Fix two RGBGFX bugs (#1671)

* Fix two RGBGFX bugs

* Fix clang-format idempotence

* Update src/gfx/rgba.cpp

Co-authored-by: Eldred Habert <me@eldred.fr>

---------

Co-authored-by: Eldred Habert <me@eldred.fr>

src/gfx/pal_spec.cpp

@@ -231,8 +231,7 @@ static std::optional<U> parseDec(std::string const &str, size_t &n) {
 	return std::optional<U>{value};
 }
 
-static std::optional<Rgba>
-    parseColor(std::string const &str, size_t &n, uint16_t i) {
+static std::optional<Rgba> parseColor(std::string const &str, size_t &n, uint16_t i) {
 	std::optional<uint8_t> r = parseDec<uint8_t>(str, n);
 	if (!r) {
 		error("Failed to parse color #%d (\"%s\"): invalid red component", i + 1, str.c_str());
@@ -602,10 +601,9 @@ void parseExternalPalSpec(char const *arg) {
 	    std::tuple{"GBC", &parseGBCFile, std::ios::binary},
 	};
 
-	auto iter =
-	    std::find_if(RANGE(parsers), [&arg, &ptr](auto const &parser) {
-		    return strncasecmp(arg, std::get<0>(parser), ptr - arg) == 0;
-	    });
+	auto iter = std::find_if(RANGE(parsers), [&arg, &ptr](auto const &parser) {
+		return strncasecmp(arg, std::get<0>(parser), ptr - arg) == 0;
+	});
 	if (iter == parsers.end()) {
 		error(
 		    "Unknown external palette format \"%.*s\"",

src/gfx/process.cpp

@@ -604,9 +604,9 @@ static std::tuple<DefaultInitVec<size_t>, std::vector<Palette>>
 	// Convert the palette spec to actual palettes
 	std::vector<Palette> palettes(options.palSpec.size());
 	for (auto [spec, pal] : zip(options.palSpec, palettes)) {
-		for (size_t i = 0; i < options.nbColorsPerPal && (!spec[i] || spec[i]->isOpaque()); ++i) {
+		for (size_t i = 0; i < options.nbColorsPerPal; ++i) {
 			// If the spec has a gap, there's no need to copy anything.
-			if (spec[i]) {
+			if (spec[i].has_value() && !spec[i]->isTransparent()) {
 				pal[i] = spec[i]->cgbColor();
 			}
 		}

src/gfx/rgba.cpp

@@ -58,6 +58,7 @@ uint16_t Rgba::cgbColor() const {
 
 uint8_t Rgba::grayIndex() const {
 	assume(isGray());
-	// Convert from [0; 256[ to [0; maxOpaqueColors[
-	return static_cast<uint16_t>(255 - red) * options.maxOpaqueColors() / 256;
+	// Convert from 0..<256 to hasTransparentPixels..<nbColorsPerPal
+	// Note that `maxOpaqueColors()` already takes `hasTransparentPixels` into account
+	return (255 - red) * options.maxOpaqueColors() / 256 + options.hasTransparentPixels;
 }

test/gfx/alpha_embedded.err

@@ -0,0 +1,4 @@
+error: Failed to fit tile colors [$1527, $15cc, $1ab4] in specified palettes
+note: The following palette was specified:
+        [$1ab4, $15cc]
+Conversion aborted after 1 error

test/gfx/alpha_embedded.flags

@@ -0,0 +1 @@
+-c embedded