First of all, I found that I'm not the only one who stumbled on this
bug. See
http://groups.google.com/group/google-web-toolkit/browse_thread/thread/96f842dd3a23fc3a/cb447e0aa23997f8
Second, I have reliable workaround, at least for rectangles (and
probably for lines, ovals, etc.). I've tested in in FFx 8, IE9,
Chrome, and Safari 5.
To explain, I have a number of Rectangle's (which implement
Annotation) in an ArrayList area. On click, I test for selection:
boolean testForSelection(int x, int y) {
ghostContext.clearRect(0, 0, WIDTH, HEIGHT);
for (int i = 0; i areas.size(); i++) {
Annotation rect = areas.get(i);
if (rect.isPointInPath(ghostContext, x, y)) {
currRect = (Rectangle)rect;
return true;
}
}
return false;
}
In Rectangle, my first attempt was
@Override
public boolean isPointInPath(Context2d ctx, int x0, int y0) {
ctx.setGlobalCompositeOperation(Context2d.Composite.SOURCE_OVER);
ctx.setFillStyle(black);
ctx.fillRect(x, y, width, height);
int alpha = ctx.getImageData(x0, y0, 1, 1).getAlphaAt(0, 0);
if (alpha 0) {
GWT.log(found!);
return true;
}
return false;
}
As I said, this did not work in IE until the 3rd click. Why? I dunno.
I started looking into the GWT source code when an idea hit me.
So here's my new approach, a new method that uses path not alpha. It
works.
@Override
public boolean isPointInPath(Context2d ctx, int x0, int y0) {
ctx.beginPath();
ctx.rect(x, y, width, height);
if (ctx.isPointInPath(x0, y0)) {
GWT.log(found!);
ctx.closePath();
return true;
}
ctx.closePath();
return false;
}
Since we're dealing with a path and not an alpha, I don't set fill or
composite.
On Dec 5, 5:01 pm, Thad thad.humphr...@gmail.com wrote:
I'm working on a small canvas drawing program with GWT 2.3 and I'm
hitting a problem with IE9. After a user draws a rectangle to the
canvas, I want to allow dragging or resizing. To catch the mouse down
in the rectangle I'm using a technique similar to the one show in this
example:http://simonsarris.com/blog/225-canvas-selecting-resizing-shape
Basically I keep an ArrayList of my rectangles (other shapes will
follow). On mouse down, if my state is NONE (no drawing, dragging,
etc.) I clear a a hidden canvas and draw each item in my ArrayList to
to that canvas with fill style black and test for alpha. If alpha is
greater than zeor, I return the object clicked.
In Firefox, this works perfectly each time. However in IE I don't get
alpha 0 till the 3rd click. If keep the mouse in a rectangle--NO
MOVEMENT--it takes 3 clicks in the same spot, 3 calls to my test
method, before alpha 0.
What's the reason for this delay with IE? The example above is pure
Javascript,and it works in IE9 (if copy it locally and change the
doctype header). What gives with GWT? Is there some problem with GWT's
ImageData in IE? Is there some work around?
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