Unify some functions in utils.

src/FlatLayerVisualisation.cpp

@@ -91,10 +91,9 @@ void FlatLayerVisualisation::setVertexPositions(const int vertexNo, float *desti
             yOffset = 0;
             break;
 
-        case Ordering ::SQUARE:
+        case Ordering::SQUARE:
             const auto nodes = faceCount / 4;
-            auto columns = static_cast<int>(ceil(sqrt(nodes)));
+            auto columns = static_cast<int>(numCols(nodes));
-            while (nodes % columns) ++columns;
 
             zOffset = -2 * (vertexNo % columns);
             yOffset = 2 * (vertexNo / columns);

src/FlatLayerVisualisation.hpp

@@ -26,6 +26,6 @@ namespace fmri
         std::unique_ptr<float[]> colorBuffer;
         std::unique_ptr<int[]> indexBuffer;
 
-        void setVertexPositions(const int vertexNo, float *destination);
+        void setVertexPositions(int vertexNo, float *destination);
     };
 }

src/MultiImageVisualisation.cpp

@@ -17,8 +17,7 @@ MultiImageVisualisation::MultiImageVisualisation(const fmri::LayerData &layer)
 
     CHECK_EQ(1, images) << "Only single input image is supported" << endl;
 
-    int columns = ceil(sqrt(channels));
+    int columns = numCols(channels);
-    while (channels % columns) columns++;
 
     // Create the quads for the images.
     int r = 0, c = 0;

src/utils.cpp

@@ -0,0 +1,14 @@
+#include "utils.hpp"
+
+std::default_random_engine &fmri::rng()
+{
+    static std::default_random_engine rng;
+    static std::default_random_engine::result_type seed = 0;
+
+    if (seed == 0) {
+        std::random_device dev;
+        rng.seed(seed = dev());
+    }
+
+    return rng;
+}

src/utils.hpp

@@ -5,6 +5,7 @@
 #include <cmath>
 #include <fstream>
 #include <iterator>
+#include <random>
 #include <string>
 #include <utility>
 #include <vector>
@@ -127,4 +128,31 @@ namespace fmri
         return val / 180 * M_PI;
     }
 
+    /**
+     * Compute the ideal number of columns for dividing up a range into a rectangle.
+     *
+     * @tparam T
+     * @param elems number of elements to space out
+     * @return the ideal number of columns
+     */
+    template<class T>
+    inline T numCols(const T elems) {
+        auto cols = static_cast<T>(ceil(sqrt(elems)));
+
+        while (elems % cols) {
+            ++cols;// TODO: this should probably be done analytically
+        }
+
+        return cols;
+    }
+
+    /**
+     * Get a globally initialized random number generator.
+     *
+     * This RNG should always be used as a reference, to make sure the state actually updates.
+     *
+     * @return A reference to the global RNG.
+     */
+    std::default_random_engine& rng();
+
 }