Support rgbgfx -c dmg to imply -c dmg=e4

Fixes #1776

include/gfx/pal_spec.hpp

@@ -3,9 +3,12 @@
 #ifndef RGBDS_GFX_PAL_SPEC_HPP
 #define RGBDS_GFX_PAL_SPEC_HPP
 
+#include <stdint.h>
+
 void parseInlinePalSpec(char const * const rawArg);
 void parseExternalPalSpec(char const *arg);
 void parseDmgPalSpec(char const * const rawArg);
+void parseDmgPalSpec(uint8_t palSpecDmg);
 
 void parseBackgroundPalSpec(char const *arg);
 

man/rgbgfx.1

@@ -178,6 +178,13 @@ the low two bits 0-1 specify which gray shade goes in color index 0,
 the next two bits 2-3 specify which gray shade goes in color index 1,
 and so on.
 Gray shade 0 is the lightest (white), 3 is the darkest (black).
+If
+.Ar pal_spec
+is the case-insensitive word
+.Cm dmg ,
+then it acts like
+.Cm dmg=E4 ,
+i.e. the darkest gray will end up in color index 0, and so on.
 The same gray shade cannot go in two color indexes.
 To specify a DMG palette, the input PNG must have all its colors in shades of gray, without any transparent colors.
 .It Sy automatic palette generation

src/gfx/main.cpp

@@ -322,6 +322,9 @@ static char *parseArgv(int argc, char *argv[]) {
 				options.palSpecType = Options::EMBEDDED;
 			} else if (strcasecmp(musl_optarg, "auto") == 0) {
 				options.palSpecType = Options::NO_SPEC;
+			} else if (strcasecmp(musl_optarg, "dmg") == 0) {
+				options.palSpecType = Options::DMG;
+				parseDmgPalSpec(0xE4); // Same darkest-first order as `sortGrayscale`
 			} else if (strncasecmp(musl_optarg, "dmg=", literal_strlen("dmg=")) == 0) {
 				options.palSpecType = Options::DMG;
 				parseDmgPalSpec(&musl_optarg[literal_strlen("dmg=")]);

src/gfx/pal_spec.cpp

@@ -692,7 +692,11 @@ void parseDmgPalSpec(char const * const rawArg) {
 		return;
 	}
 
-	options.palSpecDmg = toHex(arg[0], arg[1]);
+	parseDmgPalSpec(toHex(arg[0], arg[1]));
+}
+
+void parseDmgPalSpec(uint8_t palSpecDmg) {
+	options.palSpecDmg = palSpecDmg;
 
 	// Map gray shades to their DMG color indexes for fast lookup by `Rgba::grayIndex`
 	for (uint8_t i = 0; i < 4; ++i) {

test/gfx/dmg_plte.flags

@@ -1,2 +1,3 @@
+	# Override embedded with DMG
 	-c embedded
--c DMG=E4
+	-c DMG