I tried to look deeper in the code and it seems there is a rounding
issue when float values are summed up.
Suppose a transform with scale 1.5 is used and the 'a' char advance is
10 in a dev space.
The 'a' char has advance 10 / 1.5 = 6.666666666666667 as double value
and 6.6666665 when it is cast to float in user space.
The width of a string which consists of 15 'a' chars is 15 * 6.6666665
= 100.000000.
But the same width calculated as sum of each glyph advance in
StandardGlyphVector.initPositions() method is 99.999992.
--------------
double scale = 1.5;
float advance = (float) (10 / scale);
int N = 15;
System.out.printf("%d * %f = %f\n", N, advance, N * advance);
float sum = 0;
for (int i = 0; i < N; i++) {
sum += advance;
}
System.out.printf("sum: %f\n", sum);
--------------
Because of this a string drawn from float position 99.999998 is shifted
one pixel left which affects the text selection code in Swing:
------------------------
g.scale(1.5, 1.5);
String TEXT = "aaaaaaaaaaaaaaaa";
Rectangle2D rect = font.getStringBounds(TEXT, 0, index,
g.getFontMetrics().getFontRenderContext());
float selectedTextPosition = (float) rect.getWidth(); //
99.999992
g.drawString(TEXT.substring(0, index), x, y); // non-selected text
g.drawString(TEXT.substring(index, TEXT.length()), x +
selectedTextPosition, y); // selected text is shifted to one pixel left
------------------------
Thanks,
Alexandr.
On 6/2/2016 11:41 PM, Alexandr Scherbatiy wrote:
On 5/31/2016 10:40 PM, Phil Race wrote:
I applied this and it is *much* better but there still seem to be
some tiny quirks.
When I drag the mouse to select text down and then up again, as I
pass the
original mouse click point vertically, repaint seem to jiggle
vertically by a pixel.
Perhaps a rounding issue in the repaint code's calculation of the
location of
the target y. I think I may see the same in left/right dragging along
a line too.
So I think this is repaint and not text related. Can you take a look.
I am able to reproduce this only using a floating point scale.
It looks like 2d issue. I used a test which draws a text in two
pieces. The second piece of the text is shifted from the first piece
by the floating point size of the the first piece of the text.
-----------
Rectangle2D rect = font.getStringBounds(TEXT, 0, index,
g.getFontMetrics().getFontRenderContext());
float selectedTextPosition = (float) rect.getWidth();
g.drawString(TEXT.substring(0, index), x, y);
g.drawString(TEXT.substring(index, TEXT.length()), x +
selectedTextPosition, y);
-----------
The second piece of the text can be shifted in the 2 cases:
a) graphics scale is 1.5 and translation is 1.
b) graphics scale is 2.25 without applied translation
I have filed an issue on it:
JDK-8158370 Text drawn from float pointing position and with float
pointing scale is shifted
https://bugs.openjdk.java.net/browse/JDK-8158370
Thanks,
Alexandr.
-phil.
On 05/06/2016 12:31 PM, Alexandr Scherbatiy wrote:
Hello,
Could you review the fix:
bug: https://bugs.openjdk.java.net/browse/JDK-8156217
webrev: http://cr.openjdk.java.net/~alexsch/8156217/webrev.00
This is the second part of the fix related to the fact that char
width can be fractional in user space.
http://mail.openjdk.java.net/pipermail/swing-dev/2016-May/005814.html
The Font.getStringBounds(...) method is used for the fractional
string width calculation by Swing in user space.
Thanks,
Alexandr.
