Combining Transformation Operators - Essentials of Interactive Computer Graphics - page 234

compute the M 1 operator, and at label E, the concatenated matrix at the top of the
stack is loaded into the WORLD processor for drawing of rectangle R 1 .The Pop()
operation at label C2 eliminates the M 1 operator at the top of the matrix stack and
restores the T

operator that was saved by the Push() operation at label C1.
The code at labels F and G computes M 2 and draws R 2 in a similar manner as that
for M 1 and R 1 .
This tutorial demonstrates using the matrix stack for saving/restoring shared
transform operators, and that we can load/override the matrix processor (e.g., the
WORLD matrix processor) to change the transformations of different primitives.

( t x , t y )

UWBGL_D3D_Lib9

Change summary. See p. 521
for a summary of changes to
the library.

This library extends from Lib8 by extending the D3D _ DrawHelper class to sup-
port the matrix stack and by designing the new XformInfo class to abstract the
programming of transformations.

The D3D _ DrawHelpler class. As shown in Listing 9.8, the updated implemen-
tation of UWBD3D _ DrawHelper class has an instance of the D3D matrix stack (B)
and implements the transformation functions of the DrawHelper class (A). List-
ing 9.9 shows the implementation of the transformation functions. First, notice
that for all cases, before the functions return, we load the top of the matrix stack to

class UWBD3D _ DrawHelper : public UWB _ DrawHelper {

Source file.
uwbgl _ D3DDrawHelper3.h
file in the D3D Files/
DrawHelper subfolder of
the UWBGL _ D3D _ Lib9 project.

.
A: transformation functions defined by UWB_DrawHelper (the parent class)
bool InitializeModelTransform();
bool AccumulateModelTransform( vec3 translation, vec3 scale,
float rotation _ radians, vec3 pivot);

bool PushModelTransform();
bool PopModelTransform();
private :
.
B: ID3DXMatrixStack * m _ pMatrixStack;

};

Listing 9.8. The UWBD3D _ DrawHelper class ( Lib9 ).