From aca1bceb5ab7dd87e910f0b8c5dba784ab6e8290 Mon Sep 17 00:00:00 2001
From: Charles McGarvey <chazmcgarvey@brokenzipper.com>
Date: Mon, 13 Feb 2012 14:57:05 -0700
Subject: [PATCH] make the animate script even easier to understand

---
 animate.lua | 79 +++++++++++++++++++++++++++++++----------------------
 1 file changed, 47 insertions(+), 32 deletions(-)

diff --git a/animate.lua b/animate.lua
index d04f5df..476051f 100755
--- a/animate.lua
+++ b/animate.lua
@@ -6,24 +6,39 @@
 -- mcgarvey@eng.utah.edu
 --
 
--- This program that draws a scene multiple times from different camera angles
--- and positions.  The rasters are saved in the `frames' directory, and if
--- ffmpeg is installed, they will also be combined into a video file.  The
--- camera will make a full rotation along the X and Z axes, around a specified
--- point (center), all the while looking at some other point (look).
--- This must be called from the same directory where the rasterize program is.
-
-local size      = {w = 640, h = 480}    -- width and height of the viewport
-local frames    = 512                   -- number of animation frames
-
-local look      = {x = 2, y = 1, z = 2} -- the point to look at
-local center    = {x = 0, y = 1, z = 0} -- center of rotation
-local distance  = 4                     -- the distance from the center
-local start     = math.pi               -- where is the first frame
+-- This program automates the process of creating simple fly-by animations.
+-- The rasters are saved in the `frames' directory, and if ffmpeg is
+-- installed, the frames will also be combined into a video file.  This script
+-- must be called from the same directory where the rasterize program is.
+
+-- Set the width and height of the viewport.
+local size = {w = 640, h = 480}
+
+-- Set the number of frames to be rendered for the animation.
+local frames = 512
+
+-- Define the code to calculate where the camera is, in world coordinates.
+local eye = function(frame)
+    -- just rotate around the center of the scene on the XZ plane
+    local center    = {x = 0, y = 1, z = 0}
+    local distance  = 4
+    local start     = math.pi
+    local t = start + 2 * math.pi * frame / frames
+    local v = {
+        x = math.cos(t),
+        y = 0,
+        z = math.sin(t),
+    }
+    return vec_add(vec_scale(v, distance), center)
+end
 
-local jobs      = 6                     -- number of concurrent renderings
+-- Define the code to calculate where the focal point of the scene is.
+local look = function(frame)
+    return {x = 2, y = 1, z = 2}    -- keep focused on the buddha
+end
 
--- the actual objects of the scene that will be drawn:
+-- Define the actual objects of the scene that will be rendered, in the
+-- extended u3d format.
 local scene = [[
 L 0 1000000 0 1 1 1 1 1 1
 L 0 0 1000000 1 1 1 1 1 1
@@ -49,6 +64,15 @@ t 0 -1 0
 s 0.6 0.6 0.6
 ]]
 
+-- Set the number of concurrent renderings (for multi-core machines).
+local jobs = 6
+
+
+-- end of configuration
+---------------------------------------------------------------------------
+
+local fmt   = string.format
+local write = function(...) io.write(fmt(...)) end
 
 function vec_add(a, b)
     return {x = a.x + b.x, y = a.y + b.y, z = a.z + b.z}
@@ -58,14 +82,13 @@ function vec_scale(v, s)
     return {x = v.x * s, y = v.y * s, z = v.z * s}
 end
 
-local fmt   = string.format
-local write = function(...) io.write(fmt(...)) end
-
-function render(i, v)
-    while i and v do
+function render(i)
+    while i do
         local filename  = fmt("frames/anim%04d.bmp", i)
         local command   = fmt("./rasterize -o %s >/dev/null", filename)
         local out = io.popen(command, "w")
+        local e = eye(i)
+        local l = look(i)
         write("\27[80D\27[2Kframe\t %4d / %d", i + 1, frames)
         out:write(fmt([[
 U3
@@ -76,13 +99,12 @@ U3
 1.57 %f 0.1 1000
 %s
 X
-]], size.w, size.h, v.x, v.y, v.z, look.x, look.y, look.z, size.w/size.h, scene))
-        i, v = coroutine.yield()
+]], size.w, size.h, e.x, e.y, e.z, l.x, l.y, l.z, size.w/size.h, scene))
+        i = coroutine.yield()
         out:close()
     end
 end
 
-
 print("Animating scene...")
 
 local threads = {}
@@ -92,14 +114,7 @@ end
 
 os.execute("rm -rf frames && mkdir frames >/dev/null 2>&1")
 for i = 0,(frames-1) do
-    local t = start + 2 * math.pi * i / frames
-    local v = {
-        x = math.cos(t),
-        y = 0,
-        z = math.sin(t),
-    }
-    v = vec_add(vec_scale(v, distance), center)
-    threads[1 + (i % jobs)](i, v)
+    threads[1 + (i % jobs)](i)
 end
 for _,thread in ipairs(threads) do thread(null) end
 print()
-- 
2.45.2