bmp: Improve fallback handling of palette color entries.

 * Use a better 4-bit fallback palette (use vga palette as
   indicated by variable name instead of 16 color web palette)

 * Determine if existing palette entries are grayscale and if so
   use a grayscale palette instead of the vga or web palette

 * Extend the web palette with black entries to make it eaiser
   to copy from.

1 files changed, 67 insertions, 25 deletions

diff --git a/source/fitz/load-bmp.c b/source/fitz/load-bmp.c
index 3eda1614..8b084638 100644
--- a/source/fitz/load-bmp.c
+++ b/source/fitz/load-bmp.c
@@ -37,15 +37,20 @@ static const unsigned char web_palette[] = {
 	0x00, 0xFF, 0x99, 0x33, 0xFF, 0x99, 0x66, 0xFF, 0x99, 0x99, 0xFF, 0x99, 0xCC, 0xFF, 0x99, 0xFF, 0xFF, 0x99,
 	0x00, 0xFF, 0xCC, 0x33, 0xFF, 0xCC, 0x66, 0xFF, 0xCC, 0x99, 0xFF, 0xCC, 0xCC, 0xFF, 0xCC, 0xFF, 0xFF, 0xCC,
 	0x00, 0xFF, 0xFF, 0x33, 0xFF, 0xFF, 0x66, 0xFF, 0xFF, 0x99, 0xFF, 0xFF, 0xCC, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
 };
 
 static const unsigned char vga_palette[] = {
-	0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0xFF, 0x00,
-	0x00, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0xFF, 0x00, 0xFF,
-	0xFF, 0xFF, 0x00, 0xFF, 0xFF, 0xFF, 0x00, 0x80, 0x00,
-	0x00, 0x80, 0x80, 0x80, 0x00, 0x00, 0x80, 0x00, 0x80,
-	0x80, 0x80, 0x00, 0xC0, 0xC0, 0xC0, 0x80, 0x80, 0x80,
-	0x00, 0x00, 0xFF,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0xAA, 0x00, 0xAA, 0x00, 0x00, 0xAA, 0xAA,
+	0xAA, 0x00, 0x00, 0xAA, 0x00, 0xAA, 0xAA, 0x55, 0x00, 0xAA, 0xAA, 0xAA,
+	0x55, 0x55, 0x55, 0x55, 0x55, 0xFF, 0x55, 0xFF, 0x55, 0x55, 0xFF, 0xFF,
+	0xFF, 0x55, 0x55, 0xFF, 0x55, 0xFF, 0xFF, 0xFF, 0x55, 0xFF, 0xFF, 0xFF,
 };
 
 static const unsigned char gray_palette[] = {
@@ -257,13 +262,54 @@ bmp_read_extra_masks(fz_context *ctx, struct info *info, unsigned char *p, unsig
 	return p + 12;
 }
 
+static int
+bmp_palette_is_gray(fz_context *ctx, struct info *info, int readcolors)
+{
+	int i;
+	for (i = 0; i < readcolors; i++)
+	{
+		int rgdiff = fz_absi(info->palette[3 * i + 0] - info->palette[3 * i + 1]);
+		int gbdiff = fz_absi(info->palette[3 * i + 1] - info->palette[3 * i + 2]);
+		int rbdiff = fz_absi(info->palette[3 * i + 0] - info->palette[3 * i + 2]);
+		if (rgdiff > 2 || gbdiff > 2 || rbdiff > 2)
+			return 0;
+	}
+	return 1;
+}
+
 static void
-bmp_load_default_palette(fz_context *ctx, struct info *info)
+bmp_load_default_palette(fz_context *ctx, struct info *info, int readcolors)
 {
+	int i;
+
+	fz_warn(ctx, "color table too short; loading default palette");
+
 	if (info->bitcount == 8)
-		memcpy(info->palette, web_palette, sizeof(web_palette));
+	{
+		if (!bmp_palette_is_gray(ctx, info, readcolors))
+			memcpy(&info->palette[readcolors * 3], &web_palette[readcolors * 3],
+					sizeof(web_palette) - readcolors * 3);
+		else
+			for (i = readcolors; i < 256; i++)
+			{
+				info->palette[3 * i + 0] = i;
+				info->palette[3 * i + 1] = i;
+				info->palette[3 * i + 2] = i;
+			}
+	}
 	else if (info->bitcount == 4)
-		memcpy(info->palette, vga_palette, sizeof(vga_palette));
+	{
+		if (!bmp_palette_is_gray(ctx, info, readcolors))
+			memcpy(&info->palette[readcolors * 3], &vga_palette[readcolors * 3],
+					sizeof(vga_palette) - readcolors * 3);
+		else
+			for (i = readcolors; i < 16; i++)
+			{
+				info->palette[3 * i + 0] = (i << 4) | i;
+				info->palette[3 * i + 1] = (i << 4) | i;
+				info->palette[3 * i + 2] = (i << 4) | i;
+			}
+	}
 	else if (info->bitcount == 2)
 		memcpy(info->palette, gray_palette, sizeof(gray_palette));
 	else if (info->bitcount == 1)
@@ -273,7 +319,7 @@ bmp_load_default_palette(fz_context *ctx, struct info *info)
 static unsigned char *
 bmp_read_color_table(fz_context *ctx, struct info *info, unsigned char *p, unsigned char *end)
 {
-	int i, colors;
+	int i, colors, readcolors;
 
 	if (info->bitcount > 8)
 		return p;
@@ -287,34 +333,30 @@ bmp_read_color_table(fz_context *ctx, struct info *info, unsigned char *p, unsig
 
 	if (info->palettetype == 0)
 	{
-		if (end - p < colors * 3) {
-			fz_warn(ctx, "color table too short; loading default palette");
-			bmp_load_default_palette(ctx, info);
-			colors = (end - p) / 3;
-		}
-		for (i = 0; i < colors; i++)
+		readcolors = fz_mini(colors, (end - p) / 3);
+		for (i = 0; i < readcolors; i++)
 		{
 			info->palette[3 * i + 0] = read8(p + i * 3 + 2);
 			info->palette[3 * i + 1] = read8(p + i * 3 + 1);
 			info->palette[3 * i + 2] = read8(p + i * 3 + 0);
 		}
-		return p + colors * 3;
+		if (readcolors < colors)
+			bmp_load_default_palette(ctx, info, readcolors);
+		return p + readcolors * 3;
 	}
 	else
 	{
-		if (end - p < colors * 4) {
-			fz_warn(ctx, "color table too short; loading default palette");
-			bmp_load_default_palette(ctx, info);
-			colors = (end - p) / 4;
-		}
-		for (i = 0; i < colors; i++)
+		readcolors = fz_mini(colors, (end - p) / 4);
+		for (i = 0; i < readcolors; i++)
 		{
+			/* ignore alpha channel */
 			info->palette[3 * i + 0] = read8(p + i * 4 + 2);
 			info->palette[3 * i + 1] = read8(p + i * 4 + 1);
 			info->palette[3 * i + 2] = read8(p + i * 4 + 0);
-			/* ignore alpha channel */
 		}
-		return p + colors * 4;
+		if (readcolors < colors)
+			bmp_load_default_palette(ctx, info, readcolors);
+		return p + readcolors * 4;
 	}
 
 	return p;