draw.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

	b = &p->bcache[y];
	if((p->bfilled & (1<<y)) == 0){
		p->bfilled |= 1<<y;
		*b = p->replcall(p, p->bufbase+y*p->bufdelta, y);
	}
	return *b;
}

/*
 * Alpha reading function that simply relabels the grey pointer.
 */
static Buffer
greymaskread(Param *p, uchar *buf, int y)
{
	Buffer b;

	b = p->greymaskcall(p, buf, y);
	b.alpha = b.grey;
	return b;
}

#define DBG if(0)
static Buffer
readnbit(Param *p, uchar *buf, int y)
{
	Buffer b;
	Memimage *img;
	uchar *repl, *r, *w, *ow, bits;
	int i, n, sh, depth, x, dx, npack, nbits;

	b.rgba = (ulong*)buf;
	b.grey = w = buf;
	b.red = b.blu = b.grn = w;
	b.alpha = &ones;
	b.delta = 1;

	dx = p->dx;
	img = p->img;
	depth = img->depth;
	repl = &replbit[depth][0];
	npack = 8/depth;
	sh = 8-depth;

	/* copy from p->r.min.x until end of repl rectangle */
	x = p->r.min.x;
	n = dx;
	if(n > p->img->r.max.x - x)
		n = p->img->r.max.x - x;

	r = p->bytermin + y*p->bwidth;
DBG print("readnbit dx %d %p=%p+%d*%d, *r=%d fetch %d ", dx, r, p->bytermin, y, p->bwidth, *r, n);
	bits = *r++;
	nbits = 8;
	if(i=x&(npack-1)){
DBG print("throwaway %d...", i);
		bits <<= depth*i;
		nbits -= depth*i;
	}
	for(i=0; i<n; i++){
		if(nbits == 0){
DBG print("(%.2ux)...", *r);
			bits = *r++;
			nbits = 8;
		}
		*w++ = repl[bits>>sh];
DBG print("bit %x...", repl[bits>>sh]);
		bits <<= depth;
		nbits -= depth;
	}
	dx -= n;
	if(dx == 0)
		return b;

	assert(x+i == p->img->r.max.x);

	/* copy from beginning of repl rectangle until where we were before. */
	x = p->img->r.min.x;
	n = dx;
	if(n > p->r.min.x - x)
		n = p->r.min.x - x;

	r = p->bytey0s + y*p->bwidth;
DBG print("x=%d r=%p...", x, r);
	bits = *r++;
	nbits = 8;
	if(i=x&(npack-1)){
		bits <<= depth*i;
		nbits -= depth*i;
	}
DBG print("nbits=%d...", nbits);
	for(i=0; i<n; i++){
		if(nbits == 0){
			bits = *r++;
			nbits = 8;
		}
		*w++ = repl[bits>>sh];
DBG print("bit %x...", repl[bits>>sh]);
		bits <<= depth;
		nbits -= depth;
DBG print("bits %x nbits %d...", bits, nbits);
	}
	dx -= n;
	if(dx == 0)
		return b;

	assert(dx > 0);
	/* now we have exactly one full scan line: just replicate the buffer itself until we are done */
	ow = buf;
	while(dx--)
		*w++ = *ow++;

	return b;
}
#undef DBG

#define DBG if(0)
static void
writenbit(Param *p, uchar *w, Buffer src)
{
	uchar *r;
	ulong bits;
	int i, sh, depth, npack, nbits, x, ex;

	assert(src.grey != nil && src.delta == 1);

	x = p->r.min.x;
	ex = x+p->dx;
	depth = p->img->depth;
	npack = 8/depth;

	i=x&(npack-1);
	bits = i ? (*w >> (8-depth*i)) : 0;
	nbits = depth*i;
	sh = 8-depth;
	r = src.grey;

	for(; x<ex; x++){
		bits <<= depth;
DBG print(" %x", *r);
		bits |= (*r++ >> sh);
		nbits += depth;
		if(nbits == 8){
			*w++ = bits;
			nbits = 0;
		}
	}

	if(nbits){
		sh = 8-nbits;
		bits <<= sh;
		bits |= *w & ((1<<sh)-1);
		*w = bits;
	}
DBG print("\n");
	return;
}
#undef DBG

static Buffer
readcmap(Param *p, uchar *buf, int y)
{
	Buffer b;
	int a, convgrey, copyalpha, dx, i, m;
	uchar *q, *cmap, *begin, *end, *r, *w;

	begin = p->bytey0s + y*p->bwidth;
	r = p->bytermin + y*p->bwidth;
	end = p->bytey0e + y*p->bwidth;
	cmap = p->img->cmap->cmap2rgb;
	convgrey = p->convgrey;
	copyalpha = (p->img->flags&Falpha) ? 1 : 0;

	w = buf;
	dx = p->dx;
	if(copyalpha){
		b.alpha = buf++;
		a = p->img->shift[CAlpha]/8;
		m = p->img->shift[CMap]/8;
		for(i=0; i<dx; i++){
			*w++ = r[a];
			q = cmap+r[m]*3;
			r += 2;
			if(r == end)
				r = begin;
			if(convgrey){
				*w++ = RGB2K(q[0], q[1], q[2]);
			}else{
				*w++ = q[2];	/* blue */
				*w++ = q[1];	/* green */
				*w++ = q[0];	/* red */
			}
		}
	}else{
		b.alpha = &ones;
		for(i=0; i<dx; i++){
			q = cmap+*r++*3;
			if(r == end)
				r = begin;
			if(convgrey){
				*w++ = RGB2K(q[0], q[1], q[2]);
			}else{
				*w++ = q[2];	/* blue */
				*w++ = q[1];	/* green */
				*w++ = q[0];	/* red */
			}
		}
	}

	b.rgba = (ulong*)(buf-copyalpha);

	if(convgrey){
		b.grey = buf;
		b.red = b.blu = b.grn = buf;
		b.delta = 1+copyalpha;
	}else{
		b.blu = buf;
		b.grn = buf+1;
		b.red = buf+2;
		b.grey = nil;
		b.delta = 3+copyalpha;
	}
	return b;
}

static void
writecmap(Param *p, uchar *w, Buffer src)
{
	uchar *cmap, *red, *grn, *blu;
	int i, dx, delta;

	cmap = p->img->cmap->rgb2cmap;
	
	delta = src.delta;
	red= src.red;
	grn = src.grn;
	blu = src.blu;

	dx = p->dx;
	for(i=0; i<dx; i++, red+=delta, grn+=delta, blu+=delta)
		*w++ = cmap[(*red>>4)*256+(*grn>>4)*16+(*blu>>4)];
}

#define DBG if(0)
static Buffer
readbyte(Param *p, uchar *buf, int y)
{
	Buffer b;
	Memimage *img;
	int dx, isgrey, convgrey, alphaonly, copyalpha, i, nb;
	uchar *begin, *end, *r, *w, *rrepl, *grepl, *brepl, *arepl, *krepl;
	uchar ured, ugrn, ublu;
	ulong u;

	img = p->img;
	begin = p->bytey0s + y*p->bwidth;
	r = p->bytermin + y*p->bwidth;
	end = p->bytey0e + y*p->bwidth;

	w = buf;
	dx = p->dx;
	nb = img->depth/8;

	convgrey = p->convgrey;	/* convert rgb to grey */
	isgrey = img->flags&Fgrey;
	alphaonly = p->alphaonly;
	copyalpha = (img->flags&Falpha) ? 1 : 0;

DBG print("copyalpha %d alphaonly %d convgrey %d isgrey %d\n", copyalpha, alphaonly, convgrey, isgrey);
	/* if we can, avoid processing everything */
	if(!(img->flags&Frepl) && !convgrey && (img->flags&Fbytes)){
		memset(&b, 0, sizeof b);
		if(p->needbuf){
			memmove(buf, r, dx*nb);
			r = buf;
		}
		b.rgba = (ulong*)r;
		if(copyalpha)
			b.alpha = r+img->shift[CAlpha]/8;
		else
			b.alpha = &ones;
		if(isgrey){
			b.grey = r+img->shift[CGrey]/8;
			b.red = b.grn = b.blu = b.grey;
		}else{
			b.red = r+img->shift[CRed]/8;
			b.grn = r+img->shift[CGreen]/8;
			b.blu = r+img->shift[CBlue]/8;
		}
		b.delta = nb;
		return b;
	}

DBG print("2\n");
	rrepl = replbit[img->nbits[CRed]];
	grepl = replbit[img->nbits[CGreen]];
	brepl = replbit[img->nbits[CBlue]];
	arepl = replbit[img->nbits[CAlpha]];
	krepl = replbit[img->nbits[CGrey]];

	for(i=0; i<dx; i++){
		u = r[0] | (r[1]<<8) | (r[2]<<16) | (r[3]<<24);
		if(copyalpha) {
			*w++ = arepl[(u>>img->shift[CAlpha]) & img->mask[CAlpha]];
DBG print("a %x\n", w[-1]);
		}

		if(isgrey)
			*w++ = krepl[(u >> img->shift[CGrey]) & img->mask[CGrey]];
		else if(!alphaonly){
			ured = rrepl[(u >> img->shift[CRed]) & img->mask[CRed]];
			ugrn = grepl[(u >> img->shift[CGreen]) & img->mask[CGreen]];
			ublu = brepl[(u >> img->shift[CBlue]) & img->mask[CBlue]];
			if(convgrey){
DBG print("g %x %x %x\n", ured, ugrn, ublu);
				*w++ = RGB2K(ured, ugrn, ublu);
DBG print("%x\n", w[-1]);
			}else{
				*w++ = brepl[(u >> img->shift[CBlue]) & img->mask[CBlue]];
				*w++ = grepl[(u >> img->shift[CGreen]) & img->mask[CGreen]];
				*w++ = rrepl[(u >> img->shift[CRed]) & img->mask[CRed]];
			}
		}
		r += nb;
		if(r == end)
			r = begin;
	}
	
	b.alpha = copyalpha ? buf : &ones;
	b.rgba = (ulong*)buf;
	if(alphaonly){
		b.red = b.grn = b.blu = b.grey = nil;
		if(!copyalpha)
			b.rgba = nil;
		b.delta = 1;
	}else if(isgrey || convgrey){
		b.grey = buf+copyalpha;
		b.red = b.grn = b.blu = buf+copyalpha;
		b.delta = copyalpha+1;
DBG print("alpha %x grey %x\n", b.alpha ? *b.alpha : 0xFF, *b.grey);
	}else{
		b.blu = buf+copyalpha;
		b.grn = buf+copyalpha+1;
		b.grey = nil;
		b.red = buf+copyalpha+2;
		b.delta = copyalpha+3;
	}
	return b;
}
#undef DBG

#define DBG if(0)
static void
writebyte(Param *p, uchar *w, Buffer src)
{
	Memimage *img;
	int i, isalpha, isgrey, nb, delta, dx, adelta;
	uchar ff, *red, *grn, *blu, *grey, *alpha;
	ulong u, mask;

	img = p->img;

	red = src.red;
	grn = src.grn;
	blu = src.blu;
	alpha = src.alpha;
	delta = src.delta;
	grey = src.grey;
	dx = p->dx;

	nb = img->depth/8;
	mask = (nb==4) ? 0 : ~((1<<img->depth)-1);

	isalpha = img->flags&Falpha;
	isgrey = img->flags&Fgrey;
	adelta = src.delta;

	if(isalpha && (alpha == nil || alpha == &ones)){
		ff = 0xFF;
		alpha = &ff;
		adelta = 0;
	}

	for(i=0; i<dx; i++){
		u = w[0] | (w[1]<<8) | (w[2]<<16) | (w[3]<<24);
DBG print("u %.8lux...", u);
		u &= mask;
DBG print("&mask %.8lux...", u);
		if(isgrey){
			u |= ((*grey >> (8-img->nbits[CGrey])) & img->mask[CGrey]) << img->shift[CGrey];
DBG print("|grey %.8lux...", u);
			grey += delta;
		}else{
			u |= ((*red >> (8-img->nbits[CRed])) & img->mask[CRed]) << img->shift[CRed];
			u |= ((*grn >> (8-img->nbits[CGreen])) & img->mask[CGreen]) << img->shift[CGreen];
			u |= ((*blu >> (8-img->nbits[CBlue])) & img->mask[CBlue]) << img->shift[CBlue];
			red += delta;
			grn += delta;
			blu += delta;
DBG print("|rgb %.8lux...", u);
		}

		if(isalpha){
			u |= ((*alpha >> (8-img->nbits[CAlpha])) & img->mask[CAlpha]) << img->shift[CAlpha];
			alpha += adelta;
DBG print("|alpha %.8lux...", u);
		}

		w[0] = u;
		w[1] = u>>8;
		w[2] = u>>16;
		w[3] = u>>24;
		w += nb;
	}
}
#undef DBG

static Readfn*
readfn(Memimage *img)
{
	if(img->depth < 8)
		return readnbit;
	if(img->nbits[CMap] == 8)
		return readcmap;
	return readbyte;
}

static Readfn*
readalphafn(Memimage *m)
{
	USED(m);
	return readbyte;
}

static Writefn*
writefn(Memimage *img)
{
	if(img->depth < 8)
		return writenbit;
	if(img->chan == CMAP8)
		return writecmap;
	return writebyte;
}

static void
nullwrite(Param *p, uchar *s, Buffer b)
{
	USED(p);
	USED(s);
	USED(b);
}

static Buffer
readptr(Param *p, uchar *s, int y)
{
	Buffer b;
	uchar *q;

	USED(s);
	q = p->bytermin + y*p->bwidth;
	b.red = q;	/* ptr to data */
	b.grn = b.blu = b.grey = b.alpha = nil;
	b.rgba = (ulong*)q;
	b.delta = p->img->depth/8;
	return b;
}

static Buffer
boolmemmove(Buffer bdst, Buffer bsrc, Buffer b1, int dx, int i, int o)
{
	USED(i);
	USED(o);
	USED(b1);
	USED(bsrc);
	memmove(bdst.red, bsrc.red, dx*bdst.delta);
	return bdst;
}

static Buffer
boolcopy8(Buffer bdst, Buffer bsrc, Buffer bmask, int dx, int i, int o)
{
	uchar *m, *r, *w, *ew;

	USED(i);
	USED(o);
	m = bmask.grey;
	w = bdst.red;
	r = bsrc.red;
	ew = w+dx;
	for(; w < ew; w++,r++)
		if(*m++)
			*w = *r;
	return bdst;	/* not used */
}

static Buffer
boolcopy16(Buffer bdst, Buffer bsrc, Buffer bmask, int dx, int i, int o)
{
	uchar *m;
	ushort *r, *w, *ew;

	USED(i);
	USED(o);
	m = bmask.grey;
	w = (ushort*)bdst.red;
	r = (ushort*)bsrc.red;
	ew = w+dx;
	for(; w < ew; w++,r++)
		if(*m++)
			*w = *r;
	return bdst;	/* not used */
}

static Buffer
boolcopy24(Buffer bdst, Buffer bsrc, Buffer bmask, int dx, int i, int o)
{
	uchar *m;
	uchar *r, *w, *ew;

	USED(i);
	USED(o);
	m = bmask.grey;
	w = bdst.red;
	r = bsrc.red;
	ew = w+dx*3;
	while(w < ew){
		if(*m++){
			*w++ = *r++;
			*w++ = *r++;
			*w++ = *r++;
		}else{
			w += 3;
			r += 3;
		}
	}
	return bdst;	/* not used */
}

static Buffer
boolcopy32(Buffer bdst, Buffer bsrc, Buffer bmask, int dx, int i, int o)
{
	uchar *m;
	ulong *r, *w, *ew;

	USED(i);
	USED(o);
	m = bmask.grey;
	w = (ulong*)bdst.red;
	r = (ulong*)bsrc.red;
	ew = w+dx;
	for(; w < ew; w++,r++)
		if(*m++)
			*w = *r;
	return bdst;	/* not used */
}

static Buffer
genconv(Param *p, uchar *buf, int y)
{
	Buffer b;
	int nb;
	uchar *r, *w, *ew;

	/* read from source into RGB format in convbuf */
	b = p->convreadcall(p, p->convbuf, y);

	/* write RGB format into dst format in buf */
	p->convwritecall(p->convdpar, buf, b);

	if(p->convdx){
		nb = p->convdpar->img->depth/8;
		r = buf;
		w = buf+nb*p->dx;
		ew = buf+nb*p->convdx;
		while(w<ew)
			*w++ = *r++;
	}

	b.red = buf;
	b.blu = b.grn = b.grey = b.alpha = nil;
	b.rgba = (ulong*)buf;
	b.delta = 0;
	
	return b;
}

static Readfn*
convfn(Memimage *dst, Param *dpar, Memimage *src, Param *spar, int *ndrawbuf)
{
	if(dst->chan == src->chan && !(src->flags&Frepl)){
//if(drawdebug) iprint("readptr...");
		return readptr;
	}

	if(dst->chan==CMAP8 && (src->chan==GREY1||src->chan==GREY2||src->chan==GREY4)){
		/* cheat because we know the replicated value is exactly the color map entry. */
//if(drawdebug) iprint("Readnbit...");
		return readnbit;
	}

	spar->convreadcall = readfn(src);
	spar->convwritecall = writefn(dst);
	spar->convdpar = dpar;

	/* allocate a conversion buffer */
	spar->convbufoff = *ndrawbuf;
	*ndrawbuf += spar->dx*4;

	if(spar->dx > Dx(spar->img->r)){
		spar->convdx = spar->dx;
		spar->dx = Dx(spar->img->r);
	}

//if(drawdebug) iprint("genconv...");
	return genconv;
}

static ulong
pixelbits(Memimage *i, Point pt)
{
	uchar *p;
	ulong val;
	int off, bpp, npack;

	val = 0;
	p = byteaddr(i, pt);
	switch(bpp=i->depth){
	case 1:
	case 2:
	case 4:
		npack = 8/bpp;