ecmascript:

function initialize ()
{
   tracePrint ('initialize() begin...');
   if (materials[index] != null)
   {
	viewedMaterial.diffuseColor     = materials[index].diffuseColor;
	viewedMaterial.emissiveColor    = materials[index].emissiveColor;
	viewedMaterial.specularColor    = materials[index].specularColor;
	viewedMaterial.shininess        = materials[index].shininess;
	viewedMaterial.ambientIntensity = materials[index].ambientIntensity;
	viewedMaterial.transparency     = materials[index].transparency;
	interpolateMaterialValues();
   }
   else alwaysPrint ('warning: no initialization Material node provided for materials[' + index + ']'
                    + ', materials.length=' + materials.length);

   tracePrint ('initialize() complete');
}

function set_index (value, timestamp)
{
   if (value == index) return;
   else if ((value >= 0) && (value < materials.length))
   {
	index = value;
	viewedMaterial.diffuseColor     = materials[index].diffuseColor;
	viewedMaterial.emissiveColor    = materials[index].emissiveColor;
	viewedMaterial.specularColor    = materials[index].specularColor;
	viewedMaterial.shininess        = materials[index].shininess;
	viewedMaterial.ambientIntensity = materials[index].ambientIntensity;
	viewedMaterial.transparency     = materials[index].transparency;
	interpolateMaterialValues();
	index_changed = value; // chain input event to output event
	tracePrint ('set_index(' + value + ') complete');
   }
   else if (value == -1)
   {
	tracePrint ('set_index(' + value + ') out of range, use default Material values');
	index = value;
	viewedMaterial.diffuseColor     = defaultMaterial.diffuseColor;
	viewedMaterial.emissiveColor    = defaultMaterial.emissiveColor;
	viewedMaterial.specularColor    = defaultMaterial.specularColor;
	viewedMaterial.shininess        = defaultMaterial.shininess;
	viewedMaterial.ambientIntensity = defaultMaterial.ambientIntensity;
	viewedMaterial.transparency     = defaultMaterial.transparency;
	index_changed = value; // chain input event to output event
   }
   else if (priorBadIndex != value)
   {
	alwaysPrint ('set_index(' + value + ') out of range (only '
		+ materials.length + ' Material nodes)');
	priorBadIndex = value;
   }
}

function set_fraction(value, timestamp)
{
	tracePrint ('set_fraction(' + value + ')');
	if (fraction != value) // only update if value is changed
	{
		fraction = value;
		interpolateMaterialValues();
	}
}

function interpolateMaterialValues()
{
	f = fraction % 1;  // nonzero remainder (modulo 1) within range [0..1]
	tracePrint ('interpolateMaterialValues(index=' + index + ', fraction=' + fraction +  ', f=' + f + ')');
	// reset Material index if fraction is above 1
	if (Math.floor(fraction) >= 1)
	{
		index = Math.floor(fraction);
		tracePrint ('index=' + index + ' (reset from fraction)');
	}
	fraction = f;  // no need to retain integral part of fraction once index is set correspondingly
	// check OK to proceed
	if (index <  0) return;				// avoid index underflow
	if (index >= materials.length - 1) return;	// avoid index overflow
	if (f == 0.0) return; 				// avoid zero interpolation
	viewedMaterial.diffuseColor.r     = materials[index].diffuseColor.r +
		f * (materials[index+1].diffuseColor.r - materials[index].diffuseColor.r);
	viewedMaterial.diffuseColor.g     = materials[index].diffuseColor.g +
		f * (materials[index+1].diffuseColor.g - materials[index].diffuseColor.g);
	viewedMaterial.diffuseColor.b     = materials[index].diffuseColor.r +
		f * (materials[index+1].diffuseColor.b - materials[index].diffuseColor.b);
	tracePrint ('viewedMaterial.diffuseColor=' + viewedMaterial.diffuseColor);

	viewedMaterial.emissiveColor.r    = materials[index].emissiveColor.r +
		f * (materials[index+1].emissiveColor.r - materials[index].emissiveColor.r);
	viewedMaterial.emissiveColor.g    = materials[index].emissiveColor.r +
		f * (materials[index+1].emissiveColor.g - materials[index].emissiveColor.g);
	viewedMaterial.emissiveColor.b    = materials[index].emissiveColor.b +
		f * (materials[index+1].emissiveColor.b - materials[index].emissiveColor.b);

	viewedMaterial.specularColor.r    = materials[index].specularColor.r +
		f * (materials[index+1].specularColor.r - materials[index].specularColor.r);
	viewedMaterial.specularColor.g    = materials[index].specularColor.g +
		f * (materials[index+1].specularColor.g - materials[index].specularColor.g);
	viewedMaterial.specularColor.b    = materials[index].specularColor.b +
		f * (materials[index+1].specularColor.b - materials[index].specularColor.b);

	viewedMaterial.shininess        = materials[index].shininess +
		f * (materials[index+1].shininess - materials[index].shininess);
	viewedMaterial.ambientIntensity = materials[index].ambientIntensity +
		f * (materials[index+1].ambientIntensity - materials[index].ambientIntensity);
	viewedMaterial.transparency     = materials[index].transparency +
		f * (materials[index+1].transparency - materials[index].transparency);
}

function next(trigger)
{
	tracePrint ('next(' + trigger + ')');
	if ((trigger == true) && (materials.length > 0))
	{
		value = index + 1;
		if (value >= materials.length) value = 0;
		set_index (value); // update Material, test, etc.
	}
}

function previous(trigger)
{
	tracePrint ('previous(' + trigger + ')');
	if ((trigger == true) && (materials.length > 0))
	{
		value = index - 1;
		if (value < 0) value = materials.length - 1;
		set_index (value); // update Material, test, etc.
	}
}

function appendMaterial(newMaterial)
{
	tracePrint ('appendMaterial(' + newMaterial + ')');
	newMaterialCopy = new SFNode ('Material {}');
	tracePrint ('newMaterial.diffuseColor=' + newMaterial.diffuseColor);
	newMaterialCopy.diffuseColor     = newMaterial.diffuseColor;
	newMaterialCopy.emissiveColor    = newMaterial.emissiveColor;
	newMaterialCopy.specularColor    = newMaterial.specularColor;
	newMaterialCopy.shininess        = newMaterial.shininess;
	newMaterialCopy.ambientIntensity = newMaterial.ambientIntensity;
	newMaterialCopy.transparency     = newMaterial.transparency;
	materials[materials.length]      = newMaterialCopy;
	set_index (materials.length-1); // update Material, test, etc.
}

function deleteAllMaterials(trigger)
{
	if ((trigger == true) && (materials.length > 0))
	{
		materials.length = 0; // deletes all objects in materials MFNode array
		index = 0; // must be different to trigger node reset by set_index()
		set_index (-1);
		tracePrint ('deleteAllMaterials() materials.length=' + materials.length);
	}
}

function deleteMaterial(materialIndex)
{
	if ((materialIndex >= materials.length) || materialIndex < 0)
		alwaysPrint ('deleteMaterial(materialIndex=' + materialIndex + ') out of range, materials.length=' +  materials.length);
	else
	{
		for (i = materialIndex; i <= materials.length - 2; i++)
		{
			materials[i] = materials[i+1];
		}
		materials.length = materials.length - 1;
		if ((index == 0) && (materialIndex == 0) && (materials.length > 0))
		{
			index = -1; // allow reset back to 0
			set_index (0);
		}
		else if (index >= materialIndex) set_index (index-1); // decrement to remain same
		tracePrint ('deleteMaterial(materialIndex=' + materialIndex + ') complete,  materials.length=' + materials.length);
	}
}

function tracePrint(outputString)
{
	if (traceEnabled) Browser.println ('[MaterialChoice] ' + outputString);
}
function alwaysPrint(outputString)
{
	Browser.println ('[MaterialChoice] ' + outputString);
}