[Rev 03] RFR: 8088198: Exception thrown from snapshot if dimensions are larger than max texture size

[Nir Lisker]

On Sat, 25 Jan 2020 19:55:23 GMT, Nir Lisker <nlisker at openjdk.org> wrote:

>> With regard as to why the tiling version is significantly slower, though, I do have a pretty good idea; as Kevin hinted, the pixel copy into a temporary buffer before copying into the final image is where most the extra time is spent.
>> The reason why it is so much slower is a little bit of a pity, though; profiling a run of the benchmark shows that a lot of time is spent into `IntTo4ByteSameConverter::doConvert`. As it turns out, the reason for this is that, under Windows and the D3D pipeline anyway, the `WriteableImage` used to collate the tiles and the tiles returned from the RTTexture have different pixel formats (IntARGB for the tile and byteBGRA for the `WriteableImage`).
>> So if we could use a `WriteableImage` with an IntARGB pixel format as the recipient for the snapshot (at least as long as no image was provided by the caller), I suspect that the copy would be much faster.
>> Unfortunately it seems the only way to choose the pixel format for a `WritableImage` is to initialize it with a `PixelBuffer`, but then one can no longer use a `PixelWriter` to update it and it desn't seems to me that there is a way to safely access the `PixelBuffer` from an image's reference alone.
>> I'm pretty new to this code base though (which is quite large; I haven't read it all quite yet... ;-), so hopefully there's a way to do that that has simply eluded me so far.
> 
>> profiling a run of the benchmark shows that a lot of time is spent into `IntTo4ByteSameConverter::doConvert`
> 
> This is a bit naive, but what if you parallelize the code there? I didn't test that this produces the correct result, but you can try to replace the loops with this:
> IntStream.range(0, h).parallel().forEach(y -> {    
>     IntStream.range(0, w).parallel().forEach(x -> {
>         int pixel = srcarr[srcoff++];              
>         dstarr[dstoff++] = (byte) (pixel      );   
>         dstarr[dstoff++] = (byte) (pixel >>  8);   
>         dstarr[dstoff++] = (byte) (pixel >> 16);   
>         dstarr[dstoff++] = (byte) (pixel >> 24);   
>     });                                            
>     srcoff += srcscanints;                         
>     dstoff += dstscanbytes;                        
> });

> the `WriteableImage` used to collate the tiles and the tiles returned from the `RTTexture` have different pixel formats (`IntARGB` for the tile and `byteBGRA` for the `WriteableImage`).

Where did you see these?

> Unfortunately it seems the only way to choose the pixel format for a `WritableImage` is to initialize it with a `PixelBuffer`, but then one can no longer use a `PixelWriter` to update it...

You can update it with `PixelBuffer#updateBuffer`. I think that you will want to pass the stitched tile as the dirty region.

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PR: https://git.openjdk.java.net/jfx/pull/68