add arrow support (#2989)

* add arrow support

* correctly handle arrow.side = :both

src/backends/pgfplotsx.jl

@@ -396,10 +396,53 @@ function pgfx_add_series!(::Val{:path}, axis, series_opt, series, series_func, o
                 pgfx_filllegend!(series_opt, opt)
             end
         end
-        coordinates = PGFPlotsX.Table(pgfx_series_arguments(series, opt, rng)...)
+        # handle arrows
-        segment_plot =
+        arrow = opt[:arrow]
-            series_func(merge(series_opt, segment_opt), coordinates)
+        if arrow isa Arrow
-        push!(axis, segment_plot)
+            arrow_opt = merge(
+                segment_opt,
+                PGFPlotsX.Options("quiver" => PGFPlotsX.Options(
+                    "u" => "\\thisrow{u}",
+                    "v" => "\\thisrow{v}",
+                    pgfx_arrow(arrow, :head) => nothing,
+                    )
+                )
+            )
+            if arrow.side == :head
+                x_arrow = opt[:x][rng][end-1:end]
+                y_arrow = opt[:y][rng][end-1:end]
+                x_path  = opt[:x][rng][1:end-1]
+                y_path  = opt[:y][rng][1:end-1]
+            elseif arrow.side == :tail
+                x_arrow = opt[:x][rng][2:-1:1]
+                y_arrow = opt[:y][rng][2:-1:1]
+                x_path  = opt[:x][rng][2:end]
+                y_path  = opt[:y][rng][2:end]
+            elseif arrow.side == :both
+                x_arrow = opt[:x][rng][[2,1,end-1,end]]
+                y_arrow = opt[:y][rng][[2,1,end-1,end]]
+                x_path  = opt[:x][rng][2:end-1]
+                y_path  = opt[:y][rng][2:end-1]
+            end
+            coordinates = PGFPlotsX.Table([
+                    :x => x_arrow[1:2:end-1],
+                    :y => y_arrow[1:2:end-1],
+                    :u => [x_arrow[i] - x_arrow[i-1] for i in 2:2:lastindex(x_arrow)],
+                    :v => [y_arrow[i] - y_arrow[i-1] for i in 2:2:lastindex(y_arrow)],
+                ])
+            arrow_plot =
+                series_func(merge(series_opt, arrow_opt), coordinates)
+            push!(axis, arrow_plot)
+            coordinates = PGFPlotsX.Table(x_path, y_path)
+            segment_plot =
+                series_func(merge(series_opt, segment_opt), coordinates)
+            push!(axis, segment_plot)
+        else
+            coordinates = PGFPlotsX.Table(pgfx_series_arguments(series, opt, rng)...)
+            segment_plot =
+                series_func(merge(series_opt, segment_opt), coordinates)
+            push!(axis, segment_plot)
+        end
         # fill between functions
         if sf isa Tuple && series[:ribbon] === nothing
             sf1, sf2 = sf
@@ -716,7 +759,7 @@ end
 ## --------------------------------------------------------------------------------------
 # Generates a colormap for pgfplots based on a ColorGradient
 pgfx_arrow(::Nothing) = "every arrow/.append style={-}"
-function pgfx_arrow(arr::Arrow)
+function pgfx_arrow(arr::Arrow, side = arr.side)
     components = String[]
     head = String[]
     push!(head, "{stealth[length = $(arr.headlength)pt, width = $(arr.headwidth)pt")
@@ -725,11 +768,11 @@ function pgfx_arrow(arr::Arrow)
     end
     push!(head, "]}")
     head = join(head, "")
-    if arr.side == :both || arr.side == :tail
+    if side == :both || side == :tail
         push!(components, head)
     end
     push!(components, "-")
-    if arr.side == :both || arr.side == :head
+    if side == :both || side == :head
         push!(components, head)
     end
     components = join(components, "")