Hands On DarkBASIC Pro - Digital Skills

LISTING-31.12
A Problem with Cones
and Cylinders
FIG-31.52
Hidden Surfaces on
Cones and Cylinders
Storage Methods
REM *** Set screen mode ***
SET DISPLAY MODE 1280,1024,32
REM *** Make and position cone and cylinder ***
MAKE OBJECT CONE 1, 5
POSITION OBJECT 1,-6,-5,0
XROTATE OBJECT 1, 45
MAKE OBJECT CYLINDER 2,5
POSITION OBJECT 2, 6,-5,0
REM *** End program ***
WAIT KEY
END
Activity 31.26
Type in and test the program in LISTING-31.12 (object3D15.dbpro).
What problem occurs with both shapes?
The inside surfaces of both shapes have not been drawn (see FIG-31.52).
But we can solve this problem by switching off culling, so that the hidden polygons
are drawn.
Activity 31.27
The inside surfaces
of both shapes are not
drawn
Modify your previous program so that culling is switched off for both the cone
and the cylinder.
When a 3D object is shown on screen, the coordinates of its vertices are stored in
memory in an area known as a vertex buffer. Normally, each object will have its
own vertex buffer. However, some video cards allow different objects to share
vertex buffers, other video cards don't. As a default, 3D objects in DARKBASIC
Pro do not share vertex buffers - this ensures compatibility with the maximum
number of video cards. However, it is possible to force vertex buffer sharing and,
if your video card can handle this, improve the performance of your program.
The SET GLOBAL OBJECT CREATION Statement
To force vertex buffer sharing, we use the SET GLOBAL OBJECT CREATION
statement which has the format shown in FIG-31.53.
DarkBASIC Pro: 3D Primitives 785