Collapse ascii-art

Question

Challenge

Given a rectangular grid of printable ascii characters as a string or through standard input, write a function or program that collapses the non-space characters into a pile on the bottom.

The rules:

• The output has the same dimensions and characters as the input.
• A non-space character at (row a,column b) can't have a space character ' ' at (a-1, b), (a-1,b-1) or (a-1,b+1), where rows are numbered up from the bottom-most. This has the consequence that all vertical piles should collapse sideways.
• A non-space character can travel at most (initial height - final height) places to the left or right (see Fig. 1).
• You can assume the picture has enough space to collapse without characters falling out of the screen.

Figure 1: possible final locations for characters @#$ shown as x,y,z, respectively.

..............
...@..........
..xxx.........
.xxxxx...#....
xxxxxxx.yyy.$.

The order in which characters collapse can be chosen freely. Trailing spaces are not okay but trailing newlines are.

This is code-golf, so the shortest answer in bytes wins!

Example

                 (__)
                 (oo)
           /------\/
          / |    ||
         *  /\---/\
            ~~   ~~
..."Have you mooed today?"...

One possible output:

 
 
 
                --(_
           /----|/|(o_)
          /|/~\---~\\/o)
..."Have*you~mooed~today?"...

Answer 1

JavaScript (ES6), 100 90 88 bytes

f=s=>s==(l=s.search`
`,s=s.replace(eval(`/(\\S)([^]{${l-1},${l+1}}) /`),` $2$1`))?s:f(s)
s=`                 (__)        
                 (oo)        
           /------\\/         
          / |    ||          
         *  /\\---/\\          
            ~~   ~~          
..."Have you mooed today?"...`
console.log(s)
console.log(f(s))

Requires the the string to have at least two lines and all lines padded to equal length. Output for the example image:

              ( --           
            /|---/|-(o__     
          */~~\---~\|\/o))   
..."Have you/mooed~today?"...

Note that as it tries to move elements to the right if possible, the * did not fall between the Have and the you.

Edit: Saved 10% thanks to @ETHproductions. Saved another 2 bytes thanks to @DanielIndie.

Retina 0.8.2, 50 bytes

+`(?<=(.)*)(\S)(.*¶(?<-1>)?(?>(?<-1>.)*).?) 
 $3$2

Try it online! A slightly different approach to my JavaScript answer, this uses a balancing group to match a space below the non-space character; the (?<-1>)? allows the space to be one column to the left while the .? allows the space to be one column to the right.

Retina, 40 bytes

~0L$`.(.*)¶
+s`(\S)(.{$.1,$.&}) ¶ $$2$$1

Try it online! Port of my JavaScript answer. The 0L$ atomic stage takes the input and substitutes the two lengths into the second line resulting in the command that actually performs the replacement, which is then evaluated on the original input by the ~ compound stage.

Answer 2

Python 2, 298 bytes

a=input()
L=len(a);s=' '
a=[list(s*L+l.ljust(L+max(map(len,a))))for l in a]
t=1
while t:
 t=0
 for y in range(L-1):
  for x in range(len(a[y])):
   c=a[y][x];C=a[y+1][x-1:x+2]
   if s!=c and s in C:t=1;a[y][x]=s;a[y+1][[[x+1,x][C[1]==s],x-1][C[0]==s]]=c
for l in map(''.join,a):print l[L:].rstrip()

Takes input as a list of strings (one per line)

Example: Input:

['                 (__)',
'                 (oo)',
'           /------\/',
'          / |    ||',
'         *  /\---/\ ',
'            ~~   ~~',
'..."Have you mooed today?"...']

Output:

              (
            -----/|-(o__
         //|~~\---~\|\/o))
..."Have*you/mooed~today?"...

Answer 3

C, 252 bytes

e=1,l,c,i,j,p,r,w,a[999];f(){while((i=getchar())>0)a[w++]=i,i<16?l++:0,l?0:c++;while(e)for(i=e=0;i<c;i++)for(j=l;j>=0;j--)e=(r=a[p=j*(c+1)+i]-32?a[r=p+c+1]-32?a[r=p+c]-32?a[r=p+c+2]-32?0:r:r:r:0)?l=a[p],a[p]=a[r],a[r]=l:e;for(i=0;i<w;)putchar(a[i++]);}

Ungolfed test code:

#include <stdio.h>

e=1,l,c,i,j,p,r,w,a[999];
f()
{
    // counting lines and columns
    while ((i = getchar())>0)a[w++] = i, i<16 ? l++ : 0, l ? 0 : c++;
    // main shaking loop
    while (e) // repeat while collapsing
        for (i = e = 0; i < c; i++) // columns loop
            for (j = l; j >= 0; j--) // lines loop
                e = ( // remember that collapsing was
                     r = // find place to collapse
                         a[p = j*(c + 1) + i] - 32 ? // if not space
                             a[r = p + c + 1] - 32 ? // if char under the current is not a space
                                 a[r = p + c] - 32 ? // see one position left
                                    a[r = p + c + 2] - 32 ? 0 // then one position right
                                                          : r
                                    : r
                                 : r
                             : 0
                         ) ? // and if place was found
                           l=a[p],a[p]=a[r],a[r]=l // replace values in positions p and r
                           : e;
    //print resulting picture
    for(i=0;i<w;)putchar(a[i++]);
}

int main(void)
{
    int cnt;
    FILE * testf = fopen("caw.txt","w");
    char testd[][31] = {
        "                 (__)        \n",
        "                 (oo)        \n", 
        "           /------\\/         \n", 
        "          / |    ||          \n", 
        "         *  /\\---/\\          \n", 
        "            ~~   ~~          \n", 
        "...\"Have you mooed today ? \"...",
        "" };
    // prepare data for test
    printf("Initial data:\n");
    for(cnt = 0; cnt < 7; cnt++)
    {
        printf("%s", testd[cnt]);
        fprintf(testf, testd[cnt]);
    }
    fclose(testf);
    // redirect standard input
    freopen("caw.txt", "r", stdin);
    printf("\n\nResult:\n");
    // start test
    f();
}

Result of test:

Answer 4

JavaScript, 286 bytes

b=>eval('f=b=>b==null||" "==b;b=b.split`\n`.map(b=>[...b]);a:for(;;){for(c=0;c<b.length-1;c++)for(g=b[c],d=0;d<g.length;d++){h=g[d];if(!f(h)){e=0;f(b[c+1][d])?e=2:f(b[c+1][d-1])?e=1:f(b[c+1][d+1])&&(e=3);if(e){b[c+1][d+e-2]=h;b[c][d]=" ";continue a}}}break}b.map(b=>b.join``).join`\n`')

Examples

// Here I assume that you've assigned the above function to `fall`
console.log(fall(`
                 (__)
                 (oo)
           /------\/
          / |    ||
         *  /\---/\\
            ~~   ~~
..."Have you mooed today?"...`))

Output:

                -       
            /--(-\--(__  
          /|~~---/~||/oo))
..."Have*you/mooed~today?"...

Another example:

console.log(fall(`
 (\__/)  .~    ~. ))
 /O O  ./      .'
{O__,   \    {
  / .  . )    \\
  |-| '-' \    }
 .(   _(   )_.'
'---.~_ _ _&`))

Output:

    _ , /            
  OO/__'_.. .         
 {.(|-|.(O'))/.~{      
/('---.~___-_&)_.'}\~.'))

Ungolfed function

function fall(input) {
  let move = true
  let lines = input.split("\n").map(line => line.split(""))
  let isSpace = c => c == null || c == " "
  loop: for (;;) {
    for (let y = 0; y < lines.length - 1; y++) {
      let line = lines[y]
      for (let x = 0; x < line.length; x++) {
        let ch = line[x]
        if (!isSpace(ch)) {
          let dx = 0
          if (isSpace(lines[y+1][x])) { dx = 2 }
          else if (isSpace(lines[y+1][x-1])) { dx = 1 }
          else if (isSpace(lines[y+1][x+1])) { dx = 3 }
          if (dx) {
            lines[y + 1][x + dx - 2] = ch
            lines[y][x] = " "
            continue loop
          }
        }
      }
    }
    break
  }
  return lines.map(line => line.join("")).join("\n")
}