do not add brims to anchors

src/mode/fdm/prepare.js

@@ -386,6 +386,8 @@
                 }
                 layerout.z = z + slice.height / 2;
                 layerout.height = layerout.height || slice.height;
+                // mark layer as anchor if slice is belt and flag set
+                layerout.anchor = slice.belt && slice.belt.anchor;
                 // detect extruder change and print purge block
                 if (!lastOut || lastOut.extruder !== slice.extruder) {
                     printPoint = purge(slice.extruder, track, layerout, printPoint, slice.z);
@@ -493,6 +495,10 @@
                 if (firstLayerBrimTrig > 0 && mins > firstLayerBrimTrig) {
                     continue;
                 }
+                // do not add brims to anchor layers
+                if (layer.anchor) {
+                    continue;
+                }
                 // add brim, if specified
                 if (first && firstLayerBrim) {
                     let {emit, tool } = first;

src/mode/fdm/slice.js

@@ -330,11 +330,13 @@
                     let addto = start.down;
                     if (!addto) {
                         addto = newSlice(start.z - sliceHeight);
+                        addto.belt = { };
                         addto.height = start.height;
                         addto.up = start;
                         start.down = addto;
                         slices.splice(0,0,addto);
                     }
+                    addto.belt.anchor = true;
                     let z = addto.z;
                     let y = z - smin - (nozzleSize / 2);
                     let splat = BASE.newPolygon().add(wb.min.x, y, z).add(wb.max.x, y, z).setOpen();