stretch histogram vmin/vmax dynamic step size (spacetelescope#2388)

* stretch histogram vmin/vmax dynamic step size

CHANGES.rst

@@ -19,6 +19,9 @@ Imviz
 
 - The stretch histogram within plot options can now be popped-out into its own window. [#2314]
 
+- vmin/vmax step size in the plot options plugin is now dynamic based on the full range of the
+  image. [#2388]
+
 - Footprints plugin for plotting overlays of instrument footprints in the image viewer. [#2341]
 
 Mosviz

jdaviz/configs/default/plugins/plot_options/plot_options.py

@@ -187,6 +187,8 @@ class PlotOptions(PluginTemplateMixin):
     stretch_preset_value = Any().tag(sync=True)  # glue will pass either a float or string
     stretch_preset_sync = Dict().tag(sync=True)
 
+    stretch_vstep = Float(0.1).tag(sync=True)  # dynamic based on full range from image
+
     stretch_vmin_value = Float().tag(sync=True)
     stretch_vmin_sync = Dict().tag(sync=True)
 
@@ -621,6 +623,12 @@ def _update_stretch_histogram(self, msg={}):
             if len(sub_data) > 0:
                 hist_lims = interval.get_limits(sub_data)
                 hist_mark.min, hist_mark.max = hist_lims
+                # set the stepsize for vmin/vmax to be approximately 1% of the range of the
+                # histogram (within the percentile interval), rounded to 1-2 significant digits
+                # to avoid random step sizes.  This logic is somewhat arbitrary and can be safely
+                # modified or eventually exposed to the user if that would be useful.
+                stretch_vstep = (hist_lims[1] - hist_lims[0]) / 100.
+                self.stretch_vstep = np.round(stretch_vstep, decimals=-int(np.log10(stretch_vstep))+1)  # noqa
             hist_mark.bins = self.stretch_hist_nbins
             # in case only the sample has changed but its length has not,
             # we'll force the traitlet to trigger a change

jdaviz/configs/default/plugins/plot_options/plot_options.vue

@@ -341,11 +341,25 @@
     </glue-state-sync-wrapper>
 
     <glue-state-sync-wrapper :sync="stretch_vmin_sync" :multiselect="multiselect" @unmix-state="unmix_state('stretch_vmin')">
-      <glue-float-field label="Stretch VMin" :value.sync="stretch_vmin_value" />
+      <v-text-field
+        ref="stretch_vmin"
+        type="number"
+        label="Stretch VMin"
+        v-model.number="stretch_vmin_value"
+        type="number"
+        :step="stretch_vstep"
+      ></v-text-field>
     </glue-state-sync-wrapper>
 
     <glue-state-sync-wrapper :sync="stretch_vmax_sync" :multiselect="multiselect" @unmix-state="unmix_state('stretch_vmax')">
-      <glue-float-field label="Stretch VMax" :value.sync="stretch_vmax_value" />
+      <v-text-field
+        ref="stretch_vmax"
+        type="number"
+        label="Stretch VMax"
+        v-model.number="stretch_vmax_value"
+        type="number"
+        :step="stretch_vstep"
+      ></v-text-field>
     </glue-state-sync-wrapper>
 
     <div v-if="stretch_function_sync.in_subscribed_states">