Working prototype. Initialization not consistent.

examples/editor/index.html

@@ -498,6 +498,11 @@
     gui.addColor(guiOptions, "backgroundColor").name("Background color").onChange((value) => {
       scene.background.set(value);
     });
+    // spark.defaultView.stochastic = true;
+    gui.add(spark.defaultView, "stochastic").name("Stochastic sort-free").listen().onChange(() => {
+      // spark.prepareViewpoint();
+      touch();
+    });
 
     const debugFolder = gui.addFolder("Debug").close();
     const normalColor = dyno.dynoBool(false);
@@ -524,10 +529,6 @@
     debugFolder.add(spark.defaultView, "sort32").name("Float32 sort").listen();
     debugFolder.add(spark, "maxPixelRadius", 1, 1024, 1).name("Max pixel radius").listen();
     debugFolder.add(spark, "minAlpha", 0, 1, 0.001).name("Min alpha").listen();
-    spark.defaultView.stochastic = true;
-    debugFolder.add(spark.defaultView, "stochastic").name("Stochastic sort-free").listen().onChange(() => {
-      spark.prepareViewpoint();
-    });
 
     debugFolder.add(spark, "premultipliedAlpha").name("Premultiplied alpha").listen();
     const accumFolder = debugFolder.addFolder("Accumulator encoding").close();;
@@ -778,6 +779,8 @@
       lastTime = time;
       stats.begin();
 
+      renderer.clear(true, true, false);
+
       if (guiOptions.autoRotate) {
         frame.rotation.y += deltaTime / 5000;
       }

src/SparkRenderer.ts

@@ -260,6 +260,7 @@ export class SparkRenderer extends THREE.Mesh {
   private lastUpdateTime: number | null = null;
   // List of cameras used for the current viewpoint (for WebXR)
   private defaultCameras: THREE.Matrix4[] = [];
+  private lastStochastic: boolean | null = null;
 
   // Should be set to the defaultView, but can be temporarily changed to another
   // viewpoint using prepareViewpoint() for rendering from a different viewpoint.
@@ -533,6 +534,10 @@ export class SparkRenderer extends THREE.Mesh {
       this.uniforms.deltaTime.value = deltaTime;
       // Alternating debug flag that can aid in visual debugging
       this.uniforms.debugFlag.value = (performance.now() / 1000.0) % 2.0 < 1.0;
+
+      // if (viewpoint.stochastic) {
+      //   (this.geometry as SplatGeometry).instanceCount = this.uniforms.numSplats.value;
+      // }
     }
 
     if (viewpoint.target) {
@@ -577,6 +582,13 @@ export class SparkRenderer extends THREE.Mesh {
     this.uniforms.clipXY.value = this.clipXY;
     this.uniforms.focalAdjustment.value = this.focalAdjustment;
 
+    if (this.lastStochastic !== !viewpoint.stochastic) {
+      this.lastStochastic = !viewpoint.stochastic;
+      this.material.transparent = !viewpoint.stochastic;
+      this.material.depthWrite = viewpoint.stochastic;
+      this.material.needsUpdate = true;
+    }
+
     if (this.splatTexture) {
       const { enable, texture, multiply, add, near, far, mid } =
         this.splatTexture;
@@ -638,6 +650,7 @@ export class SparkRenderer extends THREE.Mesh {
       this.geometry = geometry;
       this.material.transparent = !this.viewpoint.stochastic;
       this.material.depthWrite = this.viewpoint.stochastic;
+      this.material.needsUpdate = true;
     } else {
       // No Gsplats to display for this viewpoint yet
       this.uniforms.numSplats.value = 0;

src/SparkViewpoint.ts

@@ -569,7 +569,9 @@ export class SparkViewpoint {
     let activeSplats = 0;
     let ordering = this.orderingFreelist.alloc(maxSplats);
 
-    if (numSplats > 0) {
+    if (this.stochastic) {
+      activeSplats = numSplats;
+    } else if (numSplats > 0) {
       const {
         reader,
         doubleSortReader,

src/shaders/splatFragment.glsl

@@ -28,6 +28,7 @@ out vec4 fragColor;
 in vec4 vRgba;
 in vec2 vSplatUv;
 in vec3 vNdc;
+flat in uint vSplatIndex;
 
 void main() {
     vec4 rgba = vRgba;
@@ -72,18 +73,16 @@ void main() {
     }
 
     if (stochastic) {
-        uint uTime = floatBitsToUint(time);
+        const bool STEADY = false;
+        uint uTime = STEADY ? 0u : floatBitsToUint(time);
         uvec2 coord = uvec2(gl_FragCoord.xy);
-        uint state = uTime + 0x9e3779b9u * coord.x + 0x85ebca6bu * coord.y;
+        uint state = uTime + 0x9e3779b9u * coord.x + 0x85ebca6bu * coord.y + 0xc2b2ae35u * uint(vSplatIndex);
         state = state * 747796405u + 2891336453u;
         uint hash = ((state >> ((state >> 28u) + 4u)) ^ state) * 277803737u;
         hash = (hash >> 22u) ^ hash;
-        float rand = float(hash) / 4294967295.0;
+        float rand = float(hash) / 4294967296.0;
-        // rand *= 2.0;
         if (rand < rgba.a) {
             fragColor = vec4(rgba.rgb, 1.0);
-            // gl_FragDepth = gl_FragCoord.z;
-            // fragColor = vec4(rgba.r, 0.0, 0.0, 1.0);
         } else {
             discard;
         }

src/shaders/splatVertex.glsl

@@ -10,6 +10,7 @@ attribute uint splatIndex;
 out vec4 vRgba;
 out vec2 vSplatUv;
 out vec3 vNdc;
+flat out uint vSplatIndex;
 
 uniform vec2 renderSize;
 uniform uint numSplats;
@@ -21,6 +22,7 @@ uniform float time;
 uniform float deltaTime;
 uniform bool debugFlag;
 uniform float minAlpha;
+uniform bool stochastic;
 uniform bool enable2DGS;
 uniform float blurAmount;
 uniform float preBlurAmount;
@@ -39,16 +41,25 @@ void main() {
     if (uint(gl_InstanceID) >= numSplats) {
         return;
     }
-    if (splatIndex == 0xffffffffu) {
-        // Special value reserved for "no splat"
-        return;
-    }
 
-    ivec3 texCoord = ivec3(
+    ivec3 texCoord;
-        splatIndex & SPLAT_TEX_WIDTH_MASK,
+    if (stochastic) {
-        (splatIndex >> SPLAT_TEX_WIDTH_BITS) & SPLAT_TEX_HEIGHT_MASK,
+        texCoord = ivec3(
-        splatIndex >> SPLAT_TEX_LAYER_BITS
+            uint(gl_InstanceID) & SPLAT_TEX_WIDTH_MASK,
-    );
+            (uint(gl_InstanceID) >> SPLAT_TEX_WIDTH_BITS) & SPLAT_TEX_HEIGHT_MASK,
+            (uint(gl_InstanceID) >> SPLAT_TEX_LAYER_BITS)
+        );
+    } else {
+        if (splatIndex == 0xffffffffu) {
+            // Special value reserved for "no splat"
+            return;
+        }
+        texCoord = ivec3(
+            splatIndex & SPLAT_TEX_WIDTH_MASK,
+            (splatIndex >> SPLAT_TEX_WIDTH_BITS) & SPLAT_TEX_HEIGHT_MASK,
+            splatIndex >> SPLAT_TEX_LAYER_BITS
+        );
+    }
     uvec4 packed = texelFetch(packedSplats, texCoord, 0);
 
     vec3 center, scales;
@@ -85,6 +96,9 @@ void main() {
         return;
     }
 
+    // Record the splat index for entropy
+    vSplatIndex = splatIndex;
+
     // Compute view space quaternion of splat
     vec4 viewQuaternion = quatQuat(renderToViewQuat, quaternion);