <radius> <offset>\n", argv[0]);
	exit (1);
    }
    cylinder = strncmp(argv[1], "sphere", 1);
    rows = atoi(argv[2]);
    cols = atoi(argv[3]);
    radius = atof(argv[4]);
    offset = atof(argv[5]);
    
    fprintf (stderr, "Creating ascii Inventor file...\n");    
    printf ("#Inventor V2.1 ascii\n\n");


    /*** Red markers ***/
    genHorizontalLines (1,    cols, radius, 1.0f, 0.0f, 0.0f);
    genVerticalLines   (rows, 0,    radius, 1.0f, 0.0f, 0.0f, offset);
    genDiagonalLines   (rows, cols, radius, 1.0f, 0.0f, 0.0f);
    /*** White mesh ***/
    genHorizontalLines (rows, cols, radius, 1.0f, 1.0f, 1.0f);
    genVerticalLines   (rows, cols, radius, 1.0f, 1.0f, 1.0f, offset);
}


void 
genHorizontalLines (int rows, int cols, float radius, float r, float g, float b)
{
    int   i, j, k;
    float psi, theta;    


    printf ("Separator {\n");
    printf ("\tMaterial {\n");
    printf ("\t\tdiffuseColor   %f %f %f\n", r, g, b); 
    printf ("\t}");
    printf ("\tCoordinate3 {\n");
    printf ("\t\t\tpoint [\n");
    
    k = 0;
    psi = DEGREES * 180.0f / (float)cols;


    for ( i = 0; i < rows + 1; i++)
    {
	if (cylinder)
	    theta = 0.0f * DEGREES;
	else
	    theta = ((float)rows / 2.0f - (float)i) * DEGREES * 6.0f;
	
	for (j = 0; j < cols + 1; j++)
	{
	    if (i != rows / 2)
	    {
		vertices[k][0] = -cosf ((float)j * psi) *
		                  cosf (theta) * radius;
		vertices[k][2] = -sinf ((float)j * psi) * 
		                  cosf (theta) * radius;
				 
		if (rows == 1)
		    vertices[k][1] = 0.0f;
		else
		{
		    if (cylinder)
			vertices[k][1] = ((float)rows / 2.0f - (float)i) * 2.0f;
		    else
			vertices[k][1] = sinf (theta) * radius;
		}
		
		printf ("\t\t\t\t%f %f %f , \n", 
			vertices[k][0], vertices[k][1], vertices[k][2]);
		k++;
	    }
	}
    }    
    printf ("\t\t\t]\n");
    printf ("\t}\n");
    printf ("\tLineSet {\n");


    printf ("\t\tnumVertices\t[");
    
    for (i = 0; i < rows; i++)
	printf (" %d,", cols + 1);
    printf (" ]\n");
     printf ("\t}\n");
    printf ("}\n");
}


void 
genVerticalLines (int rows, int cols, float radius, 
                  float r, float g, float b, float offset)
{
    int   i, j, k;
    float psi, theta;    
    int limit = (cols) ? cols + 1 : 7; /*** vertical mesh or 7 markers ***/
    
    printf ("Separator {\n");
    printf ("\tMaterial {\n");
    printf ("\t\tdiffuseColor   %f %f %f\n", r, g, b); 
    printf ("\t}");
    printf ("\tCoordinate3 {\n");
    printf ("\t\t\tpoint [\n");
    
    for (i = 0, k = 0; i < limit; i++)
    {
	if (cols)
	    psi = 180.0f * DEGREES / (float)cols * (float)i;
	else
	    switch (i)
	    {
		case 0: psi = DEGREES * 0.0f;
			break;
		case 1: psi = DEGREES * 90.0f;
			break;
		case 2: psi = DEGREES * 180.0f;
			break;
		case 3: psi = DEGREES * (90.0f - offset);
			break;
		case 4: psi = DEGREES * (90.0f + offset);
			break;
		case 5: psi = DEGREES * (90.0f - offset / 2.0f);
			break;
		case 6: psi = DEGREES * (90.0f + offset / 2.0f);
			break;
	    }
	if (i != 0 && i != cols / 2 && i != cols || cols == 0)
	{
	    for (j = 0; j < rows + 1; j++)
	    {
		if (cylinder)
		    theta = 0.0f * DEGREES;
		else
		    theta = ((float)rows / 2.0f - (float)j) * 6.0f * DEGREES;
	    
		vertices[k][0] = -cosf (psi) *
				  cosf (theta) * radius;
		vertices[k][2] = -sinf (psi) * 
				  cosf (theta) * radius;
				 
		if (cylinder)
		    vertices[k][1] = ((float)rows / 2.0f - (float)j) * 2.0f;
		else
		    vertices[k][1] = sinf (theta) * radius;
		
		printf ("\t\t\t\t%f %f %f , \n", 
			vertices[k][0], vertices[k][1], vertices[k][2]);
		k++;
	    }
	}
    }
    printf ("\t\t\t]\n");
    printf ("\t}\n");
    printf ("\tLineSet {\n");


    printf ("\t\tnumVertices\t[");
    
    for (i = 0; i < k / (rows + 1); i++)
	printf (" %d,", rows + 1);
    printf (" ]\n");
    printf ("\t}\n");
    printf ("}\n");
}


void 
genDiagonalLines (int rows, int cols, float radius, float r, float g, float b)
{
    int   i, j, k;
    float psi, theta;    


    printf ("Separator {\n");
    printf ("\tMaterial {\n");
    printf ("\t\tdiffuseColor   %f %f %f\n", r, g, b); 
    printf ("\t}");
    printf ("\tCoordinate3 {\n");
    printf ("\t\t\tpoint [\n");
    
    k = 0;
    psi = DEGREES * 180.0f / (float)cols;


    for ( i = 0; i < 2; i++)
    {
	float sign = (i == 0) ? 1.0f : -1.0f;


	if (cylinder)
	    theta = 0.0f * DEGREES;


	for (j = 0; j < cols + 1; j++)
	{
	    if (!cylinder)
		theta = ((float)rows / 2.0f - 
		        ((float)rows / (float)cols) * (float)j) * 
			DEGREES * 6.0f;


	    vertices[k][0] = -cosf ((float)j * psi) *
			      cosf (theta) * radius;
	    vertices[k][2] = -sinf ((float)j * psi) * 
		              cosf (theta) * radius;


	    if (cylinder)
	    {
		if (i == 0)
		    vertices[k][1] = (float)rows - ((float)j * 
				     2.0f * ((float)rows / (float)cols));
		else
		    vertices[k][1] = (float)rows - ((float)(cols - j) *
				     2.0f * ((float)rows / (float)cols));
	    }
	    else
		vertices[k][1] =  sinf (theta) * radius * sign;
	    				 
	    printf ("\t\t\t\t%f %f %f , \n", 
		    vertices[k][0], vertices[k][1], vertices[k][2]);
	    k++;
	}
    }    
    printf ("\t\t\t]\n");
    printf ("\t}\n");
    printf ("\tLineSet {\n");


    printf ("\t\tnumVertices\t[");
    
    for (i = 0; i < 2; i++)
	printf (" %d,", cols + 1);
    printf (" ]\n");
     printf ("\t}\n");
    printf ("}\n");
}

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