Render both temperature and dewpoint on Skew-T

lib/xmet/skew_t.py

@@ -1,6 +1,10 @@
 import math
 import cairo
 
+from typing import Iterable, Callable
+
+from xmet.sounding import SoundingSample
+
 PRESSURE_MAX  = 1050 # millibar
 PRESSURE_MIN  =  100
 PRESSURE_STEP =   50
@@ -84,6 +88,48 @@ class SkewT():
             cr.line_to(x + screen_x2, y + screen_y2)
             cr.stroke()
 
-    def draw(self, cr: cairo.Context, x: float, y: float):
+    def draw_samples(self,
+                     cr: cairo.Context,
+                     x: float,
+                     y: float,
+                     samples: Iterable[SoundingSample],
+                     fn: Callable):
+        first = True
+
+        for sample in samples:
+            if sample.pressure < PRESSURE_MIN:
+                break
+
+            #
+            # Temperature may possibly be dewpoint, depending on the
+            # return value of the callback.
+            #
+            temp, pressure = fn(sample)
+
+            if temp is None:
+                continue
+
+            gx, gy = self.sample_to_graph(temp, pressure)
+            sx, sy = self.graph_to_screen(gx, gy)
+
+            if first:
+                cr.move_to(x + sx, y + sy)
+                first = False
+            else:
+                cr.line_to(x + sx, y + sy)
+
+        cr.stroke()
+
+    def draw(self,
+             cr: cairo.Context,
+             x: float,
+             y: float,
+             samples: Iterable[SoundingSample]):
         self.draw_isotherms(cr, x, y)
         self.draw_isobars(cr, x, y)
+
+        cr.set_source_rgb(1, 0, 0)
+        self.draw_samples(cr, x, y, samples, lambda s: (s.temp, s.pressure))
+
+        cr.set_source_rgb(0, 1, 0)
+        self.draw_samples(cr, x, y, samples, lambda s: (s.dewpoint, s.pressure))