[sigma] Fixes some attachment labels issue

The issue was that hovering a node in the attachment-label example was
making all edges disappear, until any re-rendering was triggered (by
leaving the node, zooming, panning...).

Details:
- Adds regression test for the observed bug on label-attachment example
- Adds gl.activeTexture() call before gl.bindTexture() in
  regenerateAtlas to fix the issue

Author: jacomyal

packages/sigma/src/rendering/nodes/attachments/attachment-manager.test.ts

@@ -0,0 +1,44 @@
+/**
+ * Regression test for texture unit corruption in AttachmentManager.
+ *
+ * When regenerateAtlas() creates a GL texture it must bind it to a dedicated
+ * texture unit, not to whichever unit happens to be active. Otherwise, it
+ * overwrites unrelated data-texture bindings (e.g. the edge data texture on
+ * unit 4), causing edges to vanish until the next full render rebinds them.
+ */
+import { describe, expect, test } from "vitest";
+
+import { createTestGL } from "../../../_test-helpers";
+import { AttachmentManager } from "./attachment-manager";
+
+describe("AttachmentManager", () => {
+  test("regenerateAtlas preserves other texture unit bindings", () => {
+    const gl = createTestGL();
+
+    // Bind a sentinel texture to unit 4 (simulates the edge data texture)
+    const sentinel = gl.createTexture();
+    gl.activeTexture(gl.TEXTURE0 + 4);
+    gl.bindTexture(gl.TEXTURE_2D, sentinel);
+
+    const manager = new AttachmentManager(gl, {}, () => {});
+
+    // Populate cache directly so regenerateAtlas actually creates a GL texture
+    const canvas = document.createElement("canvas");
+    canvas.width = 10;
+    canvas.height = 10;
+    canvas.getContext("2d")!.fillRect(0, 0, 10, 10);
+    (manager as unknown as Record<string, unknown>).cache = new Map([
+      ["n:att", { image: canvas, width: 10, height: 10 }],
+    ]);
+    (manager as unknown as Record<string, unknown>).dirty = true;
+
+    manager.regenerateAtlas();
+
+    // Unit 4 must still hold the sentinel, not the atlas texture
+    gl.activeTexture(gl.TEXTURE0 + 4);
+    expect(gl.getParameter(gl.TEXTURE_BINDING_2D)).toBe(sentinel);
+
+    gl.deleteTexture(sentinel);
+    manager.kill();
+  });
+});

packages/sigma/src/rendering/nodes/attachments/attachment-manager.ts

@@ -11,6 +11,7 @@
 import { LabelAttachmentContext, LabelAttachmentRenderer } from "../../../primitives";
 import { AtlasEntry, AtlasLookup, PackableItem, ShelfCursor, packItemsOnPage } from "../../../utils";
 import { contentToCanvas } from "./attachment-converter";
+import { ATTACHMENT_TEXTURE_UNIT } from "./attachment-program";
 
 const ATLAS_SIZE = 2048;
 
@@ -127,6 +128,7 @@ export class AttachmentManager {
     this.deleteGLTexture();
     const gl = this.gl;
     const tex = gl.createTexture()!;
+    gl.activeTexture(gl.TEXTURE0 + ATTACHMENT_TEXTURE_UNIT);
     gl.bindTexture(gl.TEXTURE_2D, tex);
     gl.pixelStorei(gl.UNPACK_PREMULTIPLY_ALPHA_WEBGL, true);
     gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, this.packCanvas);