Prevent ships from going near the arena border

TODO

@@ -22,14 +22,13 @@
 * Arena: add auto-move to attack
 * Arena: fix effects originating from real ship location instead of current sprite (when AI fires then moves)
 * Arena: add engine trail
-* Arena: draw move exclusion circles (only on clonflict or in tactical mode ?)
+* Arena: draw move exclusion circles and border (in move targetting only)
 * Remove "initial events" injection
 * Fix capacity limit effect not refreshing associated value (for example, on "limit power capacity to 3", potential "power" value change is not broadcast)
 * Actions: show power usage/recovery in power bar, on action hover
 * Actions: fix targetting not resetting when using keyboard shortcuts
 * Suspend AI operation when the game is paused (window not focused)
 * Add actions with cost dependent of distance (like current move actions)
-* Keep move and drone actions out of arena borders
 * Find incentives to move from starting position
 * Outcome: disable the loot button if there is no loot
 * Ensure that tweens and particle emitters get destroyed once animation is done (or view changes)

src/core/Target.spec.ts

@@ -52,5 +52,11 @@ module TS.SpaceTac.Specs {
             expect(target.moveOutOfCircle(8, 5, 6, 0, 5)).toEqual(Target.newFromLocation(2, 5));
             expect(target.moveOutOfCircle(2, 5, 6, 10, 5)).toEqual(Target.newFromLocation(8, 5));
         });
+
+        it("keeps a target inside a rectangle", () => {
+            var target = Target.newFromLocation(5, 5);
+            expect(target.keepInsideRectangle(0, 0, 10, 10, 0, 0)).toBe(target);
+            expect(target.keepInsideRectangle(8, 0, 13, 10, 10, 5)).toEqual(Target.newFromLocation(8, 5));
+        });
     });
 }

src/core/Target.ts

@@ -121,5 +121,36 @@ module TS.SpaceTac {
                 }
             }
         }
+
+        /**
+         * Keep the target inside a rectangle
+         * 
+         * May return the original target if it's already inside the rectangle
+         */
+        keepInsideRectangle(xmin: number, ymin: number, xmax: number, ymax: number, sourcex: number, sourcey: number): Target {
+            let length = this.getDistanceTo({ x: sourcex, y: sourcey });
+            let result: Target = this;
+            if (result.x < xmin) {
+                let factor = (xmin - sourcex) / (result.x - sourcex);
+                length *= factor;
+                result = result.constraintInRange(sourcex, sourcey, length);
+            }
+            if (result.x > xmax) {
+                let factor = (xmax - sourcex) / (result.x - sourcex);
+                length *= factor;
+                result = result.constraintInRange(sourcex, sourcey, length);
+            }
+            if (result.y < ymin) {
+                let factor = (ymin - sourcey) / (result.y - sourcey);
+                length *= factor;
+                result = result.constraintInRange(sourcex, sourcey, length);
+            }
+            if (result.y > ymax) {
+                let factor = (ymax - sourcey) / (result.y - sourcey);
+                length *= factor;
+                result = result.constraintInRange(sourcex, sourcey, length);
+            }
+            return result;
+        }
     }
 }

src/core/actions/MoveAction.ts

@@ -59,9 +59,15 @@ module TS.SpaceTac {
             var max_distance = this.getRangeRadius(ship);
             target = target.constraintInRange(ship.arena_x, ship.arena_y, max_distance);
 
-            // Apply collision prevention
             let battle = ship.getBattle();
             if (battle) {
+                // Keep out of arena borders
+                let border = this.safety_distance * 0.5;
+                target = target.keepInsideRectangle(border, border,
+                    battle.width - border, battle.height - border,
+                    ship.arena_x, ship.arena_y);
+
+                // Apply collision prevention
                 let ships = imaterialize(ifilter(battle.iships(true), s => s !== ship));
                 ships = ships.sort((a, b) => cmp(a.getDistanceTo(ship), b.getDistanceTo(ship), true));
                 ships.forEach(s => {