> The primary API for image capture on modern Linuxes is > `gdk_pixbuf_get_from_window()` that expects both coordinates and the size > unscaled (i.e. not multiplied by the current desktop scale). At the same > time, `gtk3_interface.c:gtk3_get_drawable_data()` gets the coordinates from > `Robot` that pre-scales them (multiplying by the scale known to Java, > however, not necessarily the current desktop scale). The problem with the > size had been partly taken care of in > [JDK-8225118](https://bugs.openjdk.java.net/browse/JDK-8225118), but > coordinates are still passed to `gdk_pixbuf_get_from_window()` pre-scaled. > > The idea of the fix is to capture a possibly larger area that is guaranteed > to contain the one that is interesting to the caller and then only copy the > interesting pixels to the output image. As a positive side effect, the size > of the captured area cannot be less than 1x1 (provided the correct input, of > course). This solves the problem of zero size passed to > `(*fp_gdk_pixbuf_get_from_drawable)` when the desktop scale is 3 and we're > asked to capture just one pixel. In that case, the previous formula (`width / > (float) win_scale + 0.5`) would have yielded `0`. > > A related issue would be that tests written specifically for this general > area (`java/awt/Robot`) didn't catch this problem and only somewhat unrelated > tests (`javax/swing/...`) were affected. > > This one is solved by adding pixel-sized areas to the test image in > `HiDPIRobotScreenCaptureTest.java`, which precise colors are then verified to > match the expected ones. In addition to that, instead of verifying just the > color of the center of a large area, 4 more pixels close to the area's border > are checked. This helps to make sure that captured area coordinates aren't > way off. > > The tests under `javax/swing/...` that originally helped to identify this > problem were modified to provide more screen space for painting their > components as extreme desktop scaling (300%) on Ubuntu doesn't leave much > room due to a humongous title bar. > > The fix was tested by running all the modified tests on Ubuntu with desktop > scaling set to 100%, 200%, and 300%. The `Robot` tests were also executed on > Windows (300% scaling) and MacOS.
Maxim Kartashev has updated the pull request incrementally with one additional commit since the last revision: Renamed scaling functions and updated copyright. ------------- Changes: - all: https://git.openjdk.java.net/jdk/pull/7425/files - new: https://git.openjdk.java.net/jdk/pull/7425/files/fc651add..4a8c20af Webrevs: - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7425&range=03 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7425&range=02-03 Stats: 8 lines in 3 files changed: 0 ins; 0 del; 8 mod Patch: https://git.openjdk.java.net/jdk/pull/7425.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/7425/head:pull/7425 PR: https://git.openjdk.java.net/jdk/pull/7425
