static declaration

[jhearon]

Hi
I'm working on a QT Coin/SoQt widget. I'm confused about a static hack to the widget part I made which works, but I don't understand why. Doesn't seem right, but it works. I'm trying to do it the correct way. Hoping to get some advice. Sorry if this is a bit O.T. since QT part is not shown.

The problem is with the function dragger_moved.


If I declare the function dragger_moved in .h as
void dragger_moved(void * data, SoDragger * dragger);
as non-static, and have the .cpp function also as non-static
void Model::dragger_moved(void*, SoDragger*) I get an error.
"error: no matching function for call to 'SoDragPointDragger::addMotionCallback"

But if I declare the function dragger_moved in .h as static:
static void dragger_moved(void * data, SoDragger * dragger);
and also have the .cpp function as static:
static void Model::dragger_moved(void*, SoDragger*)
I get a different error:
"error: cannot declare member function 'static void Model::dragger_moved(void*, SoDragger*)' to have static linkage"

I came up with a hack of declaring the function dragger_moved in .h as static
static void dragger_moved(void * data, SoDragger * dragger);
but using non-static in the .cpp function as
void Model::dragger_moved(void*, SoDragger*)
and this gets thru the compiler.

That doesn't seem the best way to do it. Ideally the dragger_moved function should be static since it deals with the widget's scene graph.

model.h
 
static SoDragPointDragger ** draggers = NULL;
...
class Model : public SoQtExaminerViewer
{
 
    public:
 
    Model( QWidget *parent = NULL, const char *name=NULL, const SbBool embed=TRUE);
    ~Model(void);
 
    struct dragcb_data;
    static void dragger_moved(void * data, SoDragger * dragger);
    void setDefaultScene();
   ...
 
-----------
model.cpp
#include <model.h>
 
Model::Model( QWidget *parent, const char * name, const SbBool embed)
  : SoQtExaminerViewer( parent, name, embed, SoQtFullViewer::BUILD_ALL, SoQtViewer::BROWSER, TRUE)
{
...
struct Model::dragcb_data {
 unsigned int idx;
};
 
void Model::dragger_moved(void * data, SoDragger * dragger)
{
  SoDragPointDragger * dpd = (SoDragPointDragger *)dragger;
  struct dragcb_data * cbdata = (struct dragcb_data *)data;
  SbVec3f v = dpd->translation.getValue();
  ctrlpts->point.set1Value(cbdata->idx, v[0], v[1], v[2]);
}
 
void Model::setDefaultScene(void) {
 
...
    struct dragcb_data * data = new struct dragcb_data;
    data->idx = i;
    dpd->addMotionCallback(dragger_moved, data); 
    dpd->translation.setValue(pts[i]);
    root->addChild(dpd);
...
}

model.h

static SoDragPointDragger ** draggers = NULL;
...
class Model : public SoQtExaminerViewer
{

    public:

    Model( QWidget *parent = NULL, const char *name=NULL, const SbBool embed=TRUE);
    ~Model(void);

    struct dragcb_data;
    static void dragger_moved(void * data, SoDragger * dragger);
    void setDefaultScene();
   ...

-----------
model.cpp
#include <model.h>

Model::Model( QWidget *parent, const char * name, const SbBool embed)
  : SoQtExaminerViewer( parent, name, embed, SoQtFullViewer::BUILD_ALL, SoQtViewer::BROWSER, TRUE)
{
...
struct Model::dragcb_data {
 unsigned int idx;
};

void Model::dragger_moved(void * data, SoDragger * dragger)
{
  SoDragPointDragger * dpd = (SoDragPointDragger *)dragger;
  struct dragcb_data * cbdata = (struct dragcb_data *)data;
  SbVec3f v = dpd->translation.getValue();
  ctrlpts->point.set1Value(cbdata->idx, v[0], v[1], v[2]);
}

void Model::setDefaultScene(void) {

...
    struct dragcb_data * data = new struct dragcb_data;
    data->idx = i;
    dpd->addMotionCallback(dragger_moved, data); 
    dpd->translation.setValue(pts[i]);
    root->addChild(dpd);
...
}

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