path: root/draw/draw_paint.c

#include "fitz.h"

/*

The functions in this file implement various flavours of Porter-Duff blending.

We take the following as definitions:

	Cx = Color (from plane x)
	ax = Alpha (from plane x)
	cx = Cx.ax = Premultiplied color (from plane x)

The general PorterDuff blending equation is:

	Blend Z = X op Y	cz = Fx.cx + Fy. cy	where Fx and Fy depend on op

The two operations we use in this file are: '(X in Y) over Z' and
'S over Z'. The definitions of the 'over' and 'in' operations are as
follows:

	For S over Z,	Fs = 1, Fz = 1-as
	For X in Y,	Fx = ay, Fy = 0

We have 2 choices; we can either work with premultiplied data, or non
premultiplied data. Our

First the premultiplied case:

	Let S = (X in Y)
	Let R = (X in Y) over Z = S over Z

	cs	= cx.Fx + cy.Fy	(where Fx = ay, Fy = 0)
		= cx.ay
	as	= ax.Fx + ay.Fy
		= ax.ay

	cr	= cs.Fs + cz.Fz	(where Fs = 1, Fz = 1-as)
		= cs + cz.(1-as)
		= cx.ay + cz.(1-ax.ay)
	ar	= as.Fs + az.Fz
		= as + az.(1-as)
		= ax.ay + az.(1-ax.ay)

This has various nice properties, like not needing any divisions, and
being symmetric in color and alpha, so this is what we use. Because we
went through the pain of deriving the non premultiplied forms, we list
them here too, though they are not used.

Non Pre-multiplied case:

	Cs.as	= Fx.Cx.ax + Fy.Cy.ay	(where Fx = ay, Fy = 0)
		= Cx.ay.ax
	Cs	= (Cx.ay.ax)/(ay.ax)
		= Cx
	Cr.ar	= Fs.Cs.as + Fz.Cz.az	(where Fs = 1, Fz = 1-as)
		= Cs.as	+ (1-as).Cz.az
		= Cx.ax.ay + Cz.az.(1-ax.ay)
	Cr	= (Cx.ax.ay + Cz.az.(1-ax.ay))/(ax.ay + az.(1-ax-ay))

Much more complex, it seems. However, if we could restrict ourselves to
the case where we were always plotting onto an opaque background (i.e.
az = 1), then:

	Cr	= Cx.(ax.ay) + Cz.(1-ax.ay)
		= (Cx-Cz)*(1-ax.ay) + Cz	(a single MLA operation)
	ar	= 1

Sadly, this is not true in the general case, so we abandon this effort
and stick to using the premultiplied form.

*/

typedef unsigned char byte;

/* Blend a non-premultiplied color in mask over destination */

static inline void
fz_paint_span_with_color_2(byte * restrict dp, byte * restrict mp, int w, byte *color)
{
	int sa = FZ_EXPAND(color[1]);
	int g = color[0];
	while (w--)
	{
		int ma = *mp++;
		ma = FZ_COMBINE(FZ_EXPAND(ma), sa);
		dp[0] = FZ_BLEND(g, dp[0], ma);
		dp[1] = FZ_BLEND(255, dp[1], ma);
		dp += 2;
	}
}

static inline void
fz_paint_span_with_color_4(byte * restrict dp, byte * restrict mp, int w, byte *color)
{
	int sa = FZ_EXPAND(color[3]);
	int r = color[0];
	int g = color[1];
	int b = color[2];
	while (w--)
	{
		int ma = *mp++;
		ma = FZ_COMBINE(FZ_EXPAND(ma), sa);
		dp[0] = FZ_BLEND(r, dp[0], ma);
		dp[1] = FZ_BLEND(g, dp[1], ma);
		dp[2] = FZ_BLEND(b, dp[2], ma);
		dp[3] = FZ_BLEND(255, dp[3], ma);
		dp += 4;
	}
}

static inline void
fz_paint_span_with_color_N(byte * restrict dp, byte * restrict mp, int n, int w, byte *color)
{
	int sa = FZ_EXPAND(color[n-1]);
	int k;
	n--;
	while (w--)
	{
		int ma = *mp++;
		ma = FZ_COMBINE(FZ_EXPAND(ma), sa);
		for (k = 0; k < n; k++)
			dp[k] = FZ_BLEND(color[k], dp[k], ma);
		dp[k] = FZ_BLEND(255, dp[k], ma);
		dp += n;
	}
}

void
fz_paint_span_with_color(byte * restrict dp, byte * restrict mp, int n, int w, byte *color)
{
	switch (n)
	{
	case 2: fz_paint_span_with_color_2(dp, mp, w, color); break;
	case 4: fz_paint_span_with_color_4(dp, mp, w, color); break;
	default: fz_paint_span_with_color_N(dp, mp, n, w, color); break;
	}
}

/* Blend source in mask over destination */

static inline void
fz_paint_span_with_mask_2(byte * restrict dp, byte * restrict sp, byte * restrict mp, int w)
{
	while (w--)
	{
		int masa;
		int ma = *mp++;
		ma = FZ_EXPAND(ma);
		masa = FZ_COMBINE(sp[1], ma);
		masa = 255 - masa;
		masa = FZ_EXPAND(masa);
		*dp = FZ_COMBINE2(*sp, ma, *dp, masa);
		sp++; dp++;
		*dp = FZ_COMBINE2(*sp, ma, *dp, masa);
		sp++; dp++;
	}
}

static inline void
fz_paint_span_with_mask_4(byte * restrict dp, byte * restrict sp, byte * restrict mp, int w)
{
	while (w--)
	{
		int masa;
		int ma = *mp++;
		ma = FZ_EXPAND(ma);
		masa = FZ_COMBINE(sp[3], ma);
		masa = 255 - masa;
		masa = FZ_EXPAND(masa);
		*dp = FZ_COMBINE2(*sp, ma, *dp, masa);
		sp++; dp++;
		*dp = FZ_COMBINE2(*sp, ma, *dp, masa);
		sp++; dp++;
		*dp = FZ_COMBINE2(*sp, ma, *dp, masa);
		sp++; dp++;
		*dp = FZ_COMBINE2(*sp, ma, *dp, masa);
		sp++; dp++;
	}
}

static inline void
fz_paint_span_with_mask_N(byte * restrict dp, byte * restrict sp, byte * restrict mp, int n, int w)
{
	n--;
	while (w--)
	{
		int k = n;
		int masa;
		int ma = *mp++;
		ma = FZ_EXPAND(ma);
		masa = FZ_COMBINE(sp[n-1], ma);
		masa = 255-masa;
		masa = FZ_EXPAND(masa);
		while (k--)
		{
			*dp = FZ_COMBINE2(*sp, ma, *dp, masa);
			sp++; dp++;
		}
	}
}

static void
fz_paint_span_with_mask(byte * restrict dp, byte * restrict sp, byte * restrict mp, int n, int w)
{
	switch (n)
	{
	case 2: fz_paint_span_with_mask_2(dp, sp, mp, w); break;
	case 4: fz_paint_span_with_mask_4(dp, sp, mp, w); break;
	default: fz_paint_span_with_mask_N(dp, sp, mp, n, w); break;
	}
}

/* Blend source in constant alpha over destination */

static inline void
fz_paint_span_2_with_alpha(byte * restrict dp, byte * restrict sp, int w, int alpha)
{
	alpha = FZ_EXPAND(alpha);
	while (w--)
	{
		int masa = FZ_COMBINE(sp[1], alpha);
		*dp = FZ_BLEND(*sp, *dp, masa);
		dp++; sp++;
		*dp = FZ_BLEND(*sp, *dp, masa);
		dp++; sp++;
	}
}

static inline void
fz_paint_span_4_with_alpha(byte * restrict dp, byte * restrict sp, int w, int alpha)
{
	alpha = FZ_EXPAND(alpha);
	while (w--)
	{
		int masa = FZ_COMBINE(sp[3], alpha);
		*dp = FZ_BLEND(*sp, *dp, masa);
		sp++; dp++;
		*dp = FZ_BLEND(*sp, *dp, masa);
		sp++; dp++;
		*dp = FZ_BLEND(*sp, *dp, masa);
		sp++; dp++;
		*dp = FZ_BLEND(*sp, *dp, masa);
		sp++; dp++;
	}
}

static inline void
fz_paint_span_N_with_alpha(byte * restrict dp, byte * restrict sp, int n, int w, int alpha)
{
	alpha = FZ_EXPAND(alpha);
	while (w--)
	{
		int masa = FZ_COMBINE(sp[n-1], alpha);
		int k = n;
		while (k--)
		{
			*dp = FZ_BLEND(*sp++, *dp, masa);
			dp++;
		}
	}
}

/* Blend source over destination */

static inline void
fz_paint_span_1(byte * restrict dp, byte * restrict sp, int w)
{
	while (w--)
	{
		int t = FZ_EXPAND(255 - sp[0]);
		*dp = *sp++ + FZ_COMBINE(*dp, t);
		dp ++;
	}
}

static inline void
fz_paint_span_2(byte * restrict dp, byte * restrict sp, int w)
{
	while (w--)
	{
		int t = FZ_EXPAND(255 - sp[1]);
		*dp = *sp++ + FZ_COMBINE(*dp, t);
		dp++;
		*dp = *sp++ + FZ_COMBINE(*dp, t);
		dp++;
	}
}

static inline void
fz_paint_span_4(byte * restrict dp, byte * restrict sp, int w)
{
	while (w--)
	{
		int t = FZ_EXPAND(255 - sp[3]);
		*dp = *sp++ + FZ_COMBINE(*dp, t);
		dp++;
		*dp = *sp++ + FZ_COMBINE(*dp, t);
		dp++;
		*dp = *sp++ + FZ_COMBINE(*dp, t);
		dp++;
		*dp = *sp++ + FZ_COMBINE(*dp, t);
		dp++;
	}
}

static inline void
fz_paint_span_N(byte * restrict dp, byte * restrict sp, int n, int w)
{
	while (w--)
	{
		int k = n;
		int t = FZ_EXPAND(255 - sp[n-1]);
		while (k--)
		{
			*dp = *sp++ + FZ_COMBINE(*dp, t);
			dp++;
		}
	}
}

void
fz_paint_span(byte * restrict dp, byte * restrict sp, int n, int w, int alpha)
{
	if (alpha == 255)
	{
		switch (n)
		{
		case 1: fz_paint_span_1(dp, sp, w); break;
		case 2: fz_paint_span_2(dp, sp, w); break;
		case 4: fz_paint_span_4(dp, sp, w); break;
		default: fz_paint_span_N(dp, sp, n, w); break;
		}
	}
	else if (alpha > 0)
	{
		switch (n)
		{
		case 2: fz_paint_span_2_with_alpha(dp, sp, w, alpha); break;
		case 4: fz_paint_span_4_with_alpha(dp, sp, w, alpha); break;
		default: fz_paint_span_N_with_alpha(dp, sp, n, w, alpha); break;
		}
	}
}

/*
 * Pixmap blending functions
 */

void
fz_paint_pixmap_with_rect(fz_pixmap *dst, fz_pixmap *src, int alpha, fz_bbox bbox)
{
	unsigned char *sp, *dp;
	int x, y, w, h, n;

	assert(dst->n == src->n);

	bbox = fz_intersect_bbox(bbox, fz_bound_pixmap(dst));
	bbox = fz_intersect_bbox(bbox, fz_bound_pixmap(src));

	x = bbox.x0;
	y = bbox.y0;
	w = bbox.x1 - bbox.x0;
	h = bbox.y1 - bbox.y0;
	if ((w | h) == 0)
		return;

	n = src->n;
	sp = src->samples + ((y - src->y) * src->w + (x - src->x)) * src->n;
	dp = dst->samples + ((y - dst->y) * dst->w + (x - dst->x)) * dst->n;

	while (h--)
	{
		fz_paint_span(dp, sp, n, w, alpha);
		sp += src->w * n;
		dp += dst->w * n;
	}
}

void
fz_paint_pixmap(fz_pixmap *dst, fz_pixmap *src, int alpha)
{
	unsigned char *sp, *dp;
	fz_bbox bbox;
	int x, y, w, h, n;

	assert(dst->n == src->n);

	bbox = fz_bound_pixmap(dst);
	bbox = fz_intersect_bbox(bbox, fz_bound_pixmap(src));

	x = bbox.x0;
	y = bbox.y0;
	w = bbox.x1 - bbox.x0;
	h = bbox.y1 - bbox.y0;
	if ((w | h) == 0)
		return;

	n = src->n;
	sp = src->samples + ((y - src->y) * src->w + (x - src->x)) * src->n;
	dp = dst->samples + ((y - dst->y) * dst->w + (x - dst->x)) * dst->n;

	while (h--)
	{
		fz_paint_span(dp, sp, n, w, alpha);
		sp += src->w * n;
		dp += dst->w * n;
	}
}

void
fz_paint_pixmap_with_mask(fz_pixmap *dst, fz_pixmap *src, fz_pixmap *msk)
{
	unsigned char *sp, *dp, *mp;
	fz_bbox bbox;
	int x, y, w, h, n;

	assert(dst->n == src->n);
	assert(msk->n == 1);

	bbox = fz_bound_pixmap(dst);
	bbox = fz_intersect_bbox(bbox, fz_bound_pixmap(src));
	bbox = fz_intersect_bbox(bbox, fz_bound_pixmap(msk));

	x = bbox.x0;
	y = bbox.y0;
	w = bbox.x1 - bbox.x0;
	h = bbox.y1 - bbox.y0;
	if ((w | h) == 0)
		return;

	n = src->n;
	sp = src->samples + ((y - src->y) * src->w + (x - src->x)) * src->n;
	mp = msk->samples + ((y - msk->y) * msk->w + (x - msk->x)) * msk->n;
	dp = dst->samples + ((y - dst->y) * dst->w + (x - dst->x)) * dst->n;

	while (h--)
	{
		fz_paint_span_with_mask(dp, sp, mp, n, w);
		sp += src->w * n;
		dp += dst->w * n;
		mp += msk->w;
	}
}