Support canvas.getBuffer('raw')

This should help interface with custom image libraries like LodePNG or
WebP.

Readme.md

@@ -140,10 +140,22 @@ var stream = canvas.jpegStream({
 
 ### Canvas#toBuffer()
 
-A call to `Canvas#toBuffer()` will return a node `Buffer` instance containing all of the PNG data.
+A call to `Canvas#toBuffer()` will return a node `Buffer` instance containing image data.
 
 ```javascript
-canvas.toBuffer();
+// PNG Buffer, default settings
+var buf = canvas.toBuffer();
+
+// PNG Buffer, zlib compression level 3 (from 0-9), faster but bigger
+var buf2 = canvas.toBuffer(undefined, 3, canvas.PNG_FILTER_NONE);
+
+// ARGB32 Buffer, native-endian
+var buf3 = canvas.toBuffer('raw');
+var stride = canvas.stride;
+// In memory, this is `canvas.height * canvas.stride` bytes long.
+// The top row of pixels, in ARGB order, left-to-right, is:
+var topPixelsARGBLeftToRight = buf3.slice(0, canvas.width * 4);
+var row3 = buf3.slice(2 * canvas.stride, 2 * canvas.stride + canvas.width * 4);
 ```
 
 ### Canvas#toBuffer() async

src/Canvas.cc

@@ -45,6 +45,7 @@ Canvas::Initialize(Nan::ADDON_REGISTER_FUNCTION_ARGS_TYPE target) {
   Nan::SetPrototypeMethod(ctor, "streamJPEGSync", StreamJPEGSync);
 #endif
   Nan::SetAccessor(proto, Nan::New("type").ToLocalChecked(), GetType);
+  Nan::SetAccessor(proto, Nan::New("stride").ToLocalChecked(), GetStride);
   Nan::SetAccessor(proto, Nan::New("width").ToLocalChecked(), GetWidth, SetWidth);
   Nan::SetAccessor(proto, Nan::New("height").ToLocalChecked(), GetHeight, SetHeight);
 
@@ -91,6 +92,14 @@ NAN_GETTER(Canvas::GetType) {
   info.GetReturnValue().Set(Nan::New<String>(canvas->isPDF() ? "pdf" : canvas->isSVG() ? "svg" : "image").ToLocalChecked());
 }
 
+/*
+ * Get stride.
+ */
+NAN_GETTER(Canvas::GetStride) {
+  Canvas *canvas = Nan::ObjectWrap::Unwrap<Canvas>(info.This());
+  info.GetReturnValue().Set(Nan::New<Number>(canvas->stride()));
+}
+
 /*
  * Get width.
  */
@@ -248,6 +257,17 @@ NAN_METHOD(Canvas::ToBuffer) {
     return;
   }
 
+  if (info.Length() == 1 && info[0]->StrictEquals(Nan::New<String>("raw").ToLocalChecked())) {
+    // Return raw ARGB data -- just a memcpy()
+    cairo_surface_t *surface = canvas->surface();
+    cairo_surface_flush(surface);
+    const unsigned char *data = cairo_image_surface_get_data(surface);
+    printf("%x %x %x %x %x\n", data[0], data[1], data[2], data[3], data[4]);
+    Local<Object> buf = Nan::CopyBuffer(reinterpret_cast<const char*>(data), canvas->nBytes()).ToLocalChecked();
+    info.GetReturnValue().Set(buf);
+    return;
+  }
+
   if (info.Length() > 1 && !(info[1]->IsUndefined() && info[2]->IsUndefined())) {
     if (!info[1]->IsUndefined()) {
         bool good = true;
@@ -571,7 +591,7 @@ Canvas::Canvas(int w, int h, canvas_type_t t): Nan::ObjectWrap() {
   } else {
     _surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, w, h);
     assert(_surface);
-    Nan::AdjustExternalMemory(4 * w * h);
+    Nan::AdjustExternalMemory(nBytes());
   }
 }
 
@@ -589,8 +609,9 @@ Canvas::~Canvas() {
       cairo_surface_destroy(_surface);
       break;
     case CANVAS_TYPE_IMAGE:
+      int oldNBytes = nBytes();
       cairo_surface_destroy(_surface);
-      Nan::AdjustExternalMemory(-4 * width * height);
+      Nan::AdjustExternalMemory(-oldNBytes);
       break;
   }
 }
@@ -626,11 +647,10 @@ Canvas::resurface(Local<Object> canvas) {
       break;
     case CANVAS_TYPE_IMAGE:
       // Re-surface
-      int old_width = cairo_image_surface_get_width(_surface);
-      int old_height = cairo_image_surface_get_height(_surface);
+      size_t oldNBytes = nBytes();
       cairo_surface_destroy(_surface);
       _surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, width, height);
-      Nan::AdjustExternalMemory(4 * (width * height - old_width * old_height));
+      Nan::AdjustExternalMemory(nBytes() - oldNBytes);
 
       // Reset context
       context = canvas->Get(Nan::New<String>("context").ToLocalChecked());

src/Canvas.h

@@ -57,6 +57,7 @@ class Canvas: public Nan::ObjectWrap {
     static NAN_METHOD(New);
     static NAN_METHOD(ToBuffer);
     static NAN_GETTER(GetType);
+    static NAN_GETTER(GetStride);
     static NAN_GETTER(GetWidth);
     static NAN_GETTER(GetHeight);
     static NAN_SETTER(SetWidth);
@@ -85,6 +86,7 @@ class Canvas: public Nan::ObjectWrap {
     inline void *closure(){ return _closure; }
     inline uint8_t *data(){ return cairo_image_surface_get_data(_surface); }
     inline int stride(){ return cairo_image_surface_get_stride(_surface); }
+    inline int nBytes(){ return height * stride(); }
     Canvas(int width, int height, canvas_type_t type);
     void resurface(Local<Object> canvas);
 

test/canvas.test.js

@@ -5,7 +5,8 @@
 var Canvas = require('../')
   , assert = require('assert')
   , parseFont = Canvas.Context2d.parseFont
-  , fs = require('fs');
+  , fs = require('fs')
+  , os = require('os');
 
 console.log();
 console.log('   canvas: %s', Canvas.version);
@@ -246,6 +247,12 @@ describe('Canvas', function () {
     assert.equal(50, canvas.height);
   });
 
+  it('Canvas#stride', function() {
+    var canvas = new Canvas(24, 10);
+    assert.ok(canvas.stride >= 24, 'canvas.stride is too short');
+    assert.ok(canvas.stride < 1024, 'canvas.stride seems too long');
+  });
+
   it('Canvas#getContext("invalid")', function () {
     assert.equal(null, new Canvas(200, 300).getContext('invalid'));
   });
@@ -377,6 +384,87 @@ describe('Canvas', function () {
     });
   });
 
+  describe('#toBuffer("raw")', function() {
+    var canvas = new Canvas(10, 10)
+        , ctx = canvas.getContext('2d');
+
+    ctx.clearRect(0, 0, 10, 10);
+
+    ctx.fillStyle = 'rgba(200, 200, 200, 0.505)';
+    ctx.fillRect(0, 0, 5, 5);
+
+    ctx.fillStyle = 'red';
+    ctx.fillRect(5, 0, 5, 5);
+
+    ctx.fillStyle = '#00ff00';
+    ctx.fillRect(0, 5, 5, 5);
+
+    ctx.fillStyle = 'black';
+    ctx.fillRect(5, 5, 4, 5);
+
+    /** Output:
+     *    *****RRRRR
+     *    *****RRRRR
+     *    *****RRRRR
+     *    *****RRRRR
+     *    *****RRRRR
+     *    GGGGGBBBB-
+     *    GGGGGBBBB-
+     *    GGGGGBBBB-
+     *    GGGGGBBBB-
+     *    GGGGGBBBB-
+     */
+
+    var buf = canvas.toBuffer('raw');
+    var stride = canvas.stride;
+
+    // Buffer doesn't have readUInt32(): it only has readUInt32LE() and
+    // readUInt32BE().
+    if (os.endianness() === 'LE') buf.swap32();
+
+    function assertPixel(u32, x, y, message) {
+      var expected = '0x' + u32.toString(16);
+      var actual = '0x' + buf.readUInt32BE(y * stride + x * 4).toString(16);
+      assert.equal(actual, expected, message);
+    }
+
+    it('should have the correct size', function() {
+      assert.equal(buf.length, stride * 10);
+    });
+
+    it('does not premultiply alpha', function() {
+      assertPixel(0x80646464, 0, 0, 'first semitransparent pixel');
+      assertPixel(0x80646464, 4, 4, 'last semitransparent pixel');
+    });
+
+    it('draws red', function() {
+      assertPixel(0xffff0000, 5, 0, 'first red pixel');
+      assertPixel(0xffff0000, 9, 4, 'last red pixel');
+    });
+
+    it('draws green', function() {
+      assertPixel(0xff00ff00, 0, 5, 'first green pixel');
+      assertPixel(0xff00ff00, 4, 9, 'last green pixel');
+    });
+
+    it('draws black', function() {
+      assertPixel(0xff000000, 5, 5, 'first black pixel');
+      assertPixel(0xff000000, 8, 9, 'last black pixel');
+    });
+
+    it('leaves undrawn pixels black, transparent', function() {
+      assertPixel(0x0, 9, 5, 'first undrawn pixel');
+      assertPixel(0x0, 9, 9, 'last undrawn pixel');
+    });
+
+    it('is immutable', function() {
+      ctx.fillStyle = 'white';
+      ctx.fillRect(0, 0, 10, 10);
+      canvas.toBuffer('raw'); // (side-effect: flushes canvas)
+      assertPixel(0xffff0000, 5, 0, 'first red pixel');
+    });
+  });
+
   describe('#toDataURL()', function () {
     var canvas = new Canvas(200, 200)
       , ctx = canvas.getContext('2d');