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NOTE: This Technical Q&A has been retired. Please see the Technical Q&As page for current documentation.

Normal Line of Object Pick

Q: How can I display a line representing the normal of a pick on an object? With no transformations applied to the entire model, this works properly, but if any intermediate transformations are applied, it doesn't.

A: Try inserting the "normal" line into the document group after the object for which the normal is the pick point (you'll have to work out what the normal is in geometry coordinates). All of the transforms should be applied correctly, and the object should be drawn in the right place.


+-------------+
| translate 1 |
+-------------+
| rotation 1  |
+-------------+
| geometry 1  |
+-------------+
| *NORMAL*    | <------- Insert normal line here for pick on geometry 1.
+-------------+
| translate 2 |
+-------------+
| rotation 2  |
+-------------+
| geometry 2  |
+-------------+

If you are only trying to show picking, you can highlight just the picked face. This is considerably easier, and once you have the picking code implemented, it only requires setting the highlight attribute on for the face attribute. The following routine shows how to select an object (you'll have to refine this to select a face):


static void RenderPickAndCheckForHits(
	void)
{
	register unsigned 	long i;
	register char		*a, *b;
	unsigned long		count;
	unsigned long		numPicked;
	unsigned long		numPicked2;
	TQ3HitData			hitData;
	TQ3HitData			hitData2;
	TQ3Vector3D			scaleVec;
	TQ3Status			whatHappened;
	TQ3Vector3D			translate;
	TQ3Vector3D		tmp;
	
	Q3Vector3D_Set(&scaleVec, gZoom, gZoom, gZoom);
	Q3Vector3D_Scale(&scaleVec, gGlobalScale, &scaleVec);
	
	Q3Vector3D_Set(&tmp, gXTranslate, gYTranslate, gZTranslate);
	translate = gGlobalTranslate;
	Q3Vector3D_Add(&translate, &tmp, &translate);
	Q3View_StartPicking(gTransformationsView);
	Q3ScaleTransform_Submit(&scaleVec, gTransformationsView);
	Q3TranslateTransform_Submit(&translate, gTransformationsView);
	Q3Style_Submit(gSubdivControl, gTransformationsView);
	Q3PickIDStyle_Submit(32, gTransformationsView);
	whatHappened = ErDisplayGroup_Pick(gGroup,  pickObject, gTransformationsView);
	Q3View_EndPicking(gTransformationsView);
	
	if (!Q3Pick_GetNumHits(pickObject, &numPicked) || (numPicked == 0)) {
		Q3Object_Dispose(pickObject);
		return;
	}
	
#if 0
	count = 0;
	for (	whatHappened = ErPick_GetFirstHit(pickObject, &hitData);
			whatHappened == kQ3Success;
			whatHappened = ErPick_GetNextHit(pickObject, &hitData)) {
		if (whatHappened != kQ3Success)
			break;
		SysBeep(10);
		Q3Hit_EmptyData(&hitData);
		count++;
	}
	if (count != numPicked)
		DebugStr("\pSOMETHING SUCKS IN PICKING");
		
#else
	/*
		This code highlights the objects that were picked.
		However, the code can't be enabled until geometries
		stop returning the decomp as the object picked, which produces
		a crash.
	*/
	count = 0;
	for (	whatHappened = ErPick_GetFirstHit(pickObject, &hitData);
			whatHappened == kQ3Success;
			whatHappened = ErPick_GetNextHit(pickObject, &hitData)) {
		if (whatHappened != kQ3Success)
			break;
		SysBeep(10);
		count++;
		
		if( Q3Object_IsType(hitData.object, kQ3ShapeTypeGeometry)) {
			TQ3Switch		highlightSwitch = kQ3On;
			TQ3AttributeSet 	attribSet;
			Q3Geometry_GetAttributeSet(hitData.object, &attribSet);
			
			if( !attribSet ) {
				attribSet = Q3AttributeSet_New();
				Q3Geometry_SetAttributeSet(hitData.object, attribSet);
				Q3Object_Dispose(attribSet);
			}
			
			Q3AttributeSet_Add(attribSet, 
							   kQ3AttributeTypeHighlightState,
							   &highlightSwitch);
		}
		Q3Hit_EmptyData(&hitData);
	}
	if (count != numPicked)
		DebugStr("\pSOMETHING SUCKS IN PICKING");
	
	UpdateScreen();
	for (	whatHappened = ErPick_GetFirstHit(pickObject, &hitData);
			whatHappened == kQ3Success;
			whatHappened = ErPick_GetNextHit(pickObject, &hitData)) {
		if (whatHappened != kQ3Success)
			break;
		
		if( Q3Object_IsType(hitData.object, kQ3ShapeTypeGeometry)) {
			TQ3Switch		highlightSwitch = kQ3Off;
			TQ3AttributeSet 	attribSet;
			Q3Geometry_GetAttributeSet(hitData.object, &attribSet);
			
			if( attribSet )
				Q3AttributeSet_Add(attribSet, kQ3AttributeTypeHighlightState,
					&highlightSwitch);
		}
		Q3Hit_EmptyData(&hitData);
	}	
#endif
	
	Q3Object_Dispose(pickObject);
}
#endif

[Jun 01 1995]

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