Grid system & simple physics

1 files changed, 73 insertions, 0 deletions

diff --git a/src/systems/gridSystem.js b/src/systems/gridSystem.js
new file mode 100644
index 0000000..05ce17e
--- /dev/null
+++ b/src/systems/gridSystem.js
@@ -0,0 +1,73 @@
+game.system.GridSystem = ({ xDim, yDim, canvasWidth, canvasHeight }) => {
+  const entitiesGrid = Array(yDim).fill(null).map(() => Array(xDim).fill(null).map(() => new Map()));
+
+  const gridWidth = canvasWidth / xDim;
+  const gridHeight = canvasHeight / yDim;
+
+  const gameCoordsToGrid = ({ x, y }) => {
+    return { x: Math.floor((x+gridWidth/2) / canvasWidth * xDim), y: Math.floor((y+gridHeight/2) / canvasHeight * yDim) };
+  };
+
+  const gridCoordsToGame = ({ x, y }) => {
+    return { x: x * gridWidth, y: y * gridHeight };
+  };
+
+  const rebuildGrid = (entities) => {
+    let changedIds = new Set();
+    entities.map(entity => {
+      const { x, y } = entity.components.gridPosition;
+      if (!entitiesGrid[y][x].has(entity.id)) {
+        changedIds.add(entity.id);
+      }
+    });
+    entitiesGrid.forEach((row) => row.forEach((entitiesInCell) => {
+      for (let id of entitiesInCell.keys()) {
+        if (changedIds.has(id)) {
+          entitiesInCell.delete(id);
+        }
+      }
+    }));
+    changedIds.forEach(id => {
+      const entity = entities[id];
+      const { x, y } = entity.components.gridPosition;
+      entitiesGrid[y][x].set(entity.id, entity);
+    });
+  }
+
+  const update = (_elapsedTime, entities) => {
+    const gridEntities = Object.keys(entities).filter((x) => entities[x].hasComponent("gridPosition")).map((x) => entities[x]);
+    rebuildGrid(gridEntities);
+    gridEntities.map((entity) => {
+      if (entity.hasComponent("appearance")) {
+        entity.components.appearance.width = canvasWidth / xDim;
+        entity.components.appearance.height = canvasHeight / yDim;
+      }
+      if (entity.hasComponent("position")) {
+        const newGridCoords = gameCoordsToGrid(entity.components.position);
+        const oldGridCoords = entity.components.gridPosition;
+        if (!equivalence(newGridCoords, oldGridCoords)) {
+          const momentumVector = unitize({ 
+            dx: newGridCoords.x - oldGridCoords.x,
+            dy: newGridCoords.y - oldGridCoords.y,
+          });
+
+          // TODO: Loop in momentum direction until we find an entity that does not have "push" component
+          entity.components.gridPosition.x = entity.components.gridPosition.x + momentumVector.dx;
+          entity.components.gridPosition.y = entity.components.gridPosition.y + momentumVector.dy;
+
+          entity.components.position = {
+            ...entity.components.position,
+            ...gridCoordsToGame(entity.components.gridPosition)
+          };
+
+          if (entity.hasComponent("momentum")) {
+            entity.components.momentum.dx = 0;
+            entity.components.momentum.dy = 0;
+          }
+        }
+      }
+    });
+  };
+
+  return { entitiesGrid, gameCoordsToGrid, gridCoordsToGame, update, gridWidth, gridHeight };
+};
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