diff --git a/js/editor/helpers.js b/js/editor/helpers.js
index d6234e1..3009e28 100644
--- a/js/editor/helpers.js
+++ b/js/editor/helpers.js
@@ -1,5 +1,6 @@
 // Small helper classes used by the editor, often with their own UI for the SVG overlay.
-import { mk, mk_svg } from '../util.js';
+import { DIRECTIONS } from '../defs.js';
+import { BitVector, mk, mk_svg } from '../util.js';
 
 export class SVGConnection {
     constructor(sx, sy, dx, dy) {
@@ -31,12 +32,12 @@ export class SVGConnection {
 }
 
 
-// TODO probably need to combine this with Selection somehow since it IS one, just not committed yet
-export class PendingSelection {
+export class PendingRectangularSelection {
     constructor(owner) {
         this.owner = owner;
         this.element = mk_svg('rect.overlay-pending-selection');
-        this.owner.svg_group.append(this.element);
+        this.size_text = mk_svg('text.overlay-edit-tip');
+        this.owner.svg_group.append(this.element, this.size_text);
         this.rect = null;
     }
 
@@ -47,15 +48,20 @@ export class PendingSelection {
         this.element.setAttribute('y', this.rect.y);
         this.element.setAttribute('width', this.rect.width);
         this.element.setAttribute('height', this.rect.height);
+        this.size_text.textContent = `${this.rect.width} × ${this.rect.height}`;
+        this.size_text.setAttribute('x', this.rect.x + this.rect.width / 2);
+        this.size_text.setAttribute('y', this.rect.y + this.rect.height / 2);
     }
 
     commit() {
-        this.owner.set_from_rect(this.rect);
+        this.owner.add_rect(this.rect);
         this.element.remove();
+        this.size_text.remove();
     }
 
     discard() {
         this.element.remove();
+        this.size_text.remove();
     }
 }
 
@@ -65,113 +71,315 @@ export class Selection {
 
         this.svg_group = mk_svg('g');
         this.editor.svg_overlay.append(this.svg_group);
+        // Used for the floating preview and selection rings, which should all move together
+        this.selection_group = mk_svg('g');
+        this.svg_group.append(this.selection_group);
 
-        this.rect = null;
-        this.element = mk_svg('rect.overlay-selection.overlay-transient');
-        this.svg_group.append(this.element);
+        // Note that this is a set of the ORIGINAL coordinates of the selected cells.  Moving a
+        // floated selection doesn't change this; instead it updates floated_offset
+        this.cells = new Set;
+        this.bbox = null;
+        // I want a black-and-white outline ring so it shows against any background, but the only
+        // way to do that in SVG is apparently to just duplicate the path
+        this.ring_bg_element = mk_svg('path.overlay-selection-background.overlay-transient');
+        this.ring_element = mk_svg('path.overlay-selection.overlay-transient');
+        this.selection_group.append(this.ring_bg_element, this.ring_element);
 
         this.floated_cells = null;
         this.floated_element = null;
         this.floated_canvas = null;
+        this.floated_offset = null;
     }
 
     get is_empty() {
-        return this.rect === null;
+        return this.cells.size === 0;
     }
 
     get is_floating() {
         return !! this.floated_cells;
     }
 
+    get has_moved() {
+        return !! (this.floated_offset && (this.floated_offset[0] || this.floated_offset[0]));
+    }
+
     contains(x, y) {
         // Empty selection means everything is selected?
-        if (this.rect === null)
+        if (this.is_empty)
             return true;
 
-        return this.rect.left <= x && x < this.rect.right && this.rect.top <= y && y < this.rect.bottom;
+        if (this.floated_offset) {
+            x -= this.floated_offset[0];
+            y -= this.floated_offset[1];
+        }
+
+        return this.cells.has(this.editor.stored_level.coords_to_scalar(x, y));
     }
 
     create_pending() {
-        return new PendingSelection(this);
+        return new PendingRectangularSelection(this);
     }
 
-    set_from_rect(rect) {
-        let old_rect = this.rect;
+    add_rect(rect) {
+        let old_cells = this.cells;
+        // TODO would be nice to only store the difference between the old/new sets of cells?
+        this.cells = new Set(this.cells);
+
         this.editor._do(
-            () => this._set_from_rect(rect),
+            () => this._add_rect(rect),
             () => {
-                if (old_rect) {
-                    this._set_from_rect(old_rect);
-                }
-                else {
-                    this._clear();
-                }
+                this._set_from_set(old_cells);
             },
             false,
         );
     }
 
-    _set_from_rect(rect) {
-        this.rect = rect;
-        this.element.classList.add('--visible');
-        this.element.setAttribute('x', this.rect.x);
-        this.element.setAttribute('y', this.rect.y);
-        this.element.setAttribute('width', this.rect.width);
-        this.element.setAttribute('height', this.rect.height);
+    _add_rect(rect) {
+        let stored_level = this.editor.stored_level;
+        for (let y = rect.top; y < rect.bottom; y++) {
+            for (let x = rect.left; x < rect.right; x++) {
+                this.cells.add(stored_level.coords_to_scalar(x, y));
+            }
+        }
 
+        if (! this.bbox) {
+            this.bbox = rect;
+        }
+        else {
+            // Just recreate it from scratch to avoid mixing old and new properties
+            this.bbox = new DOMRect(
+                Math.min(this.bbox.x, rect.x),
+                Math.min(this.bbox.y, rect.y),
+                Math.max(this.bbox.right, rect.right) - this.bbox.x,
+                Math.max(this.bbox.bottom, rect.bottom) - this.bbox.y);
+        }
+
+        // XXX wait what the hell is this doing here?  why would we set_from_rect while floating, vs
+        // stamping it first?
         if (this.floated_element) {
+            console.log("what the hell is this doing here");
             let tileset = this.editor.renderer.tileset;
-            this.floated_canvas.width = rect.width * tileset.size_x;
-            this.floated_canvas.height = rect.height * tileset.size_y;
+            this.floated_canvas.width = this.bbox.width * tileset.size_x;
+            this.floated_canvas.height = this.bbox.height * tileset.size_y;
             let foreign_obj = this.floated_element.querySelector('foreignObject');
             foreign_obj.setAttribute('width', this.floated_canvas.width);
             foreign_obj.setAttribute('height', this.floated_canvas.height);
         }
+
+        this._update_outline();
+    }
+
+    _set_from_set(cells) {
+        this.cells = cells;
+
+        // Recompute bbox
+        if (cells.size === 0) {
+            this.bbox = null;
+        }
+        else {
+            let min_x = null;
+            let min_y = null;
+            let max_x = null;
+            let max_y = null;
+            for (let n of cells) {
+                let [x, y] = this.editor.stored_level.scalar_to_coords(n);
+                if (min_x === null) {
+                    min_x = x;
+                    min_y = y;
+                    max_x = x;
+                    max_y = y;
+                }
+                else {
+                    min_x = Math.min(min_x, x);
+                    max_x = Math.max(max_x, x);
+                    min_y = Math.min(min_y, y);
+                    max_y = Math.max(max_y, y);
+                }
+            }
+
+            this.bbox = new DOMRect(min_x, min_y, max_x - min_x + 1, max_y - min_y + 1);
+        }
+
+        // XXX ??? if (this.floated_element) {
+
+        this._update_outline();
+    }
+
+    // Faster internal version of contains() that ignores the floating offset
+    _contains(x, y) {
+        let stored_level = this.editor.stored_level;
+        return stored_level.is_point_within_bounds(x, y) &&
+            this.cells.has(stored_level.coords_to_scalar(x, y));
+    }
+
+    _update_outline() {
+        if (this.is_empty) {
+            this.ring_bg_element.classList.remove('--visible');
+            this.ring_element.classList.remove('--visible');
+            return;
+        }
+
+        // Convert the borders between cells to an SVG path.
+        // I don't know an especially clever way to do this so I guess I'll just make it up.  The
+        // basic idea is to start with the top-left highlighted cell, start tracing from its top
+        // left corner towards the right (which must be a border, because this is the top left
+        // selected cell, so nothing above it is selected), then just keep going until we get back
+        // to where we started.  Then we...  repeat.
+        // But how do we repeat?  My tiny insight is that every island (including holes) must cross
+        // the top of at least one cell; the only alternatives are for it to be zero width or only
+        // exist in the bottom row, and either way that makes it zero area, which isn't allowed.  So
+        // we only have to track and check the top edges of cells, and run through every cell in the
+        // grid in order, stopping to draw a new outline when we find a cell whose top edge we
+        // haven't yet examined (and whose top edge is in fact a border).  We unfortunately need to
+        // examine cells outside the selection, too, so that we can identify holes.  But we can
+        // restrict all of this to within the bbox, so that's nice.
+        // Also, note that we concern ourselves with /grid points/ here, which are intersections of
+        // grid lines, whereas the grid cells are the spaces between grid lines.
+        // TODO might be more efficient to store a list of horizontal spans instead of just cells,
+        // but of course this would be more complicated
+        let seen_tops = new BitVector(this.bbox.width * this.bbox.height);
+        // In clockwise order for ease of rotation, starting with right
+        let directions = [
+            [1, 0],
+            [0, 1],
+            [-1, 0],
+            [0, -1],
+        ];
+
+        let segments = [];
+        for (let y = this.bbox.top; y < this.bbox.bottom; y++) {
+            for (let x = this.bbox.left; x < this.bbox.right; x++) {
+                if (seen_tops.get((x - this.bbox.left) + this.bbox.width * (y - this.bbox.top)))
+                    // Already traced
+                    continue;
+                if (this._contains(x, y) === this._contains(x, y - 1))
+                    // Not a top border
+                    continue;
+
+                // Start a new segment!
+                let gx = x;
+                let gy = y;
+                let dx = 1;
+                let dy = 0;
+                let d = 0;
+
+                let segment = [];
+                segments.push(segment);
+                segment.push([gx, gy]);
+                while (segment.length < 100) {
+                    // At this point we know that d is a valid direction and we've just traced it
+                    if (dx === 1) {
+                        seen_tops.set((gx - this.bbox.left) + this.bbox.width * (gy - this.bbox.top));
+                    }
+                    else if (dx === -1) {
+                        seen_tops.set((gx - 1 - this.bbox.left) + this.bbox.width * (gy - this.bbox.top));
+                    }
+                    gx += dx;
+                    gy += dy;
+
+                    if (gx === x && gy === y)
+                        break;
+
+                    // Now we're at a new point, so search for the next direction, starting from the left
+                    // Again, this is clockwise order (tr, br, bl, tl), arranged so that direction D goes
+                    // between cells D and D + 1
+                    let neighbors = [
+                        this._contains(gx, gy - 1),
+                        this._contains(gx, gy),
+                        this._contains(gx - 1, gy),
+                        this._contains(gx - 1, gy - 1),
+                    ];
+                    let new_d = (d + 1) % 4;
+                    for (let i = 3; i <= 4; i++) {
+                        let sd = (d + i) % 4;
+                        if (neighbors[sd] !== neighbors[(sd + 1) % 4]) {
+                            new_d = sd;
+                            break;
+                        }
+                    }
+                    if (new_d !== d) {
+                        // We're turning, so this is a new point
+                        segment.push([gx, gy]);
+                        d = new_d;
+                        [dx, dy] = directions[d];
+                    }
+                }
+            }
+        }
+        // TODO do it again for the next region...  but how do i tell where the next region is?
+
+        let pathdata = [];
+        for (let subpath of segments) {
+            let first = true;
+            for (let [x, y] of subpath) {
+                if (first) {
+                    first = false;
+                    pathdata.push(`M${x},${y}`);
+                }
+                else {
+                    pathdata.push(`L${x},${y}`);
+                }
+            }
+            pathdata.push('z');
+        }
+        this.ring_bg_element.classList.add('--visible');
+        this.ring_bg_element.setAttribute('d', pathdata.join(' '));
+        this.ring_element.classList.add('--visible');
+        this.ring_element.setAttribute('d', pathdata.join(' '));
     }
 
     move_by(dx, dy) {
-        if (! this.rect)
+        if (this.is_empty)
             return;
 
-        this.rect.x += dx;
-        this.rect.y += dy;
-        this.element.setAttribute('x', this.rect.x);
-        this.element.setAttribute('y', this.rect.y);
-
-        if (! this.floated_element)
+        if (! this.floated_cells) {
+            console.error("Can't move a non-floating selection");
             return;
+        }
 
-        let bbox = this.rect;
-        this.floated_element.setAttribute('transform', `translate(${bbox.x} ${bbox.y})`);
+        this.floated_offset[0] += dx;
+        this.floated_offset[1] += dy;
+        this._update_floating_transform();
+    }
+
+    _update_floating_transform() {
+        let transform = `translate(${this.floated_offset[0]} ${this.floated_offset[1]})`;
+        this.selection_group.setAttribute('transform', transform);
     }
 
     clear() {
-        let rect = this.rect;
-        if (! rect)
+        // FIXME behavior when floating is undefined
+        if (this.is_empty)
             return;
 
+        let old_cells = this.cells;
+
         this.editor._do(
             () => this._clear(),
-            () => this._set_from_rect(rect),
+            () => {
+                this._set_from_set(old_cells);
+            },
             false,
         );
     }
 
     _clear() {
-        this.rect = null;
-        this.element.classList.remove('--visible');
+        this.cells = new Set;
+        this.bbox = null;
+        this.ring_bg_element.classList.remove('--visible');
+        this.ring_element.classList.remove('--visible');
     }
 
+    // TODO only used internally in one place?
     *iter_coords() {
-        if (! this.rect)
-            return;
-
         let stored_level = this.editor.stored_level;
-        for (let y = this.rect.top; y < this.rect.bottom; y++) {
-            for (let x = this.rect.left; x < this.rect.right; x++) {
-                let n = stored_level.coords_to_scalar(x, y);
-                yield [x, y, n];
+        for (let n of this.cells) {
+            let [x, y] = stored_level.scalar_to_coords(n);
+            if (this.floated_offset) {
+                x += this.floated_offset[0];
+                y += this.floated_offset[1];
             }
+            yield [x, y, n];
         }
     }
 
@@ -181,90 +389,143 @@ export class Selection {
         if (this.floated_cells)
             console.error("Trying to float a selection that's already floating");
 
-        let floated_cells = [];
-        let tileset = this.editor.renderer.tileset;
+        let floated_cells = new Map;
         let stored_level = this.editor.stored_level;
-        let bbox = this.rect;
-        let canvas = mk('canvas', {width: bbox.width * tileset.size_x, height: bbox.height * tileset.size_y});
-        let ctx = canvas.getContext('2d');
-        ctx.drawImage(
-            this.editor.renderer.canvas,
-            bbox.x * tileset.size_x, bbox.y * tileset.size_y, bbox.width * tileset.size_x, bbox.height * tileset.size_y,
-            0, 0, bbox.width * tileset.size_x, bbox.height * tileset.size_y);
         for (let [x, y, n] of this.iter_coords()) {
             let cell = stored_level.linear_cells[n];
             if (copy) {
-                floated_cells.push(cell.map(tile => tile ? {...tile} : null));
+                floated_cells.set(n, cell.map(tile => tile ? {...tile} : null));
             }
             else {
-                floated_cells.push(cell);
+                floated_cells.set(n, cell);
                 this.editor.replace_cell(cell, this.editor.make_blank_cell(x, y));
             }
         }
-        let floated_element = mk_svg('g', mk_svg('foreignObject', {
-            x: 0, y: 0,
-            width: canvas.width, height: canvas.height,
-            transform: `scale(${1/tileset.size_x} ${1/tileset.size_y})`,
-        }, canvas));
-        floated_element.setAttribute('transform', `translate(${bbox.x} ${bbox.y})`);
 
-        // FIXME far more memory efficient to recreate the canvas in the redo, rather than hold onto
-        // it forever
         this.editor._do(
             () => {
-                this.floated_canvas = canvas;
-                this.floated_element = floated_element;
                 this.floated_cells = floated_cells;
-                this.svg_group.append(floated_element);
+                this.floated_offset = [0, 0];
+                this._init_floated_canvas();
+                this.ring_element.classList.add('--floating');
             },
-            () => this._defloat(),
+            () => this._delete_floating(),
         );
     }
 
+    // Create floated_canvas and floated_element, based on floated_cells
+    _init_floated_canvas() {
+        let tileset = this.editor.renderer.tileset;
+        this.floated_canvas = mk('canvas', {
+            width: this.bbox.width * tileset.size_x,
+            height: this.bbox.height * tileset.size_y,
+        });
+        let ctx = this.floated_canvas.getContext('2d');
+        for (let n of this.cells) {
+            let [x, y] = this.editor.stored_level.scalar_to_coords(n);
+            this.editor.renderer.draw_static_generic({
+                // Incredibly stupid hack for just drawing one cell
+                x0: 0, x1: 0,
+                y0: 0, y1: 0,
+                width: 1,
+                cells: [this.floated_cells.get(n)],
+                ctx: ctx,
+                destx: x - this.bbox.left,
+                desty: y - this.bbox.top,
+            });
+        }
+        this.floated_element = mk_svg('g', mk_svg('foreignObject', {
+            x: 0,
+            y: 0,
+            width: this.floated_canvas.width,
+            height: this.floated_canvas.height,
+            transform: `scale(${1/tileset.size_x} ${1/tileset.size_y})`,
+        }, this.floated_canvas));
+        this.floated_element.setAttribute('transform', `translate(${this.bbox.x} ${this.bbox.y})`);
+        // This goes first, so the selection ring still appears on top
+        this.selection_group.prepend(this.floated_element);
+    }
+
     stamp_float(copy = false) {
         if (! this.floated_element)
             return;
 
         let stored_level = this.editor.stored_level;
-        let i = 0;
-        for (let [x, y, n] of this.iter_coords()) {
-            let cell = this.floated_cells[i];
+        for (let n of this.cells) {
+            let [x, y] = stored_level.scalar_to_coords(n);
+            x += this.floated_offset[0];
+            y += this.floated_offset[1];
+            // If the selection is moved so that part of it is outside the level, skip that bit
+            if (! stored_level.is_point_within_bounds(x, y))
+                continue;
+
+            let cell = this.floated_cells.get(n);
             if (copy) {
                 cell = cell.map(tile => tile ? {...tile} : null);
             }
             cell.x = x;
             cell.y = y;
-            this.editor.replace_cell(stored_level.linear_cells[n], cell);
-            i += 1;
+
+            let n2 = stored_level.coords_to_scalar(x, y);
+            this.editor.replace_cell(stored_level.linear_cells[n2], cell);
         }
     }
 
-    defloat() {
+    // Converts a floating selection back to a regular selection, including stamping it in place
+    commit_floating() {
+        // This is OK; we're idempotent
         if (! this.floated_element)
             return;
 
         this.stamp_float();
 
-        let element = this.floated_element;
-        let canvas = this.floated_canvas;
-        let cells = this.floated_cells;
+        // Actually apply the offset, so we can be a regular selection again
+        let old_cells = this.cells;
+        let old_bbox = DOMRect.fromRect(this.bbox);
+        let new_cells = new Set;
+        let stored_level = this.editor.stored_level;
+        for (let n of old_cells) {
+            let [x, y] = stored_level.scalar_to_coords(n);
+            x += this.floated_offset[0];
+            y += this.floated_offset[1];
+
+            if (stored_level.is_point_within_bounds(x, y)) {
+                new_cells.add(stored_level.coords_to_scalar(x, y));
+            }
+        }
+
+        let old_floated_cells = this.floated_cells;
+        let old_floated_offset = this.floated_offset;
         this.editor._do(
-            () => this._defloat(),
             () => {
-                this.floated_cells = cells;
-                this.floated_canvas = canvas;
-                this.floated_element = element;
-                this.svg_group.append(element);
+                this._delete_floating();
+                this._set_from_set(new_cells);
+            },
+            () => {
+                // Don't use _set_from_set here; it's not designed for an offset float
+                this.cells = old_cells;
+                this.bbox = old_bbox;
+                this._update_outline();
+
+                this.floated_cells = old_floated_cells;
+                this.floated_offset = old_floated_offset;
+                this._init_floated_canvas();
+                this._update_floating_transform();
+                this.ring_element.classList.add('--floating');
             },
             false,
         );
     }
 
-    _defloat() {
+    _delete_floating() {
+        this.selection_group.removeAttribute('transform');
+        this.ring_element.classList.remove('--floating');
         this.floated_element.remove();
+
+        this.floated_cells = null;
+        this.floated_offset = null;
         this.floated_element = null;
         this.floated_canvas = null;
-        this.floated_cells = null;
     }
 
     // Redraw the selection canvas from scratch
@@ -278,6 +539,7 @@ export class Selection {
         this.editor.renderer.draw_static_generic({
             x0: 0, y0: 0,
             x1: this.rect.width, y1: this.rect.height,
+            // FIXME this is now a set, not a flat list
             cells: this.floated_cells,
             width: this.rect.width,
             ctx: this.floated_canvas.getContext('2d'),
diff --git a/js/editor/main.js b/js/editor/main.js
index c4edc0d..35444c6 100644
--- a/js/editor/main.js
+++ b/js/editor/main.js
@@ -16,6 +16,18 @@ import { SVGConnection, Selection } from './helpers.js';
 import * as mouseops from './mouseops.js';
 import { TILES_WITH_PROPS } from './tile-overlays.js';
 
+// FIXME some idle thoughts
+// for adjust tool:
+// - preview gray button (or click to actually do it)
+// - preview wire reach
+// - preview destination teleporter (or maybe order)
+// - preview monster pathing
+// - preview ice/ff routing (what about e.g. doublemaze)
+// generally:
+// - show wires that are initially powered
+// - show traps that are initially closed
+// - show implicit red/brown connections
+// - selection and eyedropper should preserve red/brown button connections (somehow)
 
 // Edited levels are stored as follows.
 // StoredPack and StoredLevel both have an editor_metadata containing:
@@ -76,12 +88,12 @@ export class Editor extends PrimaryView {
                 mk_svg('marker', {id: 'overlay-arrowhead', markerWidth: 4, markerHeight: 4, refX: 3, refY: 2, orient: 'auto'},
                     mk_svg('polygon', {points: '0 0, 4 2, 0 4'}),
                 ),
-            ),
-            mk_svg('filter', {id: 'overlay-filter-outline'},
-                mk_svg('feMorphology', {'in': 'SourceAlpha', result: 'dilated', operator: 'dilate', radius: 0.03125}),
-                mk_svg('feFlood', {'flood-color': '#0009', result: 'fill'}),
-                mk_svg('feComposite', {'in': 'fill', in2: 'dilated', operator: 'in'}),
-                mk_svg('feComposite', {'in': 'SourceGraphic'}),
+                mk_svg('filter', {id: 'overlay-filter-outline'},
+                    mk_svg('feMorphology', {'in': 'SourceAlpha', result: 'dilated', operator: 'dilate', radius: 0.03125}),
+                    mk_svg('feFlood', {'flood-color': '#0009', result: 'fill'}),
+                    mk_svg('feComposite', {'in': 'fill', in2: 'dilated', operator: 'in'}),
+                    mk_svg('feComposite', {'in': 'SourceGraphic'}),
+                ),
             ),
             this.connections_g,
         );
@@ -143,9 +155,9 @@ export class Editor extends PrimaryView {
                         this.cancel_mouse_drag();
                     }
                     let new_rect = new DOMRect(0, 0, this.stored_level.size_x, this.stored_level.size_y);
-                    let old_rect = this.selection.rect;
-                    if (! (old_rect && old_rect.x === new_rect.x && old_rect.y === new_rect.y && old_rect.width === new_rect.width && old_rect.height === new_rect.height)) {
-                        this.selection.set_from_rect(new_rect);
+                    if (this.selection.cells.size !== this.stored_level.size_x * this.stored_level.size_y) {
+                        this.selection.clear();
+                        this.selection.add_rect(new_rect);
                         this.commit_undo();
                     }
                 }
@@ -156,7 +168,7 @@ export class Editor extends PrimaryView {
                         this.cancel_mouse_drag();
                     }
                     if (! this.selection.is_empty) {
-                        this.selection.defloat();
+                        this.selection.commit_floating();
                         this.selection.clear();
                         this.commit_undo();
                     }
@@ -285,6 +297,13 @@ export class Editor extends PrimaryView {
         });
         window.addEventListener('blur', () => {
             this.cancel_mouse_drag();
+
+            // Assume all modifiers are released
+            for (let mouse_op of this.mouse_ops) {
+                if (mouse_op) {
+                    mouse_op.clear_modifiers();
+                }
+            }
         });
         window.addEventListener('mouseleave', () => {
             this.mouse_coords = null;
@@ -1088,6 +1107,7 @@ export class Editor extends PrimaryView {
 
         this.zoom = zoom;
         this.renderer.canvas.style.setProperty('--scale', this.zoom);
+        this.svg_overlay.style.setProperty('--scale', this.zoom);
         this.actual_viewport_el.classList.toggle('--crispy', this.zoom >= 1);
         this.statusbar_zoom.textContent = `${this.zoom * 100}%`;
 
@@ -1556,6 +1576,7 @@ export class Editor extends PrimaryView {
             old_w = w;
             if (swap_dimensions) {
                 [w, h] = [h, w];
+                // FIXME this will need more interesting rearranging
                 this.selection._set_from_rect(new DOMRect(
                     this.selection.rect.x, this.selection.rect.y, w, h));
             }
diff --git a/js/editor/mouseops.js b/js/editor/mouseops.js
index 28bdea1..27d93f8 100644
--- a/js/editor/mouseops.js
+++ b/js/editor/mouseops.js
@@ -8,6 +8,15 @@ import { mk, mk_svg, walk_grid } from '../util.js';
 import { SVGConnection } from './helpers.js';
 import { TILES_WITH_PROPS } from './tile-overlays.js';
 
+// TODO some minor grievances
+// - the track overlay doesn't explain "direction" (may not be necessary anyway), allows picking a
+// bad initial switch direction
+// - track tool should add a switch to a track on right-click, if possible (and also probably delete
+// it on ctrl-right-click?)
+// - no preview tile with force floor or track tool
+// - no ice drawing tool
+// - cursor box shows with selection tool which seems inappropriate
+// - controls do not exactly stand out and are just plain text
 const MOUSE_BUTTON_MASKS = [1, 4, 2];  // MouseEvent.button/buttons are ordered differently
 export class MouseOperation {
     constructor(editor, physical_button) {
@@ -127,6 +136,13 @@ export class MouseOperation {
     _update_modifiers(ev) {
         this.ctrl = ev.ctrlKey;
         this.shift = ev.shiftKey;
+        this.alt = ev.altKey;
+    }
+
+    clear_modifiers() {
+        this.ctrl = false;
+        this.shift = false;
+        this.alt = false;
     }
 
     do_commit() {
@@ -508,16 +524,21 @@ export class FillOperation extends MouseOperation {
 
 
 // TODO also, delete
-// TODO also, non-rectangular selections
 // TODO also, better marching ants, hard to see on gravel
 export class SelectOperation extends MouseOperation {
     handle_press() {
-        if (! this.editor.selection.is_empty && this.editor.selection.contains(this.click_cell_x, this.click_cell_y)) {
+        if (this.shift) {
+            // Extend selection
+            this.mode = 'extend';
+            this.pending_selection = this.editor.selection.create_pending();
+            this.update_pending_selection();
+        }
+        else if (! this.editor.selection.is_empty &&
+            this.editor.selection.contains(this.click_cell_x, this.click_cell_y))
+        {
             // Move existing selection
             this.mode = 'float';
-            if (this.ctrl) {
-                this.make_copy = true;
-            }
+            this.make_copy = this.ctrl;
         }
         else {
             // Create new selection
@@ -569,17 +590,31 @@ export class SelectOperation extends MouseOperation {
                 );
             }
         }
-        else {
-            // If there's an existing floating selection (which isn't what we're operating on),
-            // commit it before doing anything else
-            this.editor.selection.defloat();
-            if (! this.has_moved) {
-                // Plain click clears selection
-                this.pending_selection.discard();
-                this.editor.selection.clear();
+        else {  // create/extend
+            if (this.has_moved) {
+                // Drag either creates or extends the selection
+                // If there's an existing floating selection (which isn't what we're operating on),
+                // commit it before doing anything else
+                this.editor.selection.commit_floating();
+
+                if (this.mode === 'create') {
+                    this.editor.selection.clear();
+                }
+                this.pending_selection.commit();
             }
             else {
-                this.pending_selection.commit();
+                // Plain click clears selection.  But first, if there's a floating selection and
+                // it's moved, commit that movement as a separate undo entry
+                if (this.editor.selection.is_floating) {
+                    let float_moved = this.editor.selection.has_moved;
+                    if (float_moved) {
+                        this.editor.commit_undo();
+                    }
+                    this.editor.selection.commit_floating();
+                }
+
+                this.pending_selection.discard();
+                this.editor.selection.clear();
             }
         }
         this.editor.commit_undo();
@@ -592,6 +627,13 @@ export class SelectOperation extends MouseOperation {
             this.pending_selection.discard();
         }
     }
+
+    do_destroy() {
+        // Don't let a floating selection persist when switching tools
+        this.editor.selection.commit_floating();
+        this.editor.commit_undo();
+        super.do_destroy();
+    }
 }
 
 export class ForceFloorOperation extends MouseOperation {
@@ -1166,10 +1208,7 @@ export class CameraOperation extends MouseOperation {
         this.editor.viewport_el.style.cursor = cursor;
 
         // Create a text element to show the size while editing
-        this.size_text = mk_svg('text.overlay-edit-tip', {
-            // Center it within the rectangle probably (x and y are set in _update_size_text)
-            'text-anchor': 'middle', 'dominant-baseline': 'middle',
-        });
+        this.size_text = mk_svg('text.overlay-edit-tip');
         this._update_size_text();
         this.editor.svg_overlay.append(this.size_text);
     }
diff --git a/js/util.js b/js/util.js
index 66f5fb0..f789975 100644
--- a/js/util.js
+++ b/js/util.js
@@ -337,6 +337,33 @@ export function* walk_grid(x0, y0, x1, y1, min_a, min_b, max_a, max_b) {
     }
 }
 
+
+// Baby's first bit vector
+export class BitVector {
+    constructor(size) {
+        this.array = new Uint32Array(Math.ceil(size / 32));
+    }
+
+    get(bit) {
+        let i = Math.floor(bit / 32);
+        let b = bit % 32;
+        return (this.array[i] & (1 << b)) !== 0;
+    }
+
+    set(bit) {
+        let i = Math.floor(bit / 32);
+        let b = bit % 32;
+        this.array[i] |= (1 << b);
+    }
+
+    clear(bit) {
+        let i = Math.floor(bit / 32);
+        let b = bit % 32;
+        this.array[i] &= ~(1 << b);
+    }
+}
+
+
 // Root class to indirect over where we might get files from
 // - a pool of uploaded in-memory files
 // - a single uploaded zip file
diff --git a/style.css b/style.css
index 74a7195..9546f5a 100644
--- a/style.css
+++ b/style.css
@@ -2215,8 +2215,11 @@ svg.level-editor-overlay {
     /* allow clicks to go through us! */
     pointer-events: none;
 
+    /* not used to shrink us (absolute positioning does that), just to make the stroke width a
+     * consistent size at any zoom level */
+    --scale: 1;
     /* default svg properties */
-    stroke-width: 0.0625;
+    stroke-width: calc(0.0625px / var(--scale));
     fill: none;
 }
 svg.level-editor-overlay .overlay-transient {
@@ -2226,24 +2229,33 @@ svg.level-editor-overlay .overlay-transient.--visible {
     display: initial;
 }
 svg.level-editor-overlay rect.overlay-cursor {
-    x-stroke: hsla(220, 100%, 60%, 0.5);
-    fill: hsla(220, 100%, 75%, 0.25);
+    stroke: hsla(var(--main-hue), 100%, 90%, 0.75);
+    fill: hsla(var(--main-hue), 100%, 75%, 0.25);
 }
 svg.level-editor-overlay rect.overlay-pending-selection {
-    stroke: hsla(220, 100%, 60%, 0.5);
-    fill: hsla(220, 100%, 75%, 0.25);
+    stroke: hsla(var(--selected-hue), 100%, 60%, 0.5);
+    fill: hsla(var(--selected-hue), 100%, 75%, 0.25);
 }
-svg.level-editor-overlay rect.overlay-selection {
-    stroke: #000c;
-    fill: hsla(220, 0%, 75%, 0.25);
-    stroke-dasharray: 0.125, 0.125;
-    animation: marching-ants 1s linear infinite;
+svg.level-editor-overlay path.overlay-selection-background {
+    stroke: hsla(var(--selected-hue), 10%, 90%, 0.9);
+    fill: none;
+    pointer-events: none;
+}
+svg.level-editor-overlay path.overlay-selection {
+    stroke: hsla(var(--selected-hue), 10%, 10%, 0.75);
+    fill: hsla(var(--selected-hue), 50%, 75%, 0.375);
+    stroke-width: calc(0.125px / var(--scale));
+    stroke-dasharray: calc(0.125px / var(--scale)), calc(0.125px / var(--scale));
+    animation: marching-ants 0.5s linear infinite;
     pointer-events: auto;
     cursor: move;
 }
+svg.level-editor-overlay path.overlay-selection.--floating {
+    stroke: hsla(var(--selected-hue), 80%, 50%, 0.75);
+}
 @keyframes marching-ants {
     0% {
-        stroke-dashoffset: 0.25;
+        stroke-dashoffset: calc(0.25px / var(--scale));
     }
     100% {
         stroke-dashoffset: 0;
@@ -2269,8 +2281,11 @@ svg.level-editor-overlay text {
     font-size: 1px;
 }
 svg.level-editor-overlay text.overlay-edit-tip {
+    /* Used for showing e.g. the size of a pending selection.  Centered around its anchor */
     stroke: none;
-    fill: black;
+    fill: hsl(var(--selected-hue), 80%, 30%);
+    text-anchor: middle;
+    dominant-baseline: middle;
 }
 
 .editor-big-tooltip {
@@ -2293,7 +2308,7 @@ svg.level-editor-overlay text.overlay-edit-tip {
     text-transform: none;
     text-align: left;
     color: #d8d8d8;
-    background: hsl(220, 10%, 20%);
+    background: hsl(var(--main-hue), 10%, 20%);
     box-shadow: 0 1px 2px 1px #0004;
 }
 .editor-big-tooltip h3 {