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

	isgrey = dst->flags&Fgrey;

	/*
	 * Buffering when src and dst are the same bitmap is sufficient but not 
	 * necessary.  There are stronger conditions we could use.  We could
	 * check to see if the rectangles intersect, and if simply moving in the
	 * correct y direction can avoid the need to buffer.
	 */
	needbuf = (src->data == dst->data);

	spar = getparam(src, sr, isgrey, needbuf);
	dpar = getparam(dst, r, isgrey, needbuf);
	mpar = getparam(mask, mr, 0, needbuf);

	dir = (needbuf && byteaddr(dst, r.min) > byteaddr(src, sr.min)) ? -1 : 1;
	spar.dir = mpar.dir = dpar.dir = dir;

	/*
	 * If the mask is purely boolean, we can convert from src to dst format
	 * when we read src, and then just copy it to dst where the mask tells us to.
	 * This requires a boolean (1-bit grey) mask and lack of a source alpha channel.
	 *
	 * The computation is accomplished by assigning the function pointers as follows:
	 *	rdsrc - read and convert source into dst format in a buffer
	 * 	rdmask - convert mask to bytes, set pointer to it
	 * 	rddst - fill with pointer to real dst data, but do no reads
	 *	calc - copy src onto dst when mask says to.
	 *	wrdst - do nothing
	 * This is slightly sleazy, since things aren't doing exactly what their names say,
	 * but it avoids a fair amount of code duplication to make this a case here
	 * rather than have a separate booldraw.
	 */
//if(drawdebug) iprint("flag %lud mchan %lux=?%x dd %d\n", src->flags&Falpha, mask->chan, GREY1, dst->depth);
	if(!(src->flags&Falpha) && mask->chan == GREY1 && dst->depth >= 8 && op == SoverD){
//if(drawdebug) iprint("boolcopy...");
		rdsrc = convfn(dst, &dpar, src, &spar);
		rddst = readptr;
		rdmask = readfn(mask);
		calc = boolcopyfn(dst, mask);
		wrdst = nullwrite;
	}else{
		/* usual alphadraw parameter fetching */
		rdsrc = readfn(src);
		rddst = readfn(dst);
		wrdst = writefn(dst);
		calc = alphacalc[op];

		/*
		 * If there is no alpha channel, we'll ask for a grey channel
		 * and pretend it is the alpha.
		 */
		if(mask->flags&Falpha){
			rdmask = readalphafn(mask);
			mpar.alphaonly = 1;
		}else{
			mpar.greymaskcall = readfn(mask);
			mpar.convgrey = 1;
			rdmask = greymaskread;

			/*
			 * Should really be above, but then boolcopyfns would have
			 * to deal with bit alignment, and I haven't written that.
			 *
			 * This is a common case for things like ellipse drawing.
			 * When there's no alpha involved and the mask is boolean,
			 * we can avoid all the division and multiplication.
			 */
			if(mask->chan == GREY1 && !(src->flags&Falpha))
				calc = boolcalc[op];
			else if(op == SoverD && !(src->flags&Falpha))
				calc = alphacalcS;
		}
	}

	/*
	 * If the image has a small enough repl rectangle,
	 * we can just read each line once and cache them.
	 */
	if(spar.replcache){
		spar.replcall = rdsrc;
		rdsrc = replread;
	}
	if(mpar.replcache){
		mpar.replcall = rdmask;
		rdmask = replread;
	}

	if(allocdrawbuf() < 0)
		return 0;

	/*
	 * Before we were saving only offsets from drawbuf in the parameter
	 * structures; now that drawbuf has been grown to accomodate us,
	 * we can fill in the pointers.
	 */
	spar.bufbase = drawbuf+spar.bufoff;
	mpar.bufbase = drawbuf+mpar.bufoff;
	dpar.bufbase = drawbuf+dpar.bufoff;
	spar.convbuf = drawbuf+spar.convbufoff;

	if(dir == 1){
		starty = 0;
		endy = dy;
	}else{
		starty = dy-1;
		endy = -1;
	}

	/*
	 * srcy, masky, and dsty are offsets from the top of their
	 * respective Rectangles.  they need to be contained within
	 * the rectangles, so clipy can keep them there without division.
 	 */
	srcy = (starty + sr.min.y - src->r.min.y)%Dy(src->r);
	masky = (starty + mr.min.y - mask->r.min.y)%Dy(mask->r);
	dsty = starty + r.min.y - dst->r.min.y;

	assert(0 <= srcy && srcy < Dy(src->r));
	assert(0 <= masky && masky < Dy(mask->r));
	assert(0 <= dsty && dsty < Dy(dst->r));

	for(y=starty; y!=endy; y+=dir, srcy+=dir, masky+=dir, dsty+=dir){
		clipy(src, &srcy);
		clipy(dst, &dsty);
		clipy(mask, &masky);

		bsrc = rdsrc(&spar, spar.bufbase, srcy);
DBG print("[");
		bmask = rdmask(&mpar, mpar.bufbase, masky);
DBG print("]\n");
		bdst = rddst(&dpar, dpar.bufbase, dsty);
DBG		dumpbuf("src", bsrc, dx);
DBG		dumpbuf("mask", bmask, dx);
DBG		dumpbuf("dst", bdst, dx);
		bdst = calc(bdst, bsrc, bmask, dx, isgrey, op);
		wrdst(&dpar, dpar.bytermin+dsty*dpar.bwidth, bdst);
	}

	return 1;
}
#undef DBG

static Buffer
alphacalc0(Buffer bdst, Buffer b1, Buffer b2, int dx, int grey, int op)
{
	USED(grey);
	USED(op);
	memset(bdst.rgba, 0, dx*bdst.delta);
	return bdst;
}

static Buffer
alphacalc14(Buffer bdst, Buffer bsrc, Buffer bmask, int dx, int grey, int op)
{
	Buffer obdst;
	int fd, sadelta;
	int i, sa, ma, q;
	ulong s, t;

	obdst = bdst;
	sadelta = bsrc.alpha == &ones ? 0 : bsrc.delta;
	q = bsrc.delta == 4 && bdst.delta == 4;

	for(i=0; i<dx; i++){
		sa = *bsrc.alpha;
		ma = *bmask.alpha;
		fd = MUL(sa, ma, t);
		if(op == DoutS)
			fd = 255-fd;

		if(grey){
			*bdst.grey = MUL(fd, *bdst.grey, t);
			bsrc.grey += bsrc.delta;
			bdst.grey += bdst.delta;
		}else{
			if(q){
				*bdst.rgba = MUL0123(fd, *bdst.rgba, s, t);
				bsrc.rgba++;
				bdst.rgba++;
				bsrc.alpha += sadelta;
				bmask.alpha += bmask.delta;
				continue;
			}
			*bdst.red = MUL(fd, *bdst.red, t);
			*bdst.grn = MUL(fd, *bdst.grn, t);
			*bdst.blu = MUL(fd, *bdst.blu, t);
			bsrc.red += bsrc.delta;
			bsrc.blu += bsrc.delta;
			bsrc.grn += bsrc.delta;
			bdst.red += bdst.delta;
			bdst.blu += bdst.delta;
			bdst.grn += bdst.delta;
		}
		if(bdst.alpha != &ones){
			*bdst.alpha = MUL(fd, *bdst.alpha, t);
			bdst.alpha += bdst.delta;
		}
		bmask.alpha += bmask.delta;
		bsrc.alpha += sadelta;
	}
	return obdst;
}

static Buffer
alphacalc2810(Buffer bdst, Buffer bsrc, Buffer bmask, int dx, int grey, int op)
{
	Buffer obdst;
	int fs, sadelta;
	int i, ma, da, q;
	ulong s, t;

	obdst = bdst;
	sadelta = bsrc.alpha == &ones ? 0 : bsrc.delta;
	q = bsrc.delta == 4 && bdst.delta == 4;

	for(i=0; i<dx; i++){
		ma = *bmask.alpha;
		da = *bdst.alpha;
		if(op == SoutD)
			da = 255-da;
		fs = ma;
		if(op != S)
			fs = MUL(fs, da, t);

		if(grey){
			*bdst.grey = MUL(fs, *bsrc.grey, t);
			bsrc.grey += bsrc.delta;
			bdst.grey += bdst.delta;
		}else{
			if(q){
				*bdst.rgba = MUL0123(fs, *bsrc.rgba, s, t);
				bsrc.rgba++;
				bdst.rgba++;
				bmask.alpha += bmask.delta;
				bdst.alpha += bdst.delta;
				continue;
			}
			*bdst.red = MUL(fs, *bsrc.red, t);
			*bdst.grn = MUL(fs, *bsrc.grn, t);
			*bdst.blu = MUL(fs, *bsrc.blu, t);
			bsrc.red += bsrc.delta;
			bsrc.blu += bsrc.delta;
			bsrc.grn += bsrc.delta;
			bdst.red += bdst.delta;
			bdst.blu += bdst.delta;
			bdst.grn += bdst.delta;
		}
		if(bdst.alpha != &ones){
			*bdst.alpha = MUL(fs, *bsrc.alpha, t);
			bdst.alpha += bdst.delta;
		}
		bmask.alpha += bmask.delta;
		bsrc.alpha += sadelta;
	}
	return obdst;
}

static Buffer
alphacalc3679(Buffer bdst, Buffer bsrc, Buffer bmask, int dx, int grey, int op)
{
	Buffer obdst;
	int fs, fd, sadelta;
	int i, sa, ma, da, q;
	ulong s, t, u, v;

	obdst = bdst;
	sadelta = bsrc.alpha == &ones ? 0 : bsrc.delta;
	q = bsrc.delta == 4 && bdst.delta == 4;

	for(i=0; i<dx; i++){
		sa = *bsrc.alpha;
		ma = *bmask.alpha;
		da = *bdst.alpha;
		if(op == SatopD)
			fs = MUL(ma, da, t);
		else
			fs = MUL(ma, 255-da, t);
		if(op == DoverS)
			fd = 255;
		else{
			fd = MUL(sa, ma, t);
			if(op != DatopS)
				fd = 255-fd;
		}

		if(grey){
			*bdst.grey = MUL(fs, *bsrc.grey, s)+MUL(fd, *bdst.grey, t);
			bsrc.grey += bsrc.delta;
			bdst.grey += bdst.delta;
		}else{
			if(q){
				*bdst.rgba = MUL0123(fs, *bsrc.rgba, s, t)+MUL0123(fd, *bdst.rgba, u, v);
				bsrc.rgba++;
				bdst.rgba++;
				bsrc.alpha += sadelta;
				bmask.alpha += bmask.delta;
				bdst.alpha += bdst.delta;
				continue;
			}
			*bdst.red = MUL(fs, *bsrc.red, s)+MUL(fd, *bdst.red, t);
			*bdst.grn = MUL(fs, *bsrc.grn, s)+MUL(fd, *bdst.grn, t);
			*bdst.blu = MUL(fs, *bsrc.blu, s)+MUL(fd, *bdst.blu, t);
			bsrc.red += bsrc.delta;
			bsrc.blu += bsrc.delta;
			bsrc.grn += bsrc.delta;
			bdst.red += bdst.delta;
			bdst.blu += bdst.delta;
			bdst.grn += bdst.delta;
		}
		if(bdst.alpha != &ones){
			*bdst.alpha = MUL(fs, sa, s)+MUL(fd, da, t);
			bdst.alpha += bdst.delta;
		}
		bmask.alpha += bmask.delta;
		bsrc.alpha += sadelta;
	}
	return obdst;
}

static Buffer
alphacalc5(Buffer bdst, Buffer b1, Buffer b2, int dx, int grey, int op)
{
	USED(dx);
	USED(grey);
	USED(op);
	return bdst;
}

static Buffer
alphacalc11(Buffer bdst, Buffer bsrc, Buffer bmask, int dx, int grey, int op)
{
	Buffer obdst;
	int fd, sadelta;
	int i, sa, ma, q;
	ulong s, t, u, v;

	USED(op);
	obdst = bdst;
	sadelta = bsrc.alpha == &ones ? 0 : bsrc.delta;
	q = bsrc.delta == 4 && bdst.delta == 4;

	for(i=0; i<dx; i++){
		sa = *bsrc.alpha;
		ma = *bmask.alpha;
		fd = 255-MUL(sa, ma, t);

		if(grey){
			*bdst.grey = MUL(ma, *bsrc.grey, s)+MUL(fd, *bdst.grey, t);
			bsrc.grey += bsrc.delta;
			bdst.grey += bdst.delta;
		}else{
			if(q){
				*bdst.rgba = MUL0123(ma, *bsrc.rgba, s, t)+MUL0123(fd, *bdst.rgba, u, v);
				bsrc.rgba++;
				bdst.rgba++;
				bsrc.alpha += sadelta;
				bmask.alpha += bmask.delta;
				continue;
			}
			*bdst.red = MUL(ma, *bsrc.red, s)+MUL(fd, *bdst.red, t);
			*bdst.grn = MUL(ma, *bsrc.grn, s)+MUL(fd, *bdst.grn, t);
			*bdst.blu = MUL(ma, *bsrc.blu, s)+MUL(fd, *bdst.blu, t);
			bsrc.red += bsrc.delta;
			bsrc.blu += bsrc.delta;
			bsrc.grn += bsrc.delta;
			bdst.red += bdst.delta;
			bdst.blu += bdst.delta;
			bdst.grn += bdst.delta;
		}
		if(bdst.alpha != &ones){
			*bdst.alpha = MUL(ma, sa, s)+MUL(fd, *bdst.alpha, t);
			bdst.alpha += bdst.delta;
		}
		bmask.alpha += bmask.delta;
		bsrc.alpha += sadelta;
	}
	return obdst;
}

/*
not used yet
source and mask alpha 1
static Buffer
alphacalcS0(Buffer bdst, Buffer bsrc, Buffer bmask, int dx, int grey, int op)
{
	Buffer obdst;
	int i;

	USED(op);
	obdst = bdst;
	if(bsrc.delta == bdst.delta){
		memmove(bdst.rgba, bsrc.rgba, dx*bdst.delta);
		return obdst;
	}
	for(i=0; i<dx; i++){
		if(grey){
			*bdst.grey = *bsrc.grey;
			bsrc.grey += bsrc.delta;
			bdst.grey += bdst.delta;
		}else{
			*bdst.red = *bsrc.red;
			*bdst.grn = *bsrc.grn;
			*bdst.blu = *bsrc.blu;
			bsrc.red += bsrc.delta;
			bsrc.blu += bsrc.delta;
			bsrc.grn += bsrc.delta;
			bdst.red += bdst.delta;
			bdst.blu += bdst.delta;
			bdst.grn += bdst.delta;
		}
		if(bdst.alpha != &ones){
			*bdst.alpha = 255;
			bdst.alpha += bdst.delta;
		}
	}
	return obdst;
}
*/

/* source alpha 1 */
static Buffer
alphacalcS(Buffer bdst, Buffer bsrc, Buffer bmask, int dx, int grey, int op)
{
	Buffer obdst;
	int fd;
	int i, ma;
	ulong s, t;

	USED(op);
	obdst = bdst;

	for(i=0; i<dx; i++){
		ma = *bmask.alpha;
		fd = 255-ma;

		if(grey){
			*bdst.grey = MUL(ma, *bsrc.grey, s)+MUL(fd, *bdst.grey, t);
			bsrc.grey += bsrc.delta;
			bdst.grey += bdst.delta;
		}else{
			*bdst.red = MUL(ma, *bsrc.red, s)+MUL(fd, *bdst.red, t);
			*bdst.grn = MUL(ma, *bsrc.grn, s)+MUL(fd, *bdst.grn, t);
			*bdst.blu = MUL(ma, *bsrc.blu, s)+MUL(fd, *bdst.blu, t);
			bsrc.red += bsrc.delta;
			bsrc.blu += bsrc.delta;
			bsrc.grn += bsrc.delta;
			bdst.red += bdst.delta;
			bdst.blu += bdst.delta;
			bdst.grn += bdst.delta;
		}
		if(bdst.alpha != &ones){
			*bdst.alpha = ma+MUL(fd, *bdst.alpha, t);
			bdst.alpha += bdst.delta;
		}
		bmask.alpha += bmask.delta;
	}
	return obdst;
}

static Buffer
boolcalc14(Buffer bdst, Buffer b1, Buffer bmask, int dx, int grey, int op)
{
	Buffer obdst;
	int i, ma, zero;

	obdst = bdst;

	for(i=0; i<dx; i++){
		ma = *bmask.alpha;
		zero = ma ? op == DoutS : op == DinS;

		if(grey){
			if(zero)
				*bdst.grey = 0;
			bdst.grey += bdst.delta;
		}else{
			if(zero)
				*bdst.red = *bdst.grn = *bdst.blu = 0;
			bdst.red += bdst.delta;
			bdst.blu += bdst.delta;
			bdst.grn += bdst.delta;
		}
		bmask.alpha += bmask.delta;
		if(bdst.alpha != &ones){
			if(zero)
				*bdst.alpha = 0;
			bdst.alpha += bdst.delta;
		}
	}
	return obdst;
}

static Buffer
boolcalc236789(Buffer bdst, Buffer bsrc, Buffer bmask, int dx, int grey, int op)
{
	Buffer obdst;
	int fs, fd;
	int i, ma, da, zero;
	ulong s, t;

	obdst = bdst;
	zero = !(op&1);

	for(i=0; i<dx; i++){
		ma = *bmask.alpha;
		da = *bdst.alpha;
		fs = da;
		if(op&2)
			fs = 255-da;
		fd = 0;
		if(op&4)
			fd = 255;

		if(grey){
			if(ma)
				*bdst.grey = MUL(fs, *bsrc.grey, s)+MUL(fd, *bdst.grey, t);
			else if(zero)
				*bdst.grey = 0;
			bsrc.grey += bsrc.delta;
			bdst.grey += bdst.delta;
		}else{
			if(ma){
				*bdst.red = MUL(fs, *bsrc.red, s)+MUL(fd, *bdst.red, t);
				*bdst.grn = MUL(fs, *bsrc.grn, s)+MUL(fd, *bdst.grn, t);
				*bdst.blu = MUL(fs, *bsrc.blu, s)+MUL(fd, *bdst.blu, t);
			}
			else if(zero)
				*bdst.red = *bdst.grn = *bdst.blu = 0;
			bsrc.red += bsrc.delta;
			bsrc.blu += bsrc.delta;
			bsrc.grn += bsrc.delta;
			bdst.red += bdst.delta;
			bdst.blu += bdst.delta;
			bdst.grn += bdst.delta;
		}
		bmask.alpha += bmask.delta;
		if(bdst.alpha != &ones){
			if(ma)
				*bdst.alpha = fs+MUL(fd, da, t);
			else if(zero)
				*bdst.alpha = 0;
			bdst.alpha += bdst.delta;
		}
	}
	return obdst;
}

static Buffer
boolcalc1011(Buffer bdst, Buffer bsrc, Buffer bmask, int dx, int grey, int op)
{
	Buffer obdst;
	int i, ma, zero;

	obdst = bdst;
	zero = !(op&1);

	for(i=0; i<dx; i++){
		ma = *bmask.alpha;

		if(grey){
			if(ma)
				*bdst.grey = *bsrc.grey;
			else if(zero)
				*bdst.grey = 0;
			bsrc.grey += bsrc.delta;
			bdst.grey += bdst.delta;
		}else{
			if(ma){
				*bdst.red = *bsrc.red;
				*bdst.grn = *bsrc.grn;
				*bdst.blu = *bsrc.blu;
			}
			else if(zero)
				*bdst.red = *bdst.grn = *bdst.blu = 0;
			bsrc.red += bsrc.delta;
			bsrc.blu += bsrc.delta;
			bsrc.grn += bsrc.delta;
			bdst.red += bdst.delta;
			bdst.blu += bdst.delta;
			bdst.grn += bdst.delta;
		}
		bmask.alpha += bmask.delta;
		if(bdst.alpha != &ones){
			if(ma)
				*bdst.alpha = 255;
			else if(zero)
				*bdst.alpha = 0;
			bdst.alpha += bdst.delta;
		}
	}
	return obdst;
}
/*
 * Replicated cached scan line read.  Call the function listed in the Param,
 * but cache the result so that for replicated images we only do the work once.
 */
static Buffer
replread(Param *p, uchar *s, int y)
{
	Buffer *b;

	USED(s);
	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;