PICKSQR.C

/* 
 * (c) Copyright 1993, Silicon Graphics, Inc. 
 *               1993-1995 Microsoft Corporation 
 * 
 * ALL RIGHTS RESERVED 
 * 
 * Please refer to OpenGL/readme.txt for additional information 
 * 
 */ 
 
/* 
 *  picksquare.c 
 *  Use of multiple names and picking are demonstrated.   
 *  A 3x3 grid of squares is drawn.  When the left mouse  
 *  button is pressed, all squares under the cursor position  
 *  have their color changed. 
 */ 
#include "glos.h" 
 
#include <GL/gl.h> 
#include <GL/glu.h> 
#include <GL/glaux.h> 
#include <stdio.h> 
 
void myinit(void); 
void processHits (GLint hits, GLuint buffer[]); 
void CALLBACK pickSquares(AUX_EVENTREC *event); 
void CALLBACK display(void); 
void CALLBACK myReshape(GLsizei w, GLsizei h); 
 
int board[3][3];    /*  amount of color for each square */ 
 
/*  Clear color value for every square on the board     */ 
void myinit(void) 
{ 
    int i, j; 
    for (i = 0; i < 3; i++)  
    for (j = 0; j < 3; j ++) 
        board[i][j] = 0; 
    glClearColor (0.0, 0.0, 0.0, 0.0); 
} 
 
/*  The nine squares are drawn.  In selection mode, each  
 *  square is given two names:  one for the row and the  
 *  other for the column on the grid.  The color of each  
 *  square is determined by its position on the grid, and  
 *  the value in the board[][] array. 
 */ 
void drawSquares(GLenum mode) 
{ 
    GLuint i, j; 
    for (i = 0; i < 3; i++) { 
    if (mode == GL_SELECT) 
        glLoadName (i); 
    for (j = 0; j < 3; j ++) { 
        if (mode == GL_SELECT) 
        glPushName (j); 
        glColor3f ((GLfloat) i/3.0, (GLfloat) j/3.0,  
            (GLfloat) board[i][j]/3.0); 
        glRecti (i, j, i+1, j+1); 
        if (mode == GL_SELECT) 
        glPopName (); 
    } 
    } 
} 
 
/*  processHits() prints out the contents of the  
 *  selection array. 
 */ 
void processHits (GLint hits, GLuint buffer[]) 
{ 
    int i, j; 
    GLint ii, jj, names, *ptr; 
 
    //printf ("hits = %d\n", hits); 
    ptr = (GLuint *) buffer; 
    for (i = 0; i < hits; i++) {    /*  for each hit  */ 
    names = *ptr; 
    //printf (" number of names for this hit = %d\n", names); 
    ptr++; 
    //printf ("  z1 is %u;", *ptr); 
    ptr++; 
    //printf (" z2 is %u\n", *ptr); 
    ptr++; 
    //printf ("   names are "); 
    for (j = 0; j < names; j++) {   /*  for each name */ 
        //printf ("%d ", *ptr); 
        if (j == 0) /*  set row and column  */ 
        ii = *ptr; 
        else if (j == 1) 
        jj = *ptr; 
        ptr++; 
    } 
    //printf ("\n"); 
    board[ii][jj] = (board[ii][jj] + 1) % 3; 
    } 
} 
 
/*  pickSquares() sets up selection mode, name stack,  
 *  and projection matrix for picking.  Then the  
 *  objects are drawn. 
 */ 
#define BUFSIZE 512 
 
void CALLBACK pickSquares(AUX_EVENTREC *event) 
{ 
    GLuint selectBuf[BUFSIZE]; 
    GLint hits; 
    GLint viewport[4]; 
    int x, y; 
 
    x = event->data[AUX_MOUSEX]; 
    y = event->data[AUX_MOUSEY]; 
    glGetIntegerv (GL_VIEWPORT, viewport); 
 
    glSelectBuffer (BUFSIZE, selectBuf); 
    (void) glRenderMode (GL_SELECT); 
 
    glInitNames(); 
    glPushName((unsigned)-1); 
 
    glMatrixMode (GL_PROJECTION); 
    glPushMatrix (); 
    glLoadIdentity (); 
/*  create 5x5 pixel picking region near cursor location    */ 
    gluPickMatrix ((GLdouble) x, (GLdouble) (viewport[3] - y),  
    5.0, 5.0, viewport); 
    gluOrtho2D (0.0, 3.0, 0.0, 3.0); 
    drawSquares (GL_SELECT); 
 
    glMatrixMode (GL_PROJECTION); 
    glPopMatrix (); 
    glFlush (); 
 
    hits = glRenderMode (GL_RENDER); 
    processHits (hits, selectBuf); 
}  
 
void CALLBACK display(void) 
{ 
    glClear(GL_COLOR_BUFFER_BIT); 
    drawSquares (GL_RENDER); 
    glFlush(); 
} 
 
void CALLBACK myReshape(GLsizei w, GLsizei h) 
{ 
    glViewport(0, 0, w, h); 
    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity(); 
    gluOrtho2D (0.0, 3.0, 0.0, 3.0); 
    glMatrixMode(GL_MODELVIEW); 
    glLoadIdentity(); 
} 
 
/*  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 ("Picking Squares"); 
    myinit (); 
    auxMouseFunc (AUX_LEFTBUTTON, AUX_MOUSEDOWN, pickSquares); 
    auxReshapeFunc (myReshape); 
    auxMainLoop(display); 
    return(0); 
}