Map entity rework - vectors in mapEntity (#579)

* Fixed NaN on normalize 0 vector.

* Tentative implementation in getStepLength.

* mapEntity.TileX/Y removed.

* Fixed Position and Target not being initialised in createMapEntity.

* mapEntity.Position is no longer embedded.

* mapEntity.LocationX/Y no longer used outside map_entity.go.

* mapEntity.subCellX/Y removed.

* mapEntity.LocationX/Y removed.

* mapEntity.OffsetX/Y and TargetX/Y removed.

* Direction method added to Vector, returns 0-64 direction.

* Moved Vector.Direction() to Position.DirectionTo and refactored.

* Renamed RenderOffset from SubCell and tested IsZero.

* d2math.WrapInt added for use with directions.

* Tidied up position and tests.

* Refactored d2common.AdjustWithRemainder into d2mapEntity.

* Tidying up d2mapEntity.

* Final cleanup.

* Lint warnings.

* Spelling correction.

d2common/d2math/d2vector/position.go

@@ -3,16 +3,24 @@ package d2vector
 import (
 	"fmt"
 	"math"
+
+	"github.com/OpenDiablo2/OpenDiablo2/d2common/d2math"
 )
 
-const subTilesPerTile float64 = 5
+const (
+	subTilesPerTile          float64 = 5  // The number of sub tiles that make up one map tile.
+	entityDirectionCount     float64 = 64 // The Diablo equivalent of 360 degrees when dealing with entity rotation.
+	entityDirectionIncrement float64 = 8  // One 8th of 64. There 8 possible facing directions for entities.
+	// Note: there should be 16 facing directions for entities. See Position.DirectionTo()
+)
 
-// Position is a vector in world space. The stored value is  the one returned by Position.World()
+// Position is a vector in world space. The stored value is the sub tile position.
 type Position struct {
 	Vector
 }
 
-// NewPosition creates a new Position at the given float64 world position.
+// NewPosition returns a Position struct with the given sub tile coordinates where 1 = 1 sub tile, with a fractional
+// offset.
 func NewPosition(x, y float64) Position {
 	p := Position{NewVector(x, y)}
 	p.checkValues()
@@ -20,15 +28,7 @@ func NewPosition(x, y float64) Position {
 	return p
 }
 
-// EntityPosition returns a Position struct based on the given entity spawn point.
+// Set sets this position to the given sub tile coordinates where 1 = 1 sub tile, with a fractional offset.
-// The value given should be the one set in d2mapstamp.Stamp.Entities:
-// (tileOffsetX*5)+object.X, (tileOffsetY*5)+object.Y
-// TODO: This probably doesn't support positions in between sub tiles so will only be suitable for spawning entities from map generation, not for multiplayer syncing.
-func EntityPosition(x, y int) Position {
-	return NewPosition(float64(x)/5, float64(y)/5)
-}
-
-// Set sets this position to the given x and y values.
 func (p *Position) Set(x, y float64) {
 	p.x, p.y = x, y
 	p.checkValues()
@@ -44,48 +44,45 @@ func (p *Position) checkValues() {
 	}
 }
 
-// World is the position, where 1 = one map tile.
+// World is the exact position where 1 = one map tile and 0.2 = one sub tile.
-// unused
 func (p *Position) World() *Vector {
-	return &p.Vector
+	c := p.Clone()
+	return c.DivideScalar(subTilesPerTile)
 }
 
-// Tile is the tile position, always a whole number. (tileX, tileY)
+// Tile is the position of the current map tile. It is the floor of World(), always a whole number.
 func (p *Position) Tile() *Vector {
-	c := p.World().Clone()
+	return p.World().Floor()
-	return c.Floor()
 }
 
-// TileOffset is the offset from the tile position, always < 1.
+// RenderOffset is the offset in sub tiles from the curren tile, + 1. This places the vector at the bottom vertex of an
-// unused
+// isometric diamond visually representing one sub tile. Sub tile indices increase to the lower right diagonal ('down')
-func (p *Position) TileOffset() *Vector {
+// and to the lower left diagonal ('left') of the isometric grid. This renders the target one index above which visually
-	c := p.World().Clone()
+// is one tile below.
-	return c.Subtract(p.Tile())
+func (p *Position) RenderOffset() *Vector {
+	return p.subTileOffset().AddScalar(1)
 }
 
-// SubWorld is the position, where 5 = one map tile. (locationX, locationY)
+// SubTileOffset is the offset from the current map tile in sub tiles.
-func (p *Position) SubWorld() *Vector {
+func (p *Position) subTileOffset() *Vector {
-	c := p.World().Clone()
+	t := p.Tile().Scale(subTilesPerTile)
-	return c.Scale(subTilesPerTile)
+	c := p.Clone()
+
+	return c.Subtract(t)
 }
 
-// SubTile is the tile position in sub tiles, always a multiple of 5.
+// DirectionTo returns the entity direction from this vector to the given vector.
-// unused
+func (v *Vector) DirectionTo(target Vector) int {
-func (p *Position) SubTile() *Vector {
+	direction := target.Clone()
-	return p.Tile().Scale(subTilesPerTile)
+	direction.Subtract(v)
-}
 
-// SubTileOffset is the offset from the sub tile position in sub tiles, always < 1.
+	angle := direction.SignedAngle(VectorRight())
-// unused
+	radiansPerDirection := d2math.RadFull / entityDirectionCount
-func (p *Position) SubTileOffset() *Vector {
-	return p.SubWorld().Subtract(p.SubTile())
-}
 
-// TODO: understand this and maybe improve/remove it
+	// Note: The direction is always one increment out so we must subtract one increment.
-// SubTileOffset() + 1. It's used for rendering. It seems to always do this:
+	// This might not work when we implement all 16 directions (as of this writing entities can only face one of 8
-// 	v.offsetX+int((v.subcellX-v.subcellY)*16),
+	// directions). See entityDirectionIncrement.
-//	v.offsetY+int(((v.subcellX+v.subcellY)*8)-5),
+	newDirection := int((angle / radiansPerDirection) - entityDirectionIncrement)
-// ^ Maybe similar to Viewport.OrthoToWorld? (subCellX, subCellY)
+
-func (p *Position) SubCell() *Vector {
+	return d2math.WrapInt(newDirection, int(entityDirectionCount))
-	return p.SubTileOffset().AddScalar(1)
 }

d2common/d2math/d2vector/position_test.go

@@ -6,18 +6,18 @@ import (
 	"testing"
 )
 
-func TestEntityPosition(t *testing.T) {
+func TestNewPosition(t *testing.T) {
 	x, y := rand.Intn(1000), rand.Intn(1000)
-	pos := EntityPosition(x, y)
 	locX, locY := float64(x), float64(y)
+	pos := NewPosition(locX, locY)
 
 	// old coordinate values			Position equivalent
 	locationX := locX                 // .SubWord().X()
 	locationY := locY                 // .SubWord().Y()
 	tileX := float64(x / 5)           // .Tile().X()
 	tileY := float64(y / 5)           // .Tile().Y()
-	subcellX := 1 + math.Mod(locX, 5) // .SubCell().X()
+	subcellX := 1 + math.Mod(locX, 5) // .RenderOffset().X()
-	subcellY := 1 + math.Mod(locY, 5) // .SubCell().Y()
+	subcellY := 1 + math.Mod(locY, 5) // .RenderOffset().Y()
 
 	want := NewVector(tileX, tileY)
 	got := pos.Tile()
@@ -27,14 +27,14 @@ func TestEntityPosition(t *testing.T) {
 	}
 
 	want = NewVector(subcellX, subcellY)
-	got = pos.SubCell()
+	got = pos.RenderOffset()
 
 	if !got.Equals(want) {
-		t.Errorf("sub cell position should match old value: got %s: want %s", got, want)
+		t.Errorf("render offset position should match old value: got %s: want %s", got, want)
 	}
 
 	want = NewVector(locationX, locationY)
-	got = pos.SubWorld()
+	got = &pos.Vector
 
 	if !got.Equals(want) {
 		t.Errorf("sub tile position should match old value: got %s: want %s", got, want)
@@ -51,47 +51,29 @@ func validate(description string, t *testing.T, original, got, want, unchanged V
 	}
 }
 
-func TestTile(t *testing.T) {
+func TestPosition_World(t *testing.T) {
-	p := NewPosition(1.6, 1.6)
+	p := NewPosition(5, 10)
+	unchanged := p.Clone()
+	got := p.World()
+	want := NewVector(1, 2)
+
+	validate("world position", t, p.Vector, *got, want, unchanged)
+}
+
+func TestPosition_Tile(t *testing.T) {
+	p := NewPosition(23, 24)
+	unchanged := p.Clone()
 	got := p.Tile()
-	want := NewVector(1, 1)
+	want := NewVector(4, 4)
-	unchanged := NewVector(1.6, 1.6)
 
 	validate("tile position", t, p.Vector, *got, want, unchanged)
 }
 
-func TestTileOffset(t *testing.T) {
+func TestPosition_RenderOffset(t *testing.T) {
-	p := NewPosition(1.6, 1.6)
+	p := NewPosition(12.1, 14.2)
-	got := p.TileOffset()
+	unchanged := p.Clone()
-	want := NewVector(0.6, 0.6)
+	got := p.RenderOffset()
-	unchanged := NewVector(1.6, 1.6)
+	want := NewVector(3.1, 5.2)
-
-	validate("tile offset", t, p.Vector, *got, want, unchanged)
-}
-
-func TestSubWorld(t *testing.T) {
-	p := NewPosition(1, 1)
-	got := p.SubWorld()
-	want := NewVector(5, 5)
-	unchanged := NewVector(1, 1)
-
-	validate("sub tile world position", t, p.Vector, *got, want, unchanged)
-}
-
-func TestSubTile(t *testing.T) {
-	p := NewPosition(1, 1)
-	got := p.SubTile()
-	want := NewVector(5, 5)
-	unchanged := NewVector(1, 1)
-
-	validate("sub tile with offset", t, p.Vector, *got, want, unchanged)
-}
-
-func TestSubTileOffset(t *testing.T) {
-	p := NewPosition(1.1, 1.1)
-	got := p.SubTileOffset()
-	want := NewVector(0.5, 0.5)
-	unchanged := NewVector(1.1, 1.1)
 
 	validate("offset from sub tile", t, p.Vector, *got, want, unchanged)
 }

d2common/d2math/d2vector/vector.go

@@ -49,6 +49,11 @@ func (v *Vector) CompareApprox(o Vector) (x, y int) {
 		d2math.CompareFloat64Fuzzy(v.y, o.y)
 }
 
+// IsZero returns true if this vector's values are both exactly zero.
+func (v *Vector) IsZero() bool {
+	return v.x == 0 && v.y == 0
+}
+
 // Set the vector values to the given float64 values.
 func (v *Vector) Set(x, y float64) *Vector {
 	v.x = x
@@ -95,7 +100,7 @@ func (v *Vector) Add(o *Vector) *Vector {
 	return v
 }
 
-// AddScalar the given vector to this vector.
+// AddScalar the given value to both values of this vector.
 func (v *Vector) AddScalar(s float64) *Vector {
 	v.x += s
 	v.y += s
@@ -135,7 +140,7 @@ func (v *Vector) Divide(o *Vector) *Vector {
 	return v
 }
 
-// DivideScalar divides this vector by the given float64 value.
+// DivideScalar divides both values of this vector by the given value.
 func (v *Vector) DivideScalar(s float64) *Vector {
 	v.x /= s
 	v.y /= s
@@ -219,6 +224,10 @@ func (v *Vector) Cross(o Vector) float64 {
 // Normalize sets the vector length to 1 without changing the direction. The normalized vector may be scaled by the
 // float64 return value to restore it's original length.
 func (v *Vector) Normalize() float64 {
+	if v.IsZero() {
+		return 0
+	}
+
 	multiplier := 1 / v.Length()
 	v.Scale(multiplier)
 
@@ -228,6 +237,10 @@ func (v *Vector) Normalize() float64 {
 // Angle computes the unsigned angle in radians from this vector to the given vector. This angle will never exceed half
 // a full circle. For angles describing a full circumference use SignedAngle.
 func (v *Vector) Angle(o Vector) float64 {
+	if v.IsZero() || o.IsZero() {
+		return 0
+	}
+
 	from := v.Clone()
 	from.Normalize()
 

d2common/d2math/d2vector/vector_test.go

@@ -77,7 +77,7 @@ func TestEqualsF(t *testing.T) {
 	}
 }
 
-func TestCompareF(t *testing.T) {
+func TestCompareApprox(t *testing.T) {
 	subEpsilon := d2math.Epsilon / 3
 
 	f := NewVector(1+subEpsilon, 1+subEpsilon)
@@ -108,6 +108,20 @@ func TestCompareF(t *testing.T) {
 	}
 }
 
+func TestIsZero(t *testing.T) {
+	testIsZero(NewVector(0, 0), true, t)
+	testIsZero(NewVector(1, 0), false, t)
+	testIsZero(NewVector(0, 1), false, t)
+	testIsZero(NewVector(1, 1), false, t)
+}
+
+func testIsZero(v Vector, want bool, t *testing.T) {
+	got := v.IsZero()
+	if got != want {
+		t.Errorf("%s is zero: want %t: got %t", v, want, got)
+	}
+}
+
 func TestSet(t *testing.T) {
 	v := NewVector(1, 1)
 	want := NewVector(2, 3)
@@ -337,6 +351,14 @@ func TestNormalize(t *testing.T) {
 	v.Scale(reverse)
 
 	evaluateVector(fmt.Sprintf("reverse normalizing of %s", c), want, v, t)
+
+	v = NewVector(0, 0)
+	c = v.Clone()
+	want = NewVector(0, 0)
+
+	v.Normalize()
+
+	evaluateVector(fmt.Sprintf("normalize zero vector should do nothing %s", c), want, v, t)
 }
 
 func TestAngle(t *testing.T) {

d2common/d2math/doc.go

@@ -1,2 +1,2 @@
-// Package d2math provides mathmatical functions not included in Golang's standard math library.
+// Package d2math provides mathematical functions not included in Golang's standard math library.
 package d2math

d2common/d2math/math.go

@@ -14,6 +14,11 @@ const (
 	RadFull float64 = 6.283185253783088
 )
 
+// EqualsApprox returns true if the difference between a and b is less than Epsilon.
+func EqualsApprox(a, b float64) bool {
+	return math.Abs(a-b) < Epsilon
+}
+
 // CompareFloat64Fuzzy returns an integer between -1 and 1 describing
 // the comparison of floats a and b. 0 will be returned if the
 // absolute difference between a and b is less than Epsilon.
@@ -65,3 +70,14 @@ func Lerp(a, b, x float64) float64 {
 func Unlerp(a, b, x float64) float64 {
 	return (x - a) / (b - a)
 }
+
+// WrapInt wraps x to between 0 and max. For example WrapInt(450, 360) would return 90.
+func WrapInt(x, max int) int {
+	wrapped := x % max
+
+	if wrapped < 0 {
+		return max + wrapped
+	}
+
+	return wrapped
+}

d2common/d2math/math_test.go

@@ -4,6 +4,24 @@ import (
 	"testing"
 )
 
+func TestEqualsApprox(t *testing.T) {
+	subEpsilon := Epsilon / 3
+
+	a, b := 1+subEpsilon, 1.0
+	got := EqualsApprox(a, b)
+
+	if !got {
+		t.Errorf("compare %.2f and %.2f: wanted %t: got %t", a, b, true, got)
+	}
+
+	a, b = 1+Epsilon, 1.0
+	got = EqualsApprox(a, b)
+
+	if !got {
+		t.Errorf("compare %.2f and %.2f: wanted %t: got %t", a, b, false, got)
+	}
+}
+
 func TestCompareFloat64Fuzzy(t *testing.T) {
 	subEpsilon := Epsilon / 3
 
@@ -111,3 +129,39 @@ func TestUnlerp(t *testing.T) {
 		t.Errorf(d, x, a, b, want, got)
 	}
 }
+
+func TestWrapInt(t *testing.T) {
+	want := 50
+	a, b := 1050, 100
+	got := WrapInt(a, b)
+
+	d := "wrap %d between 0 and %d: want %d: got %d"
+
+	if got != want {
+		t.Errorf(d, a, b, want, got)
+	}
+
+	want = 270
+	a, b = -1170, 360
+	got = WrapInt(a, b)
+
+	if got != want {
+		t.Errorf(d, a, b, want, got)
+	}
+
+	want = 270
+	a, b = 270, 360
+	got = WrapInt(a, b)
+
+	if got != want {
+		t.Errorf(d, a, b, want, got)
+	}
+
+	want = 90
+	a, b = -270, 360
+	got = WrapInt(a, b)
+
+	if got != want {
+		t.Errorf(d, a, b, want, got)
+	}
+}

d2common/math.go

@@ -73,25 +73,6 @@ func MinInt32(a, b int32) int32 {
 
 // ScreenToIso converts screenspace coordinates to isometric coordinates
 
-// GetAngleBetween returns the angle between two points. 0deg is facing to the right.
-func GetAngleBetween(p1X, p1Y, p2X, p2Y float64) int {
-	deltaY := p1Y - p2Y
-	deltaX := p2X - p1X
-
-	result := math.Atan2(deltaY, deltaX) * (180 / math.Pi)
-	iResult := int(result)
-
-	for iResult < 0 {
-		iResult += 360
-	}
-
-	for iResult >= 360 {
-		iResult -= 360
-	}
-
-	return iResult
-}
-
 // GetRadiansBetween returns the radians between two points. 0rad is facing to the right.
 func GetRadiansBetween(p1X, p1Y, p2X, p2Y float64) float64 {
 	deltaY := p2Y - p1Y
@@ -104,34 +85,3 @@ func GetRadiansBetween(p1X, p1Y, p2X, p2Y float64) float64 {
 func AlmostEqual(a, b, threshold float64) bool {
 	return math.Abs(a-b) <= threshold
 }
-
-// AdjustWithRemainder returns the new adjusted value, as well as any remaining amount after the max
-func AdjustWithRemainder(sourceValue, adjustment, targetvalue float64) (newValue, remainder float64) {
-	if adjustment == 0 || math.Abs(adjustment) < 0.000001 {
-		return sourceValue, 0
-	}
-
-	adjustNegative := adjustment < 0.0
-	maxNegative := targetvalue-sourceValue < 0.0
-
-	if adjustNegative != maxNegative {
-		// FIXME: This shouldn't happen but it happens all the time..
-		return sourceValue, 0
-	}
-
-	finalValue := sourceValue + adjustment
-	if !adjustNegative {
-		if finalValue > targetvalue {
-			diff := finalValue - targetvalue
-			return targetvalue, diff
-		}
-
-		return finalValue, 0
-	}
-
-	if finalValue < targetvalue {
-		return targetvalue, finalValue - targetvalue
-	}
-
-	return finalValue, 0
-}

d2core/d2map/d2mapentity/animated_entity.go

@@ -27,10 +27,12 @@ func CreateAnimatedEntity(x, y int, animation d2interface.Animation) *AnimatedEn
 
 // Render draws this animated entity onto the target
 func (ae *AnimatedEntity) Render(target d2interface.Surface) {
+	renderOffset := ae.Position.RenderOffset()
 	target.PushTranslation(
-		ae.offsetX+int((ae.subcellX-ae.subcellY)*16),
+		int((renderOffset.X()-renderOffset.Y())*16),
-		ae.offsetY+int(((ae.subcellX+ae.subcellY)*8)-5),
+		int(((renderOffset.X()+renderOffset.Y())*8)-5),
 	)
+
 	defer target.Pop()
 	ae.animation.Render(target)
 }

d2core/d2map/d2mapentity/map_entity.go

@@ -1,25 +1,20 @@
 package d2mapentity
 
 import (
-	"math"
+	"github.com/OpenDiablo2/OpenDiablo2/d2common/d2math/d2vector"
 
 	"github.com/OpenDiablo2/OpenDiablo2/d2common"
 	"github.com/OpenDiablo2/OpenDiablo2/d2common/d2astar"
 )
 
 // mapEntity represents an entity on the map that can be animated
-// TODO: Has a coordinate (issue #456)
 type mapEntity struct {
-	LocationX          float64
+	Position d2vector.Position
-	LocationY          float64
+	Target   d2vector.Position
-	TileX, TileY       int     // Coordinates of the tile the unit is within
+
-	subcellX, subcellY float64 // Subcell coordinates within the current tile
+	Speed     float64
-	offsetX, offsetY   int
+	path      []d2astar.Pather
-	TargetX            float64
+	drawLayer int
-	TargetY            float64
-	Speed              float64
-	path               []d2astar.Pather
-	drawLayer          int
 
 	done        func()
 	directioner func(direction int)
@@ -30,14 +25,8 @@ func createMapEntity(x, y int) mapEntity {
 	locX, locY := float64(x), float64(y)
 
 	return mapEntity{
-		LocationX: locX,
+		Position:  d2vector.NewPosition(locX, locY),
-		LocationY: locY,
+		Target:    d2vector.NewPosition(locX, locY),
-		TargetX:   locX,
-		TargetY:   locY,
-		TileX:     x / 5,
-		TileY:     y / 5,
-		subcellX:  1 + math.Mod(locX, 5),
-		subcellY:  1 + math.Mod(locY, 5),
 		Speed:     6,
 		drawLayer: 0,
 		path:      []d2astar.Pather{},
@@ -71,25 +60,9 @@ func (m *mapEntity) GetSpeed() float64 {
 	return m.Speed
 }
 
-func (m *mapEntity) getStepLength(tickTime float64) (float64, float64) {
+// IsAtTarget returns true if the distance between entity and target is almost zero.
-	length := tickTime * m.Speed
-
-	angle := 359 - d2common.GetAngleBetween(
-		m.LocationX,
-		m.LocationY,
-		m.TargetX,
-		m.TargetY,
-	)
-	radians := (math.Pi / 180.0) * float64(angle)
-	oneStepX := length * math.Cos(radians)
-	oneStepY := length * math.Sin(radians)
-
-	return oneStepX, oneStepY
-}
-
-// IsAtTarget returns true if the entity is within a 0.0002 square of it's target and has a path.
 func (m *mapEntity) IsAtTarget() bool {
-	return math.Abs(m.LocationX-m.TargetX) < 0.0001 && math.Abs(m.LocationY-m.TargetY) < 0.0001 && !m.HasPathFinding()
+	return m.Position.EqualsApprox(m.Target.Vector) && !m.HasPathFinding()
 }
 
 // Step moves the entity along it's path by one tick. If the path is complete it calls entity.done() then returns.
@@ -103,27 +76,16 @@ func (m *mapEntity) Step(tickTime float64) {
 		return
 	}
 
-	stepX, stepY := m.getStepLength(tickTime)
+	velocity := m.velocity(tickTime)
 
 	for {
-		if d2common.AlmostEqual(m.LocationX-m.TargetX, 0, 0.0001) {
+		// Add the velocity to the position and set new velocity to remainder
-			stepX = 0
+		applyVelocity(&m.Position.Vector, &velocity, &m.Target.Vector)
-		}
 
-		if d2common.AlmostEqual(m.LocationY-m.TargetY, 0, 0.0001) {
+		// New position is at target
-			stepY = 0
+		if m.Position.EqualsApprox(m.Target.Vector) {
-		}
-
-		m.LocationX, stepX = d2common.AdjustWithRemainder(m.LocationX, stepX, m.TargetX)
-		m.LocationY, stepY = d2common.AdjustWithRemainder(m.LocationY, stepY, m.TargetY)
-
-		m.subcellX = 1 + math.Mod(m.LocationX, 5)
-		m.subcellY = 1 + math.Mod(m.LocationY, 5)
-		m.TileX = int(m.LocationX / 5)
-		m.TileY = int(m.LocationY / 5)
-
-		if d2common.AlmostEqual(m.LocationX, m.TargetX, 0.01) && d2common.AlmostEqual(m.LocationY, m.TargetY, 0.01) {
 			if len(m.path) > 0 {
+				// Set next path node
 				m.SetTarget(m.path[0].(*d2common.PathTile).X*5, m.path[0].(*d2common.PathTile).Y*5, m.done)
 
 				if len(m.path) > 1 {
@@ -132,21 +94,61 @@ func (m *mapEntity) Step(tickTime float64) {
 					m.path = []d2astar.Pather{}
 				}
 			} else {
-				m.LocationX = m.TargetX
+				// End of path.
-				m.LocationY = m.TargetY
+				m.Position.Copy(&m.Target.Vector)
-				m.subcellX = 1 + math.Mod(m.LocationX, 5)
-				m.subcellY = 1 + math.Mod(m.LocationY, 5)
-				m.TileX = int(m.LocationX / 5)
-				m.TileY = int(m.LocationY / 5)
 			}
 		}
 
-		if stepX == 0 && stepY == 0 {
+		if velocity.IsZero() {
 			break
 		}
 	}
 }
 
+// velocity returns a vector describing the change in position this tick.
+func (m *mapEntity) velocity(tickTime float64) d2vector.Vector {
+	length := tickTime * m.Speed
+	v := m.Target.Vector.Clone()
+	v.Subtract(&m.Position.Vector)
+	v.SetLength(length)
+
+	return v
+}
+
+// applyVelocity adds velocity to position. If the new position extends beyond target from the original position, the
+// position is set to the target and velocity is set to the overshot amount.
+func applyVelocity(position, velocity, target *d2vector.Vector) {
+	// Set velocity values to zero if almost zero
+	x, y := position.CompareApprox(*target)
+	vx, vy := velocity.X(), velocity.Y()
+
+	if x == 0 {
+		vx = 0
+	}
+
+	if y == 0 {
+		vy = 0
+	}
+
+	velocity.Set(vx, vy)
+
+	dest := position.Clone()
+	dest.Add(velocity)
+
+	destDistance := position.Distance(dest)
+	targetDistance := position.Distance(*target)
+
+	if destDistance > targetDistance {
+		// Destination overshot target. Set position to target and velocity to overshot amount.
+		position.Copy(target)
+		velocity.Copy(dest.Subtract(target))
+	} else {
+		// At or before target, set position to destination and velocity to zero.
+		position.Copy(&dest)
+		velocity.Set(0, 0)
+	}
+}
+
 // HasPathFinding returns false if the length of the entity movement path is 0.
 func (m *mapEntity) HasPathFinding() bool {
 	return len(m.path) > 0
@@ -154,43 +156,26 @@ func (m *mapEntity) HasPathFinding() bool {
 
 // SetTarget sets target coordinates and changes animation based on proximity and direction.
 func (m *mapEntity) SetTarget(tx, ty float64, done func()) {
-	m.TargetX, m.TargetY = tx, ty
+	m.Target.Set(tx, ty)
 	m.done = done
 
 	if m.directioner != nil {
-		angle := 359 - d2common.GetAngleBetween(
+		d := m.Position.DirectionTo(m.Target.Vector)
-			m.LocationX,
+
-			m.LocationY,
+		m.directioner(d)
-			tx,
-			ty,
-		)
-		m.directioner(angleToDirection(float64(angle)))
 	}
 }
 
-func angleToDirection(angle float64) int {
+// GetPosition returns the entity's current tile position, always a whole number.
-	degreesPerDirection := 360.0 / 64.0
+func (m *mapEntity) GetPosition() (x, y float64) {
-	offset := 45.0 - (degreesPerDirection / 2)
+	t := m.Position.Tile()
-
+	return t.X(), t.Y()
-	newDirection := int((angle - offset) / degreesPerDirection)
-
-	if newDirection >= 64 {
-		newDirection = newDirection - 64
-	} else if newDirection < 0 {
-		newDirection = 64 + newDirection
-	}
-
-	return newDirection
 }
 
-// GetPosition returns the entity's current tile position.
+// GetPositionF returns the entity's current tile position where 0.2 is one sub tile.
-func (m *mapEntity) GetPosition() (float64, float64) {
+func (m *mapEntity) GetPositionF() (x, y float64) {
-	return float64(m.TileX), float64(m.TileY)
+	w := m.Position.World()
-}
+	return w.X(), w.Y()
-
-// GetPositionF returns the entity's current sub tile position.
-func (m *mapEntity) GetPositionF() (float64, float64) {
-	return float64(m.TileX) + (float64(m.subcellX) / 5.0), float64(m.TileY) + (float64(m.subcellY) / 5.0)
 }
 
 // Name returns the NPC's in-game name (e.g. "Deckard Cain") or an empty string if it does not have a name

d2core/d2map/d2mapentity/missile.go

@@ -32,7 +32,7 @@ func CreateMissile(x, y int, record *d2datadict.MissileRecord) (*Missile, error)
 	}
 
 	animation.SetEffect(d2enum.DrawEffectModulate)
-	//animation.SetPlaySpeed(float64(record.Animation.AnimationSpeed))
+	// animation.SetPlaySpeed(float64(record.Animation.AnimationSpeed))
 	animation.SetPlayLoop(record.Animation.LoopAnimation)
 	animation.PlayForward()
 	entity := CreateAnimatedEntity(x, y, animation)
@@ -51,8 +51,8 @@ func CreateMissile(x, y int, record *d2datadict.MissileRecord) (*Missile, error)
 func (m *Missile) SetRadians(angle float64, done func()) {
 	r := float64(m.record.Range)
 
-	x := m.LocationX + (r * math.Cos(angle))
+	x := m.Position.X() + (r * math.Cos(angle))
-	y := m.LocationY + (r * math.Sin(angle))
+	y := m.Position.Y() + (r * math.Sin(angle))
 
 	m.SetTarget(x, y, done)
 }

d2core/d2map/d2mapentity/npc.go

@@ -72,10 +72,12 @@ func selectEquip(slice []string) string {
 
 // Render renders this entity's animated composite.
 func (v *NPC) Render(target d2interface.Surface) {
+	renderOffset := v.Position.RenderOffset()
 	target.PushTranslation(
-		v.offsetX+int((v.subcellX-v.subcellY)*16),
+		int((renderOffset.X()-renderOffset.Y())*16),
-		v.offsetY+int(((v.subcellX+v.subcellY)*8)-5),
+		int(((renderOffset.X()+renderOffset.Y())*8)-5),
 	)
+
 	defer target.Pop()
 	v.composite.Render(target)
 }

d2core/d2map/d2mapentity/player.go

@@ -144,10 +144,12 @@ func (v *Player) Advance(tickTime float64) {
 
 // Render renders the animated composite for this entity.
 func (v *Player) Render(target d2interface.Surface) {
+	renderOffset := v.Position.RenderOffset()
 	target.PushTranslation(
-		v.offsetX+int((v.subcellX-v.subcellY)*16),
+		int((renderOffset.X()-renderOffset.Y())*16),
-		v.offsetY+int(((v.subcellX+v.subcellY)*8)-5),
+		int(((renderOffset.X()+renderOffset.Y())*8)-5),
 	)
+
 	defer target.Pop()
 	v.composite.Render(target)
 	// v.nameLabel.X = v.offsetX
@@ -180,6 +182,7 @@ func (v *Player) GetAnimationMode() d2enum.PlayerAnimationMode {
 	return d2enum.PlayerAnimationModeNeutral
 }
 
+// SetAnimationMode sets the Composite's animation mode weapon class and direction.
 func (v *Player) SetAnimationMode(animationMode d2enum.PlayerAnimationMode) error {
 	return v.composite.SetMode(animationMode, v.composite.GetWeaponClass())
 }

d2game/d2gamescreen/game.go

@@ -117,7 +117,9 @@ func (v *Game) Advance(tickTime float64) error {
 	if v.ticksSinceLevelCheck > 1.0 {
 		v.ticksSinceLevelCheck = 0
 		if v.localPlayer != nil {
-			tile := v.gameClient.MapEngine.TileAt(v.localPlayer.TileX, v.localPlayer.TileY)
+			tilePosition := v.localPlayer.Position.Tile()
+			tile := v.gameClient.MapEngine.TileAt(int(tilePosition.X()), int(tilePosition.Y()))
+
 			if tile != nil {
 				musicInfo := d2common.GetMusicDef(tile.RegionType)
 				v.audioProvider.PlayBGM(musicInfo.MusicFile)
@@ -142,7 +144,8 @@ func (v *Game) Advance(tickTime float64) error {
 
 	// Update the camera to focus on the player
 	if v.localPlayer != nil && !v.gameControls.FreeCam {
-		rx, ry := v.mapRenderer.WorldToOrtho(v.localPlayer.LocationX/5, v.localPlayer.LocationY/5)
+		worldPosition := v.localPlayer.Position.World()
+		rx, ry := v.mapRenderer.WorldToOrtho(worldPosition.X(), worldPosition.Y())
 		v.mapRenderer.MoveCameraTo(rx, ry)
 	}
 
@@ -169,10 +172,9 @@ func (v *Game) bindGameControls() {
 
 // OnPlayerMove sends the player move action to the server
 func (v *Game) OnPlayerMove(x, y float64) {
-	heroPosX := v.localPlayer.LocationX / 5.0
+	worldPosition := v.localPlayer.Position.World()
-	heroPosY := v.localPlayer.LocationY / 5.0
 
-	err := v.gameClient.SendPacketToServer(d2netpacket.CreateMovePlayerPacket(v.gameClient.PlayerId, heroPosX, heroPosY, x, y))
+	err := v.gameClient.SendPacketToServer(d2netpacket.CreateMovePlayerPacket(v.gameClient.PlayerId, worldPosition.X(), worldPosition.Y(), x, y))
 	if err != nil {
 		fmt.Printf("failed to send MovePlayer packet to the server, playerId: %s, x: %g, x: %g\n", v.gameClient.PlayerId, x, y)
 	}

d2networking/d2client/game_client.go

@@ -111,7 +111,8 @@ func (g *GameClient) OnPacketReceived(packet d2netpacket.NetPacket) error {
 		path, _, _ := g.MapEngine.PathFind(movePlayer.StartX, movePlayer.StartY, movePlayer.DestX, movePlayer.DestY)
 		if len(path) > 0 {
 			player.SetPath(path, func() {
-				tile := g.MapEngine.TileAt(player.TileX, player.TileY)
+				tilePosition := player.Position.Tile()
+				tile := g.MapEngine.TileAt(int(tilePosition.X()), int(tilePosition.Y()))
 				if tile == nil {
 					return
 				}
@@ -135,8 +136,8 @@ func (g *GameClient) OnPacketReceived(packet d2netpacket.NetPacket) error {
 		player.ClearPath()
 		// currently hardcoded to missile skill
 		missile, err := d2mapentity.CreateMissile(
-			int(player.LocationX),
+			int(player.Position.X()),
-			int(player.LocationY),
+			int(player.Position.Y()),
 			d2datadict.Missiles[playerCast.SkillID],
 		)
 		if err != nil {
@@ -144,8 +145,8 @@ func (g *GameClient) OnPacketReceived(packet d2netpacket.NetPacket) error {
 		}
 
 		rads := d2common.GetRadiansBetween(
-			player.LocationX,
+			player.Position.X(),
-			player.LocationY,
+			player.Position.Y(),
 			playerCast.TargetX*5,
 			playerCast.TargetY*5,
 		)