Index: web/client/scripts/draw.js
===================================================================
--- web/client/scripts/draw.js	(revision 6890)
+++ web/client/scripts/draw.js	(revision 6891)
@@ -8,8 +8,7 @@
  * @param options.comm - communication interface
  * @param options.canvas - HTML canvas rendering context
  * @param options.colors - color chart for symbolic color names
- * @param options.layerGroupMap - prescriptions based on layer group id
- * @param options.purposeMap - prescriptions based on layer group purposes
+ * @param options.layerGroups - options based on layer group id
  * @param options.onNewLayerGroup - called when a new layer group is defined
  */
 function GraphicEngine(options) {
@@ -20,8 +19,8 @@
 	this.cc = this.mainCc;
 	this.colors = options.colors;
 	this.unit = options.unit || "mm";
-	this.purposeMap = options.purposeMap && typeof options.purposeMap === "object" ?
-		options.purposeMap : {};
+	this.layerGroupOptions = options.layerGroups && typeof options.layerGroups === "object" ?
+		options.layerGroups : {};
 
 	this.cc.imageSmoothingEnabled = false;
 	this.mainCc.setTransform(1, 0, 0, 1, 0, 0);
@@ -318,19 +317,7 @@
 		this.cc = this.mainCc;
 	}
 	this.currentLayerGroup = this.layerGroups[id];
-	this.enableDrawing = true;
-	if (this.options.layerGroupMap[id] && this.options.layerGroupMap[id].hidden) {
-		this.enableDrawing = false;
-	}
-	if (this.currentLayerGroup) {
-		var purposes = this.currentLayerGroup.purposes;
-		for (var i = 0; i < purposes.length; ++i) {
-			pe = this.purposeMap[purposes[i]];
-			if (pe && pe.hidden) {
-				this.enableDrawing = false;
-			}
-		}
-	}
+	this.enableDrawing = !this.layerGroupOptions[id] || this.layerGroupOptions[id].visible;
 	if (this.enableDrawing && this.currentLayerGroup && this.currentLayerGroup.isMask) {
 		this.cc = this.maskCc;
 		this.mainCc.setTransform(1, 0, 0, 1, 0, 0);
Index: web/testclient/draw.js
===================================================================
--- web/testclient/draw.js	(revision 6890)
+++ web/testclient/draw.js	(revision 6891)
@@ -6,7 +6,7 @@
 var draw = require("../client/scripts/draw");
 var currentBuffer;
 var layerGroups = {};
-var purposes = {};
+var defaultDisabledPurposes = ["mask", "paste", "fab"];
 
 
 buildFileList();
@@ -41,9 +41,9 @@
 			console.log("drawing", url);
 			currentBuffer = new Uint8Array(req.response);
 			layerGroups = {};
-			purposes = {};
 			document.getElementById("layerGroupList").innerHTML = "";
 			drawBuffer();
+			drawBuffer();
 		}
 	};
 	req.responseType = 'arraybuffer';
@@ -58,9 +58,7 @@
 
 	var lgMap = {};
 	for (var id in layerGroups) {
-		if (layerGroups[id].hidden) {
-			lgMap[id] = { hidden: true };
-		}
+		lgMap[id] = { visible: layerGroups[id].visible };
 	}
 
 	var ge = new draw.GraphicEngine({
@@ -70,12 +68,7 @@
 		colors: {
 			mask: "#274f29"
 		},
-		layerGroupMap: lgMap,
-		purposeMap: {
-			mask: { hidden: true },
-			paste: { hidden: true },
-			fab: { hidden: true }
-		},
+		layerGroups: lgMap,
 		onNewLayerGroup: onNewLayerGroup
 	});
 
@@ -95,9 +88,20 @@
 	if (layerGroups[lg.id]) {
 		return;
 	}
+
+	// determine initial visibility
+	var visible = true;
+	for (var i = 0; i < lg.purposes.length; ++i) {
+		for (var j = 0; j < defaultDisabledPurposes.length; ++j) {
+			if (lg.purposes[i] === defaultDisabledPurposes[j])
+				visible = false;
+		}
+	}
+
 	layerGroups[lg.id] = {
 		id: lg.id,
-		purposes: lg.purposes
+		purposes: lg.purposes,
+		visible: visible
 	};
 
 	// list the group
@@ -114,9 +118,9 @@
 	var cbox = document.createElement("input");
 	cbox.type = "checkbox";
 	cbox.id = "checkbox" + lg.id;
-	cbox.checked = true;
+	cbox.checked = visible;
 	cbox.onchange = function () {
-		layerGroups[lg.id].hidden = !cbox.checked;
+		layerGroups[lg.id].visible = cbox.checked;
 		drawBuffer();
 	}
 	li.appendChild(cbox);