Light overlap

src/graphics/rendering/renderer/renderer-implementation.ts

@@ -167,6 +167,7 @@ export class RendererImplementation implements Renderer {
         {
           shadowTraceCount: settings.shadowTraceCount.toString(),
           intensityInsideRatio: settings.lightPenetrationRatio,
+          lightOverlapReduction: settings.lightOverlapReduction,
           floatLinearEnabled: this.gl.insights.floatInterpolationEnabled ? '1' : '0',
           backgroundColor: colorToString(settings.backgroundColor),
         }

src/graphics/rendering/settings/default-startup-settings.ts

@@ -10,6 +10,7 @@ export const defaultStartupSettings: StartupSettings = {
   ignoreWebGL2: false,
   backgroundColor: vec4.fromValues(1, 1, 1, 1),
   lightPenetrationRatio: 0.75,
+  lightOverlapReduction: 0,
   enableStopwatch: false,
   enableContextLostSimulator: false,
 };

src/graphics/rendering/settings/startup-settings.ts

@@ -32,6 +32,19 @@ export interface StartupSettings {
    */
   lightPenetrationRatio: number;
 
+  /**
+   * Controls how overlapping lights combine.
+   *
+   * At `0` lights are summed additively (the physically-correct default):
+   * two nearby lights brighten their overlap and their glows merge into a
+   * shape larger than either alone. At `1` overlapping lights instead take
+   * the per-channel maximum, so a combination never reads brighter or larger
+   * than its strongest contributor. Values in between blend the two.
+   *
+   * A single light looks the same at any value. Should be between 0 and 1.
+   */
+  lightOverlapReduction: number;
+
   /**
    * Gives the number of possible object colors for the scene.
    *

src/graphics/rendering/shaders/shading-fs-100.glsl

@@ -4,6 +4,9 @@ precision lowp float;
 
 #define INTENSITY_INSIDE_RATIO {intensityInsideRatio}
 #define SHADOW_TRACE_COUNT {shadowTraceCount}
+// 0.0 == lights add (overlaps brighten & merge); 1.0 == lights take the
+// per-channel max (overlaps never exceed the brighter light). See main().
+#define LIGHT_OVERLAP_REDUCTION float({lightOverlapReduction})
 
 {macroDefinitions}
 
@@ -65,8 +68,15 @@ void main() {
 
     vec3 colorAtPosition = rgbaColorAtPosition.rgb;
 
-    vec3 lighting = ambientLight;
-    vec3 lightingInside = ambientLight;
+    // Each light contributes to two accumulators: an additive sum (overlaps
+    // brighten and glows bridge into one another) and a per-channel max
+    // (overlaps read as just the brightest light). LIGHT_OVERLAP_REDUCTION
+    // blends between them. Ambient stays a separate additive base, so a single
+    // light is identical to pure-additive (sum == max for one light).
+    vec3 lightSum = vec3(0.0);
+    vec3 lightMax = vec3(0.0);
+    vec3 lightSumInside = vec3(0.0);
+    vec3 lightMaxInside = vec3(0.0);
 
     #ifdef CIRCLE_LIGHT_COUNT
     #if CIRCLE_LIGHT_COUNT > 0
@@ -78,13 +88,16 @@ void main() {
         );
 
         vec2 direction = normalize(circleLightCenters[i] - position) / squareToAspectRatioTimes2;
-        lighting += lightColorAtPosition * shadowTransparency(
+        vec3 shadowed = lightColorAtPosition * shadowTransparency(
             startingDistance,
             lightCenterDistance,
             direction
         );
 
-        lightingInside += lightColorAtPosition;
+        lightSum += shadowed;
+        lightMax = max(lightMax, shadowed);
+        lightSumInside += lightColorAtPosition;
+        lightMaxInside = max(lightMaxInside, lightColorAtPosition);
     }
     #endif
     #endif
@@ -107,17 +120,24 @@ void main() {
             continue;
         }
 
-        lighting += lightColorAtPosition * shadowTransparency(
+        vec3 shadowed = lightColorAtPosition * shadowTransparency(
             startingDistance,
             lightCenterDistance,
             direction
         );
 
-        lightingInside += lightColorAtPosition;
+        lightSum += shadowed;
+        lightMax = max(lightMax, shadowed);
+        lightSumInside += lightColorAtPosition;
+        lightMaxInside = max(lightMaxInside, lightColorAtPosition);
     }
     #endif
     #endif
 
+    vec3 lighting = ambientLight + mix(lightSum, lightMax, LIGHT_OVERLAP_REDUCTION);
+    vec3 lightingInside =
+        ambientLight + mix(lightSumInside, lightMaxInside, LIGHT_OVERLAP_REDUCTION);
+
     vec3 outsideColor = {backgroundColor}.rgb * lighting;
     vec3 insideColor = colorAtPosition * lightingInside * INTENSITY_INSIDE_RATIO;
 

src/graphics/rendering/shaders/shading-fs.glsl

@@ -5,6 +5,9 @@ precision lowp float;
 #define INTENSITY_INSIDE_RATIO {intensityInsideRatio}
 #define SHADOW_TRACE_COUNT {shadowTraceCount}
 #define FLOAT_LINEAR_ENABLED {floatLinearEnabled}
+// 0.0 == lights add (overlaps brighten & merge); 1.0 == lights take the
+// per-channel max (overlaps never exceed the brighter light). See main().
+#define LIGHT_OVERLAP_REDUCTION float({lightOverlapReduction})
 
 {macroDefinitions}
 
@@ -87,8 +90,15 @@ void main() {
 
     float startingDistance = getDistance(uvCoordinates);
 
-    vec3 lighting = ambientLight;
-    vec3 lightingInside = ambientLight;
+    // Each light contributes to two accumulators: an additive sum (overlaps
+    // brighten and glows bridge into one another) and a per-channel max
+    // (overlaps read as just the brightest light). LIGHT_OVERLAP_REDUCTION
+    // blends between them. Ambient stays a separate additive base, so a single
+    // light is identical to pure-additive (sum == max for one light).
+    vec3 lightSum = vec3(0.0);
+    vec3 lightMax = vec3(0.0);
+    vec3 lightSumInside = vec3(0.0);
+    vec3 lightMaxInside = vec3(0.0);
 
     #ifdef CIRCLE_LIGHT_COUNT
     #if CIRCLE_LIGHT_COUNT > 0
@@ -97,13 +107,16 @@ void main() {
         vec3 lightColorAtPosition = colorInPosition(i, lightCenterDistance);
 
         vec2 direction = normalize(circleLightCenters[i] - position) / squareToAspectRatioTimes2;
-        lighting += lightColorAtPosition * shadowTransparency(
+        vec3 shadowed = lightColorAtPosition * shadowTransparency(
             startingDistance,
             lightCenterDistance,
             direction
         );
 
-        lightingInside += lightColorAtPosition;
+        lightSum += shadowed;
+        lightMax = max(lightMax, shadowed);
+        lightSumInside += lightColorAtPosition;
+        lightMaxInside = max(lightMaxInside, lightColorAtPosition);
     }
     #endif
     #endif
@@ -130,17 +143,24 @@ void main() {
             continue;
         }
 
-        lighting += lightColorAtPosition * shadowTransparency(
+        vec3 shadowed = lightColorAtPosition * shadowTransparency(
             startingDistance,
             lightCenterDistance,
             direction
         );
 
-        lightingInside += lightColorAtPosition;
+        lightSum += shadowed;
+        lightMax = max(lightMax, shadowed);
+        lightSumInside += lightColorAtPosition;
+        lightMaxInside = max(lightMaxInside, lightColorAtPosition);
     }
     #endif
     #endif
 
+    vec3 lighting = ambientLight + mix(lightSum, lightMax, LIGHT_OVERLAP_REDUCTION);
+    vec3 lightingInside =
+        ambientLight + mix(lightSumInside, lightMaxInside, LIGHT_OVERLAP_REDUCTION);
+
     vec3 outsideColor = {backgroundColor}.rgb * lighting;
     vec3 insideColor = colorAtPosition * lightingInside * INTENSITY_INSIDE_RATIO;