picking under mfc

I can code simple entity picking using Win32
programs and the glut library. However,
when I try to code the same using an MFC
(microsoft foundation classes) approach, the
number of hits returned is always 0. Any
help for this beginner would be greatly
appreciated. I would be happy to list the
code if helpful.

Hi,

My solution seems to work but there is some problems when we rotate the camera. So i give you the code:

CWindowsGLDoc* pDoc = GetDocument();
ASSERT_VALID(pDoc);

CPaintDC dc(this);

GLuint selectBuffer[BUFFSIZE];
GLint hits;
GLint viewport[4];

glGetIntegerv(GL_VIEWPORT, viewport);

glSelectBuffer(BUFFSIZE, selectBuffer);
glRenderMode(GL_SELECT);

glInitNames();
glPushName(0);

double size = 0.0, s;
std::vector<Piece *>::iterator it;
for(it = pDoc->graphics.begin(); it != pDoc->graphics.end(); it++) {
s = (*it)->size();
if(s > size) size = s;
}

glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
gluPickMatrix(point.x, viewport[3]-point.y, 1.0, 1.0, viewport);
gluPerspective(30.0, 1.0, 0.01 * size, 30.0 * size);

glMatrixMode(GL_MODELVIEW);
glPushMatrix();
gluLookAt(0.0, 8.0size, 6.0size, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glRotated(angleYVue,1.0, 0.0, 0.0);
glRotated(angleXVue,0.0,1.0,0.0);

for(it = pDoc->graphics.begin(); it != pDoc->graphics.end(); it++)
(*it)->internalDraw(1);

glMatrixMode(GL_MODELVIEW);
glPopMatrix();

glMatrixMode(GL_PROJECTION);
glPopMatrix();

hits = glRenderMode(GL_RENDER);

int numPiece = Proces****s(hits, selectBuffer);

for(it = pDoc->graphics.begin(); it != pDoc->graphics.end(); it++)
if( (*it)->getNumeroGL() == numPiece ){
pDoc->pSelected = (*it);
pDoc->pSelected->setSelected();
}
else{
if((*it)->isSelected())
(*it)->setSelected();
}

Invalidate(FALSE);

I’m using glLoadName() and to retrieve the object i’m using

int CWindowsGLView::Proces****s(GLint hits,GLuint buffer)
{
int i;
int j;
int number;
int name;
GLint z1;
GLint z2;
int zMin = MAX_VALUE;
GLuint *ptr;

ptr = (GLuint *) buffer;

for(i=0;i<hits;i++){ //for each hit
number = *ptr;
ptr++;
z1 = *ptr;//zmin
ptr++;
z2 = *ptr;//zmax
ptr++;

if(z1<zMin){
for(j=0;j<number;j++){ //for each name
zMin = z1;
name = *ptr;
ptr++;
}
}
}
return name;
}

Hi,

The code i posted is correct but you must clear the buffer before after glPushName(0).

Some explanations on the code. you must replace glPerspectice by the projection matrix you use to draw your scene. Before drawing an object make a glLoadName(identifier for this object). Use only glPushName where i’used it so only one time for initializing the stack.

Bye.