fix(render): 合成器用源 nat_size 而非解码纹理尺寸 — 修预览左下角/抽搐 (#125)#129
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…the decoded texture size The shader scales its [0,1] quad by `nat` (source natural size) to recover source-pixel space before applying the affine. The compositor was feeding `tex.width/height` into that uniform instead of the nat_size the affine was built with. In the preview the frame is decoded at a downscaled max_size, so the texture is smaller than the source — the quad then covered only tex/nat of the canvas and the layer rendered shrunk into the bottom-left corner, jittering as the per-frame decoded size varied. Export decodes at full size (tex==nat) so it was unaffected — which is why export looked right but preview did not. Carry ClipPlan.nat_size through LayerDraw and use it for the uniform; the texture is sampled via crop_uv 0..1 so its actual resolution is irrelevant to geometry. Adds a GPU-gated regression test (4x4 texture, 16x16 source/canvas) asserting a full-canvas clip fills the whole frame. Verified on real GPU; existing render tests still pass. Real fix for #125 (PR #128's CSS change was necessary but not sufficient). Refs #125
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真因(用户实测 + GPU 回归测试确认)
shader 的 quad 按
nat(源自然尺寸)缩放回源像素空间再套仿射(shader.wgsl明注nat = source natural size)。但compositor.rs把 uniform 的 nat 填成了解码纹理尺寸tex.width/height,而非仿射所用的ClipPlan.nat_size。预览按
preview_box降采样解码(如源 1920 → 纹理 1280),于是 quad 只覆盖画布 tex/nat≈⅔ → 图层缩到左下角;不同 clip/帧纹理尺寸不同 → 落点跳变 = 乱抽搐。导出(#112)全分辨率解码 tex==nat 才正常,故导出对、预览错。修复
LayerDraw新增nat_size字段,从ClipPlan.nat_size透传(与仿射同基准)。draw.nat_size而非tex.width/height。纹理经crop_uv0..1 采样,其分辨率与几何无关——既修 bug 又保留预览降采样性能。gpu_downscaled_nat.rs(4×4 纹理 / 16×16 源)断言全画幅 clip 铺满整帧;本机 GPU 实测通过,既有合成测试无回归。注:PR #128 的 CSS 改动(<img objectFit:contain)是必要的(非 16:9 面板正确缩放),但不是真因。本 PR 是 #125 的真正修复。Refs #125(reopened)。
(关于'拖动不立即/一帧一帧':几何修复后帧将就地更新不再跳位;真正的即时 scrub 依赖流式播放引擎 #92/#100。)