feat(demo): transició per fosa a/desde negre en el salt títol→demo

source/core/graphics/screen_fade.cpp

@@ -0,0 +1,62 @@
+// screen_fade.cpp - Implementació de la fosa a/desde negre
+// © 2026 JailDesigner
+
+#include "core/graphics/screen_fade.hpp"
+
+#include <algorithm>
+#include <cmath>
+
+#include "core/defaults/game.hpp"
+
+namespace Graphics {
+
+    ScreenFade::ScreenFade(Rendering::Renderer* renderer)
+        : renderer_(renderer) {}
+
+    void ScreenFade::start(float from, float to, float duration) {
+        from_ = from;
+        to_ = to;
+        duration_ = duration;
+        elapsed_ = 0.0F;
+        active_ = true;
+    }
+
+    void ScreenFade::update(float delta_time) {
+        if (!active_) {
+            return;
+        }
+        elapsed_ += delta_time;
+    }
+
+    auto ScreenFade::alpha() const -> float {
+        if (!active_) {
+            return 0.0F;
+        }
+        if (duration_ <= 0.0F) {
+            return to_;
+        }
+        const float T = std::clamp(elapsed_ / duration_, 0.0F, 1.0F);
+        return std::lerp(from_, to_, T);
+    }
+
+    auto ScreenFade::isDone() const -> bool {
+        return !active_ || elapsed_ >= duration_;
+    }
+
+    void ScreenFade::draw() const {
+        const float A = alpha();
+        if (A <= 0.0F) {
+            return;
+        }
+        renderer_->pushRect(
+            0.0F,
+            0.0F,
+            static_cast<float>(Defaults::Game::WIDTH),
+            static_cast<float>(Defaults::Game::HEIGHT),
+            0.0F,
+            0.0F,
+            0.0F,
+            A);
+    }
+
+}  // namespace Graphics