feat: Add pack(), setPixel() and clear()

index.js

@@ -42,14 +42,27 @@ const fsp = require('fs-promise'),
   }),
 
   // Decodes 16 bit RGB565 into list [R,G,B]
-  rgb = n => {
+  unpack = n => {
     let r = (n & 0xF800) >> 11,
       g = (n & 0x7E0) >> 5,
       b = (n & 0x1F),
       rc = [ r << 3, g << 2, b << 3 ];
     return rc;
   },
 
+  // Encodes list [R, G, B] into 16 bit RGB565
+  pack = rgb => {
+    if (rgb.length != 3) throw new Error(`length = ${rgb.lenth} violates length = 3`);
+    let r = (rgb[0] >> 3) & 0x1F,
+      g = (rgb[1] >> 2) & 0x3F,
+      b = (rgb[2] >> 3) & 0x1F,
+      bits = (r << 11) + (g << 5) + b;
+    return bits;
+  },
+
+  // Map (x, y) into absolute byte position
+  pos = (x, y) => 2 * (y * 8 + x),
+
   // Returns a list of [R,G,B] representing the pixel specified by x and y
   // on the LED matrix. Top left = 0,0 Bottom right = 7,7
   getPixel = (fb, x, y) => {
@@ -61,8 +74,38 @@ const fsp = require('fs-promise'),
     const fd = fsp.openSync(fb, 'r');
     // fread() supports no sync'd version, so read in all 8 x 8 x 2 bytes in one shot
     const buf = fsp.readFileSync(fd);
-    const n = buf.readUInt16BE(y * 8 + x);
-    return rgb(n);
+    fsp.closeSync(fd);
+    const n = buf.readUInt16LE(pos(x, y));
+    return unpack(n);
+  },
+
+  setPixel = (fb, x, y, rgb) => {
+    if (x < 0 || x > 7) throw new Error(`x=${x} violates 0 <= x <= 7`);
+    if (y < 0 || y > 7) throw new Error(`y=${y} violates 0 <= y <= 7`);
+    rgb.map(col => {
+      if (col < 0 || col > 255) throw new Error(`RGB color ${rgb} violates` +
+        ` [0, 0, 0] < RGB < [255, 255, 255]`);
+      return col;
+    });
+    // TODO support rotation
+    let fd = fsp.openSync(fb, 'w'),
+      buf = new Buffer(2),
+      n = pack(rgb);
+    buf.writeUInt16LE(n);
+    fsp.writeSync(fd, 
+      buf, 0, buf.length,
+      pos(x, y),
+      // Wait for write to return
+      (error, written, _) => console.log(`Wrote ${written} bytes`));
+    fsp.closeSync(fd);
+  },
+
+  clear = fb => {
+    for (let y = 8; --y >= 0; ) {
+      for (let x = 8; --x >= 0; ) {
+        setPixel(fb, x, y, [0, 0, 0]);
+      }
+    }
   },
 
   rc = fb.then(a => {
@@ -77,8 +120,22 @@ const fsp = require('fs-promise'),
     }
   }),
 
+  random = (low, high) => Math.floor(Math.random() * (high - low) + low),
+
   rrc = rc.then(fb => {
     console.log(`Pixel (0,0) = ${getPixel(fb, 0, 0)}`);
+    for (let n = 1; --n >= 0; ) {
+      for (let y = 8; --y >= 0; ) {
+        for (let x = 8; --x >= 0; ) {
+          // setPixel(fb, x, y, [random(0, 255), random(0, 255), random(0, 255)]);
+          // setPixel(fb, x, y, [8 * x, 8 * y, 24]);
+          let v = (1 + y) * 32 * 256 + (1 + x) * 32;
+console.log(v);
+          setPixel(fb, x, y, unpack(v));
+        }
+      }
+    }
+    console.log(`Pixel (0,0) = ${getPixel(fb, 0, 0)}`);
   });
 
 // EOF