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@@ -105,8 +105,19 @@ Most metals however aren't purely reflective, they fuzz the reflection a little
-### Chapter 9: Glass
+### Chapter 9: Glass and Slowness
In this chapter glass and other dielectric materials have been implemented using Snell's law which describes refraction. The first attempt yields the following rendering:
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+In the later part I implemented Schlick's Approximation which approximates the reflectivity of dielectric objects depending on the angle.
+
+Here I got some strange result (actually I already noticed that the previous render had a strange cyan sheen on the upper part of the ball, but dismissed it as a result of inaccuracies).
+
+I oddly enough got this wrong result, when trying to render the hollow ball:
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+
+It took me some time to find the error and believe it or not, it was the 3% inaccuracy caused by the fast inverse square algorithm! I had to remove it and replace it with a more simple and accurate but slower calculation. The slow down is small but visible! Now I get:
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+
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