Hi,
I’m trying to develop an app that uses picking. More specifically, what I’m trying to do is change the colour of a rectangle when the user clicks on it.
I’ve had a look at the three examples in chapter 13 of the Red Book. The code I’m using is based on pickdepth.c.
When I run the app and click on the rectangle it detects the hit correctly but it doesn’t change colour.
What am I missing here?
The code I’m using is below:
#include <GL/openglut.h>
#include <stdlib.h>
#include <stdio.h>
#define BUFSIZE 512
int gX;
int gY;
//*********************************************************************\\
void init(void)
{
glClearColor(0.0, 0.0, 0.0, 0.0);
glEnable(GL_DEPTH_TEST);
glShadeModel(GL_FLAT);
glDepthRange(0.0, 1.0); /* The default z mapping */
}
//*********************************************************************\\
void drawRects(GLenum mode)
{
if(mode == GL_SELECT) // Selection mode.
{
glLoadName(1);
glBegin(GL_QUADS);
glColor3f(1.0, 0.0, 0.0); // Change colour here?
glVertex3i(2, 2, 0);
glVertex3i(2, 6, 0);
glVertex3i(6, 6, 0);
glVertex3i(6, 2, 0);
glEnd();
}
else
{
glBegin(GL_QUADS); // Normal mode.
glColor3f(1.0, 1.0, 0.0);
glVertex3i(2, 2, 0);
glVertex3i(2, 6, 0);
glVertex3i(6, 6, 0);
glVertex3i(6, 2, 0);
glEnd();
}
}
//*********************************************************************\\
void processHits(GLint hits, GLuint buffer[])
{
int i;
unsigned j;
GLuint names, *ptr;
printf("hits = %d
", hits);
ptr = (GLuint *) buffer;
for(i = 0; i < hits; i++) /* for each hit */
{
names = *ptr;
printf("Number of names for hit = %d
", names);
ptr++;
printf("z1 is %g
", (float) *ptr/0x7fffffff);
ptr++;
printf("z2 is %g
", (float) *ptr/0x7fffffff);
ptr++;
printf("The name is ");
for (j = 0; j < names; j++) /* for each name */
{
printf("%d ", *ptr);
ptr++;
}
printf("
");
}
}
//*********************************************************************\\
void pickRects(int button, int state, int x, int y)
{
GLuint selectBuf[BUFSIZE];
GLint hits;
GLint viewport[4];
gX = x;
gY = y;
printf("gX is %d
", gX);
printf("gY is %d
", gY);
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();
gluPickMatrix((GLdouble) x, (GLdouble) (viewport[3] - y), 5.0, 5.0, viewport); /* create 5x5 pixel picking region near cursor location */
glOrtho(0.0, 8.0, 0.0, 8.0, -0.5, 2.5);
drawRects(GL_SELECT);
glPopMatrix();
glFlush();
hits = glRenderMode(GL_RENDER);
processHits(hits, selectBuf);
glutPostRedisplay();
}
//*********************************************************************\\
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
drawRects(GL_RENDER);
glFlush();
glutSwapBuffers();
}
//*********************************************************************\\
void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 8.0, 0.0, 8.0, -0.5, 2.5);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
//*********************************************************************\\
void keyboard(unsigned char key, int x, int y)
{
switch(key)
{
case 27:
exit(0);
break;
}
}
//*********************************************************************\\
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize (200, 200);
glutInitWindowPosition (100, 100);
glutCreateWindow(argv[0]);
init();
glutReshapeFunc(reshape);
glutDisplayFunc(display);
glutMouseFunc(pickRects);
glutKeyboardFunc(keyboard);
glutMainLoop();
return 0;
}