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James Gregory 2013-12-30 18:34:31 +11:00
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51-06.md
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@ -91,7 +91,7 @@
In the previous chapter, I added 0.5 and truncated in order to round
values from floating-point to integer format. Here, in Listing 51.2,
I’ve switched to adding 0.5 and using the **floor()** function. For
I've switched to adding 0.5 and using the **floor()** function. For
positive values, the two approaches are equivalent; for negative values,
only the **floor()** approach works properly.
@ -105,7 +105,7 @@ only in their original, untransformed state, but in three other forms as
well: transformed to view space, transformed and projected to screen
space, and converted to screen coordinates. Earlier, we saw that it can
be convenient to store the screen coordinates within the object, so that
if the object hasn’t moved with respect to the viewer, it can be redrawn
if the object hasn't moved with respect to the viewer, it can be redrawn
without the need for recalculation, but why bother storing the view and
screen space forms of the vertices as well?
@ -115,15 +115,15 @@ by the viewer, you must first know how they look to the viewer,
accounting for perspective; screen space provides that information. (So
do the final screen coordinates, but with less accuracy, and without any
Z information.) The view space vertices are useful for collision and
proximity detection; screen space can’t be used here, because objects
proximity detection; screen space can't be used here, because objects
are distorted by the perspective projection into screen space. World
space would serve as well as view space for collision detection, but
because it’s possible to transform directly from object space to view
space with a single matrix, it’s often preferable to skip over world
space. It’s not mandatory that vertices be stored for all these
because it's possible to transform directly from object space to view
space with a single matrix, it's often preferable to skip over world
space. It's not mandatory that vertices be stored for all these
different spaces, but the coordinates in all those spaces have to be
calculated as intermediate steps anyway, so we might as well keep them
around for those occasions when they’re needed.
around for those occasions when they're needed.
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