Initial project import

node_modules/fast-png/src/helpers/decodeInterlaceNull.ts

@@ -0,0 +1,94 @@
+import type { PngDataArray } from '../types';
+
+import {
+  unfilterAverage,
+  unfilterNone,
+  unfilterPaeth,
+  unfilterSub,
+  unfilterUp,
+} from './unfilter';
+
+const uint16 = new Uint16Array([0x00ff]);
+const uint8 = new Uint8Array(uint16.buffer);
+const osIsLittleEndian = uint8[0] === 0xff;
+
+const empty = new Uint8Array(0);
+
+export interface DecodeInterlaceNullParams {
+  data: Uint8Array;
+  width: number;
+  height: number;
+  channels: number;
+  depth: number;
+}
+
+export function decodeInterlaceNull(
+  params: DecodeInterlaceNullParams,
+): PngDataArray {
+  const { data, width, height, channels, depth } = params;
+
+  const bytesPerPixel = Math.ceil(depth / 8) * channels;
+
+  const bytesPerLine = Math.ceil((depth / 8) * channels * width);
+  const newData = new Uint8Array(height * bytesPerLine);
+
+  let prevLine = empty;
+  let offset = 0;
+  let currentLine;
+  let newLine;
+
+  for (let i = 0; i < height; i++) {
+    currentLine = data.subarray(offset + 1, offset + 1 + bytesPerLine);
+    newLine = newData.subarray(i * bytesPerLine, (i + 1) * bytesPerLine);
+    switch (data[offset]) {
+      case 0:
+        unfilterNone(currentLine, newLine, bytesPerLine);
+        break;
+      case 1:
+        unfilterSub(currentLine, newLine, bytesPerLine, bytesPerPixel);
+        break;
+      case 2:
+        unfilterUp(currentLine, newLine, prevLine, bytesPerLine);
+        break;
+      case 3:
+        unfilterAverage(
+          currentLine,
+          newLine,
+          prevLine,
+          bytesPerLine,
+          bytesPerPixel,
+        );
+        break;
+      case 4:
+        unfilterPaeth(
+          currentLine,
+          newLine,
+          prevLine,
+          bytesPerLine,
+          bytesPerPixel,
+        );
+        break;
+      default:
+        throw new Error(`Unsupported filter: ${data[offset]}`);
+    }
+    prevLine = newLine;
+    offset += bytesPerLine + 1;
+  }
+
+  if (depth === 16) {
+    const uint16Data = new Uint16Array(newData.buffer);
+    if (osIsLittleEndian) {
+      for (let k = 0; k < uint16Data.length; k++) {
+        // PNG is always big endian. Swap the bytes.
+        uint16Data[k] = swap16(uint16Data[k]);
+      }
+    }
+    return uint16Data;
+  } else {
+    return newData;
+  }
+}
+
+function swap16(val: number): number {
+  return ((val & 0xff) << 8) | ((val >> 8) & 0xff);
+}