40 lines
1.6 KiB
Dart
40 lines
1.6 KiB
Dart
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// lib/editor/layout/viewport_fit.dart
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//
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// Pure fit/centering math for the viewport's initial transform + the reader
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// "fit width / fit page" actions (F3). Today this lives as untested ad-hoc
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// arithmetic in pen_editor_screen._centerPage; extracting it here makes it
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// testable and shared by the new viewport widget.
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//
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// Content coordinates are scale-1 logical px; the returned scale + offset place
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// content inside the viewport. No widgets beyond dart:ui Size/Offset.
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import 'dart:ui' show Offset, Size;
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/// Scale so content width fills the viewport width (fit-to-width, the
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/// continuous-single default). 0 for non-positive content width.
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double fitWidthScale(Size content, double viewportWidth) {
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if (content.width <= 0) return 0;
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return viewportWidth / content.width;
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}
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/// Scale so the whole content fits inside the viewport (letterboxed) —
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/// min(widthFit, heightFit). 0 for non-positive content extents.
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double fitPageScale(Size content, Size viewport) {
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if (content.width <= 0 || content.height <= 0) return 0;
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final w = viewport.width / content.width;
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final h = viewport.height / content.height;
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return w < h ? w : h;
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}
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/// Top-left translation that centers [content] scaled by [scale] within
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/// [viewport]. When the scaled content is larger than the viewport on an axis
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/// the offset is negative (content overflows equally on both sides).
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Offset centerOffset(Size content, Size viewport, double scale) {
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final scaledW = content.width * scale;
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final scaledH = content.height * scale;
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return Offset(
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(viewport.width - scaledW) / 2.0,
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(viewport.height - scaledH) / 2.0,
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);
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}
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