<Swing Dev> [9] Review request for 8162350 RepaintManager shifts repainted region when the floating point UI scale is used

[Jim Graham]

I want to clarify the following issue...

On 10/24/2016 9:11 AM, Alexandr Scherbatiy wrote:
>   Using floating point scale leads that drawing the same thing from
> different coordinates gives different results. For example filling a
> rectangle with size (1, 1) from location (0, 0) and UI scale 1.5 gives
> scaled region (0, 0, 1.5, 1.5) which is rounded to (0, 0, 2, 2). The
> same rectangle filled from the location (1, 1) gives the scaled region
> (1.5, 1.5, 3, 3) which is rounded to (2, 2, 3, 3). The first rectangle
> has size 2 in the device space and the second one has 1.

First, while those primitives would be drawn in 2 different sizes, the 
first should be 1x1 and the second should be 2x2 if they follow our fill 
rules.  Were you seeing something different?  Still, the point you bring 
up about the two being 2 different sizes is acknowledged.  Fill rule 
rounding for these rectangles should be "ceil(coordinate - 0.5)".

Drawn with an integer translation of 0,0 (i.e. before scrolling 
operations or damage repair):

scale = 1.5
translate = 0,0 in device pixels
fillRect(0, 0, 1, 1)
     transforms to 0.0, 0.0, 1.5, 1.5
     fills (0,0,1,1)
     covers 1x1 pixels
fillRect(1, 1, 1, 1)
     transforms to 1.5, 1.5, 3.0, 3.0
     fills (1,1,3,3)
     covers 2x2 pixels

scale = 1.5
translate = 1,1 in device pixels
fillRect(0, 0, 1, 1)
     transforms to 1.0, 1.0, 2.5, 2.5
     fills (1,1,2,2)
     covers 1x1 pixels
fillRect(1, 1, 1, 1)
     transforms to 2.5, 2.5, 4.0, 4.0
     fills (2,2,4,4)
     covers 2x2 pixels

No change in the relative sizes is observed.  Now, if you are talking 
about an integer translation in user space, then there is a difference, 
as in:

scale = 1.5
translate = 1,1 in user space
           = 1.5,1.5 in device space
fillRect(0, 0, 1, 1)
     transforms to 1.5, 1.5, 3.0, 3.0
     fills (1,1,3,3)
     covers 2x2 pixels
fillRect(1, 1, 1, 1)
     transforms to 3.0, 3.0, 4.5, 4.5
     fills (3,3,4,4)
     covers 1x1 pixels

That can create a problem, but only if the translation is an integer 
distance in user space.  If RepaintManager is applying integer distances 
in device space, then it should not affect the relative sizes of the 
rendered primitives.

Were you seeing that happen?  Because that would be a rendering bug in 
fillRect...

			...jim

>   As a result drawing a component from some coordinates and using
> Graphics.copyArea() to translate an image to a new location could have a
> differ results than just drawing the same component from the new location.
>   The fix suggests to disable the JScrollPane area copying for floating
> point scales.
>
> Thanks,
> Alexandr.
>
> On 10/7/2016 4:30 PM, Alexandr Scherbatiy wrote:
>> On 10/6/2016 11:42 PM, Sergey Bylokhov wrote:
>>> Hi, Alexandr.
>>> Can you please provide some standalone small example, which emulates
>>> this artifacts via java2d API. (The pattern which we use in
>>> RepainManager). It will help to understand the problem.
>>
>> The code sample [1]  draws two the same shapes (with different colors)
>> one after another into areas (x, y, w, h) and (x+w, y, w, h)
>> accordingly in different ways.
>>
>> The shape is constructed from the following parts:
>> 1. Fill clip area
>>  - set clip (x, y, w, h)
>>  - fill the whole image
>> As a result only clipped area is filled.
>>
>> 2. Fill rect
>> - fill rect(x, y, w, h) // big rect
>> - fill rect(x+1, y+1, w-2, h-2) // small rect
>>
>> 3. Draw center lines
>> - draw line (x, cy, x + w, cy)
>> - draw line (cx, y, cx, y + h)
>>
>> The program has the following options:
>>   RECT - draw two shapes one after another from point (0, 0)
>>   SHIFTED_RECT - draw two shapes one after another from point (x, y)
>>   BACKBUFFER - draw the shape into a backbuffer with size (w, h) and
>> draw the backbuffer from the point (x, y)
>>   SCALED_BACKBUFFER - draw the shape into a scaled backbuffer with
>> size (ceil(w*scale), ceil(h*scale)) with scaled graphics from point
>> (0, 0) and draw it into the rectangle (x, y, w, h)
>>   ENLARGED_SCALED_BACKBUFFER - draw the shape into a scaled backbuffer
>> with size (ceil((x+w)*scale), ceil((y+h)*scale)) with scaled graphics
>> from point (x, y) and draw it into the rectangle (0, 0, x+w, y+h)
>>
>> The resulted images are placed in the directory [2].
>> Directory name "rect-[7,5,10,8]" means that the rectangles (7,5,10,8)
>> was used for the shape drawing.
>> Each screenshot name follows the template "
>> screenshot-N-[x,y,w,h]-TYPE.png" where the type is a program option
>> used for the image generation.
>> Screenshots with suffix "-compare" compares the golden image (shape
>> drawn in to the rectangle (x, y, w, h)) with the generated image. The
>> golden image is on the top left side. The generated image is shown on
>> the right and bottom side.
>>
>> The RepaintManager has an assumption that drawing something in some
>> area (x, y, w, h) or just drawing the same thing into an image with
>> translated graphics g.translate(-x1, -y1) and drawing the image into
>> the area(x, y, w, h)  has the the same result.
>>
>> As it is shown on screenshots this statement is not true for floating
>> point scales.
>> For example the same shape drawn from the point (0,0) and (x,y) look
>> differently (see [3] and [4]).
>>
>> The solution could be just to use an enlarged backbuffer with size
>> (x+w, y+h) with scaled graphics, draw the component into the rectangle
>> (x, y, w, h) and draw the backbuffer into the area (0,0, x+w, y+h).
>> Even the scaled enlarged backbuffer is used the results can be differ
>> (see [5] where the rectangle [7, 5, 11, 9] is used. The backbuffer is
>> drawn into bigger size).
>>
>>
>> [1] code samples:
>> http://cr.openjdk.java.net/~alexsch/8162350/code/00/Java2DFPSamples.java
>> [2] dir with screenshots results:
>> http://cr.openjdk.java.net/~alexsch/8162350/results
>> [3] RECT:
>> http://cr.openjdk.java.net/~alexsch/8162350/results/rect-%5b7%2c5%2c10%2c8%5d/screenshot-01-%5b7%2c5%2c10%2c8%5d-rects.png
>> [4] SHIFTED_RECT:
>> http://cr.openjdk.java.net/~alexsch/8162350/results/rect-%5b7%2c5%2c10%2c8%5d/screenshot-02-%5b7%2c5%2c10%2c8%5d-shifted-rects.png
>> [5] ENLARGED_SCALED_BACKBUFFER compare:
>> http://cr.openjdk.java.net/~alexsch/8162350/results/rect-%5b7%2c5%2c11%2c9%5d/screenshot-05-%5b7%2c5%2c11%2c9%5d-enlarged-scaled-backbuffers-compare.png
>>
>> Thanks,
>> Alexandr.
>>
>>>
>>> On 06.10.16 20:07, Alexandr Scherbatiy wrote:
>>>> Hello,
>>>>
>>>> Could you review the fix:
>>>>   bug: https://bugs.openjdk.java.net/browse/JDK-8162350
>>>>   webrev: http://cr.openjdk.java.net/~alexsch/8162350/webrev.00
>>>>
>>>>   The fix uses the solution suggest by Jim in the email:
>>>> http://mail.openjdk.java.net/pipermail/2d-dev/2016-October/007737.html
>>>>
>>>>   To draw to a VolatileImage backbuffer its graphics transform is
>>>> set to
>>>> identity and device coordinates are used to set the buffer clip.
>>>>   Copying the backbuffer image to the graphics has some problems.
>>>>   -------------
>>>>     // Since there is no drawImage(img, float x, float y)...
>>>>     destination.translate(pixelx1 / scaleX, pixely1 / scaleY)
>>>>     destination.drawImage(img, 0, 0)
>>>>   -------------
>>>>   This code solves the problem for the top left corner of the region.
>>>> All Graphics.drawImage(...) methods scales the image size and it looks
>>>> like ceil(img.getWidth() * scaleX) can be differ from the
>>>> ceil(pixelx1 +
>>>> img.getWidth() * scaleX) - pixelx1 so the right bottom corner of the
>>>> image does not fit the required point.
>>>>   There is also a question could a line drawn from one point and then
>>>> from another has a different width in pixels because the graphics scale
>>>> is not integer.
>>>>
>>>>   The proposed fix prepares a backbuffer with size [x + w, y + h] in a
>>>> user space and a component is drawn in to the region [pixelx1, pixely1,
>>>> pixely2, pixely2] in the device space.
>>>>   After that the necessary clip is set to the graphics and whole image
>>>> is just drawn into it.
>>>>
>>>>   The new logic is used only the component graphics configuration is
>>>> scaled the graphics configuration has the same scales. So it possible
>>>> just to copy the backbuffer surface data to the graphics surface data.
>>>>   For other cases like for rotated graphics transform it seems it is
>>>> necessary to have more complicated algorithm.
>>>>
>>>>   This solves problems with repainted region but there are still
>>>> artifacts with JInternalFrame moving or a component scrolling, This can
>>>> be related to the RepaintManager.copyArea() method which needs to be
>>>> updated in the similar way. I have created an issue on it:
>>>>    JDK-8167305 RepaintManager.copyArea() method should be updated for
>>>> floating point UI scale
>>>>      https://bugs.openjdk.java.net/browse/JDK-8167305
>>>>
>>>>  Thanks,
>>>>  Alexandr.
>>>>
>>>
>>>
>>
>