<Swing Dev> [9] Review request for 8170387: JLightweightFrame#syncCopyBuffer() may throw IOOBE

[Semyon Sadetsky]

On 11/29/2016 7:59 PM, Sergey Bylokhov wrote:

> On 29.11.16 18:50, Semyon Sadetsky wrote:
>> I did not get this. The area doesn't determine any sizes or location on
>> screen.  It's simply an optimization to update area of the buffer image
>> which was really changed. It cannot be bigger than the buffer image
>> size. The logic of the rounding is to "inflate" the rectangle area to
>> its next integer coordinates in all directions. With other rounding
>> logic you will see artifacts with non-integer scales.
>
> you add this code to the fix:
> 302     int linestride = bbImage.getWidth();
> +308    if (startX + width > linestride) {
> +309        width = linestride - startX;
> +310    }
>
> the x,y,w,h passed to the method are inside the bounds of the 
> component. so the simple expectation which can be done is that
> R(x*scale),R(x*scale),R(y*scale),R(w*scale),R(h*scale) should be 
> inside the image which was created in resizeBuffer(): 
> BufferedImage(R(imgW), R(imgH)). where the "R" is a round operation.
>
> But for some reason the size of the image is smaller, I guess this is 
> because resizeBuffer() use Math.round() and syncCopyBuffer() uses 
> ceil+floor.
No. In most cases this method is called for area less than buffer image 
size. Global repaint is also possible but it is not often happens, 
usually on window resize.
Since ceil() is used in JDK as coordinates rounding method it should be 
used here as well to obtain the maximum repainted area bounds in integer 
coordinates. But for the global size the round() is used, because the 
image should fit the external size which uses another coordinates 
rounding approach.
>
>
>>>
>>> On 28.11.16 16:50, Semyon Sadetsky wrote:
>>>> Hello,
>>>>
>>>> Please review fix for JDK9:
>>>>
>>>> bug: https://bugs.openjdk.java.net/browse/JDK-8170387
>>>>
>>>> webrev: http://cr.openjdk.java.net/~ssadetsky/8170387/webrev.00/
>>>>
>>>> After the rounding the resulting rectangular area may became bigger 
>>>> than
>>>> the buffer image size and this will cause IOOB error during the
>>>> consequent System#arraycopy() calls. To prevent this error the updated
>>>> area is bounded to the buffer image size.
>>>>
>>>> --Semyon
>>>>
>>>
>>>
>>
>
>