Step51: Intro Rtatdvg (unreleased)

Polygons

I’ve never been interested into 3D (at that time), but I wanted to try vectorial drawing. I choosed to create a simple system based on polar coordinates. In this system each point is defined by an angle and a distance. All arts are geometric and based on circular shape.

The drawing is done using the blitter with line trace and surface fill.

Here is a video of a work in progress intro.

I’ve composed the music. I’ve created the samples using my synthetiser Korg M1.

The result is quite average so nothing have been released using this code.

With polygons drawing, the input data are very small. For example to draw full screen W letter, here are the data:

ObjetW:
dc.w 135,145
dc.w 110,20
dc.w 90,40
dc.w 70,20
dc.w 45,145
dc.w 10,101
dc.w 280,100
dc.w 270,50
dc.w 260,100
dc.w 170,101
dc.w $ffff

Code

The code can be read here.

The source code mentionned that I wanted to add clipping function. But this was not done. Doing clipping is a very interesting topic. I'll surely try it in my last amiga production Mel O Dee's 3 (in 2024/2025).

Filling with blitter is very easy. The line need to be traced so there is only one pixel each line (the fille routine wait for one pixel start, and one pixel end).

Fill:
Bsr wait_blitter
Move.l Current_Plan,A2 ; Screen to fill
Add.l #[40*256]-2,A2 ; -2 point to end of screen
Move.l A2,$DFF054
Move.l A2,$DFF050
Move.l #-1,$Dff044
Move.w #$09f0,$Dff040
Move.w #$0012,$Dff042
Clr.w $Dff066 ; Modulo 0
Clr.w $Dff064 ; Modulo 0
Move.w #266*64+20,$Dff058 ; Writing size make the blitter start its work
Rts

If you want to know more about line trace with blitter, I can recommand this page.

Great demo of that time

State of the Art by Spaceballs (1992)

A reference in Amiga best demos. This one use a lot polygon drawings. Everything fit on one floppy disk.

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