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janm

picking problem...

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Hi, I have a problem with picking. I'll trie to discribe my situation : I have a set of display lists generated, in a 'display' function I do each time this void GlScene::displayScene(){ for(uint i = 0; i < m_widgets_to_display.size(); i++){ glPushName(m_widgets_to_display.elementAt(i)->getPickingID()); m_widgets_to_display.elementAt(i)->display(); //The display function calls the displaylist glPopName(); } } Now, that works fine. But now I want to implement picking in my scene. So every object has a 'name' (see abov the glPushName and glPopName). I do picking on the 'normal way' - see code below - and have some troubles with the result. Sometimes an object is dedected where isn't one, otherewise there isn't an object when there is one (-> the picking fails). I trie to dedect an object on mouseclick and print the result on the console. This is my picking code : void GlScene::picking(int x, int y){ GLuint selectBuf[512]; glSelectBuffer(512,selectBuf); glRenderMode(GL_SELECT); glInitNames(); GLint viewport[4]; glGetIntegerv(GL_VIEWPORT,viewport); glMatrixMode(GL_PROJECTION); glPushMatrix(); glLoadIdentity(); gluPickMatrix(x,viewport[3]-y, 5,5,viewport); gluPerspective(60.0f, (GLfloat)viewport[2]/(GLfloat)viewport[3] , 1.0f, 150.0f); glMatrixMode(GL_MODELVIEW); displayScene(); int hits; 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); else cout<<"no hits..."<<endl; } the processHits function is a 'classical one' : void GlScene::processHits (GLint hits, GLuint buffer[]) { unsigned int i, j; GLuint names, *ptr, minZ,*ptrNames, numberOfNames; cout<<"hits = "<<hits; ptr = (GLuint *) buffer; minZ = 0xffffffff; for (i = 0; i < hits; i++) { names = *ptr; ptr++; if (*ptr < minZ) { numberOfNames = names; minZ = *ptr; ptrNames = ptr+2; } ptr += names+2; } cout<<"The closest hit names are "<<endl; ptr = ptrNames; for (j = 0; j < numberOfNames; j++,ptr++) { cout<<*ptr<<" , "<<endl; } cout<<endl; } Is there anywone who knows what I'm doing wrong? I have tried so much and can 't find a solution. Thanx, Jan

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I've build these code with the 'Nehe picking tutorial', but I don't see what I'm doing wrong (when I compare my code with the nehe Code I don't see significant differences). Is there anyone, probably more experienced than me, who sees anything I'm doing wrong?

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Have you tried pushing at least one name into the stack before pushing the one that you want to identify the object you are creating?

Example from gametutorials.com:

glInitNames(); // This clears the name stack so we always start with 0 names.

// This next line is important. If you don't push on at least ONE name,
// The selection won't work. Instead of glLoadName()/glEnd() you can use
// glPushName(TheID) and glPopName(); Then you don't need to glPushName(0);

glPushName(0); // This starts off the first object in the stack

GLUquadricObj *pObj = gluNewQuadric(); // Get a new Quadric off the stack

gluQuadricTexture(pObj, true); // This turns on texture coordinates for our Quadrics

// Bind the sun texture to the sun quadratic
glBindTexture(GL_TEXTURE_2D, g_Texture[0]); // Bind the Sun texture to the sun

// Below we call glLoadName(). We need to pass in an ID that we can check later that will
// be associated with the polygons drawn next. Here is how it works. We call glLoadName()
// and pass an ID. Then we draw any primitives or shapes, then we call glEnd() which
// stops assigning polys to that object name. We now have a group of polygons that are
// given an ID. Our ID SUN now refers to the sun Quadric we draw below.

glLoadName(SUN); // Push on our SUN label (IMPORTANT)

// If we use glLoadName(), then we need to end it with glEnd(). There is a problem
// though with some video cards that MUST have a glBegin()/glEnd() between
// the calls to glLoadName()/glEnd(). This is strange but some cards grind
// to a 2 FPS speed (VoodooCards). Since we are using Quadrics there is
// no glBegin()/glEnd() being called explicitly, so we need to fake it.
// *Remember, you only have to do this if you are using Quadrics.* So, to fix
// this we just put a empty glBegin()/glEnd() statement between each object ID passed in.
glBegin(GL_LINES);
glEnd();

// Here we push on a new matrix so we don't affect any other quadrics.
// We first translate the quadric to the origin (0, 0, 0), Then we rotate it
// about the Y axis. This gives it the spinning effect. Then we draw the
// largest of the spheres. This represents the sun with its texture map.

glPushMatrix(); // Push on a new matrix scope
glTranslatef(0, 0, 0); // Translate this sphere to the left
glRotatef(SunRotation, 0, 1.0, 0); // Rotate the sphere around the Y axis to make it spin
gluSphere(pObj, 0.5f, 20, 20); // Draw the sunwith a radius of 0.5
glPopMatrix(); // End the current scope of this matrix

// Now that we drew the sun, we want to end our Object name. We call glPopName()
// to do that. Now nothing else will be associated with the SUN ID.

glEnd(); // Stop assigning polygons to the SUN label (IMPORTANT)


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