Fixed glyph positions flipping by one pixel when atlas slot assignments changed.#1508
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… positions land on integer pixels.
Hparty
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domchen,
richardshan0614 and
shlzxjp
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July 22, 2026 05:17
shlzxjp
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Jul 22, 2026
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问题：字形图集渲染的像素对齐直接对平移分量做 std::round。平移量 = 真实设备位置 - 图集槽位坐标，当真实位置为半整数时，std::round 半值远离零的特性会使取整方向随槽位正负翻转，导致同一个字形仅因被分配到图集不同槽位（取决于渲染历史）而偏移 1px。
修改：ComputeGlyphRenderMatrix 改为先对槽位无关的设备锚点坐标（matrix * atlasLocation）取整，再减去精确的矩阵线性项回写到平移分量，渲染时与矩阵自身的缩放项精确抵消，锚点精确落在整数像素上。非复杂分支的 y 方向同样消除了对 atlasLocation.y 的取整依赖，并保留整行共享基线加逐字形偏移分别取整的原有设计；复杂与非复杂两个分支的数学形式已统一。
基准：6 个截图测试的基准版本已在 version.json 中更新（TextAlignTest x3、TextRenderTest、LayerTest、VectorLayerTest）。