ref: af36a8b50ad95196fdc21deac251919cd7bbd18a
dir: /sys/src/cmd/scat/qtree.c/
#include <u.h>
#include <libc.h>
#include <bio.h>
#include "sky.h"
static void qtree_expand(Biobuf*, uchar*, int, int, uchar*);
static void qtree_copy(uchar*, int, int, uchar*, int);
static void qtree_bitins(uchar*, int, int, Pix*, int, int);
static void read_bdirect(Biobuf*, Pix*, int, int, int, uchar*, int);
void
qtree_decode(Biobuf *infile, Pix *a, int n, int nqx, int nqy, int nbitplanes)
{
int log2n, k, bit, b, nqmax;
int nx,ny,nfx,nfy,c;
int nqx2, nqy2;
unsigned char *scratch;
/*
* log2n is log2 of max(nqx,nqy) rounded up to next power of 2
*/
nqmax = nqy;
if(nqx > nqmax)
nqmax = nqx;
log2n = log(nqmax)/LN2+0.5;
if (nqmax > (1<<log2n))
log2n++;
/*
* allocate scratch array for working space
*/
nqx2 = (nqx+1)/2;
nqy2 = (nqy+1)/2;
scratch = (uchar*)malloc(nqx2*nqy2);
if(scratch == nil) {
fprint(2, "qtree_decode: insufficient memory\n");
exits("memory");
}
/*
* now decode each bit plane, starting at the top
* A is assumed to be initialized to zero
*/
for(bit = nbitplanes-1; bit >= 0; bit--) {
/*
* Was bitplane was quadtree-coded or written directly?
*/
b = input_nybble(infile);
if(b == 0) {
/*
* bit map was written directly
*/
read_bdirect(infile, a, n, nqx, nqy, scratch, bit);
} else
if(b != 0xf) {
fprint(2, "qtree_decode: bad format code %x\n",b);
exits("format");
} else {
/*
* bitmap was quadtree-coded, do log2n expansions
* read first code
*/
scratch[0] = input_huffman(infile);
/*
* do log2n expansions, reading codes from file as necessary
*/
nx = 1;
ny = 1;
nfx = nqx;
nfy = nqy;
c = 1<<log2n;
for(k = 1; k<log2n; k++) {
/*
* this somewhat cryptic code generates the sequence
* n[k-1] = (n[k]+1)/2 where n[log2n]=nqx or nqy
*/
c = c>>1;
nx = nx<<1;
ny = ny<<1;
if(nfx <= c)
nx--;
else
nfx -= c;
if(nfy <= c)
ny--;
else
nfy -= c;
qtree_expand(infile, scratch, nx, ny, scratch);
}
/*
* copy last set of 4-bit codes to bitplane bit of array a
*/
qtree_bitins(scratch, nqx, nqy, a, n, bit);
}
}
free(scratch);
}
/*
* do one quadtree expansion step on array a[(nqx+1)/2,(nqy+1)/2]
* results put into b[nqx,nqy] (which may be the same as a)
*/
static
void
qtree_expand(Biobuf *infile, uchar *a, int nx, int ny, uchar *b)
{
uchar *b1;
/*
* first copy a to b, expanding each 4-bit value
*/
qtree_copy(a, nx, ny, b, ny);
/*
* now read new 4-bit values into b for each non-zero element
*/
b1 = &b[nx*ny];
while(b1 > b) {
b1--;
if(*b1 != 0)
*b1 = input_huffman(infile);
}
}
/*
* copy 4-bit values from a[(nx+1)/2,(ny+1)/2] to b[nx,ny], expanding
* each value to 2x2 pixels
* a,b may be same array
*/
static
void
qtree_copy(uchar *a, int nx, int ny, uchar *b, int n)
{
int i, j, k, nx2, ny2;
int s00, s10;
/*
* first copy 4-bit values to b
* start at end in case a,b are same array
*/
nx2 = (nx+1)/2;
ny2 = (ny+1)/2;
k = ny2*(nx2-1) + ny2-1; /* k is index of a[i,j] */
for (i = nx2-1; i >= 0; i--) {
s00 = 2*(n*i+ny2-1); /* s00 is index of b[2*i,2*j] */
for (j = ny2-1; j >= 0; j--) {
b[s00] = a[k];
k -= 1;
s00 -= 2;
}
}
/*
* now expand each 2x2 block
*/
for(i = 0; i<nx-1; i += 2) {
s00 = n*i; /* s00 is index of b[i,j] */
s10 = s00+n; /* s10 is index of b[i+1,j] */
for(j = 0; j<ny-1; j += 2) {
b[s10+1] = b[s00] & 1;
b[s10 ] = (b[s00]>>1) & 1;
b[s00+1] = (b[s00]>>2) & 1;
b[s00 ] = (b[s00]>>3) & 1;
s00 += 2;
s10 += 2;
}
if(j < ny) {
/*
* row size is odd, do last element in row
* s00+1, s10+1 are off edge
*/
b[s10 ] = (b[s00]>>1) & 1;
b[s00 ] = (b[s00]>>3) & 1;
}
}
if(i < nx) {
/*
* column size is odd, do last row
* s10, s10+1 are off edge
*/
s00 = n*i;
for (j = 0; j<ny-1; j += 2) {
b[s00+1] = (b[s00]>>2) & 1;
b[s00 ] = (b[s00]>>3) & 1;
s00 += 2;
}
if(j < ny) {
/*
* both row and column size are odd, do corner element
* s00+1, s10, s10+1 are off edge
*/
b[s00 ] = (b[s00]>>3) & 1;
}
}
}
/*
* Copy 4-bit values from a[(nx+1)/2,(ny+1)/2] to b[nx,ny], expanding
* each value to 2x2 pixels and inserting into bitplane BIT of B.
* A,B may NOT be same array (it wouldn't make sense to be inserting
* bits into the same array anyway.)
*/
static
void
qtree_bitins(uchar *a, int nx, int ny, Pix *b, int n, int bit)
{
int i, j;
Pix *s00, *s10;
Pix px;
/*
* expand each 2x2 block
*/
for(i=0; i<nx-1; i+=2) {
s00 = &b[n*i]; /* s00 is index of b[i,j] */
s10 = s00+n; /* s10 is index of b[i+1,j] */
for(j=0; j<ny-1; j+=2) {
px = *a++;
s10[1] |= ( px & 1) << bit;
s10[0] |= ((px>>1) & 1) << bit;
s00[1] |= ((px>>2) & 1) << bit;
s00[0] |= ((px>>3) & 1) << bit;
s00 += 2;
s10 += 2;
}
if(j < ny) {
/*
* row size is odd, do last element in row
* s00+1, s10+1 are off edge
*/
px = *a++;
s10[0] |= ((px>>1) & 1) << bit;
s00[0] |= ((px>>3) & 1) << bit;
}
}
if(i < nx) {
/*
* column size is odd, do last row
* s10, s10+1 are off edge
*/
s00 = &b[n*i];
for(j=0; j<ny-1; j+=2) {
px = *a++;
s00[1] |= ((px>>2) & 1) << bit;
s00[0] |= ((px>>3) & 1) << bit;
s00 += 2;
}
if(j < ny) {
/*
* both row and column size are odd, do corner element
* s00+1, s10, s10+1 are off edge
*/
s00[0] |= ((*a>>3) & 1) << bit;
}
}
}
static
void
read_bdirect(Biobuf *infile, Pix *a, int n, int nqx, int nqy, uchar *scratch, int bit)
{
int i;
/*
* read bit image packed 4 pixels/nybble
*/
for(i = 0; i < ((nqx+1)/2) * ((nqy+1)/2); i++) {
scratch[i] = input_nybble(infile);
}
/*
* insert in bitplane BIT of image A
*/
qtree_bitins(scratch, nqx, nqy, a, n, bit);
}