accessing a layer’s methods

[plutovman]

Hello,
I’m a big fan of your processing.org layers library. Thank you.

I have a sketch with a couple of layers, and I can’t seem to figure out how to access a layer’s methods.

So, for instance, I have a layer definition

public class L_PolyMesh extends Layer {
…
void setup();{…}
void draw(){…}
void drawPolygons(){…}

}

and in the main program, I create an instance of the layer

void setup() {
layers = new AppletLayers(this);
L_PolyMesh canvas_mesh = new L_PolyMesh (this);
layers.addLayer(canvas_mesh);
l_mesh = layers.getLayer(0);
}

My problem is that when I try to do:

l_mesh.drawPolygons();

I get a warning that says “The function drawPolygons does not exist”. I’m sure I’m missing something, but I can’t figure out what that is. Your help would be appreciated.

Thanks!

[Michael]

How is the variable “l_mesh” declared? Is it declared as type Layer?

If so, then you need to cast it to the type L_PolyMesh:

((L_PolyMesh)l_mesh).drawPolygons(); 

That is, you have to tell the compiler that your object is not only a Layer, but is specifically a L_PolyMesh object.

Alternatively, you can declare l_mesh as type L_PolyMesh. Hope that makes sense.

[plutovman]

Sneaky. That worked. My knowledge of OOP is a bit hazy, but I’m trying. Thanks for your help.
If I may ask another question, can you explain what this bit of code does to make the layers render?

void paint(java.awt.Graphics g) {
// This method MUST be present in your sketch for layers to be rendered!
if (layers != null) {
layers.paint(this);
} else {
super.paint(g);
}
} // end of paint()

Specifically what is ‘g’? I’ve seen in some old bits of code that inside layers definitions, I’ll see lines like:

img = g.get()
g.save(someimage)

Thanks again for your help.

[Michael]

The variable ‘g’ is a reference to the Processing PGraphics object which performs the drawing in Processing.

[Author]

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