diff --git a/.gitignore b/.gitignore
index ccb1692..de8079e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@
 *.jl.mem
 *.svg
 Manifest.toml
+test/data/*-comparison.png
diff --git a/src/lines.jl b/src/lines.jl
index 2122483..4589641 100644
--- a/src/lines.jl
+++ b/src/lines.jl
@@ -9,12 +9,11 @@ function graphline(g, locs_x, locs_y, nodesize::Vector{T}, arrowlength, angleoff
         j = dst(e)
         Δx = locs_x[j] - locs_x[i]
         Δy = locs_y[j] - locs_y[i]
-        d  = sqrt(Δx^2 + Δy^2)
-        θ  = atan(Δy,Δx)
+        θ = atan(Δy,Δx)
         startx = locs_x[i] + nodesize[i]*cos(θ)
         starty = locs_y[i] + nodesize[i]*sin(θ)
-        endx  = locs_x[i] + (d-nodesize[j])*1.00*cos(θ)
-        endy  = locs_y[i] + (d-nodesize[j])*1.00*sin(θ)
+        endx = locs_x[j] + nodesize[j]*cos(θ+π)
+        endy = locs_y[j] + nodesize[j]*sin(θ+π)
         lines[e_idx] = [(startx, starty), (endx, endy)]
         arr1, arr2 = arrowcoords(θ, endx, endy, arrowlength, angleoffset)
         arrows[e_idx] = [arr1, (endx, endy), arr2]
@@ -30,12 +29,11 @@ function graphline(g::AbstractGraph{T}, locs_x, locs_y, nodesize::Real, arrowlen
         j = dst(e)
         Δx = locs_x[j] - locs_x[i]
         Δy = locs_y[j] - locs_y[i]
-        d  = sqrt(Δx^2 + Δy^2)
-        θ  = atan(Δy,Δx)
+        θ = atan(Δy,Δx)
         startx = locs_x[i] + nodesize*cos(θ)
         starty = locs_y[i] + nodesize*sin(θ)
-        endx  = locs_x[i] + (d-nodesize)*1.00*cos(θ)
-        endy  = locs_y[i] + (d-nodesize)*1.00*sin(θ)
+        endx = locs_x[j] + nodesize*cos(θ+π)
+        endy = locs_y[j] + nodesize*sin(θ+π)
         lines[e_idx] = [(startx, starty), (endx, endy)]
         arr1, arr2 = arrowcoords(θ, endx, endy, arrowlength, angleoffset)
         arrows[e_idx] = [arr1, (endx, endy), arr2]
@@ -50,12 +48,11 @@ function graphline(g::AbstractGraph{T}, locs_x, locs_y, nodesize::Vector{<:Real}
         j = dst(e)
         Δx = locs_x[j] - locs_x[i]
         Δy = locs_y[j] - locs_y[i]
-        d  = sqrt(Δx^2 + Δy^2)
-        θ  = atan(Δy,Δx)
+        θ = atan(Δy,Δx)
         startx = locs_x[i] + nodesize[i]*cos(θ)
         starty = locs_y[i] + nodesize[i]*sin(θ)
-        endx  = locs_x[i] + (d-nodesize[j])*1.00*cos(θ)
-        endy  = locs_y[i] + (d-nodesize[j])*1.00*sin(θ)
+        endx = locs_x[j] + nodesize[j]*cos(θ+π)
+        endy = locs_y[j] + nodesize[j]*sin(θ+π)
         lines[e_idx] = [(startx, starty), (endx, endy)]
     end
     lines
@@ -68,103 +65,118 @@ function graphline(g::AbstractGraph{T}, locs_x, locs_y, nodesize::Real) where {T
         j = dst(e)
         Δx = locs_x[j] - locs_x[i]
         Δy = locs_y[j] - locs_y[i]
-        d  = sqrt(Δx^2 + Δy^2)
-        θ  = atan(Δy,Δx)
+        θ = atan(Δy,Δx)
         startx = locs_x[i] + nodesize*cos(θ)
         starty = locs_y[i] + nodesize*sin(θ)
-        endx  = locs_x[i] + (d-nodesize)*1.00*cos(θ)
-        endy  = locs_y[i] + (d-nodesize)*1.00*sin(θ)
+        endx = locs_x[j] + nodesize*cos(θ+π)
+        endy = locs_y[j] + nodesize*sin(θ+π)
         lines[e_idx] = [(startx, starty), (endx, endy)]
     end
     return lines
 end
 
 function graphcurve(g::AbstractGraph{T}, locs_x, locs_y, nodesize::Vector{<:Real}, arrowlength, angleoffset, outangle=pi/5) where {T<:Integer}
-    lines = Array{Vector}(ne(g))
+    curves = Matrix{Tuple{Float64,Float64}}(undef, ne(g), 4)
     arrows = Array{Vector{Tuple{Float64,Float64}}}(undef, ne(g))
     for (e_idx, e) in enumerate(edges(g))
         i = src(e)
         j = dst(e)
         Δx = locs_x[j] - locs_x[i]
         Δy = locs_y[j] - locs_y[i]
-        d  = sqrt(Δx^2 + Δy^2)
-        θ  = atan(Δy,Δx)
-        startx = locs_x[i] + nodesize[i]*cos(θ)
-        starty = locs_y[i] + nodesize[i]*sin(θ)
-        endx  = locs_x[i] + (d-nodesize[j])*1.00*cos(θ)
-        endy  = locs_y[i] + (d-nodesize[j])*1.00*sin(θ)
-        lines[e_idx] = curveedge(startx, starty, endx, endy, outangle)
-        if startx <= endx
-            arr1, arr2 = curvearrowcoords1(θ, outangle, endx, endy, arrowlength, angleoffset)
-            arrows[e_idx] = [arr1, (endx, endy), arr2]
-        else
-            arr1, arr2 = curvearrowcoords2(θ, outangle, endx, endy, arrowlength, angleoffset)
-            arrows[e_idx] = [arr1, (endx, endy), arr2]
+        θ = atan(Δy,Δx)
+        startx = locs_x[i] + nodesize[i]*cos(θ+outangle)
+        starty = locs_y[i] + nodesize[i]*sin(θ+outangle)
+        endx = locs_x[j] + nodesize[j]*cos(θ+π-outangle)
+        endy = locs_y[j] + nodesize[j]*sin(θ+π-outangle)
+
+        d = hypot(endx-startx, endy-starty)
+
+        if i == j
+            d = 2 * π * nodesize[i]
         end
+
+        curves[e_idx, :] = curveedge(startx, starty, endx, endy, θ, outangle, d)
+
+        arr1, arr2 = arrowcoords(θ-outangle, endx, endy, arrowlength, angleoffset)
+        arrows[e_idx] = [arr1, (endx, endy), arr2]
     end
-    return lines, arrows
+    return curves, arrows
 end
 
 function graphcurve(g, locs_x, locs_y, nodesize::Real, arrowlength, angleoffset, outangle=pi/5)
-    lines = Array{Vector}(ne(g))
+    curves = Matrix{Tuple{Float64,Float64}}(undef, ne(g), 4)
     arrows = Array{Vector{Tuple{Float64,Float64}}}(undef, ne(g))
     for (e_idx, e) in enumerate(edges(g))
         i = src(e)
         j = dst(e)
         Δx = locs_x[j] - locs_x[i]
         Δy = locs_y[j] - locs_y[i]
-        d  = sqrt(Δx^2 + Δy^2)
-        θ  = atan(Δy,Δx)
-        startx = locs_x[i] + nodesize*cos(θ)
-        starty = locs_y[i] + nodesize*sin(θ)
-        endx  = locs_x[i] + (d-nodesize)*1.00*cos(θ)
-        endy  = locs_y[i] + (d-nodesize)*1.00*sin(θ)
-        lines[e_idx] = curveedge(startx, starty, endx, endy, outangle)
-        if startx <= endx
-            arr1, arr2 = curvearrowcoords1(θ, outangle, endx, endy, arrowlength, angleoffset)
-            arrows[e_idx] = [arr1, (endx, endy), arr2]
-        else
-            arr1, arr2 = curvearrowcoords2(θ, outangle, endx, endy, arrowlength, angleoffset)
-            arrows[e_idx] = [arr1, (endx, endy), arr2]
+        θ = atan(Δy,Δx)
+        startx = locs_x[i] + nodesize*cos(θ+outangle)
+        starty = locs_y[i] + nodesize*sin(θ+outangle)
+        endx = locs_x[j] + nodesize*cos(θ+π-outangle)
+        endy = locs_y[j] + nodesize*sin(θ+π-outangle)
+
+        d = hypot(endx-startx, endy-starty)
+
+        if i == j
+            d = 2 * π * nodesize
         end
+
+        curves[e_idx, :] = curveedge(startx, starty, endx, endy, θ, outangle, d)
+
+        arr1, arr2 = arrowcoords(θ-outangle, endx, endy, arrowlength, angleoffset)
+        arrows[e_idx] = [arr1, (endx, endy), arr2]
     end
-    return lines, arrows
+    return curves, arrows
 end
 
 function graphcurve(g, locs_x, locs_y, nodesize::Real, outangle)
-    lines = Array{Vector}(ne(g))
+    curves = Matrix{Tuple{Float64,Float64}}(undef, ne(g), 4)
     for (e_idx, e) in enumerate(edges(g))
         i = src(e)
         j = dst(e)
         Δx = locs_x[j] - locs_x[i]
         Δy = locs_y[j] - locs_y[i]
-        d  = sqrt(Δx^2 + Δy^2)
-        θ  = atan(Δy,Δx)
-        startx = locs_x[i] + nodesize*cos(θ)
-        starty = locs_y[i] + nodesize*sin(θ)
-        endx  = locs_x[i] + (d-nodesize)*1.00*cos(θ)
-        endy  = locs_y[i] + (d-nodesize)*1.00*sin(θ)
-        lines[e_idx] = curveedge(startx, starty, endx, endy, outangle)
+        θ = atan(Δy,Δx)
+        startx = locs_x[i] + nodesize*cos(θ+outangle)
+        starty = locs_y[i] + nodesize*sin(θ+outangle)
+        endx = locs_x[j] + nodesize*cos(θ+π-outangle)
+        endy = locs_y[j] + nodesize*sin(θ+π-outangle)
+
+        d = hypot(endx-startx, endy-starty)
+
+        if i == j
+            d = 2 * π * nodesize
+        end
+
+        curves[e_idx, :] = curveedge(startx, starty, endx, endy, θ, outangle, d)
     end
-    lines
+    return curves
 end
 
 function graphcurve(g::AbstractGraph{T}, locs_x, locs_y, nodesize::Vector{<:Real}, outangle) where {T<:Integer}
-    lines = Array{Vector}(ne(g))
+    curves = Matrix{Tuple{Float64,Float64}}(undef, ne(g), 4)
     for (e_idx, e) in enumerate(edges(g))
         i = src(e)
         j = dst(e)
         Δx = locs_x[j] - locs_x[i]
         Δy = locs_y[j] - locs_y[i]
-        d  = sqrt(Δx^2 + Δy^2)
-        θ  = atan(Δy,Δx)
-        startx = locs_x[i] + nodesize*cos(θ)
-        starty = locs_y[i] + nodesize*sin(θ)
-        endx  = locs_x[i] + (d-nodesize)*1.00*cos(θ)
-        endy  = locs_y[i] + (d-nodesize)*1.00*sin(θ)
-        lines[e_idx] = curveedge(startx, starty, endx, endy, outangle)
+        θ = atan(Δy,Δx)
+        startx = locs_x[i] + nodesize[i]*cos(θ+outangle)
+        starty = locs_y[i] + nodesize[i]*sin(θ+outangle)
+        endx = locs_x[j] + nodesize[j]*cos(θ+π-outangle)
+        endy = locs_y[j] + nodesize[j]*sin(θ+π-outangle)
+
+        d = hypot(endx-startx, endy-starty)
+
+        if i == j
+            d = 2 * π * nodesize[i]
+        end
+
+        curves[e_idx, :] = curveedge(startx, starty, endx, endy, θ, outangle, d)
     end
-    return lines
+    return curves
 end
 
 # this function is copy from [IainNZ](https://github.com/IainNZ)'s [GraphLayout.jl](https://github.com/IainNZ/GraphLayout.jl)
@@ -176,36 +188,16 @@ function arrowcoords(θ, endx, endy, arrowlength, angleoffset=20.0/180.0*π)
     return (arr1x, arr1y), (arr2x, arr2y)
 end
 
-# using when startx <= endx
-# θ1 is the angle between line from start point to end point with x axis
-# θ2 is the out angle of edge
-function curvearrowcoords1(θ1, θ2, endx, endy, arrowlength, angleoffset=20.0/180.0*π)
-    arr1x = endx + arrowlength*cos(pi+θ1-θ2-angleoffset)
-    arr1y = endy + arrowlength*sin(pi+θ1-θ2-angleoffset)
-    arr2x = endx + arrowlength*cos(pi+θ1-θ2+angleoffset)
-    arr2y = endy + arrowlength*sin(pi+θ1-θ2+angleoffset)
-    return (arr1x, arr1y), (arr2x, arr2y)
-end
+function curveedge(x1, y1, x2, y2, θ, outangle, d; k=0.5)
 
-# using when startx > endx
-function curvearrowcoords2(θ1, θ2, endx, endy, arrowlength, angleoffset=20.0/180.0*π)
-    arr1x = endx + arrowlength*cos(pi+θ1+θ2-angleoffset)
-    arr1y = endy + arrowlength*sin(pi+θ1+θ2-angleoffset)
-    arr2x = endx + arrowlength*cos(pi+θ1+θ2+angleoffset)
-    arr2y = endy + arrowlength*sin(pi+θ1+θ2+angleoffset)
-    return (arr1x, arr1y), (arr2x, arr2y)
-end
+    r = d * k
 
-function curveedge(x1, y1, x2, y2, θ)
-    θ1 = atan((y2-y1)/(x2-x1))
-    d = sqrt((x2-x1)^2+(y2-y1)^2)
-    r = d/2cos(θ)
-    if x1 <= x2
-        x = x1 + r*cos(θ+θ1)
-        y = y1 + r*sin(θ+θ1)
-    else
-        x = x2 + r*cos(θ+θ1)
-        y = y2 + r*sin(θ+θ1)
-    end
-    return [:M, x1,y1, :Q, x, y, x2, y2]
+    # Control points for left bending curve.
+    xc1 = x1 + r * cos(θ + outangle)
+    yc1 = y1 + r * sin(θ + outangle)
+
+    xc2 = x2 + r * cos(θ + π - outangle)
+    yc2 = y2 + r * sin(θ + π - outangle)
+
+    return [(x1,y1) (xc1, yc1) (xc2, yc2) (x2, y2)]
 end
diff --git a/src/plot.jl b/src/plot.jl
index 6422589..73b34a8 100644
--- a/src/plot.jl
+++ b/src/plot.jl
@@ -195,12 +195,12 @@ function gplot(g::AbstractGraph{T},
     lines, arrows = nothing, nothing
     if linetype == "curve"
         if arrowlengthfrac > 0.0
-            lines_cord, arrows_cord = graphcurve(g, locs_x, locs_y, nodesize, arrowlengthfrac, arrowangleoffset, outangle)
-            lines = path(lines_cord)
+            curves_cord, arrows_cord = graphcurve(g, locs_x, locs_y, nodesize, arrowlengthfrac, arrowangleoffset, outangle)
+            lines = curve(curves_cord[:,1], curves_cord[:,2], curves_cord[:,3], curves_cord[:,4])
             arrows = line(arrows_cord)
         else
-            lines_cord = graphcurve(g, locs_x, locs_y, nodesize, outangle)
-            lines = path(lines_cord)
+            curves_cord = graphcurve(g, locs_x, locs_y, nodesize, outangle)
+            lines = curve(curves_cord[:,1], curves_cord[:,2], curves_cord[:,3], curves_cord[:,4])
         end
     else
         if arrowlengthfrac > 0.0
diff --git a/test/data/curve.png b/test/data/curve.png
new file mode 100644
index 0000000..668ca01
Binary files /dev/null and b/test/data/curve.png differ
diff --git a/test/data/self_directed.png b/test/data/self_directed.png
new file mode 100644
index 0000000..1eb1177
Binary files /dev/null and b/test/data/self_directed.png differ
diff --git a/test/runtests.jl b/test/runtests.jl
index 82a5ef3..7e5327f 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -10,6 +10,7 @@ using Compose
 using Random
 using Test
 using VisualRegressionTests
+using ImageMagick
 
 # global variables
 istravis = "TRAVIS" ∈ keys(ENV)
@@ -48,6 +49,13 @@ function plot_and_save(fname, g; gplot_kwargs...)
     draw(PNG(fname, 8inch, 8inch), gplot(g; layout=test_layout, gplot_kwargs...))
 end
 
+function save_comparison(result::VisualTestResult)
+    grid = hcat(result.refImage, result.testImage)
+    path = joinpath(datadir, string(basename(result.refFilename)[1:end-length(".png")], "-comparison.png"))
+    ImageMagick.save(path, grid)
+    return result
+end
+
 @testset "Karate Net" begin
     # auxiliary variables
     nodelabel = collect(1:nv(g))
@@ -56,12 +64,12 @@ end
     # test nodesize
     plot_and_save1(fname) = plot_and_save(fname, g, nodesize=nodesize.^0.3, nodelabel=nodelabel, nodelabelsize=nodesize.^0.3)
     refimg1 = joinpath(datadir, "karate_different_nodesize.png")
-    @test test_images(VisualTest(plot_and_save1, refimg1), popup=!istravis) |> success
+    @test test_images(VisualTest(plot_and_save1, refimg1), popup=!istravis) |> save_comparison |> success
 
     # test directed graph
     plot_and_save2(fname) = plot_and_save(fname, g, arrowlengthfrac=0.02, nodelabel=nodelabel)
     refimg2 = joinpath(datadir, "karate_straight_directed.png")
-    @test test_images(VisualTest(plot_and_save2, refimg2), popup=!istravis) |> success
+    @test test_images(VisualTest(plot_and_save2, refimg2), popup=!istravis) |> save_comparison |> success
 
     # test node membership
     membership = [1,1,1,1,1,1,1,1,2,1,1,1,1,1,2,2,1,1,2,1,2,1,2,2,2,2,2,2,2,2,2,2,2,2]
@@ -69,12 +77,33 @@ end
     nodefillc = nodecolor[membership]
     plot_and_save3(fname) = plot_and_save(fname, g, nodelabel=nodelabel, nodefillc=nodefillc)
     refimg3 = joinpath(datadir, "karate_groups.png")
-    @test test_images(VisualTest(plot_and_save3, refimg3), popup=!istravis) |> success
+    @test test_images(VisualTest(plot_and_save3, refimg3), popup=!istravis) |> save_comparison |> success
 end
 
 @testset "WheelGraph" begin
     # default options
     plot_and_save1(fname) = plot_and_save(fname, h)
     refimg1 = joinpath(datadir, "wheel10.png")
-    @test test_images(VisualTest(plot_and_save1, refimg1), popup=!istravis) |> success
+    @test test_images(VisualTest(plot_and_save1, refimg1), popup=!istravis) |> save_comparison |> success
+end
+
+@testset "Curves" begin
+
+    g2 = DiGraph(2)
+    add_edge!(g2, 1,2)
+    add_edge!(g2, 2,1)
+
+    plot_and_save1(fname) = plot_and_save(fname, g2, linetype="curve")
+    refimg1 = joinpath(datadir, "curve.png")
+    @test test_images(VisualTest(plot_and_save1, refimg1), popup=!istravis) |> save_comparison |> success
+
+    g3 = DiGraph(2)
+    add_edge!(g3, 1,1)
+    add_edge!(g3, 1,2)
+    add_edge!(g3, 2,1)
+
+    plot_and_save2(fname) = plot_and_save(fname, g3, linetype="curve")
+    refimg2 = joinpath(datadir, "self_directed.png")
+    @test test_images(VisualTest(plot_and_save2, refimg2), popup=!istravis) |> save_comparison |> success
+
 end