### Post by Jamis on Dec 24, 2018 16:51:05 GMT

Merry Christmas, all! Here's a challenge for you--the scene description for the following image:

What makes this particular image a challenge is the branches: the needles are all triangles, and the scene contains over 5000 of them. Your ray tracer will need some optimizations in place in order to render this in a sane amount of time. Bounding boxes are highly recommended. (The good news: I'm currently working on a bonus chapter about bounding boxes!)

Another potential challenge with this image: the branches are generated programmatically, rather than defined statically. The following scene description includes pseudocode for the function that generates the branches, which will hopefully give you an idea of how to implement it in your own program, if you'd like. You can reduce the number of triangles in the scene by playing with some of the settings in that function, specifically the "segments" and "per_segment" values.

One last note: because the light sources are placed inside of spheres, so they show up as reflections on the ornament, you'll need to have implemented the optional feature allowing objects to opt out of the shadow calculations. If you decide not to do that, you can omit those spheres, and set the specular value on the ornament to something more than 0 (0.5 or so, perhaps).

Good luck!

What makes this particular image a challenge is the branches: the needles are all triangles, and the scene contains over 5000 of them. Your ray tracer will need some optimizations in place in order to render this in a sane amount of time. Bounding boxes are highly recommended. (The good news: I'm currently working on a bonus chapter about bounding boxes!)

Another potential challenge with this image: the branches are generated programmatically, rather than defined statically. The following scene description includes pseudocode for the function that generates the branches, which will hopefully give you an idea of how to implement it in your own program, if you'd like. You can reduce the number of triangles in the scene by playing with some of the settings in that function, specifically the "segments" and "per_segment" values.

One last note: because the light sources are placed inside of spheres, so they show up as reflections on the ornament, you'll need to have implemented the optional feature allowing objects to opt out of the shadow calculations. If you decide not to do that, you can omit those spheres, and set the specular value on the ornament to something more than 0 (0.5 or so, perhaps).

Good luck!

`# ======================================================`

# christmas.yml

#

# This file describes a scene depicting a red Christmas

# ornament nestled among several fir branches.

#

# As each branch is generated programmatically, they

# cannot be described in this YAML format. Here is

# pseudo-code for the fir_branch object that appears in

# the YAML description.

#

# function fir_branch()

# # the length of the branch

# let length ← 2.0

#

# # the radius of the branch

# let radius ← 0.025

#

# # how many groups of needles cover the branch

# let segments ← 20

#

# # how needles per group, or segment

# let per_segment ← 24

#

# # the branch itself, just a cylinder

# let branch ← closed cylinder from y=0 to y=length

# set_transform(branch, scaling(radius, 1, radius))

# branch.material ← material with:

# color ← color(0.5, 0.35, 0.26)

# ambient ← 0.2

# specular ← 0.0

# diffuse ← 0.6

#

# # how much branch each segment gets

# let seg_size ← length / (segments - 1)

#

# # the radial distance, in radians, between adjacent needles

# # in a group

# let theta ← 2.1 * π / per_segment

#

# # the maximum length of each needle

# let max_length ← 20.0 * radius

#

# # the group that will contain the branch and all needles

# let object ← group(branch)

#

# for y ← 0 to segments - 1

# # create a subgroup for each segment of needles

# let subgroup ← group()

#

# for i ← 0 to per_segment - 1

# # each needle is a triangle.

# # y_base y coordinate of the base of the triangle

# let y_base ← seg_size * y + rand() * seg_size

#

# # y_tip is the y coordinate of the tip of the triangle

# let y_tip ← y_base - rand() * seg_size

#

# # y_angle is angle (in radians) that the needle should be

# # rotated around the branch.

# let y_angle ← i * theta + rand() * theta

#

# # how long is the needle?

# let needle_length ← max_length / 2 * (1 + rand())

#

# # how much is the needle offset from the center of the branch?

# let ofs ← radius / 2

#

# # the three points of the triangle that form the needle

# let p1 ← point(ofs, y_base, ofs)

# let p2 ← point(-ofs, y_base, ofs)

# let p3 ← point(0.0, y_tip, needle_length)

#

# # create, transform, and texture the needle

# let tri ← triangle(p1, p2, p3)

# set_transform(tri, rotation_y(y_angle))

# tri.material ← material with:

# color ← color(0.26, 0.36, 0.16)

# specular ← 0.1

#

# add_child(subgroup, tri)

# end for

#

# add_child(object, subgroup)

# end for

#

# return object

# end function

#

# by Jamis Buck <jamis@jamisbuck.org>

# ======================================================

# ======================================================

# the camera

# ======================================================

- add: camera

width: 400

height: 300

field-of-view: 1.047

from: [0, 0, -4]

to: [0, 0, 0]

up: [0, 1, 0]

# ======================================================

# the light sources are all coupled with physical

# objects, so that they appear as reflections on the

# ornament.

# ======================================================

- add: light

at: [-10, 10, -10]

intensity: [0.6, 0.6, 0.6]

- add: sphere

shadow: false

transform:

- [ scale, 1.5, 1.5, 1.5 ]

- [ translate, -10, 10, -10 ]

material:

color: [1, 1, 1]

ambient: 0.6

diffuse: 0

specular: 0

- add: light

at: [10, 10, -10]

intensity: [0.6, 0.6, 0.6]

- add: sphere

shadow: false

transform:

- [ scale, 1.5, 1.5, 1.5 ]

- [ translate, 10, 10, -10 ]

material:

color: [1, 1, 1]

ambient: 0.6

diffuse: 0

specular: 0

- add: light

at: [-2, 1, -6]

intensity: [0.2, 0.1, 0.1]

- add: sphere

shadow: false

transform:

- [ scale, 0.4, 0.4, 0.4 ]

- [ translate, -2, 1, -6 ]

material:

color: [1, 0.5, 0.5]

ambient: 0.6

diffuse: 0

specular: 0

- add: light

at: [-1, -2, -6]

intensity: [0.1, 0.2, 0.1]

- add: sphere

shadow: false

transform:

- [ scale, 0.4, 0.4, 0.4 ]

- [ translate, -1, -2, -6 ]

material:

color: [0.5, 1, 0.5]

ambient: 0.6

diffuse: 0

specular: 0

- add: light

at: [3, -1, -6]

intensity: [0.2, 0.2, 0.2]

- add: sphere

shadow: false

transform:

- [ scale, 0.5, 0.5, 0.5 ]

- [ translate, 3, -1, -6 ]

material:

color: [1, 1, 1]

ambient: 0.6

diffuse: 0

specular: 0

# ======================================================

# the scene

# ======================================================

# The ornament itself. Note that specular=0, because we're

# making the ornament reflective and then putting each light

# source inside another sphere, so that they show up as

# reflections. The specular component of Phong shading

# simulates this sort of reflection, so we don't need it here.

- add: sphere

material:

color: [1, 0.25, 0.25]

ambient: 0

specular: 0

diffuse: 0.5

reflective: 0.5

# the silver crown atop the ornament

- add: cylinder

min: 0.0

max: 1.0

transform:

- [ scale, 0.2, 0.3, 0.2 ]

- [ translate, 0, 0.9, 0 ]

- [ rotate-z, -0.1 ]

material:

pattern:

type: checkers

colors:

- [ 1, 1, 1 ]

- [ 0.94, 0.94, 0.94 ]

transform:

- [ scale, 0.2, 0.2, 0.2 ]

ambient: 0.02

diffuse: 0.7

specular: 0.8

shininess: 20

reflective: 0.05

# the branches

# WARNING: by default, each branch consists of 20 segments * 24 needles per

# segment, or 480 triangles. There are 11 branches, so there are

# 5,280 triangles used by default. While bounding boxes are not necessary

# to render this, you will find your ray tracer works much, MUCH more quickly

# with them, than without them.

- add: fir_branch

transform:

- [ translate, 0, -0.5, 0 ]

- [ rotate-x, -1.5708 ]

- [ rotate-y, 0.349 ]

- [ translate, -1, -1, 0 ]

- add: fir_branch

transform:

- [ translate, 0, -0.5, 0 ]

- [ rotate-x, -1.5708 ]

- [ rotate-y, 0.349 ]

- [ translate, -1, 1, 0 ]

- add: fir_branch

transform:

- [ translate, 0, -0.5, 0 ]

- [ rotate-x, -1.5708 ]

- [ rotate-y, -0.1745 ]

- [ translate, 1, -1, 0 ]

- add: fir_branch

transform:

- [ translate, 0, -0.5, 0 ]

- [ rotate-x, -1.5708 ]

- [ rotate-y, -0.349 ]

- [ translate, 1, 1, 0 ]

- add: fir_branch

transform:

- [ translate, 0, -0.5, 0 ]

- [ rotate-x, -1.5708 ]

- [ rotate-y, -0.349 ]

- [ translate, 0.2, -1.25, 0 ]

- add: fir_branch

transform:

- [ translate, 0, -0.5, 0 ]

- [ rotate-x, -1.5708 ]

- [ rotate-y, 0.349 ]

- [ translate, -0.2, -1.25, 0 ]

- add: fir_branch

transform:

- [ translate, 0, -0.5, 0 ]

- [ rotate-x, -1.5708 ]

- [ rotate-x, 0.087 ]

- [ rotate-y, 0.5236 ]

- [ translate, -1.2, 0.1, 0 ]

- add: fir_branch

transform:

- [ translate, 0, -0.5, 0 ]

- [ rotate-x, -1.5708 ]

- [ rotate-x, -0.1745 ]

- [ rotate-y, 0.5236 ]

- [ translate, -1.2, -0.35, 0.5 ]

- add: fir_branch

transform:

- [ translate, 0, -0.5, 0 ]

- [ rotate-x, -1.5708 ]

- [ rotate-x, 0.087 ]

- [ rotate-y, -0.5236 ]

- [ translate, -0.2, 1.5, 0.25 ]

- add: fir_branch

transform:

- [ translate, 0, -0.5, 0 ]

- [ rotate-x, -1.5708 ]

- [ rotate-x, -0.087 ]

- [ rotate-y, -0.5236 ]

- [ translate, 1.3, 0.4, 0 ]

- add: fir_branch

transform:

- [ translate, 0, -0.5, 0 ]

- [ rotate-x, -1.5708 ]

- [ rotate-x, 0.087 ]

- [ rotate-y, -0.1745 ]

- [ translate, 1.5, -0.4, 0 ]