Bug 7007 - Graphics.SetClip gives incorrect results if PageUnit is not Pixel on Mac runtime
Summary: Graphics.SetClip gives incorrect results if PageUnit is not Pixel on Mac runtime
Status: NEW
Alias: None
Product: Class Libraries
Classification: Mono
Component: System.Drawing ()
Version: unspecified
Hardware: Macintosh Mac OS
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
Depends on:
Reported: 2012-09-08 09:52 UTC by xamarinbugs
Modified: 2012-09-08 09:52 UTC (History)
1 user (show)

Is this bug a regression?: ---
Last known good build:

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Description xamarinbugs 2012-09-08 09:52:25 UTC
If Graphics.SetClip is used in combination with changing the PageUnit and applying transformations, then the resulting clip area does not match the results in Windows .net 2 runtime.  It appears that some of the transformation and/or unit change logic is applied to the clipping area, which is ignored within the Microsoft runtime.  However the exact results are strange enough that I've been unable to deduce exactly what is occurring in order to devise a work-around.

To reproduce, create a blank Windows.Forms form at least 60mm * 60mm, and add this code to the form Paint event:

			Rectangle rct = new Rectangle(5, 5, 50, 50);
			e.Graphics.PageUnit = GraphicsUnit.Millimeter;
			e.Graphics.DrawRectangle(Pens.Red, rct); // draw expected target area
			// try to set clipping area just inside drawn line...
			rct.Inflate(-1, -1);
			e.Graphics.TranslateTransform(5, 5); // has no effect on clipped area in Windows
			e.Graphics.Clear(Color.Green); // shows clipping area by colouring entire (clipped) graphics surface
			// resulting rectangle should be just inside red rectangle
			// or: e.Graphics.FillRectangle(Brushes.Green, 0, 0, 50, 50);

Results differ between Windows and Mac with Mono runtime, with the latter giving illogical/unpredictable results.  The order of changing page unit, clipping and applying transformations appears to make little difference - results are incorrect no matter which order effects are applied.  I believe the same issue occurs with other transformations, not just TranslateTransform.
If the PageUnit is left as pixel, the code above works correctly showing the clipped area inside the (now smaller) rectangle, matching the results on Windows.