Splat Texture (#79)

* Add experimental Splat Texture rendering and examples/splat-texture. Added star.png and heart.png to assets.json and to assets repo. Update examples/depth-of-field to compute from metric aperture size. Added SparkRenderer.renderScale debug parameter. Updated examples/editor: set default highDPI to true, added logFocalDistance, apertureAngle, refactored, grouped into debugFolder, default settings open, preset buttons for nonAA and AA settings.

* Set default highDpi in examples/editor to not(isMobile).

src/shaders/splatFragment.glsl

@@ -4,11 +4,21 @@ precision highp int;
 
 #include <splatDefines>
 
+uniform float near;
+uniform float far;
 uniform bool encodeLinear;
 uniform float maxStdDev;
 uniform bool disableFalloff;
 uniform float falloff;
 
+uniform bool splatTexEnable;
+uniform sampler3D splatTexture;
+uniform mat2 splatTexMul;
+uniform vec2 splatTexAdd;
+uniform float splatTexNear;
+uniform float splatTexFar;
+uniform float splatTexMid;
+
 out vec4 fragColor;
 
 in vec4 vRgba;
@@ -16,20 +26,45 @@ in vec2 vSplatUv;
 in vec3 vNdc;
 
 void main() {
+    vec4 rgba = vRgba;
+
     float z = dot(vSplatUv, vSplatUv);
-    if (z > (maxStdDev * maxStdDev)) {
-        discard;
+    if (!splatTexEnable) {
+        if (z > (maxStdDev * maxStdDev)) {
+            discard;
+        }
+    } else {
+        vec2 uv = splatTexMul * vSplatUv + splatTexAdd;
+        float ndcZ = vNdc.z;
+        float depth = (2.0 * near * far) / (far + near - ndcZ * (far - near));
+        float clampedFar = max(splatTexFar, splatTexNear);
+        float clampedDepth = clamp(depth, splatTexNear, clampedFar);
+        float logDepth = log2(clampedDepth + 1.0);
+        float logNear = log2(splatTexNear + 1.0);
+        float logFar = log2(clampedFar + 1.0);
+
+        float texZ;
+        if (splatTexMid > 0.0) {
+            float clampedMid = clamp(splatTexMid, splatTexNear, clampedFar);
+            float logMid = log2(clampedMid + 1.0);
+            texZ = (clampedDepth <= clampedMid) ?
+                (0.5 * ((logDepth - logNear) / (logMid - logNear))) :
+                (0.5 * ((logDepth - logMid) / (logFar - logMid)) + 0.5);
+        } else {
+            texZ = (logDepth - logNear) / (logFar - logNear);
+        }
+
+        vec4 modulate = texture(splatTexture, vec3(uv, 1.0 - texZ));
+        rgba *= modulate;
     }
 
-    float alpha = vRgba.a;
-    alpha *= mix(1.0, exp(-0.5 * z), falloff);
-    if (alpha < MIN_ALPHA) {
+    rgba.a *= mix(1.0, exp(-0.5 * z), falloff);
+
+    if (rgba.a < MIN_ALPHA) {
         discard;
     }
-
-    vec3 rgb = vRgba.rgb;
     if (encodeLinear) {
-        rgb = srgbToLinear(rgb);
+        rgba.rgb = srgbToLinear(rgba.rgb);
     }
-    fragColor = vec4(rgb, alpha);
+    fragColor = rgba;
 }