add NCPLOT_OPTIONS_DETECTMAXONLY #610

include/notcurses/notcurses.h

@@ -2851,14 +2851,15 @@ API int ncmenu_destroy(struct ncmenu* n);
 //
 // This options structure works for both the ncuplot (uint64_t) and ncdplot
 // (double) types.
-#define NCPLOT_OPTION_LABELTICKSD  0x0001ull // show labels for dependent axis
-#define NCPLOT_OPTION_EXPONENTIALD 0x0002ull // exponential dependent axis
-#define NCPLOT_OPTION_VERTICALI    0x0004ull // independent axis is vertical
-#define NCPLOT_OPTION_NODEGRADE    0x0008ull // fail rather than degrade blitter
+#define NCPLOT_OPTION_LABELTICKSD   0x0001ull // show labels for dependent axis
+#define NCPLOT_OPTION_EXPONENTIALD  0x0002ull // exponential dependent axis
+#define NCPLOT_OPTION_VERTICALI     0x0004ull // independent axis is vertical
+#define NCPLOT_OPTION_NODEGRADE     0x0008ull // fail rather than degrade blitter
+#define NCPLOT_OPTION_DETECTMAXONLY 0x0010ull // use domain detection only for max
 
 typedef struct ncplot_options {
-  // channels for the maximum and minimum levels. linear interpolation will be
-  // applied across the domain between these two.
+  // channels for the maximum and minimum levels. linear or exponential
+  // interpolation will be applied across the domain between these two.
   uint64_t maxchannel;
   uint64_t minchannel;
   // if you don't care, pass NCBLIT_DEFAULT and get NCBLIT_8x1 (assuming

src/lib/plot.h

@@ -14,16 +14,24 @@ class ncppplot {
  // these were all originally plain C, sorry for the non-idiomatic usage FIXME
  // ought admit nullptr opts FIXME
  static bool create(ncppplot<T>* ncpp, ncplane* n, const ncplot_options* opts, T miny, T maxy) {
-   // if miny == maxy, they both must be equal to 0
+   struct notcurses* nc = n->nc;
+   // if miny == maxy (enabling domain detection), they both must be equal to 0
    if(miny == maxy && miny){
+     logerror(nc, "Supplied non-zero domain detection param %d\n", miny);
      return false;
    }
    if(opts->rangex < 0){
+     logerror(nc, "Supplied negative independent range %d\n", opts->rangex);
      return false;
    }
    if(maxy < miny){
      return false;
    }
+   // DETECTMAXONLY can't be used without domain detection
+   if(opts->flags & NCPLOT_OPTION_DETECTMAXONLY && (miny != maxy)){
+     logerror(nc, "Supplied DETECTMAXONLY without domain detection");
+     return false;
+   }
    ncblitter_e blitter = opts ? opts->gridtype : NCBLIT_DEFAULT;
    if(blitter == NCBLIT_DEFAULT){
      if(notcurses_canutf8(ncplane_notcurses(n))){
@@ -272,8 +280,10 @@ class ncppplot {
      if(val > maxy){
        maxy = val;
      }
-     if(val < miny){
-       miny = val;
+     if(!detectonlymax){
+       if(val < miny){
+         miny = val;
+       }
      }
      return 0;
    }
@@ -356,7 +366,8 @@ class ncppplot {
  int slotstart; // index of most recently-written slot
  bool labelaxisd; // label dependent axis (consumes PREFIXCOLUMNS columns)
  bool exponentiali; // exponential independent axis
- bool detectdomain; // is domain detection in effect (stretch the domain)?
+ bool detectdomain;   // is domain detection in effect (stretch the domain)?
+ bool detectonlymax;  // domain detection applies only to max, not min
 
 };