Add fz_blend_pixel_function.

Inspired by Sumatras gdi devices need for such a function expose
the blending functions. Note that we produce unsigned char's
where Zenikos original produces ints, but it's otherwise
identical.

This requires us to make various knockon changes throughout the code
from int to unsigned char, none of which should make any difference
at all - I hope!

We reserve the right to change/amend this function in future to
operate on blocks of pixels (or pixels in different colorspaces)
(or anything else we think of) in future.

2 files changed, 49 insertions, 13 deletions

diff --git a/draw/draw_blend.c b/draw/draw_blend.c
index 518d3ab4..1a6fcc13 100644
--- a/draw/draw_blend.c
+++ b/draw/draw_blend.c
@@ -122,7 +122,7 @@ static inline int fz_exclusion_byte(int b, int s)
 /* Non-separable blend modes */
 
 static void
-fz_luminosity_rgb(int *rd, int *gd, int *bd, int rb, int gb, int bb, int rs, int gs, int bs)
+fz_luminosity_rgb(unsigned char *rd, unsigned char *gd, unsigned char *bd, int rb, int gb, int bb, int rs, int gs, int bs)
 {
 	int delta, scale;
 	int r, g, b, y;
@@ -153,13 +153,13 @@ fz_luminosity_rgb(int *rd, int *gd, int *bd, int rb, int gb, int bb, int rs, int
 		b = y + (((b - y) * scale + 0x8000) >> 16);
 	}
 
-	*rd = r;
-	*gd = g;
-	*bd = b;
+	*rd = CLAMP(r, 0, 255);
+	*gd = CLAMP(g, 0, 255);
+	*bd = CLAMP(b, 0, 255);
 }
 
 static void
-fz_saturation_rgb(int *rd, int *gd, int *bd, int rb, int gb, int bb, int rs, int gs, int bs)
+fz_saturation_rgb(unsigned char *rd, unsigned char *gd, unsigned char *bd, int rb, int gb, int bb, int rs, int gs, int bs)
 {
 	int minb, maxb;
 	int mins, maxs;
@@ -172,6 +172,7 @@ fz_saturation_rgb(int *rd, int *gd, int *bd, int rb, int gb, int bb, int rs, int
 	if (minb == maxb)
 	{
 		/* backdrop has zero saturation, avoid divide by 0 */
+		gb = CLAMP(gb, 0, 255);
 		*rd = gb;
 		*gd = gb;
 		*bd = gb;
@@ -211,25 +212,59 @@ fz_saturation_rgb(int *rd, int *gd, int *bd, int rb, int gb, int bb, int rs, int
 		b = y + (((b - y) * scale + 0x8000) >> 16);
 	}
 
-	*rd = r;
-	*gd = g;
-	*bd = b;
+	*rd = CLAMP(r, 0, 255);
+	*gd = CLAMP(g, 0, 255);
+	*bd = CLAMP(b, 0, 255);
 }
 
 static void
-fz_color_rgb(int *rr, int *rg, int *rb, int br, int bg, int bb, int sr, int sg, int sb)
+fz_color_rgb(unsigned char *rr, unsigned char *rg, unsigned char *rb, int br, int bg, int bb, int sr, int sg, int sb)
 {
 	fz_luminosity_rgb(rr, rg, rb, sr, sg, sb, br, bg, bb);
 }
 
 static void
-fz_hue_rgb(int *rr, int *rg, int *rb, int br, int bg, int bb, int sr, int sg, int sb)
+fz_hue_rgb(unsigned char *rr, unsigned char *rg, unsigned char *rb, int br, int bg, int bb, int sr, int sg, int sb)
 {
-	int tr, tg, tb;
+	unsigned char tr, tg, tb;
 	fz_luminosity_rgb(&tr, &tg, &tb, sr, sg, sb, br, bg, bb);
 	fz_saturation_rgb(rr, rg, rb, tr, tg, tb, br, bg, bb);
 }
 
+void
+fz_blend_pixel(unsigned char dp[3], unsigned char bp[3], unsigned char sp[3], int blendmode)
+{
+	int k;
+	/* non-separable blend modes */
+	switch (blendmode)
+	{
+	case FZ_BLEND_HUE: fz_hue_rgb(&dp[0], &dp[1], &dp[2], bp[0], bp[1], bp[2], sp[0], sp[1], sp[2]); return;
+	case FZ_BLEND_SATURATION: fz_saturation_rgb(&dp[0], &dp[1], &dp[2], bp[0], bp[1], bp[2], sp[0], sp[1], sp[2]); return;
+	case FZ_BLEND_COLOR: fz_color_rgb(&dp[0], &dp[1], &dp[2], bp[0], bp[1], bp[2], sp[0], sp[1], sp[2]); return;
+	case FZ_BLEND_LUMINOSITY: fz_luminosity_rgb(&dp[0], &dp[1], &dp[2], bp[0], bp[1], bp[2], sp[0], sp[1], sp[2]); return;
+	}
+	/* separable blend modes */
+	for (k = 0; k < 3; k++)
+	{
+		switch (blendmode)
+		{
+		default:
+		case FZ_BLEND_NORMAL: dp[k] = sp[k]; break;
+		case FZ_BLEND_MULTIPLY: dp[k] = fz_mul255(bp[k], sp[k]); break;
+		case FZ_BLEND_SCREEN: dp[k] = fz_screen_byte(bp[k], sp[k]); break;
+		case FZ_BLEND_OVERLAY: dp[k] = fz_overlay_byte(bp[k], sp[k]); break;
+		case FZ_BLEND_DARKEN: dp[k] = fz_darken_byte(bp[k], sp[k]); break;
+		case FZ_BLEND_LIGHTEN: dp[k] = fz_lighten_byte(bp[k], sp[k]); break;
+		case FZ_BLEND_COLOR_DODGE: dp[k] = fz_color_dodge_byte(bp[k], sp[k]); break;
+		case FZ_BLEND_COLOR_BURN: dp[k] = fz_color_burn_byte(bp[k], sp[k]); break;
+		case FZ_BLEND_HARD_LIGHT: dp[k] = fz_hard_light_byte(bp[k], sp[k]); break;
+		case FZ_BLEND_SOFT_LIGHT: dp[k] = fz_soft_light_byte(bp[k], sp[k]); break;
+		case FZ_BLEND_DIFFERENCE: dp[k] = fz_difference_byte(bp[k], sp[k]); break;
+		case FZ_BLEND_EXCLUSION: dp[k] = fz_exclusion_byte(bp[k], sp[k]); break;
+		}
+	}
+}
+
 /* Blending loops */
 
 void
@@ -285,7 +320,7 @@ fz_blend_nonseparable(byte * restrict bp, byte * restrict sp, int w, int blendmo
 {
 	while (w--)
 	{
-		int rr, rg, rb;
+		unsigned char rr, rg, rb;
 
 		int sa = sp[3];
 		int ba = bp[3];
@@ -485,7 +520,7 @@ fz_blend_nonseparable_nonisolated(byte * restrict bp, byte * restrict sp, int w,
 				 * src, so: */
 				int invha = ha ? 255 * 256 / ha : 0;
 
-				int rr, rg, rb;
+				unsigned char rr, rg, rb;
 
 				/* ugh, division to get non-premul components */
 				int invsa = sa ? 255 * 256 / sa : 0;
diff --git a/fitz/fitz.h b/fitz/fitz.h
index 1f971cd3..73017e2f 100644
--- a/fitz/fitz.h
+++ b/fitz/fitz.h
@@ -1405,6 +1405,7 @@ void fz_paint_pixmap_with_mask(fz_pixmap *dst, fz_pixmap *src, fz_pixmap *msk);
 void fz_paint_pixmap_with_rect(fz_pixmap *dst, fz_pixmap *src, int alpha, fz_bbox bbox);
 
 void fz_blend_pixmap(fz_pixmap *dst, fz_pixmap *src, int alpha, int blendmode, int isolated, fz_pixmap *shape);
+void fz_blend_pixel(unsigned char dp[3], unsigned char bp[3], unsigned char sp[3], int blendmode);
 
 enum
 {