RFR: 8323108: BufferedImage.setData(Raster) should not cast float and double values to integers

[Brian Burkhalter]

On Thu, 4 May 2023 10:14:10 GMT, Martin Desruisseaux <duke at openjdk.org> wrote:

> The `BufferedImage` Javadoc does not mention any constraint about the data type. In practice, `BufferedImage` with floating point values can be rendered by Java2D as well as integers, provided that a compatible `ColorModel` was supplied at construction time. However calls to `setData(Raster)` unexpectedly cast floating point values to integers. For example sample value 0.8 become 0. This is demonstrated by the `SetData` test case in this pull request.
> 
> An easy fix, which is proposed in this pull request, is to replace the whole `BufferedImage.setData(Raster)` method body by a simple call to `WritableRaster.setRect(Raster)`, which handles all `DataBuffer` types correctly. The method contracts documented in their respective Javadoc are compatible. Furthermore an examination of their source code shows that they are equivalent, except for the differences noted in the _Behavioural changes_ section below.
> 
> # Source code comparison
> For demonstrating that delegating to `WritableRaster.setRect(Raster)` would be equivalent to the current code, one can copy the method body and apply the following changes:
> 
> * Remove `dx` parameter, replaced by 0.
> * Remove `dy` parameter, replaced by 0.
> * Rename `srcRaster` parameter as `r` (like in `BufferedImage`).
> * Rename `startY` variable as `i` (like in `BufferedImage`).
> * Rename `srcOffX` variable as `startX` (like in `BufferedImage`).
> * Rename `srcOffY` variable as `startY` (like in `BufferedImage`).
> * Replace `this.minX` by 0 and simplify.
> * Replace `this.minY` by 0 and simplify.
> * Remove the `switch` statement, keeping only the `TYPE_INT` case.
> 
> Then compare with `BufferedImage.setData(Raster)`. The modified block of code from `WritableRaster` is:
> 
> 
> int width  = r.getWidth();
> int height = r.getHeight();
> int startX = r.getMinX();
> int startY = r.getMinY();
> 
> We can see that above code is identical to `BufferedImage`. The next modified block of code from `WritableRaster`:
> 
> 
> int dstOffX = startX;
> int dstOffY = startY;
> 
> // Clip to this raster
> if (dstOffX < 0) {
>     width += dstOffX;
>     startX -= dstOffX;    // = 0 because dstOffX == startX
>     dstOffX = 0;
> }
> if (dstOffY < 0) {
>     height += dstOffY;
>     startY -= dstOffY;    // = 0 because dstOffY == startY
>     dstOffY = 0;
> }
> if (dstOffX+width > this.width) {
>     width = this.width - dstOffX;
> }
> if (dstOffY+height > this.height) {
>     height = this.height - dstOffY;
> }
> if (width <= 0 || height <= 0) {
>     return;
> }
> 
> 
> Above is equivalent to the following code from `BufferedImage`, ex...

This looks all right to me except I think the copyright years might need to be updated.

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Marked as reviewed by bpb (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13797#pullrequestreview-1833358376