Dynamic atlas: Reduce unnecessary objects generated and draw from ImageBitmap

src/renderer/atlas/DynamicCharAtlas.ts

@@ -34,9 +34,17 @@ interface IGlyphCacheValue {
   isEmpty: boolean;
 }
 
-function getGlyphCacheKey(chars: string, fg: number, bg: number, bold: boolean, dim: boolean, italic: boolean): string {
-  const styleFlags = (bold ? 0 : 4) + (dim ? 0 : 2) + (italic ? 0 : 1);
-  return `${bg}_${fg}_${styleFlags}${chars}`;
+function getGlyphCacheKey(code: number, fg: number, bg: number, bold: boolean, dim: boolean, italic: boolean): number {
+  // Note that this only returns a valid key when code < 256
+  // Layout:
+  // 0b00000000000000000000000000000001: italic (1)
+  // 0b00000000000000000000000000000010: dim (1)
+  // 0b00000000000000000000000000000100: bold (1)
+  // 0b00000000000000000000111111111000: fg (9)
+  // 0b00000000000111111111000000000000: bg (9)
+  // 0b00011111111000000000000000000000: code (8)
+  // 0b11100000000000000000000000000000: unused (3)
+  return code << 21 | bg << 12 | fg << 3 | (bold ? 0 : 4) + (dim ? 0 : 2) + (italic ? 0 : 1);
 }
 
 export default class DynamicCharAtlas extends BaseCharAtlas {
@@ -98,7 +106,7 @@ export default class DynamicCharAtlas extends BaseCharAtlas {
     x: number,
     y: number
   ): boolean {
-    const glyphKey = getGlyphCacheKey(chars, fg, bg, bold, dim, italic);
+    const glyphKey = getGlyphCacheKey(code, fg, bg, bold, dim, italic);
     const cacheValue = this._cacheMap.get(glyphKey);
     if (cacheValue !== null && cacheValue !== undefined) {
       this._drawFromCache(ctx, cacheValue, x, y);

src/renderer/atlas/LRUMap.test.ts

@@ -9,57 +9,57 @@ import LRUMap from './LRUMap';
 describe('LRUMap', () => {
   it('can be used to store and retrieve values', () => {
     const map = new LRUMap(10);
-    map.set('keya', 'valuea');
-    map.set('keyb', 'valueb');
-    map.set('keyc', 'valuec');
-    assert.strictEqual(map.get('keya'), 'valuea');
-    assert.strictEqual(map.get('keyb'), 'valueb');
-    assert.strictEqual(map.get('keyc'), 'valuec');
+    map.set(1, 'valuea');
+    map.set(2, 'valueb');
+    map.set(3, 'valuec');
+    assert.strictEqual(map.get(1), 'valuea');
+    assert.strictEqual(map.get(2), 'valueb');
+    assert.strictEqual(map.get(3), 'valuec');
   });
 
   it('maintains a size from insertions', () => {
     const map = new LRUMap(10);
     assert.strictEqual(map.size, 0);
-    map.set('a', 'value');
+    map.set(1, 'value');
     assert.strictEqual(map.size, 1);
-    map.set('b', 'value');
+    map.set(2, 'value');
     assert.strictEqual(map.size, 2);
   });
 
   it('deletes the oldest entry when the capacity is exceeded', () => {
     const map = new LRUMap(4);
-    map.set('a', 'value');
-    map.set('b', 'value');
-    map.set('c', 'value');
-    map.set('d', 'value');
-    map.set('e', 'value');
-    assert.isNull(map.get('a'));
-    assert.isNotNull(map.get('b'));
-    assert.isNotNull(map.get('c'));
-    assert.isNotNull(map.get('d'));
-    assert.isNotNull(map.get('e'));
+    map.set(1, 'value');
+    map.set(2, 'value');
+    map.set(3, 'value');
+    map.set(4, 'value');
+    map.set(5, 'value');
+    assert.isNull(map.get(1));
+    assert.isNotNull(map.get(2));
+    assert.isNotNull(map.get(3));
+    assert.isNotNull(map.get(4));
+    assert.isNotNull(map.get(5));
     assert.strictEqual(map.size, 4);
   });
 
   it('prevents a recently accessed entry from getting deleted', () => {
     const map = new LRUMap(2);
-    map.set('a', 'value');
-    map.set('b', 'value');
-    map.get('a');
+    map.set(1, 'value');
+    map.set(2, 'value');
+    map.get(1);
     // a would normally get deleted here, except that we called get()
-    map.set('c', 'value');
-    assert.isNotNull(map.get('a'));
+    map.set(3, 'value');
+    assert.isNotNull(map.get(1));
     // b got deleted instead of a
-    assert.isNull(map.get('b'));
-    assert.isNotNull(map.get('c'));
+    assert.isNull(map.get(2));
+    assert.isNotNull(map.get(3));
   });
 
   it('supports mutation', () => {
     const map = new LRUMap(10);
-    map.set('keya', 'oldvalue');
-    map.set('keya', 'newvalue');
+    map.set(1, 'oldvalue');
+    map.set(1, 'newvalue');
     // mutation doesn't change the size
     assert.strictEqual(map.size, 1);
-    assert.strictEqual(map.get('keya'), 'newvalue');
+    assert.strictEqual(map.get(1), 'newvalue');
   });
 });

src/renderer/atlas/LRUMap.ts

@@ -6,12 +6,12 @@
 interface ILinkedListNode<T> {
   prev: ILinkedListNode<T>;
   next: ILinkedListNode<T>;
-  key: string;
+  key: number;
   value: T;
 }
 
 export default class LRUMap<T> {
-  private _map: { [key: string]: ILinkedListNode<T> } = {};
+  private _map: { [key: number]: ILinkedListNode<T> } = {};
   private _head: ILinkedListNode<T> = null;
   private _tail: ILinkedListNode<T> = null;
   private _nodePool: ILinkedListNode<T>[] = [];
@@ -68,7 +68,7 @@ export default class LRUMap<T> {
     }
   }
 
-  public get(key: string): T | null {
+  public get(key: number): T | null {
     // This is unsafe: We're assuming our keyspace doesn't overlap with Object.prototype. However,
     // it's faster than calling hasOwnProperty, and in our case, it would never overlap.
     const node = this._map[key];
@@ -85,7 +85,7 @@ export default class LRUMap<T> {
     return head === null ? null : head.value;
   }
 
-  public set(key: string, value: T): void {
+  public set(key: number, value: T): void {
     // This is unsafe: See note above.
     let node = this._map[key];
     if (node !== undefined) {