[Format] Add writeobj support (Wavefront OBJ)

docs/src/formats/output.md

@@ -9,6 +9,7 @@ Currently supported output file formats with different models:
 | File type          | Point cloud | Surface model | Volume model | Charges included |
 |--------------------|:-----------:|:-------------:|:------------:|:----------------:|
 | [HMO](@ref hmoout) |             | ✓             |              | ✓                |
+| [OBJ](@ref)        |             | ✓             |              |                  |
 | [SKEL](@ref)       |             | ✓             | ✓            |                  |
 | [STL](@ref stlout) |             | ✓             |              |                  |
 | [VTK](@ref)        |             | ✓             | ✓            |                  |
@@ -20,6 +21,11 @@ Currently supported output file formats with different models:
     writehmo
 ```
 
+## OBJ
+```@docs
+    writeobj
+```
+
 ## SKEL
 ```@docs
     writeskel

src/Format.jl

@@ -14,6 +14,9 @@ export readmcsf
 include("format/msms.jl")
 export readmsms
 
+include("format/obj.jl")
+export writeobj
+
 include("format/off.jl")
 export readoff
 

src/format/obj.jl

@@ -0,0 +1,51 @@
+# =========================================================================================
+"""
+    function writeobj{T}(
+        stream::IOStream,
+        model ::Model{T, Triangle{T}}
+    )
+
+Creates a Wavefront OBJ file from a given surface model.
+
+# Specification
+    <https://www.loc.gov/preservation/digital/formats/fdd/fdd000507.shtml>
+    <http://paulbourke.net/dataformats/obj/>
+
+# Return type
+`Void`
+
+# Alias
+
+    writeobj{T}(
+        fname::String,
+        model::Model{T, Triangle{T}}
+    )
+
+Creates the OBJ file by name rather than `IOStream` object.
+"""
+function writeobj(
+    stream::IOStream,
+    model ::Model{T, Triangle{T}}
+) where T
+    # nodes
+    for node in model.nodes
+        println(stream, "v ", node[1], " ", node[2], " ", node[3])
+    end
+    # vertex normals
+    vns = vertexnormals(model)
+    for vn in vns
+        println(stream, "vn ", vn[1], " ", vn[2], " ", vn[3])
+    end
+    # elements
+    ridx = reverseindex(model.nodes)
+    for elm in model.elements
+        print(stream, "f ")
+        print(stream, ridx[objectid(elm.v1)], "//", ridx[objectid(elm.v1)], " ")
+        print(stream, ridx[objectid(elm.v2)], "//", ridx[objectid(elm.v2)], " ")
+        println(stream, ridx[objectid(elm.v3)], "//", ridx[objectid(elm.v3)])
+    end
+end
+
+function writeobj(fname::String, model::Model{T, Triangle{T}}) where T
+    open(fh -> writeobj(fh, model), fname, "w")
+end

test/format/obj.jl

@@ -0,0 +1,3 @@
+@testset "writeobj" begin
+    @test_skip writeobj
+end

test/runtests.jl

@@ -15,6 +15,7 @@ const tests = [
     "format/hmo.jl",
     "format/mcsf.jl",
     "format/msms.jl",
+    "format/obj.jl",
     "format/off.jl",
     "format/pqr.jl",
     "format/skel.jl",