Working with Multiple Layers - KineticJS

问题

I'm using KineticJS 4.0.5 and I'm currently trying to draw the contents of several layers but only the last one added to stage is drawn... If I understood the documentation correctly this should be possible, otherwise why would we need a layer?

I have three different layers:

a background layer with just a Kinectic.Rect object;
a elements layer with several types of shapes;
and a top layer with elements I want to be always on top of everything.

I populate those layers inside a draw function I have inside a object I created, this object also has a shape attribute which refers to the background and a contents attribute with the elements to add to the elements layer. My code for the draw function is the following:

this.draw = function() {
    var stage = E.game.stage, layers = E.game.layers;

    stage.clear();

    // Add Background
    this.shape.setSize(stage.getWidth(), stage.getHeight());
    layers.background.add(this.shape);

    // Iterate over contents
    for(var i = 0; i < this.contents.length; i++) {
        layers.elements.add(this.contents[i].shape);
    }

    // Draw Everything
    stage.add(layers.background);
    stage.add(layers.elements);
    stage.add(layers.top); // This one is currently empty
    stage.draw();
}

After running this function, only layers.top is drawn in the canvas, and if I comment the line where it is added only layers.elements is drawn. However the stage has 3 childrens (I checked it with inspect element on chrome) and in the documentation it says the draw function draws all layers... Am I doing something wrong here? Or it isn't possible? And if it's not possible why would I need a layer and a stage? Wouldn't one be enough?

Thank you in advance.

Edit: I was able to solve the problem, I was applying a white background color with css to the canvas element and since each layer creates a new canvas element above the others I could only see the contents for the top most layer (in this case just white).

However, I still have a problem related with multiple layers that I didn't have before with just one layer. When I use the clear function on the stage it should clear the layers right? But instead the layers remain exactly the same, even if I try to call clear on each individual layer they won't change... I'm also using the stage draw function after clearing them but still no changes at all... The only solution I found until now was by removing the layer from the stage and adding it again :s Is there a better way to reset the layers contents?

Thank you again and sorry for the confusion with the first question.

回答1:

Clear is simply for clearing the canvas before redrawing it. It does not remove the objects added to the layers. So for your case, use the remove function to take out the objects attached to the layer or otherwise like you are doing, removing the entire layer itself.

来源：https://stackoverflow.com/questions/13324582/working-with-multiple-layers-kineticjs

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