From ee972fbfa1093fe2e8641dc450e1c20347df2b04 Mon Sep 17 00:00:00 2001
From: Robin Watts <robin.watts@artifex.com>
Date: Tue, 24 May 2016 13:46:28 +0100
Subject: Avoid unnecessary alphas when decompressing images from streams.

---
 source/fitz/colorspace.c  | 14 ++++++++------
 source/fitz/draw-unpack.c |  5 +++--
 source/fitz/image.c       |  7 +++++--
 3 files changed, 16 insertions(+), 10 deletions(-)

(limited to 'source')

diff --git a/source/fitz/colorspace.c b/source/fitz/colorspace.c
index b4d511e8..7923446a 100644
--- a/source/fitz/colorspace.c
+++ b/source/fitz/colorspace.c
@@ -1930,31 +1930,32 @@ fz_new_indexed_colorspace(fz_context *ctx, fz_colorspace *base, int high, unsign
 }
 
 fz_pixmap *
-fz_expand_indexed_pixmap(fz_context *ctx, fz_pixmap *src)
+fz_expand_indexed_pixmap(fz_context *ctx, const fz_pixmap *src, int alpha)
 {
 	struct indexed *idx;
 	fz_pixmap *dst;
-	unsigned char *s, *d;
+	const unsigned char *s;
+	unsigned char *d;
 	int y, x, k, n, high;
 	unsigned char *lookup;
 	fz_irect bbox;
 	int s_line_inc, d_line_inc;
 
 	assert(src->colorspace->to_rgb == indexed_to_rgb);
-	assert(src->n == 2);
+	assert(src->n == 1 + alpha);
 
 	idx = src->colorspace->data;
 	high = idx->high;
 	lookup = idx->lookup;
 	n = idx->base->n;
 
-	dst = fz_new_pixmap_with_bbox(ctx, idx->base, fz_pixmap_bbox(ctx, src, &bbox), src->alpha);
+	dst = fz_new_pixmap_with_bbox(ctx, idx->base, fz_pixmap_bbox(ctx, src, &bbox), alpha);
 	s = src->samples;
 	d = dst->samples;
 	s_line_inc = src->stride - src->w * src->n;
 	d_line_inc = dst->stride - dst->w * dst->n;
 
-	if (src->alpha)
+	if (alpha)
 	{
 		for (y = 0; y < src->h; y++)
 		{
@@ -1962,9 +1963,10 @@ fz_expand_indexed_pixmap(fz_context *ctx, fz_pixmap *src)
 			{
 				int v = *s++;
 				int a = *s++;
+				int aa = a + (a>>7);
 				v = fz_mini(v, high);
 				for (k = 0; k < n; k++)
-					*d++ = fz_mul255(lookup[v * n + k], a);
+					*d++ = (aa * lookup[v * n + k] + 128)>>8;
 				*d++ = a;
 			}
 			s += s_line_inc;
diff --git a/source/fitz/draw-unpack.c b/source/fitz/draw-unpack.c
index ccb3c62f..0211b7e4 100644
--- a/source/fitz/draw-unpack.c
+++ b/source/fitz/draw-unpack.c
@@ -179,7 +179,8 @@ fz_decode_indexed_tile(fz_context *ctx, fz_pixmap *pix, const float *decode, int
 	unsigned char *p = pix->samples;
 	int stride = pix->stride - pix->w * pix->n;
 	int len;
-	int n = pix->n - 1;
+	int pn = pix->n;
+	int n = pn - pix->alpha;
 	int needed;
 	int k;
 	int h;
@@ -208,7 +209,7 @@ fz_decode_indexed_tile(fz_context *ctx, fz_pixmap *pix, const float *decode, int
 				int value = (add[k] + (((p[k] << 8) * mul[k]) >> 8)) >> 8;
 				p[k] = fz_clampi(value, 0, 255);
 			}
-			p += n + 1;
+			p += pn;
 		}
 		p += stride;
 	}
diff --git a/source/fitz/image.c b/source/fitz/image.c
index bd6e0b62..c49580bf 100644
--- a/source/fitz/image.c
+++ b/source/fitz/image.c
@@ -198,7 +198,10 @@ fz_decomp_image_from_stream(fz_context *ctx, fz_stream *stm, fz_compressed_image
 
 	fz_try(ctx)
 	{
-		tile = fz_new_pixmap(ctx, image->colorspace, w, h, 1);
+		int alpha = (image->colorspace == NULL);
+		if (image->use_colorkey)
+			alpha = 1;
+		tile = fz_new_pixmap(ctx, image->colorspace, w, h, alpha);
 		tile->interpolate = image->interpolate;
 
 		stride = (w * image->n * image->bpc + 7) / 8;
@@ -276,7 +279,7 @@ fz_decomp_image_from_stream(fz_context *ctx, fz_stream *stm, fz_compressed_image
 		{
 			fz_pixmap *conv;
 			fz_decode_indexed_tile(ctx, tile, image->decode, (1 << image->bpc) - 1);
-			conv = fz_expand_indexed_pixmap(ctx, tile);
+			conv = fz_expand_indexed_pixmap(ctx, tile, alpha);
 			fz_drop_pixmap(ctx, tile);
 			tile = conv;
 		}
-- 
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