Coordinate Axes

* Add coordinate axes renderable
 * Add debug helper
 * Add example asset
 * Fix bug with dynamic loading of assets. (#763)

data/assets/examples/debugcoordinateaxes.asset

@@ -0,0 +1,19 @@
+local transforms = asset.require('scene/solarsystem/planets/earth/transforms')
+local debugHelper = asset.require('util/debug_helper')
+
+local earthRadius = 6.371E6
+
+debugHelper.registerCartesianAxes(asset, {
+    Parent = transforms.EarthBarycenter.Identifier,
+    Scale = earthRadius * 3.5
+})
+
+debugHelper.registerCartesianAxes(asset, {
+    Parent = transforms.EarthInertial.Identifier,
+    Scale = earthRadius * 2.5
+})
+
+debugHelper.registerCartesianAxes(asset, {
+    Parent = transforms.EarthIAU.Identifier,
+    Scale = earthRadius * 1.5
+})

data/assets/util/debug_helper.asset

@@ -0,0 +1,133 @@
+local identifierGeneratorFunction = function (suffix)
+    local nextIndex = 0
+    return function (specification)
+        nextIndex = nextIndex + 1
+        return specification.Identifier or
+            (specification.Parent .. suffix .. nextIndex)
+    end
+end
+
+local generateGridIdentifier = identifierGeneratorFunction("Grid")
+
+local addGrid = function (specification)
+    local identifier = specification.Identifier or
+        generateGridIdentifier(specification)
+
+    local name = specification.Name
+    local color = specification.Color
+    local parent = specification.Parent
+    local scale = specification.Scale
+    local position = specification.Position
+    local rotation = specification.Rotation
+
+    local grid = {
+        Identifier = identifier,
+        Parent = parent,
+        Transform = {
+            Scale = {
+                Type = "StaticScale",
+                Scale = scale;
+            },
+            Translation = {
+                Type = "StaticTranslation",
+                Position = position
+            },
+            Rotation = {
+                Type = "StaticRotation",
+                Rotation = rotation
+            }
+        },
+        Renderable = {
+            Type = "RenderableSphericalGrid",
+            Enabled = true,
+            LineWidth = 2.0,
+            GridColor = color
+        },
+        GUI = {
+            Name = name,
+            Path = "/Other/Grids"
+        }
+    }
+    openspace.addSceneGraphNode(grid)
+    return identifier;
+end
+
+local generateAxesIdentifier = identifierGeneratorFunction("Axes")
+
+local addCartesianAxes = function (specification)
+    local identifier = specification.Identifier or
+        generateAxesIdentifier(specification)
+
+    local name = specification.Name or specification.Identifier
+    local parent = specification.Parent or "Root"
+    local scale = specification.Scale or 1.0
+    local position = specification.Position or {0.0, 0.0, 0.0}
+    local rotation = specification.Rotation or {0.0, 0.0, 0.0}
+
+    local axes = {
+        Identifier = identifier,
+        Parent = parent,
+        Transform = {
+            Scale = {
+                Type = "StaticScale",
+                Scale = scale;
+            },
+            Translation = {
+                Type = "StaticTranslation",
+                Position = position
+            },
+            Rotation = {
+                Type = "StaticRotation",
+                Rotation = rotation
+            }
+        },
+        Renderable = {
+            Type = "RenderableCartesianAxes",
+            Enabled = true,
+            XColor = {1.0, 0.0, 0.0, 1.0},
+            YColor = {0.0, 1.0, 0.0, 1.0},
+            ZColor = {0.0, 0.0, 1.0, 1.0}
+        },
+        GUI = {
+            Name = name,
+            Path = "/Other/Coordinate Systems"
+        }
+    }
+    openspace.addSceneGraphNode(axes)
+    return identifier;
+end
+
+
+local registerNode = function(
+    containerAsset,
+    nodeCreationFunction,
+    identifierGeneratorFunction,
+    specification
+)
+    local identifier = specification.Identifier or
+        identifierGeneratorFunction(specification)
+
+    specification.Identifier = identifier
+
+    containerAsset.onInitialize(function ()
+        nodeCreationFunction(specification)
+    end)
+    containerAsset.onDeinitialize(function ()
+        openspace.removeSceneGraphNode(identifier)
+    end)
+end
+
+local registerGrid = function(gridAsset, specification)
+    registerNode(gridAsset, addGrid, generateGridIdentifier, specification)
+end
+
+local registerCartesianAxes = function(axesAsset, specification)
+    registerNode(axesAsset, addCartesianAxes, generateAxesIdentifier, specification)
+end
+
+asset.export("addGrid", addGrid)
+asset.export("registerGrid", registerGrid)
+
+asset.export("addCartesianAxes", addGrid)
+asset.export("registerCartesianAxes", registerCartesianAxes)
+