Custom/extended splat encoding ranges, Premultiplied alpha for hyper-saturated colors (#134)

* Externalized SparkRenderer.maxPixelRadius and .minAlpha settings. Added to documentation. Added to examples/editor under Debug folder, moved sort32 there.

* Added SplatEncoding concept, applied individually to SparkRenderer (rgbMin/Max, lnScaleMinMax), SplatMesh (additionally sh1Min/Max, sh2, sh3). Updated examples/editor to control settings via gui. Updated all related code to pipe along settings where needed.
Added SparkRenderer.premultipliedAlpha to control blend mode and enable hyper-saturated color contributions by default.

* Fix SplatLoader not passing along encoding. Complete renaming to splat encoding.

src/SplatLoader.ts

@@ -1,6 +1,10 @@
 import { unzipSync } from "fflate";
 import { FileLoader, Loader, type LoadingManager } from "three";
-import { PackedSplats } from "./PackedSplats";
+import {
+  DEFAULT_SPLAT_ENCODING,
+  PackedSplats,
+  type SplatEncoding,
+} from "./PackedSplats";
 import { SplatMesh } from "./SplatMesh";
 import { PlyReader } from "./ply";
 import { withWorker } from "./splatWorker";
@@ -110,11 +114,14 @@ export class SplatLoader extends Loader {
 
         await Promise.all(promises);
         if (onLoad) {
+          const splatEncoding =
+            this.packedSplats?.splatEncoding ?? DEFAULT_SPLAT_ENCODING;
           const decoded = await unpackSplats({
             input,
             extraFiles,
             fileType,
             pathOrUrl: resolvedURL,
+            splatEncoding,
           });
 
           if (this.packedSplats) {
@@ -396,11 +403,13 @@ export async function unpackSplats({
   extraFiles,
   fileType,
   pathOrUrl,
+  splatEncoding,
 }: {
   input: Uint8Array | ArrayBuffer;
   extraFiles?: Record<string, ArrayBuffer>;
   fileType?: SplatFileType;
   pathOrUrl?: string;
+  splatEncoding?: SplatEncoding;
 }): Promise<{
   packedArray: Uint32Array;
   numSplats: number;
@@ -422,7 +431,11 @@ export async function unpackSplats({
       await ply.parseHeader();
       const numSplats = ply.numSplats;
       const maxSplats = getTextureSize(numSplats).maxSplats;
-      const args = { fileBytes, packedArray: new Uint32Array(maxSplats * 4) };
+      const args = {
+        fileBytes,
+        packedArray: new Uint32Array(maxSplats * 4),
+        splatEncoding,
+      };
       return await withWorker(async (worker) => {
         const { packedArray, numSplats, extra } = (await worker.call(
           "unpackPly",
@@ -441,6 +454,7 @@ export async function unpackSplats({
           "decodeSpz",
           {
             fileBytes,
+            splatEncoding,
           },
         )) as {
           packedArray: Uint32Array;
@@ -456,6 +470,7 @@ export async function unpackSplats({
           "decodeAntiSplat",
           {
             fileBytes,
+            splatEncoding,
           },
         )) as { packedArray: Uint32Array; numSplats: number };
         return { packedArray, numSplats };
@@ -465,7 +480,7 @@ export async function unpackSplats({
       return await withWorker(async (worker) => {
         const { packedArray, numSplats, extra } = (await worker.call(
           "decodeKsplat",
-          { fileBytes },
+          { fileBytes, splatEncoding },
         )) as {
           packedArray: Uint32Array;
           numSplats: number;
@@ -478,7 +493,7 @@ export async function unpackSplats({
       return await withWorker(async (worker) => {
         const { packedArray, numSplats, extra } = (await worker.call(
           "decodePcSogs",
-          { fileBytes, extraFiles },
+          { fileBytes, extraFiles, splatEncoding },
         )) as {
           packedArray: Uint32Array;
           numSplats: number;
@@ -491,7 +506,7 @@ export async function unpackSplats({
       return await withWorker(async (worker) => {
         const { packedArray, numSplats, extra } = (await worker.call(
           "decodePcSogsZip",
-          { fileBytes },
+          { fileBytes, splatEncoding },
         )) as {
           packedArray: Uint32Array;
           numSplats: number;