feat(grid): graella verda fosca de fons al playfield (16x8)

source/core/defaults.hpp

@@ -17,6 +17,7 @@
 #include "core/defaults/entities.hpp"
 #include "core/defaults/floating_score.hpp"
 #include "core/defaults/game.hpp"
+#include "core/defaults/grid.hpp"
 #include "core/defaults/hud.hpp"
 #include "core/defaults/math.hpp"
 #include "core/defaults/notifier.hpp"

source/core/defaults/grid.hpp

@@ -0,0 +1,12 @@
+// grid.hpp - Configuració de la grilla de fons del playfield
+// © 2026 JailDesigner
+
+#pragma once
+
+namespace Defaults::Grid {
+
+    constexpr int COLUMNS = 16;          // cel·les omplen tota la PLAYAREA: cell_w = w/16
+    constexpr int ROWS = 8;              // cel·les omplen tota la PLAYAREA: cell_h = h/8 (≈2% més altes que amples)
+    constexpr float BRIGHTNESS = 0.20F;  // intensitat respecte al color global (border = 1.0)
+
+}  // namespace Defaults::Grid

source/core/graphics/playfield_grid.cpp

@@ -0,0 +1,37 @@
+// playfield_grid.cpp - Implementació de la grilla de fons
+// © 2026 JailDesigner
+
+#include "core/graphics/playfield_grid.hpp"
+
+#include "core/defaults.hpp"
+#include "core/rendering/line_renderer.hpp"
+
+namespace Graphics {
+
+    PlayfieldGrid::PlayfieldGrid(Rendering::Renderer* renderer)
+        : renderer_(renderer) {}
+
+    void PlayfieldGrid::draw() const {
+        const SDL_FRect& zona = Defaults::Zones::PLAYAREA;
+        const float CELL_W = zona.w / static_cast<float>(Defaults::Grid::COLUMNS);
+        const float CELL_H = zona.h / static_cast<float>(Defaults::Grid::ROWS);
+
+        const int X1 = static_cast<int>(zona.x);
+        const int Y1 = static_cast<int>(zona.y);
+        const int X2 = static_cast<int>(zona.x + zona.w);
+        const int Y2 = static_cast<int>(zona.y + zona.h);
+
+        // Línies verticals interiors (i=1..COLUMNS-1: no repetim el border)
+        for (int i = 1; i < Defaults::Grid::COLUMNS; i++) {
+            const int X = static_cast<int>(zona.x + (static_cast<float>(i) * CELL_W));
+            Rendering::linea(renderer_, X, Y1, X, Y2, Defaults::Grid::BRIGHTNESS);
+        }
+
+        // Línies horitzontals interiors (j=1..ROWS-1: no repetim el border)
+        for (int j = 1; j < Defaults::Grid::ROWS; j++) {
+            const int Y = static_cast<int>(zona.y + (static_cast<float>(j) * CELL_H));
+            Rendering::linea(renderer_, X1, Y, X2, Y, Defaults::Grid::BRIGHTNESS);
+        }
+    }
+
+}  // namespace Graphics

source/core/graphics/playfield_grid.hpp

@@ -0,0 +1,23 @@
+// playfield_grid.hpp - Grilla de fons del playfield (línies verdes fosques)
+// © 2026 JailDesigner
+
+#pragma once
+
+#include "core/rendering/render_context.hpp"
+
+namespace Graphics {
+
+    // Pinta una graella interior dins de Defaults::Zones::PLAYAREA.
+    // Cel·les quadrades; el nombre de columnes és fix (Defaults::Grid::COLUMNS),
+    // les files es deriven del que cap dins de l'altura.
+    // Color: oscil·lador global (mateix to que el border); brightness fixa al 25%.
+    class PlayfieldGrid {
+       public:
+        explicit PlayfieldGrid(Rendering::Renderer* renderer);
+        void draw() const;
+
+       private:
+        Rendering::Renderer* renderer_;
+    };
+
+}  // namespace Graphics