New recipe: lens (#2372)

* create recipe, add box and line

* add subplot

* improve linking

* add ghost subplot

* draw line only if inset is in subplot

* sp_bbox -> inset_bbox

* better linking

* add lens! shorthand

* apply keywords only to inset

* check bbox type

* add lens example

* fix typo and stray *

* move legend out of the plot

* move lens example down

src/examples.jl

@@ -853,6 +853,28 @@ const _examples = PlotExample[
             ),
         ],
     ),
+    PlotExample(
+        "Lens",
+        "A lens lets you easily magnify a region of a plot. x and y coordinates refer to the to be magnified region and the via the `inset` keyword the subplot index and the bounding box (in relative coordinates) of the inset plot with the magnified plot can be specified. Additional attributes count for the inset plot.",
+        [
+            quote
+                begin
+                    plot(
+                        [(0, 0), (0, 0.9), (1, 0.9), (2, 1), (3, 0.9), (80, 0)],
+                        legend = :outertopright,
+                    )
+                    plot!([(0, 0), (0, 0.9), (2, 0.9), (3, 1), (4, 0.9), (80, 0)])
+                    plot!([(0, 0), (0, 0.9), (3, 0.9), (4, 1), (5, 0.9), (80, 0)])
+                    plot!([(0, 0), (0, 0.9), (4, 0.9), (5, 1), (6, 0.9), (80, 0)])
+                    lens!(
+                        [1, 6],
+                        [0.9, 1.1],
+                        inset = (1, bbox(0.5, 0.0, 0.4, 0.4)),
+                    )
+                end
+            end,
+        ],
+    ),
 ]
 
 # Some constants for PlotDocs and PlotReferenceImages

src/recipes.jl

@@ -899,6 +899,91 @@ end
 # note: don't add dependencies because this really isn't a drop-in replacement
 
 
+# ---------------------------------------------------------------------------
+# lens! - magnify a region of a plot
+lens!(args...;kwargs...) = plot!(args...; seriestype=:lens, kwargs...)
+export lens!
+@recipe function f(::Type{Val{:lens}}, plt::AbstractPlot)
+    sp_index, inset_bbox = plotattributes[:inset_subplots]
+    if !(width(inset_bbox) isa Measures.Length{:w,<:Real})
+        throw(ArgumentError("Inset bounding box needs to in relative coordinates."))
+    end
+    sp = plt.subplots[sp_index]
+    xl1, xl2 = xlims(plt.subplots[sp_index])
+    bbx1 = xl1 + left(inset_bbox).value * (xl2 - xl1)
+    bbx2 = bbx1 + width(inset_bbox).value * (xl2 - xl1)
+    yl1, yl2 = ylims(plt.subplots[sp_index])
+    bby1 = yl1 + (1 - bottom(inset_bbox).value) * (yl2 - yl1)
+    bby2 = bby1 + height(inset_bbox).value * (yl2 - yl1)
+    bbx = bbx1 + width(inset_bbox).value * (xl2 - xl1) / 2
+    bby = bby1 + height(inset_bbox).value * (yl2 - yl1) / 2
+    lens_index = last(plt.subplots)[:subplot_index] + 1
+    x1, x2 = plotattributes[:x]
+    y1, y2 = plotattributes[:y]
+    seriestype := :path
+    label := ""
+    linecolor := :lightgray
+    bbx_mag = (x1 + x2) / 2
+    bby_mag = (y1 + y2) / 2
+    xi_lens, yi_lens = intersection_point(bbx_mag, bby_mag, bbx, bby, abs(bby2 - bby1), abs(bbx2 - bbx1))
+    xi_mag, yi_mag = intersection_point(bbx, bby, bbx_mag, bby_mag, abs(y2 - y1), abs(x2 - x1))
+    # add lines
+    if xl1 < xi_lens < xl2 &&
+        yl1 < yi_lens < yl2
+        @series begin
+            subplot := sp_index
+            x := [xi_mag, xi_lens]
+            y := [yi_mag, yi_lens]
+            ()
+        end
+    end
+    # add magnification shape
+    @series begin
+        subplot := sp_index
+        x := [x1, x1, x2, x2, x1]
+        y := [y1, y2, y2, y1, y1]
+        ()
+    end
+    # add subplot
+    for series in sp.series_list
+        @series begin
+            plotattributes = merge(plotattributes, copy(series.plotattributes))
+            subplot := lens_index
+            label := ""
+            xlims := (x1, x2)
+            ylims := (y1, y2)
+            ()
+        end
+    end
+    backup = copy(plotattributes)
+    empty!(plotattributes)
+    seriestype := :path
+    series_plotindex := backup[:series_plotindex]
+end
+
+function intersection_point(xA, yA, xB, yB, h, w)
+    s = (yA - yB) / (xA - xB)
+    hh = h / 2
+    hw = w / 2
+    # left or right?
+    if -hh <= s * hw <= hh
+        if xA > xB
+            # right
+            return xB + hw, yB + s * hw
+        else # left
+            return xB - hw, yB - s * hw
+        end
+    # top or bot?
+    elseif -hw <= hh/s <= hw
+        if yA > yB
+            # top
+            return xB + hh/s, yB + hh
+        else
+            # bottom
+            return xB - hh/s, yB - hh
+        end
+    end
+end
 # ---------------------------------------------------------------------------
 # contourf - filled contours