Adding result cache. Fixes #87. (#148)

src/components/App/index.tsx

@@ -6,6 +6,7 @@ import Output from '../Output';
 import Options from '../Options';
 import { FileDropEvent } from './custom-els/FileDrop';
 import './custom-els/FileDrop';
+import ResultCache from './result-cache';
 
 import * as quantizer from '../../codecs/imagequant/quantizer';
 import * as optiPNG from '../../codecs/optipng/encoder';
@@ -39,7 +40,7 @@ import { cleanMerge, cleanSet } from '../../lib/clean-modify';
 
 type Orientation = 'horizontal' | 'vertical';
 
-interface SourceImage {
+export interface SourceImage {
   file: File;
   bmp: ImageBitmap;
   data: ImageData;
@@ -138,7 +139,8 @@ export default class App extends Component<Props, State> {
     orientation: this.widthQuery.matches ? 'horizontal' : 'vertical',
   };
 
-  private snackbar?: SnackBarElement;
+  snackbar?: SnackBarElement;
+  readonly encodeCache = new ResultCache();
 
   constructor() {
     super();
@@ -254,19 +256,38 @@ export default class App extends Component<Props, State> {
     const image = images[index];
 
     let file;
-    try {
-      // Special case for identity
-      if (image.encoderState.type === identity.type) {
-        file = source.file;
-      } else {
-        if (!skipPreprocessing || !image.preprocessed) {
-          image.preprocessed = await preprocessImage(source, image.preprocessorState);
+    let preprocessed;
+    let bmp;
+    const cacheResult = this.encodeCache.match(source, image.preprocessorState, image.encoderState);
+
+    if (cacheResult) {
+      ({ file, preprocessed, bmp } = cacheResult);
+    } else {
+      try {
+        // Special case for identity
+        if (image.encoderState.type === identity.type) {
+          ({ file, bmp } = source);
+        } else {
+          preprocessed = (skipPreprocessing && image.preprocessed)
+            ? image.preprocessed
+            : await preprocessImage(source, image.preprocessorState);
+
+          file = await compressImage(preprocessed, image.encoderState, source.file.name);
+          bmp = await decodeImage(file);
+
+          this.encodeCache.add({
+            source,
+            bmp,
+            preprocessed,
+            file,
+            encoderState: image.encoderState,
+            preprocessorState: image.preprocessorState,
+          });
         }
-        file = await compressImage(image.preprocessed, image.encoderState, source.file.name);
+      } catch (err) {
+        this.showError(`Processing error (type=${image.encoderState.type}): ${err}`);
+        throw err;
       }
-    } catch (err) {
-      this.showError(`Encoding error (type=${image.encoderState.type}): ${err}`);
-      throw err;
     }
 
     const latestImage = this.state.images[index];
@@ -275,17 +296,10 @@ export default class App extends Component<Props, State> {
       return;
     }
 
-    let bmp;
-    try {
-      bmp = await decodeImage(file);
-    } catch (err) {
-      this.setState({ error: `Encoding error (type=${image.encoderState.type}): ${err}` });
-      throw err;
-    }
-
-    images = cleanMerge(this.state.images, '' + index, {
+    images = cleanMerge(this.state.images, index, {
       file,
       bmp,
+      preprocessed,
       downloadUrl: URL.createObjectURL(file),
       loading: images[index].loadingCounter !== loadingCounter,
       loadedCounter: loadingCounter,

src/components/App/result-cache.ts

@@ -0,0 +1,68 @@
+import { EncoderState } from '../../codecs/encoders';
+import { shallowEqual } from '../../lib/util';
+import { SourceImage } from '.';
+import { PreprocessorState } from '../../codecs/preprocessors';
+
+import * as identity from '../../codecs/identity/encoder';
+
+interface CacheResult {
+  preprocessed: ImageData;
+  bmp: ImageBitmap;
+  file: File;
+}
+
+interface CacheEntry extends CacheResult {
+  preprocessorState: PreprocessorState;
+  encoderState: EncoderState;
+  source: SourceImage;
+}
+
+const SIZE = 5;
+
+export default class ResultCache {
+  private readonly _entries: CacheEntry[] = [];
+  private _nextIndex: number = 0;
+
+  add(entry: CacheEntry) {
+    if (entry.encoderState.type === identity.type) throw Error('Cannot cache identity encodes');
+    this._entries[this._nextIndex] = entry;
+    this._nextIndex = (this._nextIndex + 1) % SIZE;
+  }
+
+  match(
+    source: SourceImage,
+    preprocessorState: PreprocessorState,
+    encoderState: EncoderState,
+  ): CacheResult | undefined {
+    const matchingEntry = this._entries.find((entry) => {
+      // Check for quick exits:
+      if (entry.source !== source) return false;
+      if (entry.encoderState.type !== encoderState.type) return false;
+
+      // Check that each set of options in the preprocessor are the same
+      for (const prop in preprocessorState) {
+        if (
+          !shallowEqual(
+            (preprocessorState as any)[prop],
+            (entry.preprocessorState as any)[prop],
+          )
+        ) return false;
+      }
+
+      // Check detailed encoder options
+      if (!shallowEqual(encoderState.options, entry.encoderState.options)) return false;
+
+      return true;
+    });
+
+    if (matchingEntry) {
+      return {
+        bmp: matchingEntry.bmp,
+        preprocessed: matchingEntry.preprocessed,
+        file: matchingEntry.file,
+      };
+    }
+
+    return undefined;
+  }
+}