Figure 44

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Figure 44
=======================
Note: It responds to clicks. The second windows displays which window was clicked and other coordinates.
=======================


/*
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*/
// picksquare.cpp : Defines the entry point for the console application.
//


/* */

/*
* 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
#include
#include

int board[3][3]; /* amount of color for each square */

/* Clear color value for every square on the board */
void init(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[])
{
unsigned int i, j;
GLuint 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 %g;", (float) *ptr/0x7fffffff); ptr++;
printf(" z2 is %g\n", (float) *ptr/0x7fffffff); 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 pickSquares(int button, int state, int x, int y)
{
GLuint selectBuf[BUFSIZE];
GLint hits;
GLint viewport[4];

if (button != GLUT_LEFT_BUTTON || state != GLUT_DOWN)
return;

glGetIntegerv (GL_VIEWPORT, viewport);

glSelectBuffer (BUFSIZE, selectBuf);
(void) glRenderMode (GL_SELECT);

glInitNames();
glPushName(0);

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);
glutPostRedisplay();
}

void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
drawSquares (GL_RENDER);
glFlush();
}

void reshape(int w, int h)
{
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D (0.0, 3.0, 0.0, 3.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}

void keyboard(unsigned char key, int x, int y)
{
switch (key) {
case 27:
exit(0);
break;
}
}

/* Main Loop */
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize (100, 100);
glutInitWindowPosition (100, 100);
glutCreateWindow (argv[0]);
init ();
glutReshapeFunc (reshape);
glutDisplayFunc(display);
glutMouseFunc (pickSquares);
glutKeyboardFunc (keyboard);
glutMainLoop();
return 0;
}