display: clamp coordinates to framebuffer range#186
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gaberudy wants to merge 1 commit intokasmtech:masterfrom
Open
display: clamp coordinates to framebuffer range#186gaberudy wants to merge 1 commit intokasmtech:masterfrom
gaberudy wants to merge 1 commit intokasmtech:masterfrom
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absX/absY and clientToElement could produce negative or out-of-range values when the cursor leaves the primary screen on a side with no adjacent virtual screen. Without clamping, the negative value got packed into a uint16 on the wire and the server saw a huge positive coord, snapping the cursor to the far edge. Clamps to [0, fbWidth-1] and [0, fbHeight-1] in absX, absY, and clientToElement (multi-screen path).
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Problem
absX,absY, and the multi-screen branch ofclientToElementcan producenegative or out-of-range values when the cursor exits the primary screen on
a side with no adjacent virtual screen (e.g. dragging a window's title bar
above the top edge so the pointer's logical Y goes < 0).
The negative
intresult reachesRFB.messages.pointerEventand gets packedas a
uint16on the wire. The server decodes it as a huge positive coord andsnaps the cursor to the far edge of the framebuffer.
In practice this manifests as: drag a window upward, pointer touches the top
of the canvas, cursor jumps to the bottom edge, drag glitches.
Fix
Clamp the result of each coordinate transform to
[0, fbWidth-1]/[0, fbHeight-1]before returning. The clamp is applied in three places:absX(x)— single-screen pathabsY(y)— single-screen pathclientToElement(...)— multi-screen extension path (which can also yieldnegative values for the same reason)
_fbWidth/_fbHeightmay be 0 before resize negotiation completes; theupper-bound check is gated on truthy width/height to preserve current behavior
during connect.
Repro
Connect via kasmweb to a session, grab a window's title bar, drag upward past
the top of the canvas. The window snaps to the bottom of the screen. With this patch the cursor stays clamped at y=0 and the drag behaves as expected (window stays pinned to the top of the screen).