time: review feedback

Author: hollasch

books/RayTracingTheNextWeek.html

@@ -46,15 +46,16 @@
 
 In a real camera, the shutter remains open for a short time interval, during which the camera and
 objects in the world may move. To accurately reproduce such a camera shot, we seek an average of
-all the instant images that the camera perceives while its shutter is open to the world.
+what the camera senses while its shutter is open to the world.
 
 
 Introduction of SpaceTime Ray Tracing
 --------------------------------------
-We can get a random estimate of a single photon by sending a single ray at some random instant in
-time when the shutter is open. As long as the objects are where they should be at that instant, we
-can get an accurate measure of the light for that ray at that same instant. This is yet another
-example of how random (Monte Carlo) ray tracing ends up being quite simple. Brute force wins again!
+We can get a random estimate of a single (simplified) photon by sending a single ray at some random
+instant in time while the shutter is open. As long as we can determine where the objects are
+supposed to be at that instant, we can get an accurate measure of the light for that ray at that
+same instant. This is yet another example of how random (Monte Carlo) ray tracing ends up being
+quite simple. Brute force wins again!
 
 <div class='together'>
 Since the “engine” of the ray tracer can just make sure the objects are where they need to be for
@@ -95,27 +96,28 @@
 
 Managing Time
 --------------
-Before continuing, let's think about time, and how we might manage it across one or more renders.
-There are two aspects of shutter timing to think about: the time from one shutter opening to the
-next shutter opening, and how long the shutter stays open for each frame. Standard movie film used
-to be shot at 24 frames per second. Modern digital films can be 30 or even 60 frames per second.
-Each frame can have its own shutter speed, which need not be -- and typically isn't -- the maximum
-duration of the entire shutter period. You could have the shutter open for 1/1000th of a second per
-frame, or 1/60th of a second. It may surprise you to learn that for most film motion pictures, the
-screen is actually dark more than it is lit up with the movie frames!
+Before continuing, let's think about time, and how we might manage it across one or more successive
+renders. There are two aspects of shutter timing to think about: the time from one shutter opening
+to the next shutter opening, and how long the shutter stays open for each frame. Standard movie film
+used to be shot at 24 frames per second. Modern digital movies can be 24, 30, 48, 60, 120 or however
+many frames per second director wants.
+
+Each frame can have its own shutter speed. This shutter speed need not be -- and typically isn't --
+the maximum duration of the entire frame. You could have the shutter open for 1/1000th of a second
+every frame, or 1/60th of a second.
 
 If you wanted to render a sequence of images, you would need to set up the camera with the
 appropriate shutter timings: frame-to-frame period, shutter/render duration, and the total number of
-frames (or total shot time). If the camera is moving and the world is static, you're good to go.
-However, if anything in the world is moving, you would need to add a method to `hittable` to
-broadcast the current shot timing to every object in the world. This method would then provide a way
-for all animate objects to set up their motion during that frame.
+frames (total shot time). If the camera is moving and the world is static, you're good to go.
+However, if anything in the world is moving, you would need to add a method to `hittable` so that
+every object could be made aware of the current frame's time period. This method would provide a way
+for all animated objects to set up their motion during that frame.
 
 This is fairly straight-forward, and definitely a fun avenue for you to experiment with if you wish.
-However, for our purposes right now, we're going to proceed with a drastically simplified model. We
-will be render only a single frame, assuming a start at time = 0 and ending at time = 1. Our first
-task is to modify the camera to launch rays with random times in $[0,1]$, and our second task will
-be the creation of an animate sphere class.
+However, for our purposes right now, we're going to proceed with a much simpler model. We will
+render only a single frame, implicitly assuming a start at time = 0 and ending at time = 1. Our
+first task is to modify the camera to launch rays with random times in $[0,1]$, and our second task
+will be the creation of an animated sphere class.
 
 
 Updating the Camera to Simulate Motion Blur
@@ -155,8 +157,8 @@
 Adding Moving Spheres
 ----------------------
 Now to create a moving object. I’ll create a sphere class that has its center move linearly from
-`center0` at time 0 to `center1` at time 1. (It continues on outside that time interval, so it
-really can be sampled at any time.)
+`center0` at time=0 to `center1` at time=1. (It continues on indefinitely outside that time
+interval, so it really can be sampled at any time.)
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     #ifndef MOVING_SPHERE_H