Use an array for packed colors

tools/gbcpal.c

@@ -29,6 +29,9 @@ struct Color {
 	uint8_t r, g, b;
 };
 
+const struct Color BLACK = {0, 0, 0};
+const struct Color WHITE = {31, 31, 31};
+
 uint16_t pack_color(struct Color color) {
 	return (color.b << 10) | (color.g << 5) | color.r;
 }
@@ -48,7 +51,8 @@ double luminance(struct Color color) {
 int compare_colors(const void *color1, const void *color2) {
 	double lum1 = luminance(*(const struct Color *)color1);
 	double lum2 = luminance(*(const struct Color *)color2);
-	return (lum1 < lum2) - (lum1 > lum2); // sort lightest to darkest
+	// sort lightest to darkest, or darkest to lightest if reversed
+	return reverse ? (lum1 > lum2) - (lum1 < lum2) : (lum1 < lum2) - (lum1 > lum2);
 }
 
 void read_gbcpal(const char *filename, struct Color **colors, size_t *num_colors) {
@@ -76,18 +80,19 @@ void filter_colors(struct Color **colors, size_t *num_colors) {
 	size_t num_filtered = 0;
 	struct Color *filtered = xmalloc((sizeof **colors) * *num_colors);
 
+	// filter out black, white, and duplicate colors
 	for (size_t i = 0; i < *num_colors; i++) {
 		struct Color color = (*colors)[i];
-		if (color.r == 0 && color.g == 0 && color.b == 0) {
-			continue; // filter out black
+		if (color.r == BLACK.r && color.g == BLACK.g && color.b == BLACK.b) {
+			continue;
 		}
-		if (color.r == 31 && color.g == 31 && color.b == 31) {
-			continue; // filter out white
+		if (color.r == WHITE.r && color.g == WHITE.g && color.b == WHITE.b) {
+			continue;
 		}
 		if (num_filtered > 0) {
 			struct Color last = filtered[num_filtered - 1];
 			if (color.r == last.r && color.g == last.g && color.b == last.b) {
-				continue; // filter out duplicates
+				continue;
 			}
 		}
 		filtered[num_filtered++] = color;
@@ -118,34 +123,22 @@ int main(int argc, char *argv[]) {
 	qsort(colors, num_colors, sizeof(*colors), compare_colors);
 	filter_colors(&colors, &num_colors);
 
-	uint16_t first, second;
-	if (num_colors == 0) {
-		// colors are white and black
-		first = 0x7fff;
-		second = 0x0000;
-	} else if (num_colors == 1) {
-		// colors are both the same one
-		first = pack_color(colors[0]);
-		second = first;
-	} else if (num_colors == 2) {
-		// colors are light and dark
-		first = pack_color(colors[0]);
-		second = pack_color(colors[1]);
-		if (reverse) {
-			// darker color is first
-			uint16_t tmp = first;
-			first = second;
-			second = tmp;
-		}
-	} else {
+	if (num_colors > 2) {
 		error_exit("%s: more than 2 colors besides black and white (%zu)\n", out_filename, num_colors);
 	}
 
+	uint16_t packed_colors[4] = {
+		pack_color(WHITE),
+		pack_color(num_colors > 0 ? colors[0] : WHITE),
+		pack_color(num_colors > 1 ? colors[1] : num_colors > 0 ? colors[0] : BLACK),
+		pack_color(BLACK),
+	};
+
 	uint8_t bytes[8] = {
-		0xff, 0x7f, // white
-		first & 0xff, first >> 8,
-		second & 0xff, second >> 8,
-		0x00, 0x00, // black
+		packed_colors[0] & 0xff, packed_colors[0] >> 8,
+		packed_colors[1] & 0xff, packed_colors[1] >> 8,
+		packed_colors[2] & 0xff, packed_colors[2] >> 8,
+		packed_colors[3] & 0xff, packed_colors[3] >> 8,
 	};
 	write_u8(out_filename, bytes, COUNTOF(bytes));