Fix: clear the display mark on a view with no area - #867
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Both display walks reach a subview only when the rectangle being displayed and the subview's frame overlap. A subview whose frame has no width or height never overlaps anything, so it is never displayed, its mark is never cleared, and both walks copy that mark up to every view above it. An NSBox two pixels high is enough: its content view is left with a height of zero, and from then on the content view and the frame view of that window answer YES to -needsDisplay for good. When the overlap is empty because the subview itself has no area, let the subview run the display for an empty rectangle, which clears its own mark. A subview that has an area and merely falls outside the rectangle keeps its mark, as it should.
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Cool thing to spot. |
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Looks great, but I will have to review the whole working here. I wrote most of that, but that was a long time ago and I have to understand all of it again. Sorry,we could also just merge and I go through that later on. |
START_SET creates an autorelease pool and END_SET releases it, so the pool these tests create around the set is redundant.
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Both of NSView's display walks reach a subview only when the rectangle being displayed and the subview's frame overlap. A subview with no width or height never overlaps anything, so it is never displayed, its mark is never cleared, and both walks copy that mark up to every view above it. An NSBox two pixels high is enough: it leaves its content view a height of zero, and from then on that view, the box, the window's content view and the frame view all answer YES to -needsDisplay for good.
When the overlap is empty because the subview has no area, it is now asked to display an empty rectangle, which clears its mark. A subview that has an area and merely falls outside the rectangle keeps its mark, and there is an assertion for that.
This turned up in the alert panel of #80, whose separator is such a box. The symptom reported there, contents invisible until the panel is moved, does not reproduce on Windows against current master, whether the alert is raised before the application loop starts or from inside a running one. This mark is the only defect found on that path.
Tests/gui/NSView/emptyViewNeedsDisplay.m: 5 of its 7 assertions fail before the change and none after. Tests/gui runs 4345 assertions green.
Closes #80