add iterative rendering mode for faster results

In normal mode, the image is rendered one pixel at a time, taking multiple samples per pixel and averaging them before continuing with the next pixel.

In iterative mode, the image is rendered one sample at a time, taking one sample per pixel, then taking another sample and averaging it with the one before, and so on.

src/main/java/eu/jonahbauer/raytracing/Main.java

@@ -36,6 +36,7 @@ public class Main {
         var renderer = SimpleRenderer.builder()
                 .withSamplesPerPixel(500)
                 .withMaxDepth(50)
+                .withIterative(true)
                 .build();
 
         var image = new LiveCanvas(new Image(camera.getWidth(), camera.getHeight()));

src/main/java/eu/jonahbauer/raytracing/render/renderer/SimpleRenderer.java

@@ -17,6 +17,9 @@ public final class SimpleRenderer implements Renderer {
     private final int maxDepth;
     private final double gamma;
 
+    private final boolean parallel;
+    private final boolean iterative;
+
     public static @NotNull Builder builder() {
         return new Builder();
     }
@@ -29,6 +32,9 @@ public final class SimpleRenderer implements Renderer {
         this.samplesPerPixel = builder.samplesPerPixel;
         this.maxDepth = builder.maxDepth;
         this.gamma = builder.gamma;
+
+        this.parallel = builder.parallel;
+        this.iterative = builder.iterative;
     }
 
     @Override
@@ -37,7 +43,27 @@ public final class SimpleRenderer implements Renderer {
             throw new IllegalArgumentException("sizes of camera and canvas are different");
         }
 
-        getPixelStream(camera.getWidth(), camera.getHeight()).parallel().forEach(pixel -> {
+        if (iterative) {
+            // render one sample after the other
+            for (int i = 1 ; i <= samplesPerPixel; i++) {
+                var sample = i;
+                getPixelStream(camera.getWidth(), camera.getHeight(), parallel).forEach(pixel -> {
+                    var y = (int) (pixel >> 32);
+                    var x = (int) pixel;
+                    var ray = camera.cast(x, y);
+                    var c = getColor(scene, ray);
+                    canvas.set(x, y, Color.average(canvas.get(x, y), c, sample));
+                });
+            }
+            // apply gamma correction
+            getPixelStream(camera.getWidth(), camera.getHeight(), parallel).forEach(pixel -> {
+                var y = (int) (pixel >> 32);
+                var x = (int) pixel;
+                canvas.set(x, y, Color.gamma(canvas.get(x, y), gamma));
+            });
+        } else {
+            // render one pixel after the other
+            getPixelStream(camera.getWidth(), camera.getHeight(), parallel).forEach(pixel -> {
                 var y = (int) (pixel >> 32);
                 var x = (int) pixel;
 
@@ -50,6 +76,7 @@ public final class SimpleRenderer implements Renderer {
                 canvas.set(x, y, Color.gamma(color, gamma));
             });
         }
+    }
 
     /**
      * {@return the color of the given ray in the given scene}
@@ -77,10 +104,11 @@ public final class SimpleRenderer implements Renderer {
      * {@return a stream of the pixels in a canvas with the given size} The pixels {@code x} and {@code y} coordinate
      * are encoded in the longs lower and upper 32 bits respectively.
      */
-    private static @NotNull LongStream getPixelStream(int width, int height) {
-        return IntStream.range(0, height)
+    private static @NotNull LongStream getPixelStream(int width, int height, boolean parallel) {
+        var stream = IntStream.range(0, height)
                 .mapToObj(y -> IntStream.range(0, width).mapToLong(x -> (long) y << 32 | x))
                 .flatMapToLong(Function.identity());
+        return parallel ? stream.parallel() : stream;
     }
 
     /**
@@ -100,6 +128,8 @@ public final class SimpleRenderer implements Renderer {
         private int samplesPerPixel = 100;
         private int maxDepth = 10;
         private double gamma = 2.0;
+        private boolean parallel = true;
+        private boolean iterative = false;
 
         public @NotNull Builder withSamplesPerPixel(int samples) {
             if (samples <= 0) throw new IllegalArgumentException("samples must be positive");
@@ -119,6 +149,16 @@ public final class SimpleRenderer implements Renderer {
             return this;
         }
 
+        public @NotNull Builder withParallel(boolean parallel) {
+            this.parallel = parallel;
+            return this;
+        }
+
+        public @NotNull Builder withIterative(boolean iterative) {
+            this.iterative = iterative;
+            return this;
+        }
+
         public @NotNull SimpleRenderer build() {
             return new SimpleRenderer(this);
         }