feat(demo): transició títol→demo amb dive de càmera + cortinilla negra (substitueix el fundido)

source/core/graphics/curtain.cpp

@@ -0,0 +1,71 @@
+// curtain.cpp - Implementació de la cortinilla negra
+// © 2026 JailDesigner
+
+#include "core/graphics/curtain.hpp"
+
+#include <algorithm>
+
+#include "core/defaults/game.hpp"
+#include "core/math/easing.hpp"
+
+namespace Graphics {
+
+    namespace {
+        constexpr float SCREEN_H = static_cast<float>(Defaults::Game::HEIGHT);
+        constexpr float SCREEN_W = static_cast<float>(Defaults::Game::WIDTH);
+    }  // namespace
+
+    Curtain::Curtain(Rendering::Renderer* renderer)
+        : renderer_(renderer) {}
+
+    void Curtain::cover(float duration) {
+        // Caire superior de -H (fora, a dalt) fins a 0 (tela tapant tota la pantalla).
+        from_ = -SCREEN_H;
+        to_ = 0.0F;
+        duration_ = duration;
+        elapsed_ = 0.0F;
+        active_ = true;
+    }
+
+    void Curtain::reveal(float duration) {
+        // Caire superior de 0 (tapant) fins a +H (tela fora per baix).
+        from_ = 0.0F;
+        to_ = SCREEN_H;
+        duration_ = duration;
+        elapsed_ = 0.0F;
+        active_ = true;
+    }
+
+    void Curtain::update(float delta_time) {
+        if (!active_) {
+            return;
+        }
+        elapsed_ += delta_time;
+    }
+
+    auto Curtain::topY() const -> float {
+        if (duration_ <= 0.0F) {
+            return to_;
+        }
+        const float T = std::clamp(elapsed_ / duration_, 0.0F, 1.0F);
+        // Ease-in: la tela "cau" accelerant, com per gravetat.
+        return Easing::lerp(from_, to_, Easing::easeInQuad(T));
+    }
+
+    auto Curtain::isDone() const -> bool {
+        return !active_ || elapsed_ >= duration_;
+    }
+
+    void Curtain::draw() const {
+        if (!active_) {
+            return;
+        }
+        const float TOP = topY();
+        // Si la tela ja ha sortit completament per baix, no hi ha res a pintar.
+        if (TOP >= SCREEN_H) {
+            return;
+        }
+        renderer_->pushRect(0.0F, TOP, SCREEN_W, SCREEN_H, 0.0F, 0.0F, 0.0F, 1.0F);
+    }
+
+}  // namespace Graphics