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Andrew Bond · Guest

I have recently tried to get OpenGL working in C++Builder and have hit a
snag. Can anyone help me please? (I have also posted this message on the
OpenGL.org newsgroups, with no reply so far).

I am trying to get picking to work, but despite reading about it in the
OpenGL Super Bible and studying the NeHe examples for C++Builder 6, I can't
get it to work properly.

I am able to pick some objects but not all, and only in certain views
(typically perspective and isometric, not cross-section, elevation, or
plan). Some objects are picked when I click near them (noy on them)!

Can anyone see what is wong wih my code please? I would be happy to supply
ALL the code (written for C++Builder 6) if that helps.

Many thanks in anticipation

Andrew

***
Here are (what I think are) the most significant functions:

void OnResize(int width, int height)
{
glViewport(0, 0, width, height);
}

void OnPaint()
{
glLoadIdentity();
glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
if(projection == Perspective) {
double aspect(double(width) / height);
double near_plane(size * width / 10);
double far_plane(near_plane * 1000);
gluPerspective(45, aspect, near_plane, far_plane);
}
else {
double h(size * height); // in cm
double w(size * width); // in cm
glOrtho(-w, w, -h, h, -w, w);
}
glMatrixMode(GL_MODELVIEW);

LocateCamera(); // see below
RenderScene(); // see below
SwapBuffers();
::ValidateRect(hwnd, NULL);
}

void LocateCamera()
{
switch(projection) {
case CrossSection:
gluLookAt(1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, -1.0, 0.0);
break;
case Plan:
gluLookAt(0.0, -1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0);
break;
case Elevation:
gluLookAt(0.0, 0.0, -1.0, 0.0, 0.0, 0.0, 0.0, -1.0, 0.0);
break;
case Isometric:
gluLookAt(-1.0, -1.0, -1.0, 0.0, 0.0, 0.0, 0.0, -1.0, 0.0);
break;
case Perspective:
gluLookAt(-20.0, -20.0, -20.0, 0.0, 0.0, 0.0, 0.0, -1.0, 0.0);
break;
default:
throw std::invalid_argument(__FUNC__);
}
}

void RenderScene()
{
glMatrixMode(GL_MODELVIEW);
glPushMatrix();

glInitNames();
glPushName(0);

glScaled(scale, scale, scale);
glScaled(100, 100, 100); // we are working in cm per pixel

assert(Draw);
Draw(); // draws the obejcts and pushes names onto the name stack

glPopMatrix();
}

bool HitTest(int x, int y)
{
glSelectBuffer(name_stack.size(), &name_stack[0]);

int viewport[4];
glGetIntegerv(GL_VIEWPORT, viewport);

glRenderMode(GL_SELECT);

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

gluPickMatrix((double)x, viewport[3] - (double)y, 20, 20, viewport);

double aspect(double(width) / height);
double near_plane(size * width / 10.0);
double far_plane(near_plane * 100);
gluPerspective(45, aspect, near_plane, far_plane);

glMatrixMode(GL_MODELVIEW);
RenderScene();
glMatrixMode(GL_PROJECTION);

unsigned int hits = glRenderMode(GL_RENDER);

// pop the projection matrix
glPopMatrix();

return hits;
}
// end of code

Andrew Bond · Guest

I found the problem - I was passing Screen coordinates to OpenGL instead of
Window coordinates.

Stupid me <g>.

Andrew

"Andrew Bond" <andrew.bond (AT) geocentrix (DOT) co.uk> wrote