unix_main: Support configuring modifier keys

The new `-k` argument takes some comma-separated assignments, such
as `-k ctrl=option,alt=command`. In this configuration, the SDL
control keys are mapped to the mac option key, and the SDL alt keys
are mapped to the Mac command key. The SDL "gui" keys remain
associated with the Mac command key, and so the (non-existent on mac
plus) Mac control key cannot be pressed with this particular
configuration.

When `-k` is not specified, the behavior is intended to be unchanged.

README.md

@@ -175,6 +175,10 @@ screen memory (see `tools/mem2scr.c`).
 
 For a `DEBUG` build, add `-i` to get a disassembly trace of execution.
 
+To use a different modifier layout, use `-k`. For instance, to map
+host ctrl keys to mac Option and host Alt keys to mac Command, use
+`ctrl=option,alt=command`.
+
 Finally, the `-W <file>` parameter writes out the ROM image after
 patches are applied.  This can be useful to prepare a ROM image for
 embedded builds, so as to avoid having to patch the ROM at runtime.

include/keymap_sdl.h

@@ -9,6 +9,9 @@
 
 #include "keymap.h"
 
+enum { UNIX_CTRL, UNIX_ALT, UNIX_GUI };
+static int sdl_mods[3] = { MKC_Control, MKC_Option, MKC_Command };
+
 static inline int SDLScan2MacKeyCode(SDL_Scancode i)
 {
 	int v = MKC_None;
@@ -103,11 +106,11 @@ static inline int SDLScan2MacKeyCode(SDL_Scancode i)
         case SDL_SCANCODE_RSHIFT:
         case SDL_SCANCODE_LSHIFT: v = MKC_Shift; break;
         case SDL_SCANCODE_RCTRL:
-        case SDL_SCANCODE_LCTRL: v = MKC_Control; break;
+        case SDL_SCANCODE_LCTRL: v = sdl_mods[UNIX_CTRL]; break;
         case SDL_SCANCODE_RALT:
-        case SDL_SCANCODE_LALT: v = MKC_Option; break;
+        case SDL_SCANCODE_LALT: v = sdl_mods[UNIX_ALT]; break;
         case SDL_SCANCODE_RGUI:
-        case SDL_SCANCODE_LGUI: v = MKC_Command; break;
+        case SDL_SCANCODE_LGUI: v = sdl_mods[UNIX_GUI]; break;
 
         case SDL_SCANCODE_KP_A: v = MKC_A; break;
         case SDL_SCANCODE_KP_B: v = MKC_B; break;

src/unix_main.c

@@ -78,6 +78,33 @@ static void     copy_fb(uint32_t *fb_out, uint8_t *fb_in)
         }
 }
 
+/* Accept a keyboard modifier configuration string */
+static void parse_modifier_config(const char *arg) {
+	while(*arg) {
+		int src, mod;
+		if(!strncmp(arg, "ctrl", 4)) { src = UNIX_CTRL; arg += 4; }
+		else if(!strncmp(arg, "alt", 3)) { src = UNIX_ALT; arg += 3; }
+		else if(!strncmp(arg, "gui", 3)) { src = UNIX_GUI; arg += 3; }
+		else {
+parse_error:
+			printf("Unrecognized modifier configuration starting at '%s'\n", arg);
+			abort();
+		}
+		if(*arg != '=') goto parse_error;
+		arg++;
+		if(!strncmp(arg, "option", 6)) { mod = MKC_Option; arg += 6; }
+		else if(!strncmp(arg, "control", 7)) { mod = MKC_Control; arg += 7; }
+		else if(!strncmp(arg, "command", 7)) { mod = MKC_Command; arg += 7; }
+		else goto parse_error;
+
+		sdl_mods[src] = mod;
+		if (!*arg) break;
+		if (*arg != ',') goto parse_error;
+		arg++;
+	}
+}
+
+
 /**********************************************************************/
 
 /* The emulator core expects to be given ROM and RAM pointers,
@@ -104,7 +131,7 @@ int     main(int argc, char *argv[])
         ////////////////////////////////////////////////////////////////////////
         // Args
 
-        while ((ch = getopt(argc, argv, "r:d:W:ihw")) != -1) {
+        while ((ch = getopt(argc, argv, "r:d:k:W:ihw")) != -1) {
                 switch (ch) {
                 case 'r':
                         rom_filename = strdup(optarg);
@@ -118,6 +145,10 @@ int     main(int argc, char *argv[])
                         disc_filename = strdup(optarg);
                         break;
 
+                case 'k':
+                        parse_modifier_config(optarg);
+                        break;
+
                 case 'w':
                         opt_write = 1;
                         break;