Fix text labels packed past TEXTURE_HEIGHT (clipped/stretched rendering)

[jhotadhari]

Fixes #1313

Problem

Large captions occasionally rendered vertically clipped/stretched (flat cut at the bottom plus a halo smear), because TextBucket.prepare() only checked y + height > TEXTURE_HEIGHT inside the x + width > TEXTURE_WIDTH row-break branch. A label that fit horizontally into an existing bottom row was packed with its cell extending past the 256 px texture height: the glyphs were rasterized clipped at the bitmap's bottom edge, while the quad's texture coordinates still covered the full cell (out-of-bounds rows sample the last row via CLAMP_TO_EDGE).

Only the largest font styles were affected (smaller cells never exceed TEXTURE_HEIGHT), and the artifact came and went with panning/zooming because it depends on the atlas packing order for the visible label set — see the issue for screenshots and repro details.

Fix

Run the new-texture overflow check for every label instead of only on row breaks, so any cell that would exceed TEXTURE_HEIGHT starts a new texture:

if (x + width > TEXTURE_WIDTH) {
    x = 0;
    y += advanceY;
    advanceY = (int) (height + 0.5f);
}

if (y + height > TEXTURE_HEIGHT) {
    ... start new texture ...
}

One file changed (TextBucket.java, 16 insertions / 11 deletions). No API changes.

Verification

• Instrumented build on device: atlas dumps + vertex/uv logs confirmed the clipped-cell mechanism (label cell 210–272.5 in a 256 px texture, glyphs cut at row 256).
• With the fix, no reproduction across repeated pan/zoom sessions on the same device/map/theme.

Notes

• The label pipeline derives the cell height from the cached TextStyle.fontHeight while the width is measured live via paint.measureText(). We considered (and tested) switching the height to live paint metrics as hardening — it's not required for this bug, but a tested reference implementation is available on my fork if maintainers are interested: jhotadhari/vtm branch keep/live-paint-text-metrics
• This also fixes the same latent issue on any platform, not just Android.

Proposed CHANGELOG entry

- Fix text labels packed past TEXTURE_HEIGHT (clipped/stretched labels) [#XXXX](https://github.com/mapsforge/vtm/pull/XXXX)

(placed under ## Next version in docs/Changelog.md)

[devemux86]

Thank you, we need to check if this affects the performance on Android.

Regarding your first note:
It is best to make changes only when they are truly necessary and produce different results.
Given that performance is always a priority, it is best to avoid additional measurement calls.

[jhotadhari]

Hi,

True, good point, we should ensure that it doesn't effect the performance.

I can't use my laptop the next days, maybe for a week, I'm sitting in mud. When I'm back in civilization, I can try to measure the performance.

Proposal: we can design it as opt-in. Maybe as a static property. Similar to org.oscim.backend.CanvasAdapter.textScale but boolean. If it affects performance, it has to be an opt-in feature, if implemented at all.

Regarding your first note:
It is best to make changes only when they are truly necessary and produce different results.

I agree.