font2png: Parse background color

Decode background color from font blobs

font2png.cc

@@ -24,6 +24,7 @@ struct Font {
   unsigned numChars;
   unsigned charHeight;
   unsigned maxCharWidth;
+  uint8_t bgColor;
   std::vector<Image> chars;
 };
 
@@ -31,8 +32,9 @@ struct FontHeader { // little endian
   uint32_t unknown1; // (always)? "1.\0\0"
   uint32_t entries;
   uint32_t charWidth;
-  uint32_t unknown3; // (always)? 0x000000ff
-};
+  uint8_t bgColor;
+  char unknown3[3];
+} __attribute__((__packed__));
 
 Font parseFont(FILE* file, size_t length)
 {
@@ -89,6 +91,7 @@ Font parseFont(FILE* file, size_t length)
   ret.numChars = header.entries;
   ret.charHeight = char_width;
   ret.maxCharWidth = 0;
+  ret.bgColor = header.bgColor;
   for (auto const& index : indices) {
     uint32_t len;
     if (fseeko(file, index, SEEK_SET) != 0)
@@ -160,12 +163,12 @@ Image makeFontImage(Font const& font)
 	unsigned charNo = c_y*charsPerLine+c_x;
 	if (charNo > font.numChars) {
 	  for (unsigned x = 0;x < font.maxCharWidth;++x)
-	    ret.data.push_back(0xff);
+	    ret.data.push_back(font.bgColor);
 	} else {
 	  for (unsigned x = 0;x < font.chars[charNo].width;++x)
 	    ret.data.push_back(font.chars[charNo].data[y*font.chars[charNo].width+x]);
 	  for (unsigned x = font.chars[charNo].width; x < font.maxCharWidth;++x)
-	    ret.data.push_back(0xff);
+	    ret.data.push_back(font.bgColor);
 	}
       }
     }