/*
* Trivial draw implementation.
* Color values are passed around as ulongs containing ααRRGGBB
*/
/*
* Convert v, which is nhave bits wide, into its nwant bits wide equivalent.
* Replicates to widen the value, truncates to narrow it.
*/
ulong
replbits(ulong v, int nhave, int nwant)
{
v &= (1<<nhave)-1;
for(; nhave<nwant; nhave*=2)
v |= v<<nhave;
v >>= (nhave-nwant);
return v & ((1<<nwant)-1);
}
/*
* Decode a pixel into the uchar* values.
*/
void
pixtorgba(ulong v, uchar *r, uchar *g, uchar *b, uchar *a)
{
*a = v>>24;
*r = v>>16;
*g = v>>8;
*b = v;
}
/*
* Convert uchar channels into ulong pixel.
*/
ulong
rgbatopix(uchar r, uchar g, uchar b, uchar a)
{
return (a<<24)|(r<<16)|(g<<8)|b;
}
/*
* Retrieve the pixel value at pt in the image.
*/
ulong
getpixel(Memimage *img, Point pt)
{
uchar r, g, b, a, *p;
int nbits, npack, bpp;
ulong v, c, rbits, bits;
r = g = b = 0;
a = ~0; /* default alpha is full */
p = byteaddr(img, pt);
v = p[0]|(p[1]<<8)|(p[2]<<16)|(p[3]<<24);
bpp = img->depth;
if(bpp<8){
/*
* Sub-byte greyscale pixels.
*
* We want to throw away the top pt.x%npack pixels and then use the next bpp bits
* in the bottom byte of v. This madness is due to having big endian bits
* but little endian bytes.
*/
npack = 8/bpp;
v >>= 8 - bpp*(pt.x%npack+1);
v &= (1<<bpp)-1;
r = g = b = replbits(v, bpp, 8);
}else{
/*
* General case. We need to parse the channel descriptor and do what it says.
* In all channels but the color map, we replicate to 8 bits because that's the
* precision that all calculations are done at.
*
* In the case of the color map, we leave the bits alone, in case a color map
* with less than 8 bits of index is used. This is currently disallowed, so it's
* sort of silly.
*/
for(c=img->chan; c; c>>=8){
nbits = NBITS(c);
bits = v & ((1<<nbits)-1);
rbits = replbits(bits, nbits, 8);
v >>= nbits;
switch(TYPE(c)){
case CRed:
r = rbits;
break;
case CGreen:
g = rbits;
break;
case CBlue:
b = rbits;
break;
case CGrey:
r = g = b = rbits;
break;
case CAlpha:
a = rbits;
break;
case CMap:
p = img->cmap->cmap2rgb + 3*bits;
r = p[0];
g = p[1];
b = p[2];
break;
case CIgnore:
break;
default:
fprint(2, "unknown channel type %lud\n", TYPE(c));
abort();
}
}
}
return rgbatopix(r, g, b, a);
}
/*
* Return the greyscale equivalent of a pixel.
*/
uchar
getgrey(Memimage *img, Point pt)
{
uchar r, g, b, a;
pixtorgba(getpixel(img, pt), &r, &g, &b, &a);
return RGB2K(r, g, b);
}
/*
* Return the value at pt in image, if image is interpreted
* as a mask. This means the alpha channel if present, else
* the greyscale or its computed equivalent.
*/
uchar
getmask(Memimage *img, Point pt)
{
if(img->flags&Falpha)
return getpixel(img, pt)>>24;
else
return getgrey(img, pt);
}
#undef DBG
#define DBG if(0)
/*
* Write a pixel to img at point pt.
*
* We do this by reading a 32-bit little endian
* value from p and then writing it back
* after tweaking the appropriate bits. Because
* the data is little endian, we don't have to worry
* about what the actual depth is, as long as it is
* less than 32 bits.
*/
void
putpixel(Memimage *img, Point pt, ulong nv)
{
uchar r, g, b, a, *p, *q;
ulong c, mask, bits, v;
int bpp, sh, npack, nbits;
pixtorgba(nv, &r, &g, &b, &a);
p = byteaddr(img, pt);
v = p[0]|(p[1]<<8)|(p[2]<<16)|(p[3]<<24);
bpp = img->depth;
DBG print("v %.8lux...", v);
if(bpp < 8){
/*
* Sub-byte greyscale pixels. We need to skip the leftmost pt.x%npack pixels,
* which is equivalent to skipping the rightmost npack - pt.x%npack - 1 pixels.
*/
npack = 8/bpp;
sh = bpp*(npack - pt.x%npack - 1);
bits = RGB2K(r,g,b);
DBG print("repl %lux 8 %d = %lux...", bits, bpp, replbits(bits, 8, bpp));
bits = replbits(bits, 8, bpp);
mask = (1<<bpp)-1;
DBG print("bits %lux mask %lux sh %d...", bits, mask, sh);
mask <<= sh;
bits <<= sh;
DBG print("(%lux & %lux) | (%lux & %lux)", v, ~mask, bits, mask);
v = (v & ~mask) | (bits & mask);
} else {
/*
* General case. We need to parse the channel descriptor again.
*/
sh = 0;
for(c=img->chan; c; c>>=8){
nbits = NBITS(c);
switch(TYPE(c)){
case CRed:
bits = r;
break;
case CGreen:
bits = g;
break;
case CBlue:
bits = b;
break;
case CGrey:
bits = RGB2K(r, g, b);
break;
case CAlpha:
bits = a;
break;
case CIgnore:
bits = 0;
break;
case CMap:
q = img->cmap->rgb2cmap;
bits = q[(r>>4)*16*16+(g>>4)*16+(b>>4)];
break;
default:
SET(bits);
fprint(2, "unknown channel type %lud\n", TYPE(c));
abort();
}
DBG print("repl %lux 8 %d = %lux...", bits, nbits, replbits(bits, 8, nbits));
if(TYPE(c) != CMap)
bits = replbits(bits, 8, nbits);
mask = (1<<nbits)-1;
DBG print("bits %lux mask %lux sh %d...", bits, mask, sh);
bits <<= sh;
mask <<= sh;
v = (v & ~mask) | (bits & mask);
sh += nbits;
}
}
DBG print("v %.8lux\n", v);
p[0] = v;
p[1] = v>>8;
p[2] = v>>16;
p[3] = v>>24;
}
#undef DBG
#define DBG if(0)
void
drawonepixel(Memimage *dst, Point dp, Memimage *src, Point sp, Memimage *mask, Point mp)
{
uchar m, M, sr, sg, sb, sa, sk, dr, dg, db, da, dk;
pixtorgba(getpixel(dst, dp), &dr, &dg, &db, &da);
pixtorgba(getpixel(src, sp), &sr, &sg, &sb, &sa);
m = getmask(mask, mp);
M = 255-(sa*m)/255;
DBG print("dst %x %x %x %x src %x %x %x %x m %x = ", dr,dg,db,da, sr,sg,sb,sa, m);
if(dst->flags&Fgrey){
/*
* We need to do the conversion to grey before the alpha calculation
* because the draw operator does this, and we need to be operating
* at the same precision so we get exactly the same answers.
*/
sk = RGB2K(sr, sg, sb);
dk = RGB2K(dr, dg, db);
dk = (sk*m + dk*M)/255;
dr = dg = db = dk;
da = (sa*m + da*M)/255;
}else{
/*
* True color alpha calculation treats all channels (including alpha)
* the same. It might have been nice to use an array, but oh well.
*/
dr = (sr*m + dr*M)/255;
dg = (sg*m + dg*M)/255;
db = (sb*m + db*M)/255;
da = (sa*m + da*M)/255;
}
DBG print("%x %x %x %x\n", dr,dg,db,da);
putpixel(dst, dp, rgbatopix(dr, dg, db, da));
}
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