FEEDBACK.C

/* 
 * (c) Copyright 1993, Silicon Graphics, Inc. 
 *               1993-1995 Microsoft Corporation 
 * 
 * ALL RIGHTS RESERVED 
 * 
 * Please refer to OpenGL/readme.txt for additional information 
 * 
 */ 
 
/* 
 *  feedback.c 
 *  This program demonstrates use of OpenGL feedback.  First, 
 *  a lighting environment is set up and a few lines are drawn. 
 *  Then feedback mode is entered, and the same lines are  
 *  drawn.  The results in the feedback buffer are printed. 
 */ 
#include "glos.h" 
 
#include <GL/gl.h> 
#include <GL/glu.h> 
#include <GL/glaux.h> 
#include <stdio.h> 
 
void myinit(void); 
void drawGeometry (GLenum mode); 
void print3DcolorVertex (GLint size, GLint *count, GLfloat *buffer); 
void printBuffer(GLint size, GLfloat *buffer); 
void CALLBACK myReshape(GLsizei w, GLsizei h); 
void CALLBACK display(void); 
 
/*  Initialize lighting. 
 */ 
void myinit(void) 
{ 
    glEnable(GL_LIGHTING); 
    glEnable(GL_LIGHT0); 
} 
 
/*  Draw a few lines and two points, one of which will  
 *  be clipped.  If in feedback mode, a passthrough token  
 *  is issued between the each primitive. 
 */ 
void drawGeometry (GLenum mode) 
{ 
    glBegin (GL_LINE_STRIP); 
    glNormal3f (0.0, 0.0, 1.0); 
    glVertex3f (30.0, 30.0, 0.0); 
    glVertex3f (50.0, 60.0, 0.0); 
    glVertex3f (70.0, 40.0, 0.0); 
    glEnd (); 
    if (mode == GL_FEEDBACK) 
    glPassThrough (1.0); 
    glBegin (GL_POINTS); 
    glVertex3f (-100.0, -100.0, -100.0);    /*  will be clipped  */ 
    glEnd (); 
    if (mode == GL_FEEDBACK) 
    glPassThrough (2.0); 
    glBegin (GL_POINTS); 
    glNormal3f (0.0, 0.0, 1.0); 
    glVertex3f (50.0, 50.0, 0.0); 
    glEnd (); 
} 
 
/*  Write contents of one vertex to stdout. */ 
void print3DcolorVertex (GLint size,  
    GLint *count, GLfloat *buffer) 
{ 
    int i; 
 
    //printf ("  "); 
    for (i = 0; i < 7; i++) { 
    //printf ("%4.2f ", buffer[size-(*count)]); 
    *count = *count - 1; 
    } 
    //printf ("\n"); 
} 
 
/*  Write contents of entire buffer.  (Parse tokens!)   */ 
void printBuffer(GLint size, GLfloat *buffer) 
{ 
    GLint count; 
    GLfloat token; 
 
    count = size; 
    while (count) { 
    token = buffer[size-count]; count--; 
    if (token == GL_PASS_THROUGH_TOKEN) { 
        //printf ("GL_PASS_THROUGH_TOKEN\n"); 
        //printf ("  %4.2f\n", buffer[size-count]); 
        count--; 
    } 
    else if (token == GL_POINT_TOKEN) { 
        //printf ("GL_POINT_TOKEN\n"); 
        print3DcolorVertex (size, &count, buffer); 
    } 
    else if (token == GL_LINE_TOKEN) { 
        //printf ("GL_LINE_TOKEN\n"); 
        print3DcolorVertex (size, &count, buffer); 
        print3DcolorVertex (size, &count, buffer); 
    } 
    else if (token == GL_LINE_RESET_TOKEN) { 
        //printf ("GL_LINE_RESET_TOKEN\n"); 
        print3DcolorVertex (size, &count, buffer); 
        print3DcolorVertex (size, &count, buffer); 
    } 
    } 
} 
 
void CALLBACK display(void) 
{ 
    GLfloat feedBuffer[1024]; 
    GLint size; 
 
    glMatrixMode (GL_PROJECTION); 
    glLoadIdentity (); 
    glOrtho (0.0, 100.0, 0.0, 100.0, 0.0, 1.0); 
 
    glClearColor (0.0, 0.0, 0.0, 0.0); 
    glClear(GL_COLOR_BUFFER_BIT); 
    drawGeometry (GL_RENDER); 
 
    glFeedbackBuffer (1024, GL_3D_COLOR, feedBuffer); 
    (void) glRenderMode (GL_FEEDBACK); 
    drawGeometry (GL_FEEDBACK); 
 
    size = glRenderMode (GL_RENDER); 
    printBuffer (size, feedBuffer); 
} 
 
/*  Main Loop 
 *  Open window with initial window size, title bar,  
 *  RGBA display mode, and handle input events. 
 */ 
int main(int argc, char** argv) 
{ 
    auxInitDisplayMode (AUX_SINGLE | AUX_RGB); 
    auxInitPosition (0, 0, 100, 100); 
    auxInitWindow ("Feedback"); 
    myinit (); 
    auxMainLoop(display); 
    return(0); 
}