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nippysaurus

OpenGL picking ... always nothing selected

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I have a simple opengl scene with some boxes ... I am using glut ... I have given the boxes names. I dont know what else you would need to know to help me, but I have implemented some picking code from various sites, never gives any errors but the items I have given names to, when clicked, still gives no results. I am going to just paste all my code just to make sure that nothing is missed. Any help would be greatly appreciated.
#include <stdlib.h>
#include <stdio.h>
#include <GL/glut.h> // Header File For The GLUT Library 
#include <GL/gl.h>	 // Header File For The OpenGL32 Library
#include <GL/glu.h>	 // Header File For The GLu32 Library

#define DEBUG

#ifdef DEBUG
#define debugmsg(msg) {printf("DEBUG:%s\n",msg);}
#else
#define debugmsg(msg) {}
#endif

#define DEFAULT_WIDTH 800
#define DEFAULT_HEIGHT 600
#define LEFT (0-(WIDTH/2))
#define RIGHT (WIDTH/2)
#define TOP (HEIGHT/2)
#define BOTTOM (0-(HEIGHT/2))

//#define WIREFRAME

#define ONE 1
#define TWO 2
#define THREE 3
#define FOUR 4
#define FIVE 5
#define SIX 6
#define SEVEN 7
#define EIGHT 8

float r = 0.0f;
float m = 0.0f;

bool MouseLeftDown = false;
bool MouseRightDown = false;

unsigned int width = DEFAULT_WIDTH;
unsigned int height = DEFAULT_HEIGHT;

#define BUFSIZE 512
GLuint selectBuf[BUFSIZE];

// =============================================================================
// Cube.
// =============================================================================
class Cube
{
    private:
        float _wl;  // Width/Length!
        float _left,_right,_top,_bottom,_front,_back;
    public:
        Cube(float wl)
        {
            _wl = wl;
            _right = _top = _front = _wl / 2;
            _left = _bottom = _back = -_right;
        }
        void Draw()
        {
            glColor3f(1.0f, 0.0f, 0.0f);
            glBegin(GL_QUADS);
            glVertex3f(_left, _top, _front);    // FRONT
            glVertex3f(_left, _bottom, _front);
            glVertex3f(_right, _bottom, _front);
            glVertex3f(_right, _top, _front);
            glVertex3f(_left, _top, _back);     // BACK
            glVertex3f(_right, _top, _back);
            glVertex3f(_right, _bottom, _back);
            glVertex3f(_left, _bottom, _back);
            glVertex3f(_left, _top, _front);    // TOP
            glVertex3f(_right, _top, _front);
            glVertex3f(_right, _top, _back);
            glVertex3f(_left, _top, _back);
            glVertex3f(_left, _bottom, _front); // BOTTOM
            glVertex3f(_left, _bottom, _back);
            glVertex3f(_right, _bottom, _back);
            glVertex3f(_right, _bottom, _front);
            glVertex3f(_left, _bottom, _back);  // LEFT
            glVertex3f(_left, _bottom, _front);
            glVertex3f(_left, _top, _front);
            glVertex3f(_left, _top, _back);
            glVertex3f(_right, _bottom, _front);  // RIGHT
            glVertex3f(_right, _bottom, _back);
            glVertex3f(_right, _top, _back);
            glVertex3f(_right, _top, _front);
            glEnd();
        }
};

// =============================================================================
// Drawaxis.
// =============================================================================
void DrawAxis()
{
    #define AXISLINELENGTH 0.25f

    // X
    glColor3f(1.0f, 0.0f, 0.0f);
    glBegin(GL_LINES);
    glVertex3f(0.0f, 0.0f, 0.0f);
    glVertex3f(AXISLINELENGTH, 0.0f, 0.0f);
    glEnd();
    glRasterPos3f(AXISLINELENGTH, 0.0f, 0.0f);
    glutBitmapCharacter(GLUT_BITMAP_HELVETICA_10, 'X');

    // Y
    glColor3f(0.0f, 1.0f, 0.0f);
    glBegin(GL_LINES);
    glVertex3f(0.0f, 0.0f, 0.0f);
    glVertex3f(0.0f, AXISLINELENGTH, 0.0f);
    glEnd();
    glRasterPos3f(0.0f, AXISLINELENGTH, 0.0f);
    glutBitmapCharacter(GLUT_BITMAP_HELVETICA_10, 'Y');

    // Z
    glColor3f(0.0f, 0.0f, 1.0f);
    glBegin(GL_LINES);
    glVertex3f(0.0f, 0.0f, 0.0f);
    glVertex3f(0.0f, 0.0f, AXISLINELENGTH);
    glEnd();
    glRasterPos3f(0.0f, 0.0f, AXISLINELENGTH);
    glutBitmapCharacter(GLUT_BITMAP_HELVETICA_10, 'Z');
}

// =============================================================================
// Start Ortho.
// =============================================================================
void StartOrtho(void)
{
	glMatrixMode(GL_PROJECTION);    // Select Projection
	glPushMatrix();                 // Push The Matrix
	glLoadIdentity();               // Reset The Matrix
	glOrtho(0,width,height,0,-1,1); // Select Ortho Mode
	glMatrixMode(GL_MODELVIEW);     // Select Modelview Matrix
	glPushMatrix();                 // Push The Matrix
	glLoadIdentity();               // Reset The Matrix
}

// =============================================================================
// End Ortho.
// =============================================================================
void EndOrtho(void)
{
	glMatrixMode(GL_PROJECTION);    // Select Projection
	glPopMatrix();                  // Pop The Matrix
	glMatrixMode(GL_MODELVIEW);     // Select Modelview
	glPopMatrix();                  // Pop The Matrix
}

// =============================================================================
// Process Hits.
// =============================================================================
void processHits(int hits, unsigned int buffer[])
{
    debugmsg("processing hits");
    //
}

// =============================================================================
// Select.
// =============================================================================
void select(int x, int y)
{
    debugmsg("checking for hits");

	GLint viewport[4];

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

	glInitNames();
    glPushName(0);

	glMatrixMode(GL_PROJECTION);
	glPushMatrix();
	glLoadIdentity();

	glGetIntegerv(GL_VIEWPORT,viewport);
	gluPickMatrix(x,viewport[3]-y,5,5,viewport);
	gluPerspective(45,(1.0f*width/height),1.0f,100.0f);
	glMatrixMode(GL_MODELVIEW);

    int hits;
	
	// restoring the original projection matrix
	glMatrixMode(GL_PROJECTION);
	glPopMatrix();
	glMatrixMode(GL_MODELVIEW);
	glFlush();
	
	// returning to normal rendering mode
	hits = glRenderMode(GL_RENDER);
	
	// if there are hits process them
	if (hits != 0)
		processHits(hits,selectBuf);

    debugmsg("finished checking for hits");
}

// =============================================================================
// Display.
// =============================================================================
void display(void)
{
    //glTranslatef(0.0f,0.0f,0.0f);
    //glRotatef(0.0f, 0.0f, 0.0f, 0.0f);
    //GL_POLYGON
    //GL_LINES
    //GL_QUADS

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glTranslatef(0.0f, 0.0f, -4.0f);

    {
        Cube* SmallCube = new Cube(0.3f);

        glPushMatrix();
        glTranslatef(0.5f, 0.5f, 0.5f);
        glPushName(ONE);
        SmallCube->Draw();
        glPopName();
        glPopMatrix();

        glPushMatrix();
        glTranslatef(0.5f, -0.5f, 0.5f);
        glPushName(TWO);
        SmallCube->Draw();
        glPopName();
        glPopMatrix();

        glPushMatrix();
        glTranslatef(-0.5f, -0.5f, 0.5f);
        glPushName(THREE);
        SmallCube->Draw();
        glPopName();
        glPopMatrix();

        glPushMatrix();
        glTranslatef(-0.5f, 0.5f, 0.5f);
        glPushName(FOUR);
        SmallCube->Draw();
        glPopName();
        glPopMatrix();

        glPushMatrix();
        glTranslatef(0.5f, 0.5f, -0.5f);
        glPushName(FIVE);
        SmallCube->Draw();
        glPopName();
        glPopMatrix();

        glPushMatrix();
        glTranslatef(0.5f, -0.5f, -0.5f);
        glPushName(SIX);
        SmallCube->Draw();
        glPopName();
        glPopMatrix();

        glPushMatrix();
        glTranslatef(-0.5f, -0.5f, -0.5f);
        glPushName(SEVEN);
        SmallCube->Draw();
        glPopName();
        glPopMatrix();

        glPushMatrix();
        glTranslatef(-0.5f, 0.5f, -0.5f);
        glPushName(EIGHT);
        SmallCube->Draw();
        glPopName();
        glPopMatrix();

        delete SmallCube;
    }

    DrawAxis();

    StartOrtho();

    glBegin(GL_QUADS);
    glVertex2f(10, 10);
    glVertex2f(10, height-10);
    glVertex2f(50, height-10);
    glVertex2f(50, 10);
    glEnd();

    EndOrtho();

    glutSwapBuffers();
}

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

int MouseX = -1;
int MouseY = -1;

// =============================================================================
// Mousemove.
// =============================================================================
void mousemove(int x, int y)
{
    //int DiffX = x - MouseX;
    //int DiffY = y - MouseY;

    if (MouseLeftDown && MouseRightDown)
    {
        //
    }
    else if (MouseLeftDown)
    {
        //
    }
    else if (MouseRightDown)
    {
        //
    }

    MouseX = x;
    MouseY = y;
}

// =============================================================================
// Mouseclick.
// =============================================================================
void mouseclick(int button, int state, int x, int y)
{
    // button can be:
    // GLUT_LEFT_BUTTON
    // GLUT_MIDDLE_BUTTON
    // GLUT_RIGHT_BUTTON

    // state can be:
    // GLUT_DOWN
    // GLUT_UP

    // compatibility with original GLUT
    #if !defined(GLUT_WHEEL_UP)
    #  define GLUT_WHEEL_UP   3
    #  define GLUT_WHEEL_DOWN 4
    #endif

    if (state == GLUT_DOWN)
        select(x,y);

    switch(button) {
        case GLUT_LEFT_BUTTON:
            MouseLeftDown = ((state==GLUT_DOWN) ? true : false);
            break;
        case GLUT_MIDDLE_BUTTON:
            break;
        case GLUT_RIGHT_BUTTON:
            MouseRightDown = ((state==GLUT_DOWN) ? true : false);
            break;
        case GLUT_WHEEL_UP:
            break;
        case GLUT_WHEEL_DOWN:
            break;
    }

    MouseX = x;
    MouseY = y;
}

// =============================================================================
// Init.
// =============================================================================
void  init(void)
{
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glEnable(GL_DEPTH_TEST);
	glDepthFunc(GL_LEQUAL);
    glEnable(GL_CULL_FACE);

	glClearDepth(1.0f);

    #ifdef WIREFRAME
        glPolygonMode(GL_FRONT,GL_LINE);
    #else
        glPolygonMode(GL_FRONT,GL_FILL);
    #endif

    glInitNames();
}

// =============================================================================
// Resize.
// =============================================================================
void resize(int w, int h)

{
    width = w;
    height = h;


	glMatrixMode(GL_PROJECTION);

	glLoadIdentity();

	glViewport(0, 0, width, height);

	gluPerspective(45.0f, 1.0f * width / height, 1.0f, 100.0f);


	glMatrixMode(GL_MODELVIEW);

	glLoadIdentity();

}

// =============================================================================
// Entry.
// =============================================================================
int main(int argc, char* argv[])
{
    debugmsg("creating window");

    // Create window.
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowSize(width, height);
    glutCreateWindow("Seen");

    debugmsg("doing init");

    init();

    debugmsg("event loop functions");

    // Event loop functions.
    glutDisplayFunc(display);
    glutIdleFunc(display);
    glutKeyboardFunc(keyboard);
    glutReshapeFunc(resize);
    glutMotionFunc(mousemove);
    glutMouseFunc(mouseclick);

    debugmsg("starting main loop");

    // Start event loop.
    glutMainLoop();

    return 0;
}

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You're not getting any hits because you're not drawing anything in your select function. You enter selection mode, set up the matrices, restore them and go back to render mode. The missing third step should be to draw everything so the selection mechanism actually gets something to perform selection on.

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Thanks Brother Bob :)

It works now ... but it is not well implemented because in my display function I switch to ortho mode to display some UI stuff ... and I am sure that because of that there is ALWAYS one item in the picking list. I need to split the functions up so that the pickable objects can be drawn in a single function :)

Thank you for your help :)

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