Rendering artifacts with swt.autoScale=quarter at particular zoom levels

[HeikoKlare]

At particular zoom levels, some custom rendered widgets, such as the StyledText, show artifacts (black lines) as some areas are not rendered because of rounding issues when using swt.autoScale=quarter (or exact).

For example, starting an IDE at 175% zoom with monitor-specific scaling (or also just with swt.autoScale configured accordingly) and opening any Java editor, looks like this:

The goal of this is to analyze which widgets may be affected by such issues and to find places in the code in which values are not properly rounded and need to be adapted. Those places shall be corrected.

[akoch-yatta]

eclipse-platform/eclipse.platform.swt#1761 will cover the issue in StyledText

[akoch-yatta]

eclipse-platform/eclipse.platform.swt#1762 will cover the issue in GC

[akoch-yatta]

Remaining places to check:

• Path::addArc -> Floats are already used. That should be fine
• Region::intersects -> [win32] Fix scaling inside Region::intersect eclipse-platform/eclipse.platform.swt#1768
• Control::setBounds -> [win32] Unify scaling inside Control::setBounds eclipse-platform/eclipse.platform.swt#1769

eclipse-platform/eclipse.platform.swt#1783 ->

• Canvas::scroll
• Composite::drawBackground
• Control::redraw
• Scrollable::computeTrim