new UI system

interfaces/Crafter.Graphics-UILayout.cppm

@@ -0,0 +1,73 @@
+/*
+Crafter®.Graphics
+Copyright (C) 2026 Catcrafts®
+catcrafts.net
+
+This library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Lesser General Public
+License version 3.0 as published by the Free Software Foundation;
+
+This library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public
+License along with this library; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
+*/
+export module Crafter.Graphics:UILayout;
+import std;
+import :UILength;
+import :UIWidget;
+
+export namespace Crafter::UI {
+    // Convert a Length to device pixels. `parentExtent` is the parent's
+    // available extent on the same axis (already in device px). `autoFn`
+    // produces the size to use for `Auto` and `Frac` modes — for Auto this
+    // is the desired-content size, for Frac it's the same fallback (Frac
+    // is meaningful only inside a stack container, which resolves it
+    // separately; everywhere else it's just "fill what's available", same
+    // as Auto).
+    template<typename AutoFn>
+    constexpr float ResolveLength(Length len, float parentExtent, float scale, AutoFn&& autoFn) {
+        switch (len.mode) {
+            case Length::Mode::Px:   return len.value * scale;
+            case Length::Mode::Pct:  return len.value * 0.01f * parentExtent;
+            case Length::Mode::Auto: return static_cast<float>(autoFn());
+            case Length::Mode::Frac: return static_cast<float>(autoFn());
+        }
+        return 0.0f;
+    }
+
+    // Edges resolved into device pixels (no Length involvement; Edges are
+    // already plain floats in logical px).
+    struct EdgesPx {
+        float top = 0, right = 0, bottom = 0, left = 0;
+        constexpr float Horiz()    const { return left + right; }
+        constexpr float Vert()     const { return top + bottom; }
+    };
+
+    constexpr EdgesPx ResolveEdges(Edges e, float scale) {
+        return { e.top * scale, e.right * scale, e.bottom * scale, e.left * scale };
+    }
+
+    // Rect minus padding — yields the content rect.
+    constexpr Rect ShrinkBy(Rect r, EdgesPx p) {
+        return {
+            r.x + p.left,
+            r.y + p.top,
+            std::max(0.0f, r.w - p.Horiz()),
+            std::max(0.0f, r.h - p.Vert()),
+        };
+    }
+
+    // Run the two-pass measure/arrange on a root widget bound to a surface
+    // of `surfacePx` device pixels at `scale`. The root receives the full
+    // surface as its arrange rect.
+    inline void RunLayout(Widget& root, Size surfacePx, float scale) {
+        LayoutContext ctx{ .scale = scale, .surfaceSize = surfacePx };
+        root.Measure(surfacePx, ctx);
+        root.Arrange({0, 0, surfacePx.w, surfacePx.h}, ctx);
+    }
+}