Fixed collision detection in probes

This was a problem before when the probe hit an object that was further than
another object first. Now we traverse all objects all the time to find the
closest one. \o/

robot_test.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+	v "bitbucket.org/hackerbots/vector"
+	"math"
+	"testing"
+)
+
+func TestCollision(t *testing.T) {
+	tests := []struct {
+		g         game
+		r         Robot
+		target    v.Vector2d
+		location  *v.Point2d
+		collision bool
+	}{
+		// should intersect with first box
+		{
+			g: game{
+				width:  800,
+				height: 400,
+				obstacles: []Obstacle{
+					Obstacle{
+						Bounds: v.AABB2d{
+							v.Point2d{200, 100},
+							v.Point2d{300, 200},
+						},
+					},
+					Obstacle{
+						Bounds: v.AABB2d{
+							v.Point2d{400, 200},
+							v.Point2d{600, 300},
+						},
+					},
+				},
+			},
+			r: Robot{
+				Position: v.Point2d{100, 100},
+				// Heading:  v.Vector2d{1, 1},
+			},
+			target:    v.Vector2d{900, 350},
+			location:  &v.Point2d{200, 138.88889},
+			collision: true,
+		},
+		// shouldn't intersect at all
+		{
+			g: game{
+				width:  800,
+				height: 400,
+				obstacles: []Obstacle{
+					Obstacle{
+						Bounds: v.AABB2d{
+							v.Point2d{200, 100},
+							v.Point2d{300, 200},
+						},
+					},
+				},
+			},
+			r: Robot{
+				Position: v.Point2d{100, 100},
+			},
+			target:    v.Vector2d{0, 0},
+			collision: false,
+		},
+	}
+	for _, test := range tests {
+		collision, location, _ := test.r.checkCollisions(&test.g, test.target)
+		if collision != test.collision {
+			t.Errorf("expected: %t, actual: %t", test.collision, collision)
+		}
+		if test.location == nil {
+			if location != nil {
+				t.Errorf("expected: %+v, actual: %+v", test.location, location)
+			}
+		}
+		if test.location != nil {
+			if location == nil {
+				t.Errorf("expected: %+v, actual: %+v", test.location, location)
+			} else {
+				if math.Abs(float64(location.X-test.location.X)) > 1e-4 || math.Abs(float64(location.Y-test.location.Y)) > 1e-4 {
+					t.Errorf("expected: %+v, actual: %+v", test.location, location)
+				}
+			}
+		}
+	}
+}
+
+// XXX
+func TestBotBotCollisions(t *testing.T) {
+	t.Skip("NYI")
+}