Attributes and Behaviors of Primitives - Essentials of Interactive Computer Graphics - page 164

.
A1:

void UWB _ Primitive::Draw(eLevelOfDetail lod, UWB _ DrawHelper& draw _ helper) const {
.
SetupDrawAttributes(draw _ helper);
DrawPrimitive(lod, draw _ helper);
.

void UWB _ Primitive::SetVelocity( vec3 velocity){ m _ velocity = velocity; }
bool UWB _ Primitive::IsStationary() const {
return ( UWB _ ZERO _ TOLERANCE >= fabs(m _ velocity.x) && ...
.

D1:

void UWB _ Primitive::SetupDrawAttributes(UWB _ DrawHelper& draw _ helper) const {
draw _ helper.ResetAttributes();
draw _ helper.SetColor1(m _ FlatColor);
.

F1:

Listing 7.9. (cont.)

We made a design decision where for the ease of programming, we have
defined the superset of all primitive attributes in the base class. For ex-
ample, the m _ PointSize attribute is defined. However, this attribute is
only meaningful for a point primitive, and all non-point subclasses will ig-
nore this attribute. In this way, our implementation is not optimized for
memory efficiency. However, because all attributes and their correspond-
ing set/get functions are defined in the Primitive base class, all subclass
objects can have uniform public interface functions. As we will see in
the CModel implementation, this uniform interface simplifies programming
with the Primitive hierarchy.
The m _ Velocity is an unusual attribute to be defined in a primitive hierar-
chy. This is because all other primitive attributes affect the appearance of
the attribute, whereas the velocity affects the physical behavior of the prim-
itive object. Once again, we define this physical attribute in the base class
for the uniformity of public methods and the ease of programming with the
hierarchy.

• F: The subclass-responsible functions for supporting drawing. As dis-
cussed, the Draw() function specifies the drawing procedure in the form
of pure virtual functions, and the subclass must override these functions