光線追蹤總結

我們把移動眼睛??位置放到之後討論，先來做一個關於光線追蹤的總結

除了剛才討論過的，關於光線追蹤還有很多話題： 優化，折射。最終再梳理一遍至今の所有偽碼。

CanvasToViewport(x, y){
return (x * Vw/Cw, y * Vh/Ch, d)
}

ReflectRay(R, N) {
return 2*N*dot(N, R) - R
}

ComputeLighting(P, N, V, s) {
i = 0.0
for light in scene.Lights {
if light.type == ambient {
i += light.intensity
} else {
if light.type == point {
L = light.position - P
t_max = 1
}
else {
L = -light.direction
t_max = inf
}

# shadow check
shadow_sphere, shadow_t = ClosestIntersection(P, L, 0.001, t_max)
if shadow_sphere != NULL
continue

# diffuse
n_dot_l = dot(N, L)
if n_dot_l > 0
i += light.intensity*n_dot_l/(length(N)*length(L))

# specular
if s!= -1 {
R = 2*N*dot(N,L) -L
r_dot_v = dot(R, V)
if r_dot_v > 0
i += light.intensity*pow(r_dot_v/length(R)*length(V)),s)
}
}
}
return i
}

ClosestIntersection(O, D, t_min, t_max){
closest_t = inf
closest_sphere = NULL
for sphere in scene.Spheres {
t1, t2 = IntersectRaySphere(O, D, sphere)
if t1 in [t_min, t_max] && t1 < closest_t
closest_t = t1
closest_sphere = sphere
if t2 in [t_min, t_max] && t2 < closest_t
closest_t = t2
closest_sphere = sphere
}

return closest_sphere, closest_t
}

TraceRay(O, D, t_min, t_max, depth){
closest_sphere , closest_t = ClosestIntersection(O, D, t_min, t_max)

if closest_sphere == NULL
return BACKGROUND_COLOR

# local color
P = O + closest_t * D #交點P的位置
N = P - closest_sphere.center #計算P處的法向量
N = N / length(N) #normalize 法向量
local_color = closest_sphere.color * ComputeLighting(P, N, -D, sphere.specular)

# If we hit the recursion limit or the object is not reflective, were done
r = closest_sphere.reflective
if depth <= 0 or r <= 0:
return local_color

# reflected color
R = ReflectRay(-D, N)
reflected_color = TraceRay(P, R, 0.001, inf, depth - 1)

return local_color * (1 - r) + reflected_color*r
}

O = <0,0,0>

for x in [-Cw/2, Cw/2]{
for y in [-Ch/2, Ch/2]{
D = CanvasToViewport(x, y)
color = TraceRay(O, D, t_min, t_max)
canvas.putPixel(x, y, color)
}
}

這是所用的所有參數：

viewport_size = 1 x 1
projection_plane_d = 1

sphere {
center = (0, -1, 3)
radius = 1
color = (255, 0, 0) # Red
specular = 500 # Shiny
reflective = 0.2 # A bit reflective
}
sphere {
center = (-2, 1, 3)
radius = 1
color = (0, 0, 255) # Blue
specular = 500 # Shiny
reflective = 0.3 # A bit more reflective
}
sphere {
center = (2, 1, 3)
radius = 1
color = (0, 255, 0) # Green
specular = 10 # Somewhat shiny
reflective = 0.4 # Even more reflective
}
sphere {
color = (255, 255, 0) # Yellow
center = (0, -5001, 0)
radius = 5000
specular = 1000 # Very shiny
reflective = 0.5 # Half reflective
}

light {
type = ambient
intensity = 0.2
}
light {
type = point
intensity = 0.6
position = (2, 1, 0)
}
light {
type = directional
intensity = 0.2
direction = (1, 4, 4)
}

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