I wanted to achieve this effect with fill patterns for a recent project I started so I figured I'd share it here incase anyone else is interested in using it.

The local fill pattern function is shifting each row/column in the fill pattern by given x and y amount. It's using binary arithmetics and a cache of shift masks.

Here's the original code for version 1.0, takes 126 tokens:

--turns a screen-space fill pattern, into an object-space fill pattern by wrapping the patterns row and column by the given x and y amount.
function get_local_fill_pattern(x,y,fill_pattern)
    local add_bits=band(fill_pattern,0x0000.FFFF)
    fill_pattern=band(fill_pattern,0xFFFF)
    y=flr(y)%4
    if(y~=0)then
        local r_masks={0xFFF0,0xFF00,0xF000}
        local l_masks={0x000F,0x00FF,0x0FFF}
        fill_pattern=bxor(lshr(band(fill_pattern,r_masks[y]),y*4),shl(band(fill_pattern,l_masks[y]),(4-y)*4))
    end

    x=flr(x)%4
    if(x~=0)then
        local r_masks={0xEEEE,0xCCCC,0x8888}
        local l_masks={0x1111,0x3333,0x7777}
        fill_pattern=bxor(lshr(band(fill_pattern,r_masks[x]),x),shl(band(fill_pattern,l_masks[x]),4-x))
    end

    return bxor(fill_pattern,add_bits)
end

EDIT:
With great contributions and improvements by Felice here's a both faster, smaller and more API consistent version 2.0, takes 87 tokens:

_fillp_xmask_lo={[0]=0xffff,0x7777,0x3333,0x1111}
_fillp_xmask_hi={[0]=0x0000,0x8888,0xcccc,0xeeee}
_fillp_original=fillp

function fillp(p,x,y)
    if y then
        x=band(x,3)
        local p16=flr(p)
        local p32=rotr(p16+lshr(p16,16),band(y,3)*4+x)
        p+=flr(band(p32,_fillp_xmask_lo[x])+band(rotl(p32,4),_fillp_xmask_hi[x]))-p16
    end
    return _fillp_original(p)
end

Hope you find it useful!

Local Fill Pattern - Function 2.0

Cart File | Forum Post |

	More cartridges by Makke

More Cartridges [View All]

 

Local Fill Pattern - Function 2.0

by Makke

Cart #48163 | 2018-01-14 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

22

Excellent work. I've been wondering about how to implement this idea since fillp was released.

Good idea!

I refined your methods and took a fair chunk of the math and tokens off (now 80 tokens). Here's my version:

_fillp_xmask_lo={[0]=0xffff,0x7777,0x3333,0x1111}
_fillp_xmask_hi={[0]=0x0000,0x8888,0xcccc,0xeeee}

function fillp_local(x,y,p)
    x=band(x,3)
    local p16=flr(p)
    local p32=rotr(p16+lshr(p16,16),band(y,3)*4+x)
    return fillp(p-p16+flr(band(p32,_fillp_xmask_lo[x])+band(rotl(p32,4),_fillp_xmask_hi[x])))
end

And a demo thereof:

fillp_local() demo v2

by Felice

Cart #47737 | 2017-12-29 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

1

Thanks Felice,
this is a very nice addition. Would you mind if I edit the original post with an update of your refined version?

Edit: I just noticed however, that your version doesn't respect the additional (floating point?) bits you can provide to a pattern to specify ignoring the second color from drawing. For instance, this pattern would not draw as intended:

local pattern=0b1110100110011010.1
fillp_local(x,y,pattern)

Once that is fixed I'll update the OP with your improvements, given you're alright with that.

Regards.

Do as you like with the code, I marked it creative commons for that reason. :)

It should be retaining the fractional transparency bit. I don't remember testing that so I may have failed to do it right. That's what the p-p16 is where I send the value on to fillp--the original pattern minus the integer bits, leaving the fractional bits, which are added to the resulting shifted pattern.

Oh, okay, I see what I did.

When I was rearranging code, I accidentally moved that p-p16 inside of the flr(), effectively deleting it.

Easy fix. See my original post for an updated version and a demo that <gasp> actually tests the transparency support. ;)

Actually...

One option would be to write a flat-out replacement for fillp() that takes optional x,y args after the pattern and shifts the pattern if so. That would add to the API pretty seamlessly, while not adding complexity and still keeping backwards compatibility.

Something like this:

_fillp_xmask_lo={[0]=0xffff,0x7777,0x3333,0x1111}
_fillp_xmask_hi={[0]=0x0000,0x8888,0xcccc,0xeeee}
_fillp_original=fillp

function fillp(p,x,y)
    if y then
        x=band(x,3)
        local p16=flr(p)
        local p32=rotr(p16+lshr(p16,16),band(y,3)*4+x)
        p+=flr(band(p32,_fillp_xmask_lo[x])+band(rotl(p32,4),_fillp_xmask_hi[x]))-p16
    end
    return _fillp_original(p)
end

It costs 7 more tokens, but it just feels more natural, and in keeping with the rest of the API, to extend an existing function. Other calls like map() and sspr() do similar things.

Obligatory demo:

fillp() extension demo

by Felice

Cart #47739 | 2017-12-29 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

1

Felice, this is a way better approach so I'll update the original post with your improvements. Thanks and great work!

Ah, nice. I like my demo for having my name in it, but yours definitely demonstrates the functionality better. ;)

67 tokens with more arithmetic, no tables, and an otherwise pointless local x (not counting tokens for backward compatibility defaults)

local _fillp = fillp
local function fillp(p, x, y)
    p, x, y = p or 0, x or 0, y or 0 -- to maintain drop-in replacement compatibility with fillp(p)
    local p16, x = flr(p), band(x, 3)
    local f, p32 = flr(15 / 2 ^ x) * 0x1111, rotr(p16 + lshr(p16, 16), band(y, 3) * 4 + x)
    return _fillp(p - p16 + flr(band(p32, f) + band(rotl(p32, 4), 0xffff - f)))
end

and thanks to Felice's response on Discord, here it is with shl instead of ^, faster but two more tokens

local _fillp = fillp
local function fillp(p, x, y)
    p, x, y = p or 0, x or 0, y or 0 -- to maintain drop-in replacement compatibility with fillp(p)
    local p16, x = flr(p), band(x, 3)
    local f, p32 = flr(15 / shl(1,x)) * 0x1111, rotr(p16 + lshr(p16, 16), band(y, 3) * 4 + x)
    return _fillp(p - p16 + flr(band(p32, f) + band(rotl(p32, 4), 0xffff - f)))
end

Felice, I am curious why your natural extension above shifts neither x nor y when y is not present? If we want a seamless extension shouldn't it still shift x?

I was just economizing. I figured anyone wanting to shift the pattern would probably provide both parameters and that a single parameter would generally be an accident.

It's entirely reasonable to want to work with just x though. I just didn't do it. Arbitrary.

@sparr

I happened to come back and look at this. Isn't this:

flr(15 / shl(1,x)) * 0x1111

Just this?

flr(shr(15,x)) * 0x1111

I think you're right

I find it pretty neat you guys are still working this! :D

I have been banging my head all morning trying to do this and then I found this! thanks a lot

@Felice is a god when it comes to math/low-level. Let me know if you guys want me to update OP with any new/better version.