Add basic PPM generation

.gitignore

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+.dub
+docs.json
+__dummy.html
+docs/
+/oneweekend-d
+oneweekend-d.so
+oneweekend-d.dylib
+oneweekend-d.dll
+oneweekend-d.a
+oneweekend-d.lib
+oneweekend-d-test-*
+*.exe
+*.o
+*.obj
+*.lst
+owe

Makefile

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+# vim:noexpandtab
+
+.PHONY: build clean run
+
+dmd_opts = -de -w -unittest
+prog = owe
+main = source/$(prog).d
+
+run:
+	rdmd $(dmd_opts) $(main)
+
+build:
+	dmd $(dmd_opts) $(main)
+
+clean:
+	rm $(prog) $(prog).o

dub.json

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+{
+	"authors": [
+		"Michael Kohl"
+	],
+	"copyright": "Copyright © 2021, Michael Kohl",
+	"description": "Ray Tracing in One Weekend",
+	"license": "MIT",
+	"name": "oneweekend-d"
+}

source/owe.d

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+import std.conv : to;
+import std.format : format;
+import std.range : iota;
+import std.stdio;
+
+void main()
+{
+
+  // Image
+  const int imageWidth = 256;
+
+  const imageHeight = 256;
+
+  // Render
+
+  write(format("P3\n%s %s\n255\n", imageWidth, imageHeight));
+  for (int j = imageHeight - 1; j >= 0; --j)
+  {
+    stderr.write(format("\rScanlines remaining: %d", j));
+    for (int i = 0; i < imageWidth; ++i)
+    {
+      auto r = to!double(i) / (imageWidth - 1);
+      auto g = to!double(j) / (imageHeight - 1);
+      auto b = 0.25;
+
+      const int ir = to!int(255.999 * r);
+      const int ig = to!int(255.999 * g);
+      const int ib = to!int(255.999 * b);
+
+      write(format("%d %d %d\n", ir, ig, ib));
+    }
+  }
+  stderr.writeln("\nDone.");
+}