Fix blur with transparent pixels

plugins/plugin-blur/package.json

@@ -13,12 +13,16 @@
   "author": "Andrew Lisowski <[email protected]>",
   "license": "MIT",
   "dependencies": {
-    "@jimp/types": "workspace:*"
+    "@jimp/core": "workspace:*",
+    "@jimp/utils": "workspace:*"
   },
   "devDependencies": {
     "@jimp/config-eslint": "workspace:*",
     "@jimp/config-typescript": "workspace:*",
     "@jimp/config-vitest": "workspace:*",
+    "@jimp/js-png": "workspace:*",
+    "@jimp/test-utils": "workspace:*",
+    "@jimp/types": "workspace:*",
     "@vitest/browser": "^1.4.0",
     "eslint": "^8.57.0",
     "tshy": "^3.0.2",

plugins/plugin-blur/src/index.test.ts

@@ -1,5 +1,17 @@
-import { expect, test } from "vitest";
+import { describe, expect, test } from "vitest";
+import { createJimp } from "@jimp/core";
+import { getTestImagePath } from "@jimp/test-utils";
+import "@jimp/test-utils/image-snapshot";
+import png from "@jimp/js-png";
 
-test("adds 1 + 2 to equal 3", () => {
-  expect(1 + 2).toBe(3);
+import * as blur from "./index.js";
+
+const Jimp = createJimp({ formats: [png], plugins: [blur.methods] });
+
+describe("hasAlpha", () => {
+  test("image with alpha", async () => {
+    const image = await Jimp.read(getTestImagePath("dice.png"));
+    const output = await image.blur(16).getBuffer("image/png");
+    expect(output).toMatchImageSnapshot();
+  });
 });

plugins/plugin-blur/src/index.ts

@@ -1,5 +1,6 @@
 import { mulTable, shgTable } from "./blur-tables.js";
 import { JimpClass } from "@jimp/types";
+import { limit255 } from "@jimp/utils";
 
 /*
     Superfast Blur (0.5)
@@ -145,24 +146,10 @@ export const methods = {
         yi = x << 2;
 
         for (y = 0; y < image.bitmap.height; y++) {
-          pa = (asum * mulSum) >>> shgSum;
-          image.bitmap.data[yi + 3] = pa;
-
-          // normalize alpha
-          if (pa > 255) {
-            image.bitmap.data[yi + 3] = 255;
-          }
-
-          if (pa > 0) {
-            pa = 255 / pa;
-            image.bitmap.data[yi] = ((rsum * mulSum) >>> shgSum) * pa;
-            image.bitmap.data[yi + 1] = ((gsum * mulSum) >>> shgSum) * pa;
-            image.bitmap.data[yi + 2] = ((bsum * mulSum) >>> shgSum) * pa;
-          } else {
-            image.bitmap.data[yi + 2] = 0;
-            image.bitmap.data[yi + 1] = 0;
-            image.bitmap.data[yi] = 0;
-          }
+          image.bitmap.data[yi] = limit255((rsum * mulSum) >>> shgSum);
+          image.bitmap.data[yi + 1] = limit255((gsum * mulSum) >>> shgSum);
+          image.bitmap.data[yi + 2] = limit255((bsum * mulSum) >>> shgSum);
+          image.bitmap.data[yi + 3] = limit255((asum * mulSum) >>> shgSum);
 
           if (x === 0) {
             vmin[y] = ((p = y + rad1) < hm ? p : hm) * image.bitmap.width;