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Brief explanation about negative t values #771

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Oct 24, 2020
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Brief explanation about negative t values #771

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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -11,6 +11,7 @@ Change Log -- Ray Tracing in One Weekend
- Fix: Synchronize copies of `hittable_list.h`, `material.h`, `sphere.h`

### In One Weekend
- Change: Wrote brief explanation waving away negative t values in initial normal sphere
- Fix: Catch cases where `lambertian::scatter()` yields degenerate scatter rays (#619)

### The Next Week
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7 changes: 4 additions & 3 deletions books/RayTracingInOneWeekend.html
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Expand Up @@ -725,9 +725,10 @@
visualize the normals with a color map. A common trick used for visualizing normals (because it’s
easy and somewhat intuitive to assume $\mathbf{n}$ is a unit length vector -- so each
component is between -1 and 1) is to map each component to the interval from 0 to 1, and then map
x/y/z to r/g/b. For the normal, we need the hit point, not just whether we hit or not. Let’s assume
the closest hit point (smallest $t$). These changes in the code let us compute and visualize
$\mathbf{n}$:
x/y/z to r/g/b. For the normal, we need the hit point, not just whether we hit or not. We only have
one sphere in the scene, and it's directly in front of the camera, so we won't worry about negative
values of $t$ yet. We'll just assume the closest hit point (smallest $t$). These changes in the code
let us compute and visualize $\mathbf{n}$:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
double hit_sphere(const point3& center, double radius, const ray& r) {
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