Initial changes to clean up the code.

matrix.hpp

@@ -168,6 +168,10 @@ namespace matrix {
     size_t bottom = 0;
 
     box_t(MAT &mat, size_t at_x, size_t at_y, size_t size) :
+      box_t(mat, at_x, at_y, size, size) {
+      }
+
+    box_t(MAT &mat, size_t at_x, size_t at_y, size_t width, size_t height) :
       from_x(at_x), from_y(at_y)
     {
       size_t h = matrix::height(mat);
@@ -175,15 +179,15 @@ namespace matrix {
 
       // keeps it from going below zero
       // need extra -1 to compensate for the first next()
-      left = max(from_x, size) - size;
+      left = max(from_x, width) - width;
       x = left - 1;  // must be -1 for next()
       // keeps it from going above width
-      right = min(from_x + size + 1, w);
+      right = min(from_x + width + 1, w);
 
       // same for these two
-      top = max(from_y, size) - size;
+      top = max(from_y, height) - height;
       y = top - (left == 0);
-      bottom = min(from_y + size + 1, h);
+      bottom = min(from_y + height + 1, h);
     }
 
     bool next() {