Issue #414: part6: Support transparency when exporting as PNG spritesheet

Added flattenFrameAt to LayerUtils.
Added renderFrameAt to PiskelController (using flattenFrameAt)
Use renderFrameAt in PiskelRenderer (which is used for PNG spritesheet)

chore: renamed createLayerFromSpritesheet to createFramesFromSpritesheet
       (in LayerUtils)

src/js/controller/piskel/PiskelController.js

@@ -103,6 +103,10 @@
     return mergedFrame;
   };
 
+  ns.PiskelController.prototype.renderFrameAt = function (index, preserveOpacity) {
+    return pskl.utils.LayerUtils.flattenFrameAt(this.getLayers(), index, preserveOpacity);
+  };
+
   ns.PiskelController.prototype.hasFrameAt = function (index) {
     return !!this.getCurrentLayer().getFrameAt(index);
   };

src/js/rendering/PiskelRenderer.js

@@ -5,10 +5,30 @@
   ns.PiskelRenderer = function (piskelController) {
     var frames = [];
     for (var i = 0 ; i < piskelController.getFrameCount() ; i++) {
-      frames.push(piskelController.getMergedFrameAt(i));
+      frames.push(piskelController.renderFrameAt(i, true));
     }
-    ns.FramesheetRenderer.call(this, frames);
+    this.piskelController = piskelController;
+    this.frames = frames;
   };
 
-  pskl.utils.inherit(ns.PiskelRenderer, ns.FramesheetRenderer);
+  ns.PiskelRenderer.prototype.renderAsCanvas = function () {
+    var canvas = this.createCanvas_();
+    for (var i = 0 ; i < this.frames.length ; i++) {
+      var frame = this.frames[i];
+      this.drawFrameInCanvas_(frame, canvas, i * this.piskelController.getWidth(), 0);
+    }
+    return canvas;
+  };
+
+  ns.PiskelRenderer.prototype.drawFrameInCanvas_ = function (frame, canvas, offsetWidth, offsetHeight) {
+    var context = canvas.getContext('2d');
+    context.drawImage(frame, offsetWidth, offsetHeight, frame.width, frame.height);
+  };
+
+  ns.PiskelRenderer.prototype.createCanvas_ = function () {
+    var count = this.frames.length;
+    var width = count * this.piskelController.getWidth();
+    var height = this.piskelController.getHeight();
+    return pskl.utils.CanvasUtils.createCanvas(width, height);
+  };
 })();

src/js/utils/LayerUtils.js

@@ -3,12 +3,15 @@
 
   ns.LayerUtils = {
     /**
-     * Create a pskl.model.Layer from an Image object.
+     * Create a Frame array from an Image object.
      * Transparent pixels will either be converted to completely opaque or completely transparent pixels.
+     * TODO : move to FrameUtils
+     *
      * @param  {Image} image source image
-     * @return {pskl.model.Frame} corresponding frame
+     * @param  {Number} frameCount number of frames in the spritesheet
+     * @return {Array<Frame>}
      */
-    createLayerFromSpritesheet : function (image, frameCount) {
+    createFramesFromSpritesheet : function (image, frameCount) {
       var width = image.width;
       var height = image.height;
       var frameWidth = width / frameCount;
@@ -37,6 +40,22 @@
       });
       var mergedLayer = pskl.model.Layer.fromFrames(layerA.getName(), mergedFrames);
       return mergedLayer;
+    },
+
+    flattenFrameAt : function (layers, index, preserveOpacity) {
+      var width = layers[0].getFrameAt(index).getWidth();
+      var height = layers[0].getFrameAt(index).getHeight();
+      var canvas = pskl.utils.CanvasUtils.createCanvas(width, height);
+      var context = canvas.getContext('2d');
+      layers.forEach(function (l) {
+        var frameRender = pskl.utils.FrameUtils.toImage(l.getFrameAt(index));
+        if (preserveOpacity) {
+          context.globalAlpha = l.getOpacity();
+        }
+        context.drawImage(frameRender, 0, 0, width, height, 0, 0, width, height);
+      });
+
+      return canvas;
     }
   };
 

src/js/utils/serialization/Deserializer.js

@@ -49,7 +49,7 @@
     // 2 - attach the onload callback that will be triggered asynchronously
     image.onload = function () {
       // 5 - extract the frames from the loaded image
-      var frames = pskl.utils.LayerUtils.createLayerFromSpritesheet(image, layerData.frameCount);
+      var frames = pskl.utils.LayerUtils.createFramesFromSpritesheet(image, layerData.frameCount);
       // 6 - add each image to the layer
       this.addFramesToLayer(frames, layer, index);
     }.bind(this);

test/js/testutils/TestUtils.js

@@ -16,10 +16,10 @@
    * we expect this to be a 3x2 image, one black line above a white line.
    *
    * However Frame.createFromGrid needs the following input to create such an image :
-   * 
+   *
    * [[black, white],
    *  [black, white],
-   *  [black, white]] 
+   *  [black, white]]
    *
    * This helper will build the second array from the first array.
    */
@@ -41,4 +41,32 @@
       expect(color).toBe(grid[row][col]);
     });
   };
+
+  ns.imageEqualsGrid = function (image, grid) {
+    for (var x = 0 ; x < grid.length ; x++) {
+      for (var y = 0 ; y < grid[x].length ; y++) {
+        var expected = tinycolor(grid[x][y]).toRgbString();
+        var color = tinycolor(ns.getRgbaAt(image, x, y)).toRgbString();
+        expect(color).toBe(expected);
+      }
+    }
+  }
+
+  ns.getRgbaAt = function (image, x, y) {
+    var w = image.width;
+    var h = image.height;
+    var canvas = pskl.utils.CanvasUtils.createCanvas(w, h);
+    var context = canvas.getContext('2d');
+
+    context.drawImage(image, 0, 0, w, h, 0, 0, w, h);
+    var imageData = context.getImageData(0, 0, w, h).data;
+    var i = (y * w + x) * 4;
+
+    return {
+      r : imageData[i],
+      g : imageData[i + 1],
+      b : imageData[i + 2],
+      a : imageData[i + 3]/255
+    };
+  }
 })();

test/js/utils/FrameUtilsTest.js

@@ -74,7 +74,7 @@ describe("FrameUtils suite", function() {
     ]);
   });
 
-  it ("[LayerUtils] creates a layer from a simple spritesheet", function () {
+  it ("[LayerUtils] creates frames from a simple spritesheet", function () {
     var B = black, R = red;
 
     // original image in 4x2
@@ -86,7 +86,7 @@ describe("FrameUtils suite", function() {
     var spritesheet = pskl.utils.FrameUtils.toImage(frame);
 
     // split the spritesheet by 4
-    var frames = pskl.utils.LayerUtils.createLayerFromSpritesheet(spritesheet, 4);
+    var frames = pskl.utils.LayerUtils.createFramesFromSpritesheet(spritesheet, 4);
 
     // expect 4 frames of 1x2
     expect(frames.length).toBe(4);

test/js/utils/LayerUtilsTest.js

@@ -0,0 +1,56 @@
+describe("LayerUtils test", function() {
+
+  var B = '#000000';
+  var R = '#ff0000';
+  var T = Constants.TRANSPARENT_COLOR;
+  var frameEqualsGrid = test.testutils.frameEqualsGrid;
+  var imageEqualsGrid = test.testutils.imageEqualsGrid;
+
+  var frame1 = pskl.model.Frame.fromPixelGrid([
+    [B, T],
+    [T, B]
+  ]);
+
+  var frame2 = pskl.model.Frame.fromPixelGrid([
+    [T, R],
+    [R, T]
+  ]);
+
+  beforeEach(function() {});
+  afterEach(function() {});
+
+  it("flattens a frame", function() {
+    // when
+    var l1 = new pskl.model.Layer('l1');
+    l1.addFrame(frame1);
+    var l2 = new pskl.model.Layer('l2');
+    l2.addFrame(frame2);
+
+    // then
+    var flattened = pskl.utils.LayerUtils.flattenFrameAt([l1, l2], 0);
+
+    //verify
+    imageEqualsGrid(flattened, [
+      [B, R],
+      [R, B]
+    ]);
+  });
+
+  it("flattens a frame with opacity", function() {
+    // when
+    var l1 = new pskl.model.Layer('l1');
+    l1.addFrame(frame1);
+    var l2 = new pskl.model.Layer('l2');
+    l2.setOpacity(0.5);
+    l2.addFrame(frame2);
+
+    // then
+    var flattened = pskl.utils.LayerUtils.flattenFrameAt([l1, l2], 0, true);
+
+    //verify
+    imageEqualsGrid(flattened, [
+      [B, 'rgba(255,0,0,0.5)'],
+      ['rgba(255,0,0,0.5)', B]
+    ]);
+  });
+});