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Small improvement to rotate_y::hit() function
Resolves #1484
1 parent 949dec9 commit 276cf1c

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4 files changed

+76
-54
lines changed

4 files changed

+76
-54
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‎CHANGELOG.md‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -11,6 +11,7 @@ Change Log / Ray Tracing in One Weekend
1111
- Fix -- Big improvement to print version listing font size (#1595) and more compact line
1212
height for code listings in both print and browser.
1313
- Change -- Include hittable.h from material.h; drop `hit_record` forward declaration (#1609)
14+
- Fix -- Slight improvement to `rotate_y::hit()` function (#1484)
1415

1516
### In One Weekend
1617
- Fix -- Fixed usage of the term "unit cube" for a cube of diameter two (#1555, #1603)

‎books/RayTracingTheNextWeek.html‎

Lines changed: 25 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -3815,34 +3815,41 @@
38153815
public:
38163816

38173817
bool hit(const ray& r, interval ray_t, hit_record& rec) const override {
3818-
// Change the ray from world space to object space
3819-
auto origin = r.origin();
3820-
auto direction = r.direction();
38213818

3822-
origin[0] = cos_theta*r.origin()[0] - sin_theta*r.origin()[2];
3823-
origin[2] = sin_theta*r.origin()[0] + cos_theta*r.origin()[2];
3819+
// Transform the ray from world space to object space.
38243820

3825-
direction[0] = cos_theta*r.direction()[0] - sin_theta*r.direction()[2];
3826-
direction[2] = sin_theta*r.direction()[0] + cos_theta*r.direction()[2];
3821+
auto origin = point3(
3822+
(cos_theta * r.origin().x()) - (sin_theta * r.origin().z()),
3823+
r.origin().y(),
3824+
(sin_theta * r.origin().x()) + (cos_theta * r.origin().z())
3825+
);
3826+
3827+
auto direction = vec3(
3828+
(cos_theta * r.direction().x()) - (sin_theta * r.direction().z()),
3829+
r.direction().y(),
3830+
(sin_theta * r.direction().x()) + (cos_theta * r.direction().z())
3831+
);
38273832

38283833
ray rotated_r(origin, direction, r.time());
38293834

3830-
// Determine whether an intersection exists in object space (and if so, where)
3835+
// Determine whether an intersection exists in object space (and if so, where).
3836+
38313837
if (!object->hit(rotated_r, ray_t, rec))
38323838
return false;
38333839

3834-
// Change the intersection point from object space to world space
3835-
auto p = rec.p;
3836-
p[0] = cos_theta*rec.p[0] + sin_theta*rec.p[2];
3837-
p[2] = -sin_theta*rec.p[0] + cos_theta*rec.p[2];
3840+
// Transform the intersection from object space back to world space.
38383841

3839-
// Change the normal from object space to world space
3840-
auto normal = rec.normal;
3841-
normal[0] = cos_theta*rec.normal[0] + sin_theta*rec.normal[2];
3842-
normal[2] = -sin_theta*rec.normal[0] + cos_theta*rec.normal[2];
3842+
rec.p = point3(
3843+
(cos_theta * rec.p.x()) + (sin_theta * rec.p.z()),
3844+
rec.p.y(),
3845+
(-sin_theta * rec.p.x()) + (cos_theta * rec.p.z())
3846+
);
38433847

3844-
rec.p = p;
3845-
rec.normal = normal;
3848+
rec.normal = vec3(
3849+
(cos_theta * rec.normal.x()) + (sin_theta * rec.normal.z()),
3850+
rec.normal.y(),
3851+
(-sin_theta * rec.normal.x()) + (cos_theta * rec.normal.z())
3852+
);
38463853

38473854
return true;
38483855
}

‎src/TheNextWeek/hittable.h‎

Lines changed: 25 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -115,34 +115,41 @@ class rotate_y : public hittable {
115115
}
116116

117117
bool hit(const ray& r, interval ray_t, hit_record& rec) const override {
118-
// Change the ray from world space to object space
119-
auto origin = r.origin();
120-
auto direction = r.direction();
121118

122-
origin[0] = cos_theta*r.origin()[0] - sin_theta*r.origin()[2];
123-
origin[2] = sin_theta*r.origin()[0] + cos_theta*r.origin()[2];
119+
// Transform the ray from world space to object space.
124120

125-
direction[0] = cos_theta*r.direction()[0] - sin_theta*r.direction()[2];
126-
direction[2] = sin_theta*r.direction()[0] + cos_theta*r.direction()[2];
121+
auto origin = point3(
122+
(cos_theta * r.origin().x()) - (sin_theta * r.origin().z()),
123+
r.origin().y(),
124+
(sin_theta * r.origin().x()) + (cos_theta * r.origin().z())
125+
);
126+
127+
auto direction = vec3(
128+
(cos_theta * r.direction().x()) - (sin_theta * r.direction().z()),
129+
r.direction().y(),
130+
(sin_theta * r.direction().x()) + (cos_theta * r.direction().z())
131+
);
127132

128133
ray rotated_r(origin, direction, r.time());
129134

130-
// Determine whether an intersection exists in object space (and if so, where)
135+
// Determine whether an intersection exists in object space (and if so, where).
136+
131137
if (!object->hit(rotated_r, ray_t, rec))
132138
return false;
133139

134-
// Change the intersection point from object space to world space
135-
auto p = rec.p;
136-
p[0] = cos_theta*rec.p[0] + sin_theta*rec.p[2];
137-
p[2] = -sin_theta*rec.p[0] + cos_theta*rec.p[2];
140+
// Transform the intersection from object space back to world space.
138141

139-
// Change the normal from object space to world space
140-
auto normal = rec.normal;
141-
normal[0] = cos_theta*rec.normal[0] + sin_theta*rec.normal[2];
142-
normal[2] = -sin_theta*rec.normal[0] + cos_theta*rec.normal[2];
142+
rec.p = point3(
143+
(cos_theta * rec.p.x()) + (sin_theta * rec.p.z()),
144+
rec.p.y(),
145+
(-sin_theta * rec.p.x()) + (cos_theta * rec.p.z())
146+
);
143147

144-
rec.p = p;
145-
rec.normal = normal;
148+
rec.normal = vec3(
149+
(cos_theta * rec.normal.x()) + (sin_theta * rec.normal.z()),
150+
rec.normal.y(),
151+
(-sin_theta * rec.normal.x()) + (cos_theta * rec.normal.z())
152+
);
146153

147154
return true;
148155
}

‎src/TheRestOfYourLife/hittable.h‎

Lines changed: 25 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -123,34 +123,41 @@ class rotate_y : public hittable {
123123
}
124124

125125
bool hit(const ray& r, interval ray_t, hit_record& rec) const override {
126-
// Change the ray from world space to object space
127-
auto origin = r.origin();
128-
auto direction = r.direction();
129126

130-
origin[0] = cos_theta*r.origin()[0] - sin_theta*r.origin()[2];
131-
origin[2] = sin_theta*r.origin()[0] + cos_theta*r.origin()[2];
127+
// Transform the ray from world space to object space.
132128

133-
direction[0] = cos_theta*r.direction()[0] - sin_theta*r.direction()[2];
134-
direction[2] = sin_theta*r.direction()[0] + cos_theta*r.direction()[2];
129+
auto origin = point3(
130+
(cos_theta * r.origin().x()) - (sin_theta * r.origin().z()),
131+
r.origin().y(),
132+
(sin_theta * r.origin().x()) + (cos_theta * r.origin().z())
133+
);
134+
135+
auto direction = vec3(
136+
(cos_theta * r.direction().x()) - (sin_theta * r.direction().z()),
137+
r.direction().y(),
138+
(sin_theta * r.direction().x()) + (cos_theta * r.direction().z())
139+
);
135140

136141
ray rotated_r(origin, direction, r.time());
137142

138-
// Determine whether an intersection exists in object space (and if so, where)
143+
// Determine whether an intersection exists in object space (and if so, where).
144+
139145
if (!object->hit(rotated_r, ray_t, rec))
140146
return false;
141147

142-
// Change the intersection point from object space to world space
143-
auto p = rec.p;
144-
p[0] = cos_theta*rec.p[0] + sin_theta*rec.p[2];
145-
p[2] = -sin_theta*rec.p[0] + cos_theta*rec.p[2];
148+
// Transform the intersection from object space back to world space.
146149

147-
// Change the normal from object space to world space
148-
auto normal = rec.normal;
149-
normal[0] = cos_theta*rec.normal[0] + sin_theta*rec.normal[2];
150-
normal[2] = -sin_theta*rec.normal[0] + cos_theta*rec.normal[2];
150+
rec.p = point3(
151+
(cos_theta * rec.p.x()) + (sin_theta * rec.p.z()),
152+
rec.p.y(),
153+
(-sin_theta * rec.p.x()) + (cos_theta * rec.p.z())
154+
);
151155

152-
rec.p = p;
153-
rec.normal = normal;
156+
rec.normal = vec3(
157+
(cos_theta * rec.normal.x()) + (sin_theta * rec.normal.z()),
158+
rec.normal.y(),
159+
(-sin_theta * rec.normal.x()) + (cos_theta * rec.normal.z())
160+
);
154161

155162
return true;
156163
}

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