add multiple samples per pixel

in_one_weekend/src/camera.zig

@@ -0,0 +1,36 @@
+const Point3 = @import("vec3.zig").Point3;
+const Vec3 = @import("vec3.zig").Vec3;
+const Ray = @import("ray.zig").Ray;
+
+pub const Camera = struct {
+    origin: Point3,
+    lowerLeftCorner: Point3,
+    horizontal: Vec3,
+    vertical: Vec3,
+
+    pub fn init() Camera {
+        const aspectRatio = 16.0 / 9.0;
+        const viewportHeight = 2.0;
+        const viewportWidth = aspectRatio * viewportHeight;
+        const focalLength = 1.0;
+
+        const origin = Vec3{};
+        const horizontal = Vec3{ .x = viewportWidth };
+        const vertical = Vec3{ .y = viewportHeight };
+        const lowerLeftCorner = origin.sub(horizontal.div(2)).sub(vertical.div(2)).sub(Vec3{ .z = focalLength });
+
+        return Camera {
+            .origin = origin,
+            .horizontal = horizontal,
+            .vertical = vertical,
+            .lowerLeftCorner = lowerLeftCorner,
+        };
+    }
+
+    pub fn getRay(self: Camera, u: f32, v: f32) Ray {
+        return Ray{
+            .origin = self.origin,
+            .direction = self.lowerLeftCorner.add(self.horizontal.mul(u)).add(self.vertical.mul(v)).sub(self.origin),
+        };
+    }
+};

in_one_weekend/src/color.zig

@@ -0,0 +1,17 @@
+const std = @import("std");
+const math = std.math;
+const Vec3 = @import("vec3.zig").Vec3;
+
+pub const Color = Vec3;
+
+pub fn averageColor(pixelColor: Color, samplesPerPixel: i32) Color {
+    // Divide the color by the number of samples.
+    // const scale = 1.0 / @intToFloat(f32, samplesPerPixel);
+    var scaledColor = pixelColor.div(@intToFloat(f32, samplesPerPixel));
+
+    return Color{
+        .x = math.clamp(scaledColor.x, 0, 0.999),
+        .y = math.clamp(scaledColor.y, 0, 0.999),
+        .z = math.clamp(scaledColor.z, 0, 0.999),
+    };
+}

in_one_weekend/src/main.zig

@@ -3,11 +3,13 @@ const print = std.debug.print;
 const sdl = @import("sdl.zig");
 const vec3 = @import("vec3.zig");
 const Vec3 = vec3.Vec3;
-const Color = vec3.Color;
 const Point3 = vec3.Point3;
+const color = @import("color.zig");
+const Color = color.Color;
 const Ray = @import("ray.zig").Ray;
 const Sphere = @import("sphere.zig").Sphere;
 const World = @import("world.zig").World;
+const Camera = @import("camera.zig").Camera;
 
 // From: https://github.com/Nelarius/weekend-raytracer-zig/blob/master/src/main.zig
 // See https://github.com/zig-lang/zig/issues/565
@@ -53,6 +55,7 @@ pub fn main() anyerror!void {
     const aspectRatio: f32 = 16.0 / 9.0;
     const imageWidth = 600;
     const imageHeight = @floatToInt(usize, imageWidth / aspectRatio);
+    const samplesPerPixel = 100;
 
     // World
     const spheres = [_]Sphere{
@@ -62,14 +65,7 @@ pub fn main() anyerror!void {
     const world = World{ .spheres = spheres[0..spheres.len] };
 
     // Camera
-    const viewportHeight = 2.0;
-    const viewportWidth = viewportHeight * aspectRatio;
-    const focalLength = 1.0;
-
-    const origin = Vec3{};
-    const horizontal = Vec3{ .x = viewportWidth };
-    const vertical = Vec3{ .y = viewportHeight };
-    const lowerLeftCorner = origin.sub(horizontal.div(2)).sub(vertical.div(2)).sub(Vec3{ .z = focalLength });
+    const camera = Camera.init();
 
     const window = sdl.c.SDL_CreateWindow(
         "Raytracing in One Weekend",
@@ -88,6 +84,8 @@ pub fn main() anyerror!void {
         return error.SDLInitializationFailed;
     };
 
+    var prng = std.rand.DefaultPrng.init(42);
+
     {
         _ = sdl.c.SDL_LockSurface(surface);
 
@@ -95,15 +93,22 @@ pub fn main() anyerror!void {
         while (j < imageHeight) {
             var i: usize = 0;
             while (i < imageWidth) {
-                const u = @intToFloat(f32, i) / @intToFloat(f32, (imageWidth - 1));
+                var pixelColor = Color{};
+                var k: usize = 0;
+                while (k < samplesPerPixel) {
+                    const u = (@intToFloat(f32, i) + prng.random.float(f32)) / @intToFloat(f32, (imageWidth - 1));
+                    const v = (@intToFloat(f32, j) + prng.random.float(f32)) / @intToFloat(f32, (imageHeight - 1));
+                    const r = camera.getRay(u, v);
+                    const sample = rayColor(r, world);
+                    pixelColor = pixelColor.add(sample);
+
+                    k += 1;
+                }
+
+                const averageColor = color.averageColor(pixelColor, samplesPerPixel);
                 // SDL coordinate system is flipped compared to the raytracer
-                const v = @intToFloat(f32, (imageHeight - 1) - j) / @intToFloat(f32, (imageHeight - 1));
-                const r = Ray{
-                    .origin = origin,
-                    .direction = lowerLeftCorner.add(horizontal.mul(u)).add(vertical.mul(v)).sub(origin),
-                };
-                const pixelColor = rayColor(r, world);
-                sdl.setSurfacePixel(surface, i, j, pixelColor);
+                sdl.setSurfacePixel(surface, i, imageHeight - 1 - j, averageColor);
+
                 i += 1;
             }
             j += 1;

in_one_weekend/src/sdl.zig

@@ -1,5 +1,5 @@
 pub const c = @cImport({ @cInclude("SDL2/SDL.h"); });
-const Color = @import("vec3.zig").Color;
+const Color = @import("color.zig").Color;
 
 pub fn setSurfacePixel(surface: *c.SDL_Surface, i: usize, j: usize, color: Color) void {
     const bytePerPixel = 4;

in_one_weekend/src/vec3.zig

@@ -67,7 +67,6 @@ pub fn unitVector(vec: Vec3) Vec3 {
 }
 
 pub const Point3 = Vec3;
-pub const Color = Vec3;
 
 const assert = @import("std").debug.assert;