diff --git a/src/core/commands/Command.ts b/src/core/commands/Command.ts
index ecf118c3..420c6233 100644
--- a/src/core/commands/Command.ts
+++ b/src/core/commands/Command.ts
@@ -11,6 +11,25 @@ export interface Command {
   undo(project: Project): void;
 }
 
+/** A rename that is undone by renaming back. */
+export abstract class RenameCommand implements Command {
+  constructor(
+    readonly label: string,
+    private readonly from: string,
+    private readonly to: string,
+  ) {}
+
+  execute(project: Project): void {
+    this.rename(project, this.from, this.to);
+  }
+
+  undo(project: Project): void {
+    this.rename(project, this.to, this.from);
+  }
+
+  protected abstract rename(project: Project, from: string, to: string): void;
+}
+
 /** A rejected edit with a message fit for the user; the editor shows it as a notice. */
 export class CommandError extends Error {
   constructor(message: string) {
diff --git a/src/core/commands/assetCommands.ts b/src/core/commands/assetCommands.ts
index 9b400f2d..970454ae 100644
--- a/src/core/commands/assetCommands.ts
+++ b/src/core/commands/assetCommands.ts
@@ -110,22 +110,24 @@ export function buildTextureAsset(name: string, image: TextureImage, id = newId(
 }
 
 /**
- * The image is uploaded before the command runs; this only records the result, so undo and redo
+ * The file is uploaded before the command runs; this only records the result, so undo and redo
  * never touch the network.
  */
-export class CreateTextureCommand implements Command {
+abstract class ImportFileCommand<A extends Asset & { file: string }> implements Command {
   readonly label: string;
-  readonly asset: TextureAsset;
 
-  constructor(name: string, image: TextureImage) {
-    this.asset = buildTextureAsset(name, image);
-    this.label = `Import texture "${name}"`;
+  constructor(
+    readonly asset: A,
+    private readonly fileNoun: string,
+    private readonly isStored: (file: string) => boolean,
+  ) {
+    this.label = `Import ${asset.type} "${asset.name}"`;
   }
 
   execute(project: Project): void {
     // The name is the hash the server derived from the bytes; anything else was never uploaded.
-    if (!isTextureFile(this.asset.file))
-      throw new CommandError(`"${this.asset.file}" is not a stored image file`);
+    if (!this.isStored(this.asset.file))
+      throw new CommandError(`"${this.asset.file}" is not a stored ${this.fileNoun} file`);
     project.assets.push(this.asset);
   }
 
@@ -134,28 +136,19 @@ export class CreateTextureCommand implements Command {
   }
 }
 
+export class CreateTextureCommand extends ImportFileCommand<TextureAsset> {
+  constructor(name: string, image: TextureImage) {
+    super(buildTextureAsset(name, image), 'image', isTextureFile);
+  }
+}
+
 export function buildFontAsset(name: string, file: string, id = newId()): FontAsset {
   return { id, name, props: defaultsFor('font'), type: 'font', file };
 }
 
-/** The typeface is uploaded before the command runs, as an image is for `CreateTextureCommand`. */
-export class CreateFontCommand implements Command {
-  readonly label: string;
-  readonly asset: FontAsset;
-
+export class CreateFontCommand extends ImportFileCommand<FontAsset> {
   constructor(name: string, file: string) {
-    this.asset = buildFontAsset(name, file);
-    this.label = `Import font "${name}"`;
-  }
-
-  execute(project: Project): void {
-    if (!isFontFile(this.asset.file))
-      throw new CommandError(`"${this.asset.file}" is not a stored font file`);
-    project.assets.push(this.asset);
-  }
-
-  undo(project: Project): void {
-    project.assets = removeById(project.assets, this.asset.id);
+    super(buildFontAsset(name, file), 'font', isFontFile);
   }
 }
 
@@ -163,24 +156,9 @@ export function buildSoundAsset(name: string, file: string, id = newId()): Sound
   return { id, name, props: defaultsFor('sound'), type: 'sound', file };
 }
 
-/** The sound is uploaded before the command runs, as a typeface is for `CreateFontCommand`. */
-export class CreateSoundCommand implements Command {
-  readonly label: string;
-  readonly asset: SoundAsset;
-
+export class CreateSoundCommand extends ImportFileCommand<SoundAsset> {
   constructor(name: string, file: string) {
-    this.asset = buildSoundAsset(name, file);
-    this.label = `Import sound "${name}"`;
-  }
-
-  execute(project: Project): void {
-    if (!isSoundFile(this.asset.file))
-      throw new CommandError(`"${this.asset.file}" is not a stored sound file`);
-    project.assets.push(this.asset);
-  }
-
-  undo(project: Project): void {
-    project.assets = removeById(project.assets, this.asset.id);
+    super(buildSoundAsset(name, file), 'sound', isSoundFile);
   }
 }
 
diff --git a/src/core/commands/portCommands.ts b/src/core/commands/portCommands.ts
index 86cd43a5..60b7d446 100644
--- a/src/core/commands/portCommands.ts
+++ b/src/core/commands/portCommands.ts
@@ -19,7 +19,7 @@ import {
 import type { PropertyValue } from '../model/Properties';
 import type { Project } from '../model/Project';
 import { type Removed, removeFirst, removeWhere, restoreAt } from '../util/list';
-import { type Command, CommandError } from './Command';
+import { type Command, CommandError, RenameCommand } from './Command';
 import { nextFieldName } from './naming';
 import { requireBehavior, requireNode, requireNodeDef } from './require';
 
@@ -260,27 +260,17 @@ export class SetPortWriteCommand implements Command {
 }
 
 /** Rewrites the edges and inline values pointing at the port too, in every graph that has any. */
-export class RenamePortCommand implements Command {
-  readonly label: string;
-
+export class RenamePortCommand extends RenameCommand {
   constructor(
     private readonly assetId: string,
     private readonly nodeId: string,
-    private readonly from: string,
-    private readonly to: string,
+    from: string,
+    to: string,
   ) {
-    this.label = `Rename ${from}`;
+    super(`Rename ${from}`, from, to);
   }
 
-  execute(project: Project): void {
-    this.rename(project, this.from, this.to);
-  }
-
-  undo(project: Project): void {
-    this.rename(project, this.to, this.from);
-  }
-
-  private rename(project: Project, from: string, to: string): void {
+  protected rename(project: Project, from: string, to: string): void {
     if (from === to) return;
     const node = requireNode(project, this.assetId, this.nodeId);
     const sites = portSites(project, this.assetId, node);
diff --git a/src/core/commands/variableCommands.ts b/src/core/commands/variableCommands.ts
index 1a804547..d213d037 100644
--- a/src/core/commands/variableCommands.ts
+++ b/src/core/commands/variableCommands.ts
@@ -17,7 +17,7 @@ import {
   variableDef,
 } from '../properties/PropertySchema';
 import { type Removed, removeFirst, restoreAt } from '../util/list';
-import { type Command, CommandError } from './Command';
+import { type Command, CommandError, RenameCommand } from './Command';
 import { renameVariablePorts } from './portCommands';
 import { requireVariableOwner } from './require';
 
@@ -117,26 +117,16 @@ export class RemoveVariableCommand implements Command {
 }
 
 /** Renames everywhere: definition, default, instance overrides and the graph nodes referring to it. */
-export class RenameVariableCommand implements Command {
-  readonly label: string;
-
+export class RenameVariableCommand extends RenameCommand {
   constructor(
     private readonly assetId: string,
-    private readonly from: string,
-    private readonly to: string,
+    from: string,
+    to: string,
   ) {
-    this.label = `Rename variable ${from}`;
+    super(`Rename variable ${from}`, from, to);
   }
 
-  execute(project: Project): void {
-    this.rename(project, this.from, this.to);
-  }
-
-  undo(project: Project): void {
-    this.rename(project, this.to, this.from);
-  }
-
-  private rename(project: Project, from: string, to: string): void {
+  protected rename(project: Project, from: string, to: string): void {
     const asset = requireVariableOwner(project, this.assetId);
     if (from === to) return;
     if (!isValidVariableName(to)) throw new CommandError(INVALID_NAME);
@@ -316,27 +306,17 @@ export class RemoveStructFieldCommand implements Command {
   }
 }
 
-export class RenameStructFieldCommand implements Command {
-  readonly label: string;
-
+export class RenameStructFieldCommand extends RenameCommand {
   constructor(
     private readonly assetId: string,
     private readonly key: string,
-    private readonly from: string,
-    private readonly to: string,
+    from: string,
+    to: string,
   ) {
-    this.label = `Rename field ${from}`;
+    super(`Rename field ${from}`, from, to);
   }
 
-  execute(project: Project): void {
-    this.rename(project, this.from, this.to);
-  }
-
-  undo(project: Project): void {
-    this.rename(project, this.to, this.from);
-  }
-
-  private rename(project: Project, from: string, to: string): void {
+  protected rename(project: Project, from: string, to: string): void {
     const owner = requireFieldOwner(project, this.assetId, this.key);
     if (from === to) return;
     if (!isValidFieldName(to)) throw new CommandError(INVALID_FIELD);
diff --git a/src/core/graph/GraphInterpreter.ts b/src/core/graph/GraphInterpreter.ts
index 80cda921..56836aea 100644
--- a/src/core/graph/GraphInterpreter.ts
+++ b/src/core/graph/GraphInterpreter.ts
@@ -19,8 +19,8 @@ const MAX_STEPS_PER_FIRE = 100_000;
 
 /**
  * How far exec edges may nest. The interpreter recurses along them, so this is what keeps a flow
- * feeding back into itself off the call stack – a job the step budget can no longer do now that a
- * legitimate pulse may run tens of thousands of steps.
+ * feeding back into itself off the call stack – the step budget cannot, since a legitimate pulse
+ * may run tens of thousands of steps.
  */
 const MAX_DEPTH = 1000;
 
diff --git a/src/core/graph/emitGraph.ts b/src/core/graph/emitGraph.ts
new file mode 100644
index 00000000..f719a1ec
--- /dev/null
+++ b/src/core/graph/emitGraph.ts
@@ -0,0 +1,106 @@
+import { edgesInto, findNode, type Graph, type GraphNode } from './Graph';
+import { nodeDef, type NodeDef, type PortDef } from './NodeRegistry';
+
+export interface EmitRules<D extends NodeDef, T> {
+  isDef: (def: NodeDef) => def is D;
+  /** Names the node kind in "Not a … node". */
+  noun: string;
+  /** A node's outputs from its inputs; called once per node, in dependency order. */
+  emit: (def: D, inputs: Record<string, T>, node: GraphNode) => Record<string, T>;
+  /** An input without an edge: the typed-in value or what the node says it means unfed. */
+  unfed: (node: GraphNode, port: PortDef, def: D | undefined) => T | null;
+  /** An edge's value on its way into `port`; null (after reporting a problem) when it cannot go in. */
+  conform?: (node: GraphNode, port: PortDef, value: T) => T | null;
+}
+
+export interface GraphEmitter<T> {
+  /** Per node id, the first thing that keeps the graph from compiling. */
+  readonly problems: Record<string, string>;
+  problem(node: GraphNode, text: string): void;
+  /** What feeds an input, emitting whatever it depends on first. */
+  input(node: GraphNode, port: PortDef): T | null;
+  /** Whether the walk reached the node. */
+  reached(node: GraphNode): boolean;
+  /** Reports property names that are invalid (`invalid` returns the text) or taken twice. */
+  checkNames(
+    nodes: GraphNode[],
+    nameOf: (node: GraphNode) => string,
+    invalid: (name: string) => string,
+  ): void;
+  /** The problem of the first node in graph order, or null when there is none. */
+  firstProblem(): string | null;
+}
+
+/**
+ * The walk shared by the graph compilers: every node reachable from where `input` is first asked
+ * is emitted once, before anything that reads it, and a node feeding itself is a problem.
+ */
+export function graphEmitter<D extends NodeDef, T>(graph: Graph, rules: EmitRules<D, T>): GraphEmitter<T> {
+  const problems: Record<string, string> = {};
+  const emitted = new Map<string, Record<string, T>>();
+  const visiting = new Set<string>();
+
+  const problem = (node: GraphNode, text: string) => {
+    if (!(node.id in problems)) problems[node.id] = text;
+  };
+
+  const emitNode = (node: GraphNode): Record<string, T> | null => {
+    const done = emitted.get(node.id);
+    if (done) return done;
+    if (visiting.has(node.id)) {
+      problem(node, 'Feeds itself');
+      return null;
+    }
+    const def = nodeDef(node.type);
+    if (!def || !rules.isDef(def)) {
+      problem(node, `Not a ${rules.noun} node`);
+      return null;
+    }
+    visiting.add(node.id);
+    const inputs: Record<string, T> = {};
+    let complete = true;
+    for (const port of def.inputs) {
+      const value = input(node, port);
+      if (value) inputs[port.key] = value;
+      else complete = false;
+    }
+    visiting.delete(node.id);
+    if (!complete) return null;
+    const outputs = rules.emit(def, inputs, node);
+    emitted.set(node.id, outputs);
+    return outputs;
+  };
+
+  const input = (node: GraphNode, port: PortDef): T | null => {
+    const edge = edgesInto(graph, node.id, port.key)[0];
+    if (edge) {
+      const source = findNode(graph, edge.from.node);
+      const value = (source && emitNode(source))?.[edge.from.port];
+      if (!value) return null;
+      return rules.conform ? rules.conform(node, port, value) : value;
+    }
+    const def = nodeDef(node.type);
+    return rules.unfed(node, port, def && rules.isDef(def) ? def : undefined);
+  };
+
+  return {
+    problems,
+    problem,
+    input,
+    reached: (node) => emitted.has(node.id),
+    checkNames(nodes, nameOf, invalid) {
+      const names = new Set<string>();
+      for (const node of nodes) {
+        const name = nameOf(node);
+        const text = invalid(name);
+        if (text) problem(node, text);
+        else if (names.has(name)) problem(node, `Another property is named "${name}"`);
+        names.add(name);
+      }
+    },
+    firstProblem() {
+      const first = graph.nodes.find((n) => n.id in problems);
+      return first ? problems[first.id]! : null;
+    },
+  };
+}
diff --git a/src/core/particles/compile.ts b/src/core/particles/compile.ts
index 2b0ce4cc..e2df539c 100644
--- a/src/core/particles/compile.ts
+++ b/src/core/particles/compile.ts
@@ -1,5 +1,6 @@
-import { edgesInto, findNode, type Graph, type GraphNode } from '../graph/Graph';
-import { nodeDef, type PortDef } from '../graph/NodeRegistry';
+import { graphEmitter } from '../graph/emitGraph';
+import type { Graph } from '../graph/Graph';
+import { nodeDef } from '../graph/NodeRegistry';
 import type { FlatDef } from '../properties/PropertySchema';
 import {
   isParticlePropertyNode,
@@ -13,6 +14,7 @@ import {
   PARTICLE_OUTPUTS,
   PARTICLE_TIME,
   type ParticleEnv,
+  type ParticleNodeDef,
   type ParticleExpr,
   type ParticleOutputKey,
 } from './nodes';
@@ -44,79 +46,40 @@ export interface ParticlesBuild {
  * particle. There is no interpreter and no eval – the compiler composes closures.
  */
 export function compileParticles(graph: Graph): ParticlesBuild {
-  const problems: Record<string, string> = {};
-  const problem = (node: GraphNode, text: string) => {
-    if (!(node.id in problems)) problems[node.id] = text;
-  };
-
-  const names = new Set<string>();
-  for (const node of graph.nodes) {
-    if (!isParticlePropertyNode(node)) continue;
-    const name = propertyNameOf(node);
-    if (!isValidParticlePropertyName(name))
-      problem(node, 'Name must be one word: letters, digits, _ – and not one of the source’s own rows');
-    else if (names.has(name)) problem(node, `Another property is named "${name}"`);
-    names.add(name);
-  }
-
   const params = particleParamDefs(graph);
   const paramIndex = (name: string) => params.findIndex((row) => row.key === name);
-
   const ops: ParticleExpr[] = [];
-  const emitted = new Map<string, Record<string, ParticleExpr>>();
-  const visiting = new Set<string>();
 
-  const emitNode = (node: GraphNode): Record<string, ParticleExpr> | null => {
-    const done = emitted.get(node.id);
-    if (done) return done;
-    if (visiting.has(node.id)) {
-      problem(node, 'Feeds itself');
-      return null;
-    }
-    const def = nodeDef(node.type);
-    if (!def || !isParticleNodeDef(def)) {
-      problem(node, 'Not a particle node');
-      return null;
-    }
-    visiting.add(node.id);
-    const inputs: Record<string, ParticleExpr> = {};
-    let complete = true;
-    for (const port of def.inputs) {
-      const expr = input(node, port);
-      if (expr) inputs[port.key] = expr;
-      else complete = false;
-    }
-    visiting.delete(node.id);
-    if (!complete) return null;
-    const outputs: Record<string, ParticleExpr> = {};
-    for (const [key, expr] of Object.entries(
-      def.emit(inputs, node.params, { nodeId: node.id, paramIndex }),
-    )) {
-      const slot = ops.length;
-      ops.push(expr);
-      outputs[key] = (_env, locals) => locals[slot]!;
-    }
-    emitted.set(node.id, outputs);
-    return outputs;
-  };
+  const walk = graphEmitter<ParticleNodeDef, ParticleExpr>(graph, {
+    isDef: isParticleNodeDef,
+    noun: 'particle',
+    emit: (def, inputs, node) => {
+      const outputs: Record<string, ParticleExpr> = {};
+      for (const [key, expr] of Object.entries(
+        def.emit(inputs, node.params, { nodeId: node.id, paramIndex }),
+      )) {
+        const slot = ops.length;
+        ops.push(expr);
+        outputs[key] = (_env, locals) => locals[slot]!;
+      }
+      return outputs;
+    },
+    unfed: (node, port, def) => {
+      if (port.field) {
+        const typed = Number(node.params[port.key] ?? port.default ?? 0);
+        const value = Number.isFinite(typed) ? typed : 0;
+        return () => value;
+      }
+      return def?.unfed?.[port.key] ?? (() => 0);
+    },
+  });
+  const { problems } = walk;
 
-  /** What feeds an input: the edge's source, the typed-in value, or what the node says (`unfed`). */
-  const input = (node: GraphNode, port: PortDef): ParticleExpr | null => {
-    const edge = edgesInto(graph, node.id, port.key)[0];
-    if (edge) {
-      const source = findNode(graph, edge.from.node);
-      const outputs = source && emitNode(source);
-      return outputs?.[edge.from.port] ?? null;
-    }
-    if (port.field) {
-      const typed = Number(node.params[port.key] ?? port.default ?? 0);
-      const value = Number.isFinite(typed) ? typed : 0;
-      return () => value;
-    }
-    const def = nodeDef(node.type);
-    const unfed = def && isParticleNodeDef(def) ? def.unfed?.[port.key] : undefined;
-    return unfed ?? (() => 0);
-  };
+  walk.checkNames(graph.nodes.filter(isParticlePropertyNode), propertyNameOf, (name) =>
+    isValidParticlePropertyName(name)
+      ? ''
+      : 'Name must be one word: letters, digits, _ – and not one of the source’s own rows',
+  );
 
   const output = graph.nodes.find((n) => n.type === PARTICLE_OUTPUT);
   if (!output) return { compiled: null, problems, reason: 'No Output node' };
@@ -124,17 +87,17 @@ export function compileParticles(graph: Graph): ParticlesBuild {
   const reads: ParticleExpr[] = [];
   for (const key of PARTICLE_OUTPUTS) {
     const port = outputDef.inputs.find((p) => p.key === key)!;
-    const expr = input(output, port);
+    const expr = walk.input(output, port);
     if (!expr) break;
     reads.push(expr);
   }
 
-  const first = graph.nodes.find((n) => n.id in problems);
-  if (first || reads.length !== PARTICLE_OUTPUTS.length)
-    return { compiled: null, problems, reason: first ? problems[first.id]! : 'Cannot compile' };
+  const failed = walk.firstProblem();
+  if (failed !== null || reads.length !== PARTICLE_OUTPUTS.length)
+    return { compiled: null, problems, reason: failed ?? 'Cannot compile' };
 
   const locals = new Float64Array(ops.length);
-  const time = graph.nodes.some((n) => n.type === PARTICLE_TIME && emitted.has(n.id));
+  const time = graph.nodes.some((n) => n.type === PARTICLE_TIME && walk.reached(n));
   const compiled: CompiledParticles = {
     params,
     time,
diff --git a/src/core/shader/compile.ts b/src/core/shader/compile.ts
index 83bd25f8..cb49c13a 100644
--- a/src/core/shader/compile.ts
+++ b/src/core/shader/compile.ts
@@ -1,5 +1,6 @@
-import { edgesInto, findNode, type Graph, type GraphNode } from '../graph/Graph';
-import { nodeDef, type PortDef } from '../graph/NodeRegistry';
+import { graphEmitter } from '../graph/emitGraph';
+import { edgesInto, type Graph } from '../graph/Graph';
+import { nodeDef } from '../graph/NodeRegistry';
 import { colorOf } from '../model/Properties';
 import { isSpriteProp, isValidFieldName } from '../properties/PropertySchema';
 import { isPropertyNode, propertyName, shaderParamDefs } from '../properties/shaders';
@@ -14,6 +15,7 @@ import {
   SHADER_OUTPUT,
   SHADER_SAMPLE,
   SHADER_TIME,
+  type ShaderNodeDef,
   SHEET_EDGE,
   STRAIGHT_FN,
   TEXEL_ALPHA,
@@ -55,101 +57,61 @@ export interface ShaderBuild {
  * arrives premultiplied, so the prelude unpremultiplies and the epilogue multiplies back.
  */
 export function compileShader(graph: Graph): ShaderBuild {
-  const problems: Record<string, string> = {};
-  const problem = (node: GraphNode, text: string) => {
-    if (!(node.id in problems)) problems[node.id] = text;
-  };
-
-  const names = new Set<string>();
-  for (const node of graph.nodes) {
-    if (!isPropertyNode(node)) continue;
-    const name = propertyName(node);
-    if (!isValidFieldName(name)) problem(node, 'Name must be one word: letters, digits, _');
-    else if (isSpriteProp(name)) problem(node, `"${name}" is a sprite property`);
-    else if (names.has(name)) problem(node, `Another property is named "${name}"`);
-    names.add(name);
-  }
-
   const lines: string[] = [];
-  const emitted = new Map<string, Record<string, Expr>>();
-  const visiting = new Set<string>();
   let count = 0;
 
-  const emitNode = (node: GraphNode): Record<string, Expr> | null => {
-    const done = emitted.get(node.id);
-    if (done) return done;
-    if (visiting.has(node.id)) {
-      problem(node, 'Feeds itself');
-      return null;
-    }
-    const def = nodeDef(node.type);
-    if (!def || !isShaderNodeDef(def)) {
-      problem(node, 'Not a shader node');
-      return null;
-    }
-    visiting.add(node.id);
-    const inputs: Record<string, Expr> = {};
-    let complete = true;
-    for (const port of def.inputs) {
-      const expr = input(node, port);
-      if (expr) inputs[port.key] = expr;
-      else complete = false;
-    }
-    visiting.delete(node.id);
-    if (!complete) return null;
-    const outputs: Record<string, Expr> = {};
-    for (const [key, expr] of Object.entries(def.emit(inputs, node.params))) {
-      const local = `n${count++}_${key}`;
-      lines.push(`${expr.type} ${local} = ${expr.code};`);
-      outputs[key] = { code: local, type: expr.type };
-    }
-    emitted.set(node.id, outputs);
-    return outputs;
-  };
+  const walk = graphEmitter<ShaderNodeDef, Expr>(graph, {
+    isDef: isShaderNodeDef,
+    noun: 'shader',
+    emit: (def, inputs, node) => {
+      const outputs: Record<string, Expr> = {};
+      for (const [key, expr] of Object.entries(def.emit(inputs, node.params))) {
+        const local = `n${count++}_${key}`;
+        lines.push(`${expr.type} ${local} = ${expr.code};`);
+        outputs[key] = { code: local, type: expr.type };
+      }
+      return outputs;
+    },
+    // With nothing to type and nothing the node says, an input is the texel: its colour for a
+    // colour port, its alpha for a number.
+    unfed: (node, port, def) => {
+      const typed = node.params[port.key] ?? port.default;
+      if (port.field?.kind === 'color')
+        return { code: vec3Literal(colorOf(typed ?? 0xffffff, 0xffffff)), type: 'vec3' };
+      if (port.field) return { code: floatLiteral(Number(typed ?? 0)), type: 'float' };
+      return def?.unfed?.[port.key] ?? (port.type === 'number' ? TEXEL_ALPHA : TEXEL_COLOR);
+    },
+    conform: (node, port, expr) => {
+      if (port.type === 'number' && expr.type === 'vec3') {
+        walk.problem(node, `"${port.key}" needs a number, not a colour`);
+        return null;
+      }
+      if (port.type === 'vec3' && expr.type === 'float') return { code: asVec3(expr), type: 'vec3' };
+      return expr;
+    },
+  });
+  const { problems } = walk;
 
-  /**
-   * What feeds an input: the edge's source, the typed-in value, or – with nothing to type – what
-   * the node says (`unfed`), else the texel: its colour for a colour port, its alpha for a number.
-   */
-  const input = (node: GraphNode, port: PortDef): Expr | null => {
-    const edge = edgesInto(graph, node.id, port.key)[0];
-    if (edge) {
-      const source = findNode(graph, edge.from.node);
-      const outputs = source && emitNode(source);
-      const expr = outputs?.[edge.from.port];
-      if (!expr) return null;
-      return conform(node, port, expr);
-    }
-    const typed = node.params[port.key] ?? port.default;
-    if (port.field?.kind === 'color')
-      return { code: vec3Literal(colorOf(typed ?? 0xffffff, 0xffffff)), type: 'vec3' };
-    if (port.field) return { code: floatLiteral(Number(typed ?? 0)), type: 'float' };
-    const def = nodeDef(node.type);
-    const unfed = def && isShaderNodeDef(def) ? def.unfed?.[port.key] : undefined;
-    return unfed ?? (port.type === 'number' ? TEXEL_ALPHA : TEXEL_COLOR);
-  };
-
-  const conform = (node: GraphNode, port: PortDef, expr: Expr): Expr | null => {
-    if (port.type === 'number' && expr.type === 'vec3') {
-      problem(node, `"${port.key}" needs a number, not a colour`);
-      return null;
-    }
-    if (port.type === 'vec3' && expr.type === 'float') return { code: asVec3(expr), type: 'vec3' };
-    return expr;
-  };
+  walk.checkNames(graph.nodes.filter(isPropertyNode), propertyName, (name) =>
+    !isValidFieldName(name)
+      ? 'Name must be one word: letters, digits, _'
+      : isSpriteProp(name)
+        ? `"${name}" is a sprite property`
+        : '',
+  );
 
   const output = graph.nodes.find((n) => n.type === SHADER_OUTPUT);
   if (!output) return { compiled: null, problems, reason: 'No Output node' };
   const outputDef = nodeDef(SHADER_OUTPUT)!;
-  const color = input(output, outputDef.inputs[0]!);
-  const alpha = input(output, outputDef.inputs[1]!);
+  const color = walk.input(output, outputDef.inputs[0]!);
+  const alpha = walk.input(output, outputDef.inputs[1]!);
 
-  const first = graph.nodes.find((n) => n.id in problems);
-  if (first || !color || !alpha)
-    return { compiled: null, problems, reason: first ? problems[first.id]! : 'Cannot compile' };
+  const failed = walk.firstProblem();
+  if (failed !== null || !color || !alpha)
+    return { compiled: null, problems, reason: failed ?? 'Cannot compile' };
 
   const uniforms = shaderParamDefs(graph).map((row) => ({ name: row.key, default: row.default }));
-  const time = graph.nodes.some((n) => n.type === SHADER_TIME && emitted.has(n.id));
+  const time = graph.nodes.some((n) => n.type === SHADER_TIME && walk.reached(n));
   // The fragment runs in the sprite's own draw (#77). `vColor` is the tint, premultiplied like the
   // texel; it goes in before the graph, so `Texture color` is the sprite as it draws without a shader.
   // The version line is what makes Pixi compile the program as GLSL ES 3.00 (`GlProgram` looks for
@@ -179,7 +141,7 @@ export function compileShader(graph: Graph): ShaderBuild {
   const shifted = graph.nodes.some(
     (n) =>
       n.type === SHADER_SAMPLE &&
-      emitted.has(n.id) &&
+      walk.reached(n) &&
       (edgesInto(graph, n.id, 'u').length > 0 || edgesInto(graph, n.id, 'v').length > 0),
   );
   const edge = shifted ? edgeOf(output.params) : SHEET_EDGE;
diff --git a/src/editor/debugHook.ts b/src/editor/debugHook.ts
index 4ba88e7c..44f0db02 100644
--- a/src/editor/debugHook.ts
+++ b/src/editor/debugHook.ts
@@ -361,7 +361,7 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
       canvasRect: () => editor.stateMachineEditor.canvas.canvasRect(),
       center: () => centreOf(editor.stateMachineEditor.canvas),
       snapping: () => editor.stateMachineEditor.canvas.snapEnabled,
-      /** Where a state's hidden pin sits. It is no longer grabbable – `portGrabbable` is the check. */
+      /** Where a state's hidden pin sits; it cannot be grabbed – `portGrabbable` is the check. */
       portAt: (nodeId: string, port: string, isOutput: boolean) =>
         editor.stateMachineEditor.canvas.portGlobal(nodeId, port, isOutput),
       portGrabbable: (nodeId: string, port: string, isOutput: boolean) =>
diff --git a/src/editor/framing.ts b/src/editor/framing.ts
index 2a2977a4..2f3493dd 100644
--- a/src/editor/framing.ts
+++ b/src/editor/framing.ts
@@ -68,16 +68,22 @@ export interface Framing {
   panY: number;
 }
 
+function bandBounds(band: Band): { minX: number; maxX: number; minY: number; maxY: number } {
+  return {
+    minX: Math.min(band.x1, band.x2),
+    maxX: Math.max(band.x1, band.x2),
+    minY: Math.min(band.y1, band.y2),
+    maxY: Math.max(band.y1, band.y2),
+  };
+}
+
 /**
  * Ids of every box the band overlaps. Nodes are large rectangles, so – unlike the scene view,
  * which tests an object's position – touching counts: a band drawn across a node that visibly
  * caught it would otherwise leave it out.
  */
 export function boxesInBand(boxes: readonly Box[], band: Band): string[] {
-  const minX = Math.min(band.x1, band.x2);
-  const maxX = Math.max(band.x1, band.x2);
-  const minY = Math.min(band.y1, band.y2);
-  const maxY = Math.max(band.y1, band.y2);
+  const { minX, maxX, minY, maxY } = bandBounds(band);
   return boxes
     .filter((b) => b.x <= maxX && b.x + b.w >= minX && b.y <= maxY && b.y + b.h >= minY)
     .map((b) => b.id);
@@ -90,10 +96,7 @@ export function boxesInBand(boxes: readonly Box[], band: Band): string[] {
  * Enclosing it is a deliberate gesture, and it is the one the eye reads as "this box, too".
  */
 export function boxesWithinBand(boxes: readonly Box[], band: Band): string[] {
-  const minX = Math.min(band.x1, band.x2);
-  const maxX = Math.max(band.x1, band.x2);
-  const minY = Math.min(band.y1, band.y2);
-  const maxY = Math.max(band.y1, band.y2);
+  const { minX, maxX, minY, maxY } = bandBounds(band);
   return boxes
     .filter((b) => b.x >= minX && b.x + b.w <= maxX && b.y >= minY && b.y + b.h <= maxY)
     .map((b) => b.id);
diff --git a/src/editor/graph/GraphCanvas.ts b/src/editor/graph/GraphCanvas.ts
index b1cb01d7..faead646 100644
--- a/src/editor/graph/GraphCanvas.ts
+++ b/src/editor/graph/GraphCanvas.ts
@@ -1143,6 +1143,21 @@ export class GraphCanvas extends Widget {
     }
   }
 
+  private launchBeads(assetId: string, trace: Trace | null): void {
+    if (!trace || assetId !== this.beadAsset) {
+      this.beadTimes.clear();
+      this.beadFired.clear();
+      this.beadAsset = assetId;
+    }
+    for (const [id, time] of trace?.edges ?? []) {
+      if (this.beadFired.get(id) === time) continue;
+      this.beadFired.set(id, time);
+      const times = this.beadTimes.get(id) ?? [];
+      this.beadTimes.set(id, times);
+      launchBead(times, time);
+    }
+  }
+
   /** A port's centre in graph coordinates. */
   private anchorPoint(side: PortSide | null): { x: number; y: number } | null {
     if (!side) return null;
@@ -1170,9 +1185,7 @@ export class GraphCanvas extends Widget {
   portGlobal(nodeId: string, port: string, isOutput: boolean): { x: number; y: number } | null {
     const view = this.views.get(nodeId);
     const p = view?.portPosition(port, isOutput);
-    if (!view || !p) return null;
-    const g = view.toGlobal({ x: p.x, y: p.y });
-    return { x: g.x, y: g.y };
+    return view && p ? globalPoint(view, p) : null;
   }
 
   /** The port a running edge drag would connect to, or null when the drop would do nothing. */
@@ -1222,8 +1235,7 @@ export class GraphCanvas extends Widget {
       .drawnMarks()
       .find((m) => m.edgeIds.includes(edgeId) && m.isOutput === isOutput);
     if (!mark) return null;
-    const g = this.canvas.toGlobal({ x: mark.x, y: mark.y });
-    return { x: g.x, y: g.y, links: mark.edgeIds.length, label: mark.text };
+    return { ...globalPoint(this.canvas, mark), links: mark.edgeIds.length, label: mark.text };
   }
 
   nodeRect(nodeId: string): Rect | null {
@@ -1272,21 +1284,6 @@ export class GraphCanvas extends Widget {
     return this.views.get(nodeId)?.inputLines ?? null;
   }
 
-  private launchBeads(assetId: string, trace: Trace | null): void {
-    if (!trace || assetId !== this.beadAsset) {
-      this.beadTimes.clear();
-      this.beadFired.clear();
-      this.beadAsset = assetId;
-    }
-    for (const [id, time] of trace?.edges ?? []) {
-      if (this.beadFired.get(id) === time) continue;
-      this.beadFired.set(id, time);
-      const times = this.beadTimes.get(id) ?? [];
-      this.beadTimes.set(id, times);
-      launchBead(times, time);
-    }
-  }
-
   beadsDrawn(): readonly { edgeId: string; progress: number; x: number; y: number }[] {
     return this.edgeLayer.drawnBeads();
   }
@@ -1298,9 +1295,7 @@ export class GraphCanvas extends Widget {
   /** Global screen position of a node's title bar centre. */
   nodeGlobal(nodeId: string): { x: number; y: number } | null {
     const view = this.views.get(nodeId);
-    if (!view) return null;
-    const g = view.toGlobal({ x: view.w / 2, y: TITLE_HEIGHT / 2 });
-    return { x: g.x, y: g.y };
+    return view ? globalPoint(view, { x: view.w / 2, y: TITLE_HEIGHT / 2 }) : null;
   }
 
   /** Every group and comment as it is drawn: the box, the text on it, and both its colours. */
@@ -1334,8 +1329,7 @@ export class GraphCanvas extends Widget {
     const local = corner
       ? { x: view.w - RESIZE_HANDLE / 2, y: view.h - RESIZE_HANDLE / 2 }
       : { x: view.w / 2, y: ANNOTATION_TITLE_HEIGHT / 2 };
-    const g = view.toGlobal(local);
-    return { x: g.x, y: g.y };
+    return globalPoint(view, local);
   }
 
   /** The rectangle a box is drawn as, on screen – what a fit has to bring into view. */
@@ -1352,6 +1346,11 @@ export class GraphCanvas extends Widget {
 
 type Rect = { x: number; y: number; w: number; h: number };
 
+function globalPoint(target: Container, local: { x: number; y: number }): { x: number; y: number } {
+  const g = target.toGlobal({ x: local.x, y: local.y });
+  return { x: g.x, y: g.y };
+}
+
 function globalRect(target: Container, w: number, h: number): Rect {
   const topLeft = target.toGlobal({ x: 0, y: 0 });
   const bottomRight = target.toGlobal({ x: w, y: h });
diff --git a/src/editor/inspector/portSection.ts b/src/editor/inspector/portSection.ts
index 36412b00..8ca73b8b 100644
--- a/src/editor/inspector/portSection.ts
+++ b/src/editor/inspector/portSection.ts
@@ -175,12 +175,7 @@ function buildPickedPortSection(
   for (const port of ports) {
     const toggle = writeToggle(host, assetId, node, port);
     if (custom) {
-      const name = new TextField(port.key, {
-        width: NAME_WIDTH,
-        onChange: (next) =>
-          host.state.execute(new RenamePortCommand(assetId, node.id, port.key, next.trim())),
-      });
-      portRow(host, assetId, node, port, name, toggle);
+      portRow(host, assetId, node, port, portNameField(host, assetId, node, port), toggle);
       continue;
     }
     const def = choices.find((d) => d.key === port.key);
@@ -236,13 +231,14 @@ export function buildPortSection(
           : 'No outputs yet. Every output added here becomes a result of running this behavior.',
     );
 
-  for (const port of ports) {
-    const name = new TextField(port.key, {
-      width: NAME_WIDTH,
-      onChange: (next) => host.state.execute(new RenamePortCommand(assetId, node.id, port.key, next.trim())),
-    });
-    portRow(host, assetId, node, port, name);
-  }
+  for (const port of ports) portRow(host, assetId, node, port, portNameField(host, assetId, node, port));
+}
+
+function portNameField(host: InspectorHost, assetId: string, node: GraphNode, port: DeclaredPort): TextField {
+  return new TextField(port.key, {
+    width: NAME_WIDTH,
+    onChange: (next) => host.state.execute(new RenamePortCommand(assetId, node.id, port.key, next.trim())),
+  });
 }
 
 function writeToggle(host: InspectorHost, assetId: string, node: GraphNode, port: DeclaredPort): Widget[] {
diff --git a/src/ui/widgets/Popup.ts b/src/ui/widgets/Popup.ts
index 92e003c3..c8248c6f 100644
--- a/src/ui/widgets/Popup.ts
+++ b/src/ui/widgets/Popup.ts
@@ -28,8 +28,8 @@ export function screenMargin(screenHeight: number): number {
 /**
  * Where a popup of `height` ends up when it was asked to open at `wanted`. The margin has to be
  * enforced here, not only in `roomFor`: a popup anchored low is *shifted* up to fit, and shifting
- * it against the raw canvas height parks it on the bottom edge – which is why the gap used to be
- * visible above and missing below.
+ * it against the raw canvas height would park it on the bottom edge, with the gap above it and none
+ * below.
  *
  * Downwards only, though. Above the popup the margin is what the height cap spends, not a distance
  * to keep: a menu hanging off a button near the top of the screen belongs under its button, and
diff --git a/src/viewport/FileLibrary.ts b/src/viewport/FileLibrary.ts
new file mode 100644
index 00000000..7c9fc01d
--- /dev/null
+++ b/src/viewport/FileLibrary.ts
@@ -0,0 +1,52 @@
+/**
+ * Uploaded files the view draws with, keyed by file name. Nothing is evicted: file names are
+ * content addressed, so a loaded file can never go stale. A miss is not an error – the subclass
+ * starts the load and reports "not yet", and `onChange` fires when the file lands.
+ */
+export abstract class FileLibrary<T> {
+  private base: string;
+  private readonly loading = new Set<string>();
+  /** Never retried, so one broken reference cannot spam the network. */
+  private readonly failed = new Set<string>();
+  private readonly listeners = new Set<() => void>();
+
+  constructor(
+    base: string,
+    private readonly tag: string,
+  ) {
+    this.base = base;
+  }
+
+  /** Where the files are served from. Set once at start-up, before anything draws. */
+  configure(base: string): void {
+    this.base = base.replace(/\/+$/, '');
+  }
+
+  /** Runs `fn` whenever a file has arrived; returns the unsubscribe. */
+  onChange(fn: () => void): () => void {
+    this.listeners.add(fn);
+    return () => this.listeners.delete(fn);
+  }
+
+  protected abstract fetchFile(url: string, file: string): Promise<T>;
+
+  /** Keeps what arrived; the listeners run right after. */
+  protected abstract keep(file: string, loaded: T): void;
+
+  protected startLoading(file: string): void {
+    if (this.loading.has(file) || this.failed.has(file)) return;
+    this.loading.add(file);
+    void this.fetchFile(`${this.base}/${file}`, file).then(
+      (loaded) => {
+        this.loading.delete(file);
+        this.keep(file, loaded);
+        for (const listener of this.listeners) listener();
+      },
+      (error: unknown) => {
+        this.loading.delete(file);
+        this.failed.add(file);
+        console.error(`[${this.tag}] cannot load ${file}`, error);
+      },
+    );
+  }
+}
diff --git a/src/viewport/FontLibrary.ts b/src/viewport/FontLibrary.ts
index c1225d58..ea1a3159 100644
--- a/src/viewport/FontLibrary.ts
+++ b/src/viewport/FontLibrary.ts
@@ -1,24 +1,15 @@
 import { fontFamilyOf } from '../core/model/font';
-
-const DEFAULT_BASE = '/game-maker/data/fonts';
+import { FileLibrary } from './FileLibrary';
 
 /**
- * Registers uploaded typefaces with the browser, keyed by file name – the image library's twin.
- * Nothing is evicted: file names are content addressed, so a face can never go stale. A miss is
- * not an error; it starts the load and reports the fallback, and the redraw comes when the face
- * lands. Text therefore appears in the default typeface for a frame or two and then reflows.
+ * Registers uploaded typefaces with the browser. Text appears in the default typeface for a frame
+ * or two and then reflows when the face lands.
  */
-export class FontLibrary {
-  private base = DEFAULT_BASE;
+export class FontLibrary extends FileLibrary<FontFace> {
   private readonly ready = new Set<string>();
-  private readonly loading = new Set<string>();
-  /** Never retried, so one broken reference cannot spam the network. */
-  private readonly failed = new Set<string>();
-  private readonly listeners = new Set<() => void>();
 
-  /** Where the files are served from. Set once at start-up, before anything draws. */
-  configure(base: string): void {
-    this.base = base.replace(/\/+$/, '');
+  constructor() {
+    super('/game-maker/data/fonts', 'fonts');
   }
 
   /**
@@ -32,31 +23,15 @@ export class FontLibrary {
     return '';
   }
 
-  /** Runs `fn` whenever a typeface has arrived; returns the unsubscribe. */
-  onChange(fn: () => void): () => void {
-    this.listeners.add(fn);
-    return () => this.listeners.delete(fn);
+  // `FontFace` rather than a stylesheet rule: it reports when the bytes are actually usable,
+  // and a family name is asked for by the same content-addressed key that fetched them.
+  protected fetchFile(url: string, file: string): Promise<FontFace> {
+    return new FontFace(fontFamilyOf(file), `url("${url}")`).load();
   }
 
-  private startLoading(file: string): void {
-    if (this.loading.has(file) || this.failed.has(file)) return;
-    this.loading.add(file);
-    // `FontFace` rather than a stylesheet rule: it reports when the bytes are actually usable,
-    // and a family name is asked for by the same content-addressed key that fetched them.
-    const face = new FontFace(fontFamilyOf(file), `url("${this.base}/${file}")`);
-    void face.load().then(
-      (loaded) => {
-        this.loading.delete(file);
-        document.fonts.add(loaded);
-        this.ready.add(file);
-        for (const listener of this.listeners) listener();
-      },
-      (error: unknown) => {
-        this.loading.delete(file);
-        this.failed.add(file);
-        console.error(`[fonts] cannot load ${file}`, error);
-      },
-    );
+  protected keep(file: string, loaded: FontFace): void {
+    document.fonts.add(loaded);
+    this.ready.add(file);
   }
 }
 
diff --git a/src/viewport/TextureLibrary.ts b/src/viewport/TextureLibrary.ts
index afa31dad..a2509222 100644
--- a/src/viewport/TextureLibrary.ts
+++ b/src/viewport/TextureLibrary.ts
@@ -1,8 +1,7 @@
 import { Assets, CanvasSource, Texture } from 'pixi.js';
 import type { FrameRect, TextureRef } from '../core/model/texture';
 import { type EdgeMode, SHEET_EDGE } from '../core/shader/nodes';
-
-const DEFAULT_BASE = '/game-maker/data/textures';
+import { FileLibrary } from './FileLibrary';
 
 /**
  * Pixi turns `clamp-to-edge` into `repeat` on every texture a Graphics fill draws with
@@ -22,24 +21,14 @@ const ADDRESS_MODE: Record<EdgeMode, 'repeat' | 'mirror-repeat' | 'clamp-to-edge
   clamp: 'clamp-to-edge',
 };
 
-/**
- * Keeps uploaded images on the GPU, keyed by file name. Nothing is evicted: file names are
- * content addressed, so a cached texture can never go stale. A miss is not an error – it starts
- * the load and reports "not yet", so callers never await and get a redraw when the picture lands.
- */
-export class TextureLibrary {
-  private base = DEFAULT_BASE;
+/** Keeps uploaded images on the GPU; callers never await and get a redraw when the picture lands. */
+export class TextureLibrary extends FileLibrary<Texture> {
   private readonly loaded = new Map<string, Texture>();
   /** Frames cut from their sheets, keyed by file and rectangle; kept like the files. */
   private readonly crops = new Map<string, Texture>();
-  private readonly loading = new Set<string>();
-  /** Never retried, so one broken reference cannot spam the network. */
-  private readonly failed = new Set<string>();
-  private readonly listeners = new Set<() => void>();
 
-  /** Where the files are served from. Set once at start-up, before anything draws. */
-  configure(base: string): void {
-    this.base = base.replace(/\/+$/, '');
+  constructor() {
+    super('/game-maker/data/textures', 'textures');
   }
 
   /**
@@ -83,12 +72,6 @@ export class TextureLibrary {
     return this.loaded.get(file) ?? null;
   }
 
-  /** Runs `fn` whenever a picture has arrived; returns the unsubscribe. */
-  onChange(fn: () => void): () => void {
-    this.listeners.add(fn);
-    return () => this.listeners.delete(fn);
-  }
-
   /**
    * A frame as a texture of its own, cut the first time it is asked for. Drawn from the sheet
    * through a fill matrix it showed a row of the neighbouring cell along any edge that fell
@@ -110,23 +93,14 @@ export class TextureLibrary {
     return texture;
   }
 
-  private startLoading(file: string): void {
-    if (this.loading.has(file) || this.failed.has(file)) return;
-    this.loading.add(file);
-    void Assets.load<Texture>(`${this.base}/${file}`).then(
-      (texture) => {
-        this.loading.delete(file);
-        texture.source.style.addressMode = EDGE_MODE;
-        texture.source.style.update();
-        this.loaded.set(file, texture);
-        for (const listener of this.listeners) listener();
-      },
-      (error: unknown) => {
-        this.loading.delete(file);
-        this.failed.add(file);
-        console.error(`[textures] cannot load ${file}`, error);
-      },
-    );
+  protected fetchFile(url: string): Promise<Texture> {
+    return Assets.load<Texture>(url);
+  }
+
+  protected keep(file: string, texture: Texture): void {
+    texture.source.style.addressMode = EDGE_MODE;
+    texture.source.style.update();
+    this.loaded.set(file, texture);
   }
 }