diff --git a/src/codemirror/ecs.js b/src/codemirror/ecs.js
index 869f9eab..bf3696f9 100644
--- a/src/codemirror/ecs.js
+++ b/src/codemirror/ecs.js
@@ -17,8 +17,8 @@
     var keywords1, keywords2;
 
     var directives_list = [
-      'end', 'component', 'system', 'entity', 'scope', 'using', 'demo',
-      'const', 'init', 'locals',
+      'end', 'component', 'system', 'entity', 'scope', 'using', 'demo', 'decode',
+      'const', 'locals', 'var',
       'on', 'do', 'emit', 'limit',
       'once', 'foreach', 'with', 'join', 'if',
     ];
@@ -34,7 +34,7 @@
     directives_list.forEach(function (s) { directives.set(s, 'def'); });
     keywords_list.forEach(function (s) { directives.set(s, 'keyword'); });
 
-    var opcodes = /^[a-z][a-z][a-z]\b/i;
+    var opcodes = /^\s[a-z][a-z][a-z]\s/i;
     var numbers = /^(0x[\da-f]+|[\da-f]+h|[0-7]+o|[01]+b|\d+d?)\b/i;
     var tags = /^\{\{.*\}\}/;
     var comment = /\/\/.*/;
diff --git a/src/common/ecs/compiler.ts b/src/common/ecs/compiler.ts
index b3b96948..d4e96c3a 100644
--- a/src/common/ecs/compiler.ts
+++ b/src/common/ecs/compiler.ts
@@ -1,6 +1,7 @@
 
 import { mergeLocs, Tokenizer, TokenType } from "../tokenizer";
 import { SourceLocated } from "../workertypes";
+import { newDecoder } from "./decoder";
 import { Action, ArrayType, ComponentType, DataField, DataType, DataValue, ECSError, Entity, EntityArchetype, EntityManager, EntityScope, IntType, Query, RefType, SelectType, SourceFileExport, System } from "./ecs";
 
 export enum ECSTokenType {
@@ -142,7 +143,7 @@ export class ECSCompiler extends Tokenizer {
             }
             return { dtype: 'array', index, elem, baseoffset } as ArrayType;
         }
-        this.internalError(); throw new Error();
+        this.compileError(`I expected a data type here.`); throw new Error();
     }
 
     parseDataValue(field: DataField) : DataValue {
@@ -170,7 +171,7 @@ export class ECSCompiler extends Tokenizer {
             }
             return id;
         }
-        this.internalError(); throw new Error();
+        this.compileError(`I expected a ${field.dtype} here.`); throw new Error();
     }
 
     parseDataArray() {
@@ -234,17 +235,12 @@ export class ECSCompiler extends Tokenizer {
             this.expectToken('with');
             join = this.parseQuery();
         }
-        let emits;
-        if (this.peekToken().str == 'limit') {
-            this.consumeToken();
+        if (this.ifToken('limit')) {
             if (!query) { this.compileError(`A "${select}" query can't include a limit.`); }
             else query.limit = this.expectInteger();
         }
-        if (this.peekToken().str == 'emit') {
-            this.consumeToken();
-            this.expectToken('(');
-            emits = this.parseEventList();
-            this.expectToken(')');
+        if (this.ifToken('cyclecritical')) {
+            // TODO
         }
         let text = this.parseCode();
         let action = { text, event, query, join, select };
@@ -336,33 +332,54 @@ export class ECSCompiler extends Tokenizer {
 
     parseEntity() : Entity {
         if (!this.currentScope) { this.internalError(); throw new Error(); }
-        let name = '';
+        let entname = '';
         if (this.peekToken().type == TokenType.Ident) {
-            name = this.expectIdent().str;
+            entname = this.expectIdent().str;
         }
         let etype = this.parseEntityArchetype();
-        let e = this.currentScope.newEntity(etype);
-        e.name = name;
+        let entity = this.currentScope.newEntity(etype);
+        entity.name = entname;
         let cmd;
         // TODO: remove init?
-        while ((cmd = this.expectTokens(['const', 'init', 'var', 'end']).str) != 'end') {
+        while ((cmd = this.expectTokens(['const', 'init', 'var', 'decode', 'end']).str) != 'end') {
             if (cmd == 'var') cmd = 'init';
-            // TODO: check data types
-            let name = this.expectIdent().str;
-            let comps = this.em.componentsWithFieldName([{etype: e.etype, cmatch:e.etype.components}], name);
-            if (comps.length == 0) this.compileError(`I couldn't find a field named "${name}" for this entity.`)
-            if (comps.length > 1) this.compileError(`I found more than one field named "${name}" for this entity.`)
-            let field = comps[0].fields.find(f => f.name == name);
-            if (!field) { this.internalError(); throw new Error(); }
-            this.expectToken('=');
-            let value = this.parseDataValue(field);
-            let symtype = this.currentScope.isConstOrInit(comps[0], name);
-            if (symtype && symtype != cmd)
-                this.compileError(`I can't mix const and init values for a given field in a scope.`);
-            if (cmd == 'const') this.currentScope.setConstValue(e, comps[0], name, value);
-            if (cmd == 'init') this.currentScope.setInitValue(e, comps[0], name, value);
+            if (cmd == 'init' || cmd == 'const') {
+                // TODO: check data types
+                let name = this.expectIdent().str;
+                this.setEntityProperty(entity, name, cmd, (field) : DataValue => {
+                    this.expectToken('=');
+                    return this.parseDataValue(field);
+                });
+            } else if (cmd == 'decode') {
+                let decoderid = this.expectIdent().str;
+                let code = this.expectTokenTypes([ECSTokenType.CodeFragment]).str;
+                code = code.substring(3, code.length-3);
+                let decoder = newDecoder(decoderid, code);
+                if (!decoder) { this.compileError(`I can't find a "${decoderid}" decoder.`); throw new Error() }
+                let result = decoder.parse();
+                for (let entry of Object.entries(result.properties)) {
+                    this.setEntityProperty(entity, entry[0], 'const', (field) : DataValue => {
+                        return entry[1];
+                    });
+                }
+            }
         }
-        return e;
+        return entity;
+    }
+
+    setEntityProperty(e: Entity, name: string, cmd: 'init' | 'const', valuefn: (field: DataField) => DataValue) {
+        if (!this.currentScope) { this.internalError(); throw new Error(); }
+        let comps = this.em.componentsWithFieldName([{etype: e.etype, cmatch:e.etype.components}], name);
+        if (comps.length == 0) this.compileError(`I couldn't find a field named "${name}" for this entity.`)
+        if (comps.length > 1) this.compileError(`I found more than one field named "${name}" for this entity.`)
+        let field = comps[0].fields.find(f => f.name == name);
+        if (!field) { this.internalError(); throw new Error(); }
+        let value = valuefn(field);
+        let symtype = this.currentScope.isConstOrInit(comps[0], name);
+        if (symtype && symtype != cmd)
+            this.compileError(`I can't mix const and init values for a given field in a scope.`);
+        if (cmd == 'const') this.currentScope.setConstValue(e, comps[0], name, value);
+        if (cmd == 'init') this.currentScope.setInitValue(e, comps[0], name, value);
     }
 
     parseEntityArchetype() : EntityArchetype {
diff --git a/src/common/ecs/decoder.ts b/src/common/ecs/decoder.ts
new file mode 100644
index 00000000..8f2a8617
--- /dev/null
+++ b/src/common/ecs/decoder.ts
@@ -0,0 +1,114 @@
+import { threadId } from "worker_threads";
+import { DataValue, ECSError } from "./ecs";
+
+export interface DecoderResult {
+    properties: {[name: string] : DataValue}
+}
+
+abstract class LineDecoder {
+    lines : string[][];
+
+    constructor(
+        text: string
+    ) {
+        // split the text into lines and into tokens
+        this.lines = text.split('\n').map(s => s.trim()).filter(s => !!s).map(s => s.split(/\s+/));
+    }
+
+    decodeBits(s: string, n: number, msbfirst: boolean) {
+        if (s.length != n) throw new ECSError(`Expected ${n} characters`);
+        let b = 0;
+        for (let i=0; i<n; i++) {
+            let bit;
+            if (s.charAt(i) == 'x') bit = 1;
+            else if (s.charAt(i) == '.') bit = 0;
+            else throw new ECSError('need x or .');
+            if (bit) {
+                if (msbfirst) b |= 1 << (n-1-i);
+                else b |= 1 << i;
+            }
+        }
+        return b;
+    }
+
+    assertTokens(toks: string[], count: number) {
+        if (toks.length != count) throw new ECSError(`Expected ${count} tokens on line.`);
+    }
+
+    hex(s: string) {
+        let v = parseInt(s, 16);
+        if (isNaN(v)) throw new ECSError(`Invalid hex value: ${s}`)
+        return v;
+    }
+
+    abstract parse() : DecoderResult;
+}
+
+export class VCSSpriteDecoder extends LineDecoder {
+    parse() {
+        let height = this.lines.length;
+        let bitmapdata = new Uint8Array(height);
+        let colormapdata = new Uint8Array(height);
+        for (let i=0; i<height; i++) {
+            let toks = this.lines[height - 1 - i];
+            this.assertTokens(toks, 2);
+            bitmapdata[i] = this.decodeBits(toks[0], 8, true);
+            colormapdata[i] = this.hex(toks[1]);
+        }
+        return {
+            properties: {
+                bitmapdata, colormapdata, height: height-1
+            }
+        }
+    }
+}
+
+export class VCSVersatilePlayfieldDecoder extends LineDecoder {
+    parse() {
+        let height = this.lines.length;
+        let data = new Uint8Array(192) //height * 2); TODO
+        data.fill(0x3f);
+        // pf0 pf1 pf2 colupf colubk ctrlpf trash
+        const regs = [0x0d, 0x0e, 0x0f, 0x08, 0x09, 0x0a, 0x3f];
+        let prev = [0,0,0,0,0,0,0];
+        let cur  = [0,0,0,0,0,0,0];
+        for (let i=0; i<height; i++) {
+            let toks = this.lines[i];
+            this.assertTokens(toks, 4);
+            cur[0] = this.decodeBits(toks[0].substring(0,4), 4, false) << 4;
+            cur[1] = this.decodeBits(toks[0].substring(4,12), 8, true);
+            cur[2] = this.decodeBits(toks[0].substring(12,20), 8, false);
+            if (toks[1] != '..') cur[3] = this.hex(toks[1]);
+            if (toks[2] != '..') cur[4] = this.hex(toks[2]);
+            if (toks[3] != '..') cur[5] = this.hex(toks[3]);
+            let changed = [];
+            for (let j=0; j<cur.length; j++) {
+                if (cur[j] != prev[j])
+                    changed.push(j);
+            }
+            if (changed.length > 1) {
+                console.log(changed, cur, prev);
+                throw new ECSError(`More than one register change in line ${i+1}: [${changed}]`);
+            }
+            let chgidx = changed.length ? changed[0] : regs.length-1;
+            data[height*2 - i*2 - 1] = regs[chgidx];
+            data[height*2 - i*2 - 2] = cur[chgidx];
+            prev[chgidx] = cur[chgidx];
+        }
+        return {
+            properties: {
+                data
+            }
+        }
+    }
+}
+
+export function newDecoder(name: string, text: string) : LineDecoder | undefined {
+    let cons = (DECODERS as any)[name];
+    if (cons) return new cons(text);
+}
+
+const DECODERS = {
+    'vcs_sprite': VCSSpriteDecoder,
+    'vcs_versatile': VCSVersatilePlayfieldDecoder,
+}
diff --git a/src/common/ecs/ecs.ts b/src/common/ecs/ecs.ts
index 83ee871d..fb447351 100644
--- a/src/common/ecs/ecs.ts
+++ b/src/common/ecs/ecs.ts
@@ -51,6 +51,8 @@ can you query specific entities? merge with existing queries?
 bigints?
 source/if query?
 
+only worry about intersection when non-contiguous ranges?
+
 crazy idea -- full expansion, then relooper
 
 how to avoid cycle crossing for critical code and data?
@@ -119,7 +121,6 @@ export interface ActionBase extends SourceLocated {
     select: SelectType;
     event: string;
     text: string;
-    emits?: string[];
 }
 
 export interface ActionOnce extends ActionBase {
@@ -675,7 +676,8 @@ class ActionEval {
         return this.scope.includeResource(args[0]);
     }
     __emit(args: string[]) {
-        return this.scope.generateCodeForEvent(args[0]);
+        let event = args[0];
+        return this.scope.generateCodeForEvent(event);
     }
     __local(args: string[]) {
         let tempinc = parseInt(args[0]);
@@ -1058,11 +1060,9 @@ export class EntityScope implements SourceLocated {
         }
         let s = this.dialect.code();
         //s += `\n; event ${event}\n`;
-        let emitcode: { [event: string]: string } = {};
         systems = systems.filter(s => this.systems.includes(s));
         for (let sys of systems) {
             // TODO: does this work if multiple actions?
-            // TODO: should 'emits' be on action?
             // TODO: share storage
             //if (sys.tempbytes) this.allocateTempBytes(sys.tempbytes);
             let tmplabel = `${sys.name}_tmp`;
@@ -1071,18 +1071,8 @@ export class EntityScope implements SourceLocated {
             let numActions = 0;
             for (let action of sys.actions) {
                 if (action.event == event) {
-                    if (action.emits) {
-                        for (let emit of action.emits) {
-                            if (emitcode[emit]) {
-                                console.log(`already emitted for ${sys.name}:${event}`);
-                            }
-                            //console.log('>', emit);
-                            // TODO: cycles
-                            emitcode[emit] = this.generateCodeForEvent(emit);
-                            //console.log('<', emit, emitcode[emit].length);
-                        }
-                    }
                     // TODO: use Tokenizer so error msgs are better
+                    // TODO: keep event tree
                     let codeeval = new ActionEval(this, sys, action);
                     codeeval.tmplabel = tmplabel;
                     codeeval.begin();
diff --git a/src/test/testecs.ts b/src/test/testecs.ts
index 0af4fede..05d78187 100644
--- a/src/test/testecs.ts
+++ b/src/test/testecs.ts
@@ -242,8 +242,7 @@ function testECS() {
     em.defineSystem({
         name: 'frameloop',
         actions: [
-            { text: TEMPLATE1, event: 'start', select: 'with', query: { include: [c_kernel] },
-                emits: ['preframe', 'kernel', 'postframe'] }
+            { text: TEMPLATE1, event: 'start', select: 'with', query: { include: [c_kernel] } }
         ]
     })
     em.defineSystem({
@@ -313,7 +312,7 @@ end
 
 system SimpleKernel
 locals 8
-on preframe do once [Kernel] --- JUNK_AT_END
+on preframe do with [Kernel] --- JUNK_AT_END
     lda #5
     sta #6
 Label: