mx is a minimal set of functions for working with serpentine arrays

lib/mx.js

@@ -0,0 +1,97 @@
+/* Jake & Bobby Pearse 2018.
+
+j.t.pearse@gmail.com
+
+Using a string of lights as a 2d Array
+
+A single strip can be treated as a serpentine array.
+
+We can treat a single strip of lights as a serpentine array by correcting the address of pixels on odd numbered columns
+
+Regular 2d array              serpentine array
+
+ |0|5|10|                         |0|9|10|
+ |1|6|11|                         |1|8|11|
+ |2|7|12|        Need to          |2|7|12|
+ |3|8|13|  === correct odd ===>   |3|6|13|
+ |4|9|14|   numbered columns      |4|5|14|
+
+NOTE: if for some mad reason you want to start with pixel 0 at the bottom, you should reverse EVEN numbered rows :)
+
+As we can see in a sane world, column 1 is reversed. As are all odd-numbered columns.
+address will calculate the corrected value for pixels.
+
+examples
+========
+
+  get a corrected pixel number
+  ============================
+
+  const NUM_ROWS = 5
+
+  address(6,NUM_ROWS)
+    => 8
+
+
+  light up all pixels on row 1 of strip
+  =====================================
+
+  for (const p = 0; p < strip.length; p++){
+    if (rowNum(p,NUM_ROWS) === 1){
+      strip.pixel(address(p,ROW_NUM)).color('white')
+    }
+  }
+
+*/
+const abs = Math.abs
+const floor = Math.floor
+
+// return the uncorrected row number of pixel p
+const rowNum = (p, rows) => p % rows
+
+// return the uncorrected column number of pixel p
+const columnNum = (p, rows) => floor(p/rows)
+
+// find the corrected pixel number at the top of a reversed column
+const rowZeroVal = (p,rows) => {
+
+   const columnHalf = floor(columnNum(p,rows)/2)+1
+   const doubleRows = rows * 2
+   return (columnHalf * doubleRows) - 1
+}
+
+// pixel p is in an odd numbered column => true || false
+const columnIsOdd = (p, rows) => columnNum(p, rows) % 2 > 0
+
+//corrected value of pixel p, for odd numbered columns
+const address = (p, rows) => {
+
+  if (columnIsOdd(p, rows)) {
+    return p + abs( p - rowZeroVal(p,rows)) - rowNum(p,rows)
+  }
+  return p
+}
+
+
+// check if a pixel is inside a bounding rectangle
+function inRange(p,first,last,rows){
+    return (
+    rowNum(p,rows) >= rowNum(first,rows) &&
+    rowNum(p,rows) <= rowNum(last,rows) &&
+    columnNum(p,rows) >= columnNum(first,rows) &&
+    columnNum(p,rows) <= columnNum(last,rows)
+    )
+}
+
+// reduce a 2d array with a bounding rectangle
+const rectRange = (first, last, rows, pixelArray) => pixelArray.filter(p => inRange(p, first, last, rows))
+
+module.exports = {
+  address,
+  columnNum,
+  rowZeroVal,
+  columnIsOdd,
+  rowNum,
+  inRange,
+  rectRange
+}

test/core.js

@@ -8,6 +8,8 @@ var sinon = require("sinon");
 var five = require("johnny-five");
 var pixel = require("../lib/pixel.js");
 
+var mx = require("../lib/mx");
+
 var Board = five.Board;
 
 function newBoard() {
@@ -360,3 +362,39 @@ exports["Pixel"] = {
         test.done();
     },
 };
+ exports["mx"] = {
+   rowNum : function(test) {
+     test.equals(3,mx.rowNum(13,5),"In a grid with 5 rows, pixel 13 is in row 3");
+     test.done();
+   },
+   colNum : function(test) {
+     test.equals(2,mx.columnNum(13,5), "in a grid with 5 rows, pixel 13 is in column 2");
+     test.done();
+   },
+    rowZeroVal : function(test) {
+      // pixel 5 will be in column 1
+      test.equals(9, mx.rowZeroVal(5,5), "in a grid with 5 rows pixel 9 is at the top of column 1");
+     test.done();
+   },
+   columnIsOdd : function(test) {
+     test.equals(true,mx.columnIsOdd(5,5),"in a grid with 5 rows, pixel five is in an odd-numbered column");
+     test.equals(false,mx.columnIsOdd(11,5), "in a grid with 5 rows, pixel 11 is not in an odd-numbered column");
+     test.done();
+   },
+   address: function(test) {
+     test.equals(9,mx.address(5,5),"in a grid with 5 rows pixel 5 should map to pixel 9");
+     test.equals(4,mx.address(4,5),"in a grid with 5 rows pixel 4 should not be altered")
+     test.done();
+   },
+   inRange: function(test) {
+     test.equals(true,mx.inRange(8,2,13,5),"in a grid of 5 rows pixel 8 is in the range of 2,13");
+     test.equals(false,mx.inRange(6,2,13,5),"in a grid of 5 rows pixel 6 is not in range 2,13");
+     test.done();
+   },
+   rectRange : function(test){
+     const grid = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14]
+     const rec = [2,3,7,8,12,13];
+     test.deepEqual(rec,mx.rectRange(2,13,5,grid),"in a grid of 5 rows return all pixel values which lie inside a rectangle bounded by 2 and 13")
+     test.done();
+   }
+};