Allow -Ccolor1,color2, etc to also take +h for hinge (#6796)

For an odd number of colors we may use the +h modifier when building a CPT from colors.

src/gmt_api.c

@@ -7806,10 +7806,12 @@ GMT_LOCAL int gmtapi_colors2cpt (struct GMTAPI_CTRL *API, char **str, unsigned i
 	/* Take comma-separated color entries given in lieu of a file and build a linear, discrete CPT.
 	 * This may be converted to a continuous CPT if -Z is used by makecpt/grd2cpt.
 	 * We check if a color is valid then write the given entries verbatim to the temp file.
+	 * If a soft hinge has been requested then we must add flag to temp file and pass hinge on via filename.
 	 * Returns GMT_NOTSET on error, 0 if no CPT is created (str presumably held a CPT name) and 1 otherwise.
 	*/
-	unsigned int pos = 0, z = 0;
-	char *pch = NULL, color[GMT_LEN256] = {""}, tmp_file[GMT_LEN64] = "";
+	unsigned int pos = 0;
+	int z = 0, n;
+	char *pch = NULL, color[GMT_LEN256] = {""}, tmp_file[GMT_LEN64] = "", *h = NULL;
 	double rgb[4] = {0.0, 0.0, 0.0, 0.0};
 	FILE *fp = NULL;
 
@@ -7840,6 +7842,22 @@ GMT_LOCAL int gmtapi_colors2cpt (struct GMTAPI_CTRL *API, char **str, unsigned i
 	}
 	fprintf (fp, "# COLOR_LIST\n");	/* Flag that we are building a CPT from a list of discrete colors */
 
+	if ((h = strstr (*str, "+h"))) /* See if we got a hinge modifier */
+		h[0] = '\0'; /* Hide hinge modifier */
+
+	n = gmt_count_char (API->GMT, *str, ',') + 1;	/* Number of colors */
+	if (n && (*str)[strlen(*str)-1] == ',') n--;	/* Stray trailing comma with no color ignored */
+	if (h) {	/* Check if number of colors is odd when a hinge is specified */
+		if (n%2) {	/* Should be OK */
+			fprintf (fp, "# SOFT_HINGE\n");	/* Flag that we are building a CPT with a soft hinge */
+			z = -(n - 1)/2;	/* Start z value for CPT centered on 0 */
+		}
+		else {
+			GMT_Report (API, GMT_MSG_ERROR, "Cannot build soft-hinge CPT from an even number of colors\n");
+			return (GMT_NOTSET);
+		}
+	}
+
 	if ((*mode) & GMT_CPT_CONTINUOUS) {	/* Make a continuous cpt from the colors */
 		char last_color[GMT_LEN256] = {""};
 		if (!gmt_strtok (*str, ",", &pos, last_color)) {	/* Get 1st color entry */
@@ -7852,7 +7870,7 @@ GMT_LOCAL int gmtapi_colors2cpt (struct GMTAPI_CTRL *API, char **str, unsigned i
 			fclose (fp);
 			return (GMT_NOTSET);
 		}
-		while (gmt_strtok (*str, ",", &pos, color)) {	/* Get color entries */
+		while (gmt_strtok (*str, ",", &pos, color) && color[0]) {	/* Get color entries */
 			if (gmt_getrgb (API->GMT, color, rgb)) {
 				GMT_Report (API, GMT_MSG_ERROR, "Badly formatted color entry: %s\n", color);
 				fclose (fp);
@@ -7863,14 +7881,14 @@ GMT_LOCAL int gmtapi_colors2cpt (struct GMTAPI_CTRL *API, char **str, unsigned i
 			z++;	/* Increment z-slice values */
 		}
 		*mode -= GMT_CPT_CONTINUOUS;	/* Served its purpose */
-		if (z == 0) {	/* Needed at least two colors to specify a ramp */
+		if (n == 1) {	/* Needed at least two colors to specify a ramp */
 			GMT_Report (API, GMT_MSG_ERROR, "Cannot make a continuous color ramp from a single color: %s\n", *str);
 			fclose (fp);
 			return (GMT_NOTSET);
 		}
 	}
 	else {
-		while (gmt_strtok (*str, ",", &pos, color)) {	/* Get color entries */
+		while (gmt_strtok (*str, ",", &pos, color) && color[0]) {	/* Get color entries */
 			if (gmt_getrgb (API->GMT, color, rgb)) {
 				GMT_Report (API, GMT_MSG_ERROR, "Badly formatted color entry: %s\n", color);
 				fclose (fp);
@@ -7884,6 +7902,10 @@ GMT_LOCAL int gmtapi_colors2cpt (struct GMTAPI_CTRL *API, char **str, unsigned i
 
 	GMT_Report (API, GMT_MSG_DEBUG, "Converted %s to CPT %s\n", *str, tmp_file);
 
+	if (h) { /* Restore hinge modifier and append it to filename */
+		h[0] = '+';
+		strcat (tmp_file, h);
+	}
 	gmt_M_str_free (*str);		/* Because it was allocated with strdup */
 	*str = strdup (tmp_file);	/* Pass out the temp file name instead */