API review request: ImageView.viewport behavior

[Richard Bair]

Go for it.

On May 14, 2012, at 3:25 AM, Jim Graham wrote:

> We have these two requests to clarify and fix the behavior of the viewport on an ImageView.  They don't involve any new API, just questions and suggestions on changing the behavior of the existing property:
> 
> http://javafx-jira.kenai.com/browse/RT-19962
> http://javafx-jira.kenai.com/browse/RT-19306
> 
> The history of this bug is that the code to implement viewports was ported from the Java2D source base where it had an integer "draw sub image" method.  The 2D method interpreted the subimage parameters as defining a piece of the image "a subimage" that behaved as if it were extracted and isolated and then rendered as its own image.
> 
> The FX implementation uses floating point values to define the viewport and describes it merely as defining "the portion of the image which falls within the viewport [is] displayed" and elsewhere as achieving a "zoom effect" if you narrow the viewport without narrowing the fit dimensions.
> 
> The distinction of whether the viewport/subimage is considered in isolation only matters if you are using image smoothing, which is on by default in FX and off by default in AWT.  If you are smoothing, then special math is used for the border pixels because they have no adjacent pixels to smooth against.
> 
> In 1.3 and 2.0 the math was broken in the FX version because it was ported over from the 2D version which had a different rendering model. We fixed the bugs in 2.1 and brought it into compliance with "what it seemed to be trying to do" which was to isolate the image defined by the viewport.
> 
> The problem was, when we "fixed those bugs" we realized that there wasn't really any good definition of what the "subimage" was when you are using floating point coordinates since it is hard to create an image from fractions of the border pixels.
> 
> So, we filed the above bugs to clarify this and to change the implementation of viewports to be more like what you get with "texture mapping" where they simply define the points on the image that map to the corners of the ImageView's output.
> 
> If there are no objections, I'd like to remove the synthetic "edge conditions" on the ImageView viewport so that it simply acts like a clip affecting what is seen from the original image - a sort of "narrowing lens" if you will...
> 
> 			...jim