tweakbars

src/bars.jl

@@ -20,6 +20,8 @@ will be scaled to fit in a bounding box.
 
 Text labels are drawn if the keyword `labels=true`.
 
+# Extended help
+
 The function returns a vector of points; each is the bottom center of a bar.
 
 Draw a Fibonacci sequence as a barchart:
@@ -46,38 +48,52 @@ barchart(vals, barfunction=mybarfunction)
 barchart(vals, labelfunction=mylabelfunction)
 ```
 
+```
+function myprologfunction(values, basepoint, minbarrange, maxbarrange, barchartheight)
+    @layer begin
+        setline(0.2)
+        for i in 0:10:maximum(values)
+            rule(boxbottomcenter(basepoint) + (0, -(rescale(i, minbarrange, maxbarrange) * barchartheight)))
+        end
+    end
+end
+```
 """
 function barchart(values;
-        boundingbox = BoundingBox(O + (-250, -120), O + (250, 120)),
-        bargap=10,
-        margin = 5,
-        border=false,
-        labels=false,        labelfunction = (values, i, lowpos, highpos, barwidth, scaledvalue) -> begin
-                label(string(values[i]), :n, highpos, offset=10)
-            end,
-        barfunction =  (values, i, lowpos, highpos, barwidth, scaledvalue) -> begin
-            @layer begin
-                setline(barwidth)
-                line(lowpos, highpos, :stroke)
-            end
-            end)
-    # start
+    boundingbox = BoundingBox(O + (-250, -120), O + (250, 120)),
+    bargap=10,
+    margin = 5,
+    border=false,
+    labels=false,
+    labelfunction = (values, i, lowpos, highpos, barwidth, scaledvalue) -> begin
+        label(string(values[i]), :n, highpos, offset=10)
+    end,
+    barfunction =  (values, i, lowpos, highpos, barwidth, scaledvalue) -> begin
+        @layer begin
+            setline(barwidth)
+            line(lowpos, highpos, :stroke)
+        end
+    end,
+    prologfunction = (values, basepoint, minbarrange, maxbarrange, barchartheight) -> ()
+    )
     minvalue, maxvalue = extrema(values)
     barchartwidth  = boxwidth(boundingbox)  - 2bargap - 2margin
     barchartheight = boxheight(boundingbox) - 2margin
     barwidth = (barchartwidth - 2bargap)/length(values)
     # if all bars are equal height, this will force a range
     minbarrange = minvalue - abs(minvalue)
     maxbarrange = maxvalue + abs(maxvalue)
+    basepoint = boundingbox - (0, margin)
     hpositions = between.(
-        boxbottomleft(boundingbox - (0, margin)),
-        boxbottomright(boundingbox - (0, margin)),
+        boxbottomleft(basepoint),
+        boxbottomright(basepoint),
         # skip first and last, then take every other one, which is at halfway
-        range(0.0, 1.0, length=2length(values) + 1))[2:2:end-1]
+        range(0.0, stop=1.0, length=2length(values) + 1))[2:2:end-1]
     @layer begin
         if border
             box(boundingbox, :stroke)
         end
+        prologfunction(values, basepoint, minbarrange, maxbarrange, barchartheight)
         for i in 1:length(values)
             scaledvalue = rescale(values[i], minbarrange, maxbarrange) * barchartheight
             lowposition = hpositions[i]