Automatically compute reasonable aspect ratio (#457)

Automatically compute reasonable aspect ratio in sgct lua helper

scripts/configuration_helper.lua

@@ -360,15 +360,6 @@ end
 
 function generateSingleWindowConfig(arg)
     -- First some type checking
-    assert(
-        type(arg[1]) == "number" or type(arg[1]) == "nil",
-        "First argument must be a number or nil"
-    )
-    assert(
-        type(arg[2]) == "number" or type(arg[2]) == "nil",
-        "Second argument must be a number or nil"
-    )
-
     assert(
         type(arg["res"]) == "table" or type(arg["res"]) == "nil",
         "res must be a table or nil"
@@ -400,10 +391,6 @@ function generateSingleWindowConfig(arg)
     if (type(arg["windowSize"]) == "table") then
         assert(type(arg["windowSize"][1]) == "number", "windowPos[1] must be a number")
         assert(type(arg["windowSize"][2]) == "number", "windowPos[2] must be a number")
-        assert(
-            type(arg[1]) == "nil" and type(arg[2]) == "nil",
-            "Only windowSize or the first and second arguments can be set. Not both"
-        )
     end
 
     assert(
@@ -594,9 +581,7 @@ function generateSingleWindowConfig(arg)
     end
 
     if not arg["windowSize"] then
-        arg["windowSize"] = {}
-        arg["windowSize"][1] = arg[1] or 1280
-        arg["windowSize"][2] = arg[2] or 720
+        arg["windowSize"] = {1280, 720}
     end
 
     arg["scene"] = generateScene(arg)
@@ -609,6 +594,35 @@ function generateSingleWindowConfig(arg)
 end
 
 
+function normalizeArg(arg)
+    arg = arg or {}
+
+    if (type(arg["windowSize"]) == "table") then
+        assert(
+            type(arg[1]) == "nil" and type(arg[2]) == "nil",
+            "Only windowSize or the first and second arguments can be set. Not both"
+        )
+    end
+    assert(
+        type(arg[1]) == "number" or type(arg[1]) == "nil",
+        "First argument must be a number or nil"
+    )
+    assert(
+        type(arg[2]) == "number" or type(arg[2]) == "nil",
+        "Second argument must be a number or nil"
+    )
+    if (type(arg[1]) == "number") then
+        if (type(arg[2]) == "nil") then
+            arg[2] = arg[1] * 9/16
+        end
+        arg["windowSize"] = { arg[1], arg[2] }
+        arg[1] = nil
+        arg[2] = nil
+    end
+
+    return arg
+end
+
 
 function sgct.makeConfig(config)
     local configFile = os.tmpname()
@@ -624,7 +638,12 @@ end
 
 
 function sgct.config.single(arg)
-    arg = arg or {}
+    arg = normalizeArg(arg)
+
+    assert(
+        type(arg["windowSize"]) == "table" or type(arg["windowSize"]) == "nil",
+        "windowSize must be a table or nil"
+    )
 
     assert(
         type(arg["fov"]) == "table" or type(arg["fov"]) == "nil",
@@ -635,9 +654,32 @@ function sgct.config.single(arg)
         assert(type(arg["fov"]["right"]) == "number", "fov['right'] must be a number")
         assert(type(arg["fov"]["up"]) == "number",    "fov['up'] must be a number")
         assert(type(arg["fov"]["down"]) == "number",  "fov['down'] must be a number")
+    else
+        if (type(arg["windowSize"]) == "table") then
+            assert(type(arg["windowSize"][1]) == "number", "windowPos[1] must be a number")
+            assert(type(arg["windowSize"][2]) == "number", "windowPos[2] must be a number")
+
+            local ratio = arg["windowSize"][1] / arg["windowSize"][2]
+            local horizontalFov = 30
+            local verticalFov = 30
+
+            if (ratio > 1) then
+                verticalFov = horizontalFov / ratio
+            else
+                horizontalFov = verticalFov * ratio
+            end
+
+            arg["fov"] = {
+                down = verticalFov,
+                up = verticalFov,
+                left = horizontalFov,
+                right = horizontalFov
+            }
+        else
+            arg["fov"] = { down = 16.875, up = 16.875, left = 30.0, right = 30.0 }
+        end
     end
     
-    arg["fov"] = arg["fov"] or { down = 16.875, up = 16.875, left = 30.0, right = 30.0 }
     arg["viewport"] = generateSingleViewportFOV(
         arg["fov"]["down"],
         arg["fov"]["up"], 
@@ -651,7 +693,7 @@ end
 
 
 function sgct.config.fisheye(arg)
-    arg = arg or {}
+    arg = normalizeArg(arg)
 
     assert(
         type(arg["fov"]) == "number" or type(arg["fov"]) == "nil",