Another day, another cat drawing. This time our more blocky version of a feline fellow creature. Sketch in ibisPaint X and final drawing in Commodore 64 multicolor bitmap (160 x 200 resolution, 16 colors). If I could, I’d knit him a cozy sweater.
🐱🎨👨‍💻🕹️👾

It’s always good to have a firm mental picture of one’s (artistic) process, as to not get bogged down by the details. I’ve updated the C64 multicolor illustration I did yesterday, and separated it into 4 “colors”:

• background color 0 (white)
• ditto 1 (black)
• ditto 2 (red)
• other colors

I had a few lock up with my iPad lately. Now it’s even in recovery mode, trying to restore from iCloud…

Update: I’m back on the iPad. Pfew!

I think I’m starting to grasp how to draw in C64 multicolor. You get three colors that can be used anywhere, and per 8 by 8 pixels block you get to pick another color out of 16 possible colors. Careful placement of the pixels is key. If you do it right, you can have a very colorful image
🎨👨‍💻🕹️👾

Just for kicks, I tried to color a random doodle I made. I had to redraw some of it to be able to work around the limitations of multicolor bitmap graphics on the Commodore 64. Other than that, and that it takes a lot of time, it went well.

Another day, another cat drawing for the old Commodore 64
😻 🎨 👨‍💻 🕹️ 👾

I reworked an older self-portrait that I made last year as a pixel art drawing, and turned it into an image on the Commodore 64. I like that the limited color palette doesn’t seem to limit me as much as it used to. It takes some effort (well, a lot of effort), but I think it was worth the time.
🎨 👨‍💻 🕹️ 👾

Here are some of the steps I took to create a multicolor pixel art drawing of a cat.

drawn in ibisPaint X in 4 colors

traced and redrawn in Pixaki

made into C64 runnable multicolor art with MultiPaint, loaded into VICE C64

It’s a process, taking many hours to complete. I think I’m improving.

👨‍💻🎨

Making room for two text screens, so I can use them for buffering is great, but running it from C64 Basic is one ugly hack, and slow too. But I’ve done it, which is great, since I learned a lot from it, and that was the whole point here. The code I keep, in case I need (some of) it 👨‍💻

Flipped 📷

I fired up my art app and sculpted on a canvas the size of a retro-computer’s text character (8 pixel wide and 8 pixels high). I had to struggle, because the app wanted it to look nicer than it really was.

I suppose you can already guess what it represents. You can do a lot in 64 bits of data 👨‍💻🎨

Okay, I have a Basic loader with M/L code that enables a screen buffer and has a handy relocatable M/L routine at $C000 that copies 1024 bytes. Bits 4 - 7 of $D018 control which part of memory is used to display the screen. Now I have all I need for moving a block of characters in C64 Basic, right? 👨‍💻

In my previous post in which I moved a box across the screen with a Basic program, I wanted to use a screen buffer. The default screen location starts in memory at $0400 (1024 decimal), and we can move the screen in units of 1024 bytes. The next location would be $0800 (2048 decimal), which is where Basic text lives. Luckily we can move the start of Basic up with a poke at location 44, but we also have to move the bytes of the Basic text to the new location, or you’d get a jibberish Basic text. The most obvious location is $0c01 (3097 decimal), and it makes sense to do this outside of Basic, with the raw power of the 6510 CPU.

The machine language (M/L) program enablebuffer does just that. Here’s the source code listing. It has some Basic code to run the M/L code and relocate the start of Basic text. The M/L code is a bit more complicated than it needed to be, but I like some headroom in case I want to include more Basic text in front of the M/L code or put some M/L code in a convenient location, so we can sys or usr() to it. The code should be able to copy Basic text in front of the M/L code, no matter how big it would grow.

; enablebuffer.asm
;
; Move the start of basic from $0801 to $0c01
;
; Now both 1024 - 2023 and 2048 - 3047
;      can be used as screen memory.
; This makes it possible to use a screen buffer
;      in Basic.
 
                PROCESSOR 6502

                ORG $0801
            
; Basic text in front of ML code
; 10 SYSXXXX:POKE44,12:CLR

BASIC1:
    HEX 14 08 0a 00 9e 

    .dc sys_address             ; replaces the "XXXX"

BASIC2:
    HEX 3a 97 34 34 2c 31 32 3a 9c 00 00 00

sys_address:    eqm (start_ML)d

; start of ML code

start_ML:

vect1:          eqm $02
vect2:          eqm $04
BASstart:       eqm $2B

                LDA BASstart+1
                CMP #$08        ; is start of basic at $0801 ?
                BNE exit        ; no, then exit

; set up copy process
; copy $0801 to $0C01 until the end of file
; copy start at the end towards the beginning


                CLC
                LDA #exit
                STA vect1+1
                ADC #$04        ; move 1024 positions higher in memory
                STA vect2+1
                LDY #$00

loop1:          LDA vect1+1     ; copy in blocks of 256 bytes
                CMP #$08        ; less than 256 bytes to copy?
                BEQ loop2       ; yes, then loop2 instead
loop1a:         LDA (vect1),Y   ; fast copy 256 bytes
                STA (vect2),Y
                DEY
                BNE loop1a
                DEC vect1       ; next 256 byte
                DEC vect2
                BNE loop1
                DEC vect1+1
                DEC vect2+1
                BNE loop1

loop2:          LDA (vect1),Y   ; copy remainder of bytes
                STA (vect2),Y   ; between 1 and 255
                DEC vect1
                DEC vect2
                BNE loop2b
                DEC vect1+1
                DEC vect2+1
loop2b:         LDA vect1+1
                CMP #$07
                BNE loop2

exit:           RTS

We can load the program as an ordinary Basic program and then run it.

After that we can new the Basic program and start writing a new Basic program, at location $0C01 instead of the default $0801! Of course, the M/L code will be overwritten by that new Basic program, but that’s okay, since we no longer need it at that point.

With all the blogging I do daily, I wanted to automate correct capitalization. I reworked an shortcut that no longer worked to a working state. Select text, share, pick one, paste.

• all lower case
• UPPER CASE
• Title Case in Case You Want It
• Capitalize A Okay
• Sentence. After each. Sentence.

I was wondering how to move a collection of characters (e.g. a box) across a Commodore 64 text screen. It’s rather easy to do this destructively. In Basic, I wrote something that horizontally moves a 3-by-3 character rectangle constructed out of PETSCII characters.

10 rem ***
11 rem *** setup
12 rem ***
20 restore:read w,h:for i=0 to w*h-1
30 read a(i):next i
40 data 3,3
50 data 112,64,110,93,32,93,109,64,125
60 te=200
100 rem ***
101 rem *** main loop
102 rem ***
110 os=0
120 for p=1024+12*40top+40-w
130 gosub 200:gosub 300:next p
140 os=w-1
150 for p=1024+13*40-w to p-39+w step-1
160 gosub 200:gosub 300:next p
170 goto 100
199 end
200 rem ***
201 rem *** draw a box
202 rem ***
210 for x=0 to w-1:for y=0 to h-1
220 poke p+y*40+x,a(y*w+x)
230 nexty:nextx:fort=0tote:nextt:return
300 rem ***
301 rem *** clear column
302 rem ***
310 for y=0toh-1:poke p+y*40+os,32:next
320 return

The program has to do some clean-up after it has drawn a box with the subroutine draw a box. It fills the box’s trailing text column with space characters (screen code 32). For instance, if the box moves to the right and the box has been drawn in its current position, the left-most text column of that box has to be “cleared” (filled with spaces). Otherwise it will leave behind box characters when the next position of the box is drawn—one position to the right. The main loop uses the variable os (offset) to determine which text column should be filled with spaces, using the same subroutine clear column when moving the text box to the left or to the right.

It’s all very limited in what this program can do. It can move the box either one character position to the right or the same to the left, nothing more.

For a more sophisticated draw a box subroutine, it has to know where it was before:

• restore the original content of the previous position (if any)
• read the current content where the box will appear and store it for later
• draw the box onto its position on the text screen

We can do this in Basic as well, even though it’s rather slow and has clear visual artifacts. Here’s the code for the same 3 by 3 text box, now jumping to arbitrary positions on the screen, while keeping the screen intact.

10 rem ***
11 rem *** setup
12 rem ***
20 restore:read w,h:for i=0 to w*h-1
30 read a(i):next i
40 data 3,3
50 data 112,64,110,93,32,93,109,64,125
60 te=200
70 first = (1 = 1)
100 rem ***
101 rem *** main loop
102 rem ***
110 x=int(rnd(ti)*(40-w))
120 y=int(rnd(ti)*(25-h))
130 gosub 200
140 goto 100
199 end
200 rem ***
201 rem *** draw a box
202 rem ***
210 rem *** restore any orig'l content
211 rem ***
220 if first then first=(1=0):goto 300
230 for xx =0 to w-1:for yy=0 to h-1
240 poke p+yy*40+xx,a1(yy*w+xx)
250 nextyy:nextxx
300 rem ***
301 rem *** read current text content
302 rem ***
310 p=1024+40*y+x
320 for xx=0 to w-1:for yy=0 to h-1
330 a1(xx+yy*w)=peek(p+xx+yy*40):
340 nextyy:nextxx
400 rem ***
401 rem *** put box on screen
402 rem ***
410 for xx=0 to w-1:for yy=0 to h-1
420 poke p+yy*40+xx,a(yy*w+xx)
440 nextyy:nextxx
450 for t=0 to te:next
460 return

The long wait loop (which makes the program perform so slow) is so that you can spot the random 3-by-3 box, while also making the artifacts less noticeable. You can see the box long enough, so it disappearing from screen will feel less jarring. A better solution than waiting a while would be to use a screen buffer to do the drawing and switch screen buffers when all the drawing is done for the new position of the box.

I guess that would require some machine language I have yet to write.

I wondered if a sprite rendered as a text character would make sense. It would have to move to one of the 1000 positions on a text screen of 25 lines and 40 columns in a C64. The character is 2 by 2 text characters, has 3 walking poses, and two extra text characters for the SFX. It could work 👨‍💻

I found this video game poster via an image search, which clearly isn’t from a C64 (size 640 x 400 pixels, different 16 colors than C64). I thought about recreating it in C64 multicolor for self-education. The first step in my analysis was recoloring it into the Colodore color palette, an idealized version of the C64 color palette(s). It seems to be drawn for the Amiga. It has 3 shades of red and of green; the C64 has only 2 of those. Plus, it has a flesh color, which the C64 sorely lacks.

I found an interview with the mentioned Peter Johnson on Codetapper’s Amiga Site. And it appears he rewrote the C64 version for the Amiga. No mention of who drew the poster. Peter did draw the game art, I assume. Alas, there’s no date stamp on the article, but judging from the copyright notice it’s probably from 2020, but it could be as early as 2016.

Now will I recreate the poster? Probably not, but it’s a good reference to have, to see what good illustrators were able to whip up in a short amount of time. Even back then, the games industry was brutal. Games did last as long as they were popular. There was always something newer and better to draw the attention of gamers. Time was a-wastin', always.

🎮

Luckily, the SPEEDLINK SL-650212 BKRD Competition EXTRA Joystick I bought off Dutch Amazon works with VICE C64 on my Raspberry Pi-400 computer. I read a review somewhere that it did, but reviews can be wrong, high ratings bought by the manufacturer. So I took a chance and it paid off 🎮

I would prefer owning a Mac, but I simply can’t rationalize the “Apple tax.” I used to be Mac or Die. A computer is more like a way to access the Internet nowadays, anyway 👨‍💻👾

It’s all very technical, this Commodore 64 multicolor mode. I made a special 2x1 grid in my iPad pixel editor to help me, but still I need to check in an actual multicolor editor if I made a mistake. Anyway, I’m improving as a C64 pixel artist, and that’s very cool 👨‍💻