2021-04-11 15:18:23 (UTC-03:00)

Marcel Rodrigues <marcelgmr@gmail.com>

add dashed polylines

diff --git a/poly.lua b/poly.lua
new file mode 100644
index 0000000..2996ff2
--- /dev/null
+++ b/poly.lua
@@ -0,0 +1,54 @@
+local ffi = require "ffi"
+
+ffi.cdef[[
+double hypot(double x, double y);
+]]
+local hypot = ffi.C.hypot
+
+local function dashed(points, pattern)
+    local x0, y0, x1, y1
+    local cx, cy
+    local i, j
+    local d, h
+    local polylines = {}
+    local polyline
+    local draw = true
+    x0, y0 = unpack(points[1])
+    polyline = {{x0, y0}}
+    i = 2
+    x1, y1 = unpack(points[i])
+    j = 1
+    d = pattern[j]
+    while true do
+        h = hypot(x1-x0, y1-y0)
+        if d < h then
+            cx = x0 + (x1-x0)*d/h
+            cy = y0 + (y1-y0)*d/h
+            if draw then
+                table.insert(polyline, {cx, cy})
+                table.insert(polylines, polyline)
+            else
+                polyline = {{cx, cy}}
+            end
+            x0, y0 = cx, cy
+            draw = not draw
+            if j < #pattern then j = j + 1 else j = 1 end
+            d = pattern[j]
+        else
+            if draw then
+                table.insert(polyline, {x1, y1})
+            end
+            d = d - h
+            if i < #points then i = i + 1 else break end
+            x0, y0 = x1, y1
+            x1, y1 = unpack(points[i])
+        end
+    end
+    if draw then
+        table.insert(polyline, points[i])
+        table.insert(polylines, polyline)
+    end
+    return polylines
+end
+
+return {dashed=dashed}