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

[Alexandr Scherbatiy]

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.
>>
>
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.openjdk.java.net/pipermail/swing-dev/attachments/20161007/ba2a66b6/attachment.html>