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click66
05-25-2012, 06:02 AM
I've been reading tutorials about picking and that color picking is far the most popular and simplest form.

Tried some tutorials with snowmans as example but it doesn't work for me. When I run the program , it gives me just a black sceen without anything draw on it. When I click a couple of times nothing happens except when I close the window then it sais "you haven't clicked on a snowman".

Don't know what is wrong with it can someone help me?



void GLWidget::paintGL() {
glEnable(GL_DEPTH_TEST);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glLoadIdentity();

gluLookAt(camPosx ,camPosy ,camPosz,
camPosx + camViewx,camViewy,camPosz + camViewz,
camUpx, camUpy, camUpz );

draw(); //draw the normal scene

if (mode == SELECT)
drawPickingMode();
else
drawPickingMode();

if (mode == SELECT) {
processPick();
mode = RENDER;
}
else
QGLWidget::swapBuffers();

// restore current matrix
glMatrixMode( GL_MODELVIEW );
glPopMatrix( );

}

void GLWidget::mousePressEvent(QMouseEvent * e)
{
if(e->button() == Qt::LeftButton)
{
qDebug("mouse");
qDebug("%d %d",QCursor::pos().x(),QCursor::pos().y());
this->cursorX = QCursor::pos().x(); // set x and y cord from mouse
this->cursorY = QCursor::pos().y();
mode = SELECT; // set the mode to select
}
}

void GLWidget::draw() {

// Draw ground
glColor3f(0.9f, 0.9f, 0.9f);
glBegin(GL_QUADS);
glVertex3f(-100.0f, 0.0f, -100.0f);
glVertex3f(-100.0f, 0.0f, 100.0f);
glVertex3f( 100.0f, 0.0f, 100.0f);
glVertex3f( 100.0f, 0.0f, -100.0f);
glEnd();

// Draw 4 Snowmen

glColor3f(1.0f, 1.0f, 1.0f);

for(int i = 0; i < 2; i++)
for(int j = 0; j < 2; j++) {
glPushMatrix();
glTranslatef(i*3.0,0,-j * 3.0);
glColor3f(1.0f, 1.0f, 1.0f);
glCallList(snowman_display_list);
glPopMatrix();
}

}

void GLWidget::processPick ()
{
GLint viewport[4];
GLubyte pixel[3];

glGetIntegerv(GL_VIEWPORT,viewport);

glReadPixels(cursorX,viewport[3]-cursorY,1,1,
GL_RGB,GL_UNSIGNED_BYTE,(void *)pixel);

printf("%d %d %d\n",pixel[0],pixel[1],pixel[2]);
if (pixel[0] == 255)
printf ("You picked the 1st snowman on the 1st row");
else if (pixel[1] == 255)
printf ("You picked the 1st snowman on the 2nd row");
else if (pixel[2] == 255)
printf ("You picked the 2nd snowman on the 1st row");
else if (pixel[0] == 250)
printf ("You picked the 2nd snowman on the 2nd row");
else
printf("You didn't click a snowman!");
printf ("\n");

}

void GLWidget::drawPickingMode() {

// Draw 4 SnowMen


glDisable(GL_DITHER);
for(int i = 0; i < 2; i++)
for(int j = 0; j < 2; j++) {
glPushMatrix();

// A different color for each snowman

switch (i*2+j) {
case 0: glColor3ub(255,0,0);break;
case 1: glColor3ub(0,255,0);break;
case 2: glColor3ub(0,0,255);break;
case 3: glColor3ub(250,0,250);break;
}

glTranslatef(i*3.0,0,-j * 3.0);
glCallList(snowman_display_list);
glPopMatrix();
}
glEnable(GL_DITHER);
}

void GLWidget::initializeGL() {

loadGLTextures();
//LoadXml();
glEnable(GL_TEXTURE_2D); // Enable Texture Mapping
glShadeModel(GL_SMOOTH); // Enable Smooth Shading
glClearColor(0.0f, 0.0f, 0.0f, 0.5f); // Black Background
glClearDepth(1.0f); // Depth Buffer Setup
glEnable(GL_DEPTH_TEST); // Enables Depth Testing
glDepthFunc(GL_LEQUAL); // The Type Of Depth Testing To Do
glEnable(GL_LIGHT0); // Quick And Dirty Lighting (Assumes Light0 Is Set Up)
glEnable(GL_LIGHTING); // Enable Lighting
glEnable(GL_COLOR_MATERIAL); // Enable Material Coloring
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST); // Perspective Calculations
// buildLists(2); // Creating displaylist #
glLoadIdentity();

timer->start(50);
qDebug("Init");
}


Projection matrix is set as follows:

void GLWidget::resizeGL(int width, int height) {

//set viewport
glViewport(0,0,width,height);

glMatrixMode(GL_PROJECTION);
glLoadIdentity();

//set persepective
//change the next line order to have a different perspective
aspect_ratio=(GLdouble)width/(GLdouble)height;
gluPerspective(45.0f, aspect_ratio, 0.1 , 100.0);

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}

Kind regards,

BionicBytes
05-25-2012, 08:37 AM
Tried some tutorials with snowmans as example but it doesn't work for me. When I run the program , it gives me just a black sceen without anything draw on it. When I click a couple of times nothing happens except when I close the window then it sais "you haven't clicked on a snowman".

Don't know what is wrong with it can someone help me?


Have you tried running the Santa claus program; you know the one where he drops all the presents?

Seriously? You've cut and pasted some random code from a web site (no refernece given) and say it doesn't even run properly then expect us to tell you what's wrong? Think about it.