This program uses perspective to simulate three dimensions while only using 2D commands. WARNING: THIS IS NOT ACCURATE 3D, IT IS MERELY IMITATING PERSPECTIVE. CONTROLS LEFT/RIGHT -

                                    ` This code was downloaded from The Game Creators
                                    ` It is reproduced here with full permission
                                    ` http://www.thegamecreators.com
                                    
                                    remstart
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THREE DIMENSIONS IN A 2D WORLD
--------------------------------
The main obstacle for creating a 3D world on a 2D screen is obvious; the screen is 2D! There is no depth.
So how do we create a third dimension? We need to add perspective. Perspective can be at any angle but for this
example I am using the most simple, 1:1 (X:Y). To understand what this means, think of the classic 2D drawing
of a cube. The cube is made up of 2 offset squares and four diagonal connecting lines.
{image}
Because this is a cube, we know that all lines MUST be equal in length, but in the drawing the connecting lines
are half the length of the others. This is because of perspective (1:1), half of the cube's depth was added
to the X axis, and the other half added to the Y axis, resulting in a perfectly diagonal line.

Now let's take this on another step. Lets use our cube as the boundaries to our 3D world, and lets now try and
imagine how another 3D object would be displayed in this world.
Firstly, it would be positioned according to its X and Y position, and then these would both be increased by
half its Z position. So by moving the object towards and away from us, its really travelling along a diagonal
line, left/down and right/up.
remend

`--------------------------------
` SETUP
`--------------------------------
`world Boundaries
Wx1 = 15 : Wx2 = 320
Wy1 = 200 : Wy2 = 30
Wz1 = 0 : Wz2 = 160

`Cube position
Cx = 0+Wx1
Cy = 0+Wy1
Cz = 0+Wz1

`Cube volume
Cvx = 10
Cvy = 10
Cvz = 5 : `half actual size for simplicity (no need to divide by 2)

`--------------------------------
` MAIN LOOP
`--------------------------------
sync on

DO
cls
gosub Axis
gosub Cube
gosub control
gosub bind_cube

sync
LOOP

`--------------------------------
` GOSUBS
`--------------------------------
axis:
`x-line
ink rgb(255,0,0),0
line 15,200,320,200
`y-line
ink rgb(0,255,0),0
line 15,200,15,20
`z-line (X+Y/2)
ink rgb(0,0,255),0
line 15,200,160,55
RETURN

`------

cube:
ink rgb(255,255,255),0
`* FG Square
`Fore Bottom Horizontal
line (Cx+Cz),(Cy-Cz), (Cx+Cz)+Cvx,(Cy-Cz)
`Fore Top Horizontal
line (Cx+Cz),(Cy-Cz)-Cvy, (Cx+Cz)+Cvx,(Cy-Cz)-Cvy
`Fore Left Vert
line (Cx+Cz),(Cy-Cz), (Cx+Cz),(Cy-Cz)-Cvy
`Fore Right Vert
line (Cx+Cz)+Cvx,(Cy-Cz), (Cx+Cz)+Cvx,(Cy-Cz)-Cvy

`* BG Square
`Fore Bottom Horizontal
line (Cx+Cz)+Cvz,(Cy-Cz)-Cvz, (Cx+Cz)+Cvx+Cvz,(Cy-Cz)-Cvz
`Fore Top Horizontal
line (Cx+Cz)+Cvz,(Cy-Cz)-Cvy-Cvz, (Cx+Cz)+Cvx+Cvz,(Cy-Cz)-Cvy-Cvz
`Fore Left Vert
line (Cx+Cz)+Cvz,(Cy-Cz)-Cvz, (Cx+Cz)+Cvz,(Cy-Cz)-Cvy-Cvz
`Fore Right Vert
line (Cx+Cz)+Cvx+Cvz,(Cy-Cz)-Cvz, (Cx+Cz)+Cvx+Cvz,(Cy-Cz)-Cvy-Cvz

`* Connectors
`LB
line (Cx+Cz),(Cy-Cz), (Cx+Cz)+Cvz,(Cy-Cz)-Cvz
`RB
line (Cx+Cz)+Cvx,(Cy-Cz), (Cx+Cz)+Cvx+Cvz,(Cy-Cz)-Cvz
`LT
line (Cx+Cz),(Cy-Cz)-Cvy, (Cx+Cz)+Cvz,(Cy-Cz)-Cvy-Cvz
`RT
line (Cx+Cz)+Cvx,(Cy-Cz)-Cvy, (Cx+Cz)+Cvx+Cvz,(Cy-Cz)-Cvy-Cvz

`* Y height line (ground up)
ink rgb(0,255,0),0
line (Cx+Cz)+(Cvx/1.6),(Wy1-Cz)-(Cvy/1.6), (Cx+Cz)+(Cvx/1.6),(Cy-Cz)-(Cvy/1.6)
RETURN

`------

control:
if rightkey() = 1 then inc Cx,2
if leftkey() = 1 then dec Cx,2
if upkey() = 1 then dec Cy,2
if downkey() = 1 then inc Cy,2
if shiftkey() = 1 then inc Cz,1
if controlkey() = 1 then dec Cz,1
RETURN

`------

bind_cube:
if Cx < Wx1 then Cx = Wx1
if Cx > Wx2 then Cx = Wx2
if Cy > Wy1 then Cy = Wy1
if Cy < Wy2 then Cy = Wy2
if Cz < Wz1 then Cz = Wz1
if Cz > Wz2 then Cz = Wz2
RETURN