=== Logo Swing ===

Many classic C64 intros or demos in the demo scene in the 1980's and early 1990's, onwards used to use an effect known as the swinging logo. Many demo coders today would be pretty familiar with swinging logos in their intros. 

So then, how does this work? Well, it is really hard for me to explain it properly but I can vaguely know what happens. Well, if you remember the smooth scroll method that triggers $D016 then you should hopefully be familiar with that. Actually the logo swing sort of works a similar kind of way, except that instead of reading a scroll text, you're actually reading the logo data instead. This data is called the MATRIX. 

The source for the logo swing will be coming up shortly, but first a logo will need to be drawn. A logo can only be 3 colours. So I recommend that you download a painting program, and then use [[http://noname.c64.org/csdb/release/?id=36681|Charwandler]] by Johnnie Walker to convert your hires picture into logo format. Logo format is of course 2 separate files: Char + Screen.

Secondly before you can actually swing your logo, it is recommended that you use the [[http://noname.c64.org/csdb/release/?id=47808|SHAKE IT]] logo swing converter utility by Paramount. This program will convert your original logo matrix into a swinging logo matrix. It should hopefully do the trick :) A very good program.

Now then, you'll want to do some logo swinging, so below is the ACME source. What this does is calculate the value of the sinus (movement) of the logo and also the position of the matrix, so that you can see the logo swinging forwards and backwards.

Source:
<code>
;Logo swing routine

swingpointer = $02
swingstore = $03
                       !to "logoswing.prg"
                       * = $0810
                       sei
                       jsr $ff81 ;Init screen
                       lda #$18
                       sta $d018 ;Logo font at $2000
                       lda #$00
                       sta $d020
                       sta $d021

;Fill the whole screen colours to cyan multicolour as we are using
;the most popular blue scheme. 

                       ldx #$00
shadeitcyan            lda #$0b
                       sta $d800,x
                       sta $d900,x
                       sta $da00,x
                       sta $dae8,x
                       inx
                       bne shadeitcyan
                       lda #$06
                       ldx #$0e
                       sta $d022
                       stx $d023

;Now for the IRQ init routine


                       lda #<irq
                       ldx #>irq
                       sta $0314
                       stx $0315
		       lda #$31
                       ldx #$7f
                       sta $d012
                       stx $dc0d
                       lda #$1b
                       sta $d011
                       lda #$01
                       sta $d01a
                       cli
loop                   lda #$00
                       sta $06
synchronize            cmp $06
                       beq synchronize
                       jsr logoswing
                       jmp loop

;Main IRQ routine for the logo swing

irq                    inc $d019
                       lda #$32
                       sta $d012
                       lda swingstore
                       sta $d016
                       jmp $ea7e
swinglogo	lda #$ff
			sec
			ldx swingpointer
			sbc $3800,x ;Value of sinus (Which I made in Bonzai's sinus calculator)
			lsr
			lsr
			lsr
			tax
			ldy #$00
screen		        lda $3000+0 ;Matrix to read from
			sta $0400,y ;Screen loc. to write to
			lda $3000+64,x
			sta $0400+40,y
			lda $3000+64*2,x
			sta $0400+80,y
			lda $3000+64*3,x
			sta $0400+120,y
			lda $3000+64*4,x
			sta $0400+160,y
			lda $3000+64*5,x
			sta $0400+200,y
			lda $3000+64*6,x
			sta $0400+240,y
			inx           ;Read X 256 times
			iny
			cpy #$27      ;Read y 39 times
			bne screen
			ldx swingpointer 
			lda $3800,x
			and #$07
			ora #$d0 ;Kill this if your logo is not multicolour
			sta swingstore ;The value to put into $D016
			inc swingpointer ;Add 1 to the swing pointer
			rts

;Binaries for the source.

                        * = $2000-2 
                        !binary "logochar.prg"
                        * = $3000-2
                        !binary "logomatrix.prg"
                        * = $3800-2
                        !binary "sinusdata.prg"
</code>