[Bug 41158] New: RADEON KMS: radeon_crtc_cursor_move is off by one pixel

[bugzilla-daemon@freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=41158

           Summary: RADEON KMS: radeon_crtc_cursor_move is off by one
                    pixel
           Product: DRI
           Version: XOrg CVS
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Radeon
        AssignedTo: dri-devel@lists.freedesktop.org
        ReportedBy: nmiell@gmail.com


Created an attachment (id=51555)
 --> (https://bugs.freedesktop.org/attachment.cgi?id=51555)
test cursor theme, unzip into ~/.icons and configure your desktop environment
to use it

When the mouse cursor is partially off the top or left edge of the screen, the
cursor image is drawn one pixel further to the top or left than the actual
position.

This manifests itself in two ways:

1) When the cursor transitions from entirely on the screen to partially
offscreen, the image jumps two pixels instead of moving by only one pixel. (Due
to the transition from a correctly positioned image to an off-by-one image.)

2) It is possible to move the cursor's hotspot off the screen. (Appearance
only, of course, as far as X is concerned the hotspot is still in the uppermost
or leftmost row of pixels.)

This seems obvious when you map out what the function actually does to
calculate the xorigin and yorigin values, but some doubt was raised based on
the wording of the register descriptions in the manuals. (Instead of speaking
of offsets or coordinates, the term "length" is used, and it wasn't clear
whether this length included the actual hotspot pixel.)

So I tested it empirically by constructing a rather hideous looking cursor
theme. It is a 31x31 mouse cursor image with the hotspot on the exact center
pixel.

The cursor has a one pixel red border. Immediately inside the red border is one
pixel of yellow. You will not be able to position the cursor on the screen such
that the outer red border is off the top or left but the inner yellow border is
still visible.

There is a one pixel wide yellow cross in the center of the cursor image, with
the center pixel of the cross being the cursor's hotspot. Surrounding the
yellow cross is a one pixel red border. When you move the cursor to the upper
left pixel, the yellow cross vanishes entirely, which shouldn't be possible
because you can't move the mouse cursor's hotspot off of the screen.

Neither of these things happen when you use SWcursor.

Testing was done on a RS880. I assume Evergreen is broken in the same way, but
I'm not sure about pre-Avivo chips.

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