fix(blp): handle unusually sized mip data at very small sizes

src/lib/blp/Blp.ts

@@ -6,11 +6,18 @@ import {
   BLP_PIXEL_FORMAT,
   MAX_MIP_LEVELS,
 } from './const.js';
-import { dxt1ToAbgr8888, dxt3ToAbgr8888, dxt5ToAbgr8888 } from './dxt.js';
+import {
+  dxt1ToAbgr8888,
+  dxt3ToAbgr8888,
+  dxt5ToAbgr8888,
+  getDxt1Size,
+  getDxt3Size,
+  getDxt5Size,
+} from './dxt.js';
 import { palToAbgr8888 } from './pal.js';
 import { rawAbgr8888ToArgb8888, rawArgb8888ToAbgr8888 } from './raw.js';
 import * as blpIo from './io.js';
-import { calcMipLevelCount, getSizeAtMipLevel, resizeBilinear } from './util.js';
+import { calcMipLevelCount, getResizedBytes, getSizeAtMipLevel, resizeBilinear } from './util.js';
 import BlpImage from './BlpImage.js';
 
 class Blp {
@@ -316,7 +323,12 @@ class Blp {
   #getDxt1Image(level: number, outputFormat: BLP_IMAGE_FORMAT): BlpImage {
     const width = getSizeAtMipLevel(this.#width, level);
     const height = getSizeAtMipLevel(this.#height, level);
-    const data = this.#images[level];
+
+    if (width === 0 || height === 0) {
+      return new BlpImage(width, height, new Uint8Array(0), outputFormat);
+    }
+
+    const data = getResizedBytes(this.#images[level], getDxt1Size(width, height));
 
     switch (outputFormat) {
       case BLP_IMAGE_FORMAT.IMAGE_DXT1:
@@ -333,7 +345,12 @@ class Blp {
   #getDxt3Image(level: number, outputFormat: BLP_IMAGE_FORMAT): BlpImage {
     const width = getSizeAtMipLevel(this.#width, level);
     const height = getSizeAtMipLevel(this.#height, level);
-    const data = this.#images[level];
+
+    if (width === 0 || height === 0) {
+      return new BlpImage(width, height, new Uint8Array(0), outputFormat);
+    }
+
+    const data = getResizedBytes(this.#images[level], getDxt3Size(width, height));
 
     switch (outputFormat) {
       case BLP_IMAGE_FORMAT.IMAGE_DXT3:
@@ -350,7 +367,12 @@ class Blp {
   #getDxt5Image(level: number, outputFormat: BLP_IMAGE_FORMAT) {
     const width = getSizeAtMipLevel(this.#width, level);
     const height = getSizeAtMipLevel(this.#height, level);
-    const data = this.#images[level];
+
+    if (width === 0 || height === 0) {
+      return new BlpImage(width, height, new Uint8Array(0), outputFormat);
+    }
+
+    const data = getResizedBytes(this.#images[level], getDxt5Size(width, height));
 
     switch (outputFormat) {
       case BLP_IMAGE_FORMAT.IMAGE_DXT5:

src/lib/blp/dxt.ts

@@ -262,6 +262,18 @@ const dxtToAbgr8888 = (
   return output8;
 };
 
+const getDxtSize = (width: number, height: number, blockSize: number) => {
+  const blockWidth = Math.ceil(width / DXT_BLOCK_WIDTH);
+  const blockHeight = Math.ceil(height / DXT_BLOCK_HEIGHT);
+  return blockWidth * blockHeight * blockSize;
+};
+
+const getDxt1Size = (width: number, height: number) => getDxtSize(width, height, DXT1_BLOCK_SIZE);
+
+const getDxt3Size = (width: number, height: number) => getDxtSize(width, height, DXT3_BLOCK_SIZE);
+
+const getDxt5Size = (width: number, height: number) => getDxtSize(width, height, DXT5_BLOCK_SIZE);
+
 const dxt1ToAbgr8888 = (width: number, height: number, input: Uint8Array) =>
   dxtToAbgr8888(width, height, input, DXT1_BLOCK_SIZE, dxt1DecompressBlock);
 
@@ -271,4 +283,4 @@ const dxt3ToAbgr8888 = (width: number, height: number, input: Uint8Array) =>
 const dxt5ToAbgr8888 = (width: number, height: number, input: Uint8Array) =>
   dxtToAbgr8888(width, height, input, DXT5_BLOCK_SIZE, dxt5DecompressBlock);
 
-export { dxt1ToAbgr8888, dxt3ToAbgr8888, dxt5ToAbgr8888 };
+export { dxt1ToAbgr8888, dxt3ToAbgr8888, dxt5ToAbgr8888, getDxt1Size, getDxt3Size, getDxt5Size };

src/lib/blp/util.ts

@@ -15,6 +15,22 @@ const calcMipLevelCount = (width: number, height: number) => {
 
 const getSizeAtMipLevel = (size: number, level: number) => (size / (1 << level)) | 0;
 
+const getResizedBytes = (bytes: Uint8Array, size: number) => {
+  if (bytes.byteLength === size) {
+    return bytes;
+  }
+
+  if (bytes.byteLength < size) {
+    const padded = new Uint8Array(size);
+    padded.set(bytes, 0);
+    return padded;
+  }
+
+  const trimmed = new Uint8Array(size);
+  trimmed.set(bytes.subarray(0, size), 0);
+  return trimmed;
+};
+
 const resizeBilinear = (
   data: Uint8Array,
   width: number,
@@ -63,4 +79,4 @@ const resizeBilinear = (
   return newData;
 };
 
-export { calcMipLevelCount, getSizeAtMipLevel, resizeBilinear };
+export { calcMipLevelCount, getSizeAtMipLevel, getResizedBytes, resizeBilinear };