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Q: The code for drawing and writing files is very similar to the submit call.
Why is it necessary to have the Startxxx and Endxxx calls? They require two
procedure codes -- one for drawing and one for writing.
A: The submit calls for drawing and picking are in the following routine:
//------------------------------------------------------------------
// Submit the scene for rendering/fileIO and picking
TQ3Status SubmitScene( DocumentPtr theDocument )
{
TQ3Vector3D globalScale;
TQ3Vector3D globalTranslate;
globalScale.x = globalScale.y = globalScale.z = theDocument->fGroupScale;
globalTranslate = *(TQ3Vector3D *)&theDocument->fGroupCenter;
Q3Vector3D_Scale(&globalTranslate, -1, &globalTranslate);
Q3Style_Submit(theDocument->fInterpolation, theDocument->fView);
Q3Style_Submit(theDocument->fBackFacing , theDocument->fView);
Q3Style_Submit(theDocument->fFillStyle, theDocument->fView);
Q3MatrixTransform_Submit( &theDocument->fRotation, theDocument->fView);
Q3ScaleTransform_Submit(&globalScale, theDocument->fView);
Q3TranslateTransform_Submit(&globalTranslate, theDocument->fView);
Q3DisplayGroup_Submit( theDocument->fModel, theDocument->fView);
return kQ3Success ;
}
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You can use the same routine for drawing and picking. For picking, or in this
instance, for calculating the bounding box of the geometry being displayed as
the main group, do the following:
TQ3Status status;
TQ3ViewStatus viewStatus ;
status = Q3View_StartBoundingBox( theDocument->fView,
kQ3ComputeBoundsApproximate );
do {
status = SubmitScene( theDocument ) ;
} while((viewStatus = Q3View_EndBoundingBox( theDocument->fView,
&viewBBox ))
== kQ3ViewStatusRetraverse );
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For drawing, do the following:
TQ3Status theStatus ;
Q3View_StartRendering(theDocument->fView) ;
do {
theStatus = SubmitScene( theDocument ) ;
} while (Q3View_EndRendering(theDocument->fView)
== kQ3ViewStatusRetraverse );
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The code to write to a file is complicated slightly by the need to write the
viewhints to the file. However, it is a simple matter to perform this operation
with the following code:
TQ3SharedObject viewHints;
TQ3ViewStatus fileStatus;
if (Q3File_OpenWrite(file, kQ3FileModeNormal | kQ3FileModeText) == kQ3Success )
{
Q3View_StartWriting(theView, file);
if (theView == NULL)
viewHints = NULL;
else
viewHints = Q3ViewHints_New(theView);
if (viewHints != NULL)
{
if (Q3Object_Submit(viewHints, theView) == kQ3Failure)
{
Q3File_Cancel(file);
return;
}
}
do {
theStatus = SubmitScene( theDocument ) ;
} while ((fileStatus = Q3View_EndWriting(theView)) ==
kQ3ViewStatusRetraverse);
if( Q3File_Close(file) == kQ3Failure ) {
return;
}
}
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In some instances, you should avoid nesting groups repetitively. For example, if
you create a new display group and add an existing group to it. This implies
that when you write the new group to the file, the existing group remains
nested inside. However, the file you write is not the same as the file you read
in, in that an extra level of nesting has been introduced. To avoid this, use
the following code to write objects to a file (this code avoids the nesting
problem):
void WriteGroupToFile( TQ3FileObject file, TQ3GroupObject theData,
TQ3ViewObject theView)
{
TQ3GroupPosition gPos;
TQ3Object object;
TQ3SharedObject viewHints;
TQ3ViewStatus fileStatus;
if (Q3File_OpenWrite(file, kQ3FileModeNormal | kQ3FileModeText) == kQ3Success )
{
Q3View_StartWriting(theView, file);
if (theView == NULL)
viewHints = NULL;
else
viewHints = Q3ViewHints_New(theView);
if (viewHints != NULL)
{
if (Q3Object_Submit(viewHints, theView) == kQ3Failure)
{
Q3File_Cancel(file);
return;
}
}
do {
if (theData != NULL)
{
TQ3Status status;
status = Q3Group_GetFirstPosition(theData, &gPos);
while (gPos != NULL && status == kQ3Success)
{
Q3Group_GetPositionObject(theData, gPos, &object);
status = Q3Object_Submit(object, theView);
Q3Object_Dispose(object);
if (status != kQ3Failure)
{
Q3Group_GetNextPosition(theData, &gPos);
}
}
}
} while ((fileStatus = Q3View_EndWriting(theView)) ==
kQ3ViewStatusRetraverse);
if( Q3File_Close(file) == kQ3Failure ) {
return;
}
}
return ;
}
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It's probably best to use a submit function to perform picking and drawing, but you should use different code to write to
a file to avoid the possibility of groups becoming more deeply nested each time the file is saved.
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