According to the WhatWG spec for <canvas>, getImageData() returns a
CavasPixelArray, which is an array of bytes. What if you created a
JavaScriptObject to represent it? Does GWT thunk to bytes across the
JSNI boundary OK? I know it won't pass arrays of anything back, but
individual elements maybe:
import com.google.gwt.core.client.JavaScriptObject;
public class CanvasPixelArray extends JavaScriptObject {
protected CanvasPixelArray() {
//required by GWT
}
public native int getLength() /*-{
return this.length;
}-*/;
public native byte getPixelByte(int pos) /*-{
return this[pos];
}-*/;
}
//then, create one in your code:
public byte[] getBitmap(Element canvasElement, int left, int top, int
width, int height) {
//then, create one in your code:
CanvasPixelArray cpa = getCPA(canvasElement, left, top, width,
height);
byte[] pixelBytes = new byte[cpa.length()];
for (int i = 0; i < cpa.length(); i++) {
pixelBytes[i] = cpa.getPixelByte(i);
}
return pixelBytes;
}
private native CanvasPixelArray getCPA(Element canvas, int sx, int sy,
int sw, int sh) /*-{
return canvas.getContext("2d").getImageData(sx, sy, sw, sh);
}-*/;
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