Merge pull request #15 from senzil/bmp-negative-height#14

added support for negative height in header (top-down bmp)

.gitignore

@@ -1 +1,2 @@
 node_modules
+.idea

lib/decoder.js

@@ -9,6 +9,7 @@ function BmpDecoder(buffer,is_with_alpha) {
   this.pos = 0;
   this.buffer = buffer;
   this.is_with_alpha = !!is_with_alpha;
+  this.bottom_up = true;
   this.flag = this.buffer.toString("utf-8", 0, this.pos += 2);
   if (this.flag != "BM") throw new Error("Invalid BMP File");
   this.parseHeader();
@@ -26,7 +27,7 @@ BmpDecoder.prototype.parseHeader = function() {
   this.pos += 4;
   this.width = this.buffer.readUInt32LE(this.pos);
   this.pos += 4;
-  this.height = this.buffer.readUInt32LE(this.pos);
+  this.height = this.buffer.readInt32LE(this.pos);
   this.pos += 4;
   this.planes = this.buffer.readUInt16LE(this.pos);
   this.pos += 2;
@@ -47,7 +48,7 @@ BmpDecoder.prototype.parseHeader = function() {
 
   if(this.bitPP === 16 && this.is_with_alpha){
     this.bitPP = 15
-  };
+  }
   if (this.bitPP < 15) {
     var len = this.colors === 0 ? 1 << this.bitPP : this.colors;
     this.palette = new Array(len);
@@ -64,6 +65,10 @@ BmpDecoder.prototype.parseHeader = function() {
       };
     }
   }
+  if(this.height < 0) {
+    this.height *= -1;
+    this.bottom_up = false;
+  }
 
 }
 
@@ -84,10 +89,12 @@ BmpDecoder.prototype.parseBGR = function() {
 BmpDecoder.prototype.bit1 = function() {
   var xlen = Math.ceil(this.width / 8);
   var mode = xlen%4;
+  var y = this.height >= 0 ? this.height - 1 : -this.height
   for (var y = this.height - 1; y >= 0; y--) {
+    var line = this.bottom_up ? y : this.height - 1 - y
     for (var x = 0; x < xlen; x++) {
       var b = this.buffer.readUInt8(this.pos++);
-      var location = y * this.width * 4 + x*8*4;
+      var location = line * this.width * 4 + x*8*4;
       for (var i = 0; i < 8; i++) {
         if(x*8+i<this.width){
           var rgb = this.palette[((b>>(7-i))&0x1)];
@@ -111,9 +118,10 @@ BmpDecoder.prototype.bit4 = function() {
   var xlen = Math.ceil(this.width/2);
   var mode = xlen%4;
   for (var y = this.height - 1; y >= 0; y--) {
+    var line = this.bottom_up ? y : this.height - 1 - y
     for (var x = 0; x < xlen; x++) {
       var b = this.buffer.readUInt8(this.pos++);
-      var location = y * this.width * 4 + x*2*4;
+      var location = line * this.width * 4 + x*2*4;
 
       var before = b>>4;
       var after = b&0x0F;
@@ -143,9 +151,10 @@ BmpDecoder.prototype.bit4 = function() {
 BmpDecoder.prototype.bit8 = function() {
   var mode = this.width%4;
   for (var y = this.height - 1; y >= 0; y--) {
+    var line = this.bottom_up ? y : this.height - 1 - y
     for (var x = 0; x < this.width; x++) {
       var b = this.buffer.readUInt8(this.pos++);
-      var location = y * this.width * 4 + x*4;
+      var location = line * this.width * 4 + x*4;
       if(b < this.palette.length) {
         var rgb = this.palette[b];
         this.data[location] = rgb.blue;
@@ -169,6 +178,7 @@ BmpDecoder.prototype.bit15 = function() {
   var dif_w =this.width % 3;
   var _11111 = parseInt("11111", 2),_1_5 = _11111;
   for (var y = this.height - 1; y >= 0; y--) {
+    var line = this.bottom_up ? y : this.height - 1 - y
     for (var x = 0; x < this.width; x++) {
 
       var B = this.buffer.readUInt16LE(this.pos);
@@ -178,7 +188,7 @@ BmpDecoder.prototype.bit15 = function() {
       var red = (B >> 10 & _1_5) / _1_5 * 255 | 0;
       var alpha = (B>>15)?0xFF:0x00;
 
-      var location = y * this.width * 4 + x * 4;
+      var location = line * this.width * 4 + x * 4;
       this.data[location] = red;
       this.data[location + 1] = green;
       this.data[location + 2] = blue;
@@ -194,6 +204,7 @@ BmpDecoder.prototype.bit16 = function() {
   var _11111 = parseInt("11111", 2),_1_5 = _11111;
   var _111111 = parseInt("111111", 2),_1_6 = _111111;
   for (var y = this.height - 1; y >= 0; y--) {
+    var line = this.bottom_up ? y : this.height - 1 - y
     for (var x = 0; x < this.width; x++) {
 
       var B = this.buffer.readUInt16LE(this.pos);
@@ -203,7 +214,7 @@ BmpDecoder.prototype.bit16 = function() {
       var green = (B >> 5 & _1_6 ) / _1_6 * 255 | 0;
       var red = (B >> 11) / _1_5 * 255 | 0;
 
-      var location = y * this.width * 4 + x * 4;
+      var location = line * this.width * 4 + x * 4;
       this.data[location] = red;
       this.data[location + 1] = green;
       this.data[location + 2] = blue;
@@ -217,11 +228,12 @@ BmpDecoder.prototype.bit16 = function() {
 BmpDecoder.prototype.bit24 = function() {
   //when height > 0
   for (var y = this.height - 1; y >= 0; y--) {
+    var line = this.bottom_up ? y : this.height - 1 - y
     for (var x = 0; x < this.width; x++) {
       var blue = this.buffer.readUInt8(this.pos++);
       var green = this.buffer.readUInt8(this.pos++);
       var red = this.buffer.readUInt8(this.pos++);
-      var location = y * this.width * 4 + x * 4;
+      var location = line * this.width * 4 + x * 4;
       this.data[location] = red;
       this.data[location + 1] = green;
       this.data[location + 2] = blue;
@@ -234,18 +246,19 @@ BmpDecoder.prototype.bit24 = function() {
 };
 
 /**
- * add 32bit decode func 
+ * add 32bit decode func
  * @author soubok
  */
 BmpDecoder.prototype.bit32 = function() {
   //when height > 0
   for (var y = this.height - 1; y >= 0; y--) {
+    var line = this.bottom_up ? y : this.height - 1 - y
     for (var x = 0; x < this.width; x++) {
       var blue = this.buffer.readUInt8(this.pos++);
       var green = this.buffer.readUInt8(this.pos++);
       var red = this.buffer.readUInt8(this.pos++);
       var alpha = this.buffer.readUInt8(this.pos++);
-      var location = y * this.width * 4 + x * 4;
+      var location = line * this.width * 4 + x * 4;
       this.data[location] = alpha;
       this.data[location + 1] = red;
       this.data[location + 2] = green;