Figure 42

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Figure 42
======================
Note: It responds to clicks. The second windows displays which window was clicked and other coordinates.
========================


/*
//Author: Cheikh Drame
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*/
// pick.cpp : Defines the entry point for the console application.
//


#include
#include
#include



void display()
{
glClear(GL_COLOR_BUFFER_BIT);

glPushName(0);
glColor3ub(255, 0, 0);
glRectf(0.25, -0.25, 0.75, 0.25);

glLoadName(1);
glColor3ub(0, 255, 0);
glRectf(-0.25, 0.25, 0.25, 0.75);

glLoadName(2);
glColor3ub(0, 0, 255);
glRectf(-0.75, -0.25, -0.25, 0.25);

glLoadName(3);
glColor3ub(255, 255, 0);
glRectf(-0.25, -0.75, 0.25, -0.25);

glFlush();

if (glGetError() != GL_NO_ERROR)
printf("OpenGL has reported an error.\n");
}

////////////////////////////////
// Keyboard Callback Function //
////////////////////////////////

void keyboard(unsigned char key, int x, int y)
{
if (key == 'q') exit(0);
}

/////////////////////////////
// Mouse Callback Function //
/////////////////////////////

#define SIZE 8

void mouse(int button, int state, int x, int y)
{
GLint i, j, k = 0, nhits, nnames, selectedObjectsInfo[SIZE], viewport[4];
char description[4][7] = {"RED", "GREEN", "BLUE", "YELLOW"};
GLubyte color[3];
float xx, yy;

if (state == GLUT_UP) return;

printf("--------------------------------------------\n");

if (button == GLUT_LEFT_BUTTON)
{
// Use OpenGL's selection mode

GLuint *xz=(GLuint*)selectedObjectsInfo;
glSelectBuffer(SIZE, xz);
glRenderMode(GL_SELECT);
glInitNames();

glPushMatrix();
glLoadIdentity();
glGetIntegerv(GL_VIEWPORT, viewport);
gluPickMatrix(x, viewport[3] - y, 5, 5, viewport);
gluOrtho2D(-1.0, 1.0, -1.0, 1.0);

display();
nhits = glRenderMode(GL_RENDER);
glPopMatrix();

printf("nhits = %d\n", nhits);

for (i=0; i {
nnames = selectedObjectsInfo[k];

printf("nhit %d:\n", i);
printf("k = %d: The number of names is %d\n", k, selectedObjectsInfo[k]); k++;
printf("k = %d: The minimum depth is %d\n", k, selectedObjectsInfo[k]); k++;
printf("k = %d: The maximum depth is %d\n", k, selectedObjectsInfo[k]); k++;

for (j=0; j {
printf("k = %d: The selected object has name %d\n", k, selectedObjectsInfo[k]);
k++;
}
printf("\nThe %s rectangle was selected::, k:%d, nhits::%d\n", description[selectedObjectsInfo[k-1]], k-1, nhits);
}
}
else // the right (or middle) mouse button was pressed
{
// Get the color of the pixel that the mouse points to

y = glutGet(GLUT_WINDOW_HEIGHT) - y;

glReadPixels(x, y, 1, 1, GL_RGB ,GL_UNSIGNED_BYTE, color);

if (color[0] > 0 && color[1] > 0) printf("The cursor is on a YELLOW pixel\n");
else if ( color[0] > 0) printf("The cursor is on a RED pixel\n");
else if ( color[1] > 0) printf("The cursor is on a GREEN pixel\n");
else if ( color[2] > 0) printf("The cursor is on a BLUE pixel\n");

// Calculate the world coordinates (xx,yy) and check to see if they are in a colored rectangle

xx = (2.0 / glutGet(GLUT_WINDOW_WIDTH)) * x - 1.0;
yy = (2.0 / glutGet(GLUT_WINDOW_HEIGHT)) * y - 1.0;
printf("\nWorld coordinates: (%f,%f)\n", xx, yy);

if (-0.25 < yy && yy < 0.25)
{
if (-0.75 < xx && xx < -0.25)
printf("That is within the BLUE rectangle\n");
else if (0.25 < xx && xx < 0.75)
printf("That is within the RED rectangle\n");
}

if (-0.25 < xx && xx < 0.25)
{
if (-0.75 < yy && yy < -0.25)
printf("That is within the YELLOW rectangle\n");
else if (0.25 < yy && yy < 0.75)
printf("That is within the GREEN rectangle\n");
}
}
}

//////////////////
// Main Program //
//////////////////

int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(300,300);
glutInitWindowPosition(10,10);
glutCreateWindow(argv[0]);
glutDisplayFunc(display);
glutKeyboardFunc(keyboard);
glutMouseFunc(mouse);
gluOrtho2D(-1.0, 1.0, -1.0, 1.0);
glutMainLoop();
return 0;
}