Feature/volume tools (#614)

* Create volume generation task

* Change domain bounds into a non-optional parameter

* Work on volume generation and rendering

* Example generation of time varying volume

* Example generation of time varying volume

* Compile fix in RenderableKameleonVolume

* Fix copy and paste error

* Enable spherical raycasting again

* Uniform naming

* Add some documentation and remove dead code

data/tasks/volume/generate_cartesian.task

@@ -0,0 +1,18 @@
+local fn =
+	"return function (x, y, z) " ..
+    "    if math.sqrt(x^2 + y^2 + z^2) < 0.4 then " ..
+    "        return 0.8 " ..
+    "    end " ..
+    "    return 0.0 " ..
+    "end"
+
+return {{
+    Type = "GenerateRawVolumeTask",
+    Dimensions = {32, 32, 32},
+    LowerDomainBound = {-0.5, -0.5, -0.5},
+    UpperDomainBound = {0.5, 0.5, 0.5},
+    ValueFunction = fn,
+    Time = "2018-05-04T00:00:00",
+    RawVolumeOutput = "${DATA}/assets/examples/volume/generated/cartesian/cartesian.rawvolume",
+    DictionaryOutput = "${DATA}/assets/examples/volume/generated/cartesian/cartesian.dictionary"
+}}

data/tasks/volume/generate_cartesian_sequence.task

@@ -0,0 +1,27 @@
+local length = 60
+local tasks = {}
+
+for i=1,length do
+	local radius = 0.5 * (1 - i/length)
+	local step = string.format("%02d", i-1)
+	local fn =
+		"return function (x, y, z) " .. "\n" ..
+	    "    local v = math.sqrt(x^2 + y^2 + z^2) - " .. radius .. "\n" ..
+	    "    v = (-v - 0.1) / 0.2 " .. "\n" ..
+	    "    v = math.min(math.max(v, 0), 1) " .. "\n" ..
+	    "    v = 3*v^2 - 2*v^3 " .. "\n" ..
+	    "    return v" .. "\n" ..
+	    "end"
+	tasks[#tasks+1] = {
+	    Type = "GenerateRawVolumeTask",
+	    Dimensions = {32, 32, 32},
+	    LowerDomainBound = {-0.5, -0.5, -0.5},
+	    UpperDomainBound = {0.5, 0.5, 0.5},
+	    ValueFunction = fn,
+	    Time = "2018-05-04T00:00:" .. step,
+	    RawVolumeOutput = "${DATA}/assets/examples/volume/generated/cartesiansequence/" .. step .. ".rawvolume",
+	    DictionaryOutput = "${DATA}/assets/examples/volume/generated/cartesiansequence/" .. step .. ".dictionary"
+	}
+end
+
+return tasks

data/tasks/volume/generate_spherical.task

@@ -0,0 +1,15 @@
+local fn =
+	"return function (r, phi, theta) " ..
+    "    return 1 - math.floor(r*10)/10 " ..
+    "end"
+
+return {{
+    Type = "GenerateRawVolumeTask",
+    Dimensions = {32, 32, 32},
+    LowerDomainBound = {0, 0, 0},
+    UpperDomainBound = {1, math.pi, 2 * math.pi},
+    ValueFunction = fn,
+    Time = "2018-05-04T00:00:00",
+    RawVolumeOutput = "${DATA}/assets/examples/volume/generated/spherical/spherical.rawvolume",
+    DictionaryOutput = "${DATA}/assets/examples/volume/generated/spherical/spherical.dictionary"
+}}