Disclosure: This article was generated with AI for the FrameSprite team, which has a commercial interest in FrameSprite. It received a separate AI editorial review against the cited sources. Executed synthetic fixtures are identified with their runtime and limits; no other editor, engine, production or performance test is implied.
Save the Canvas state before applying a per-cell clip and restore it after drawing that cell. A clipping region persists into later drawing operations. If the first cell's clip is still active, a second non-overlapping cell can disappear even though its source image is valid.
Key takeaway: Clipping is state, not a one-call crop. Limit its lifetime to the drawing operation that needs it.
Use two distant cells as the control
The original fixture uses a four-pixel-wide canvas. It draws a red cell at x = 0 and a blue cell at x = 3. In the failing version, the clip covers only the first cell and remains active during the second draw. The second cell is transparent.
The clip reference explains that clipping regions cannot simply be undone directly. Save before changing the region, then restore the saved state when finished.
ctx.save();
try {
ctx.beginPath();
ctx.rect(cellX, cellY, cellWidth, cellHeight);
ctx.clip();
ctx.drawImage(source, drawX, drawY);
} finally {
ctx.restore();
}
The finally block matters if a draw or another operation throws. Without it, a failed first cell can leave the rest of the export clipped too.
Keep paths and saved state distinct
Use beginPath before defining the clipping shape. A previously built path can contain more geometry than you intended. Also remember that restoring drawing state is not the same as clearing the current path; start a new path for the next independently constructed shape.
The save reference lists the saved drawing state. The Canvas specification distinguishes that state from path construction. Keep those two concepts visible in helper functions rather than relying on implicit cleanup.
Calling fillRect does not add that rectangle to the current path. If the clip should be rectangular, construct a rect path as shown instead of assuming a previously painted rectangle becomes the clip.
Check the repaired pixel rather than the preview border
Chromium 156.0.8078.4 ran two assertions in the local checker. The result records the repaired second cell as RGBA 0, 0, 255, 255. The failing control reads RGBA 0, 0, 0, 0 at the same coordinate. The input preserves the separated cell positions.
This was an authored local Canvas test, not a production sprite packer or game-engine test. The checker is part of the controlled local harness used for the recorded run; it is not presented as a standalone image editor.
Reject the wrong diagnosis
Empty output caused by a leaked clip does not require regenerating the sprite. First draw the same source on a fresh canvas with no clip. If it appears, inspect shared context state before changing the art or the atlas packing algorithm.
Use the sheet padding guide for actual gutter spacing. Use the trimmed-atlas metadata guide for source crop offsets. If a remote source draws but fails at export, use the Canvas origin-security check.
Acceptance boundary
Test two non-overlapping cells, an intentionally failing draw inside the clipped block, and a later unmasked overlay. All later drawing should remain visible according to its own state. Keep save/restore ownership in the same helper so the caller does not need to remember hidden cleanup.
Editorial ownership
Prepared by the workflow team, which has a commercial relationship with this site. This guide was drafted with AI assistance; independent editorial review is recorded separately. Report a technical correction with the relevant input, tool version and observed result.
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