Add examples catalog with subcommand dispatch

- Extract game engine from package main to engine/ library package
- Create examples/ package with registry, Entry type, and BuilderDeps
- Register default world as an example (moved from main())
- Add combat example: two teams of units facing each other
- Rewrite main.go as thin dispatch: go run . example [name]
- Update README with examples catalog one-liner

1 files changed, 127 insertions, 0 deletions

diff --git a/engine/draw.go b/engine/draw.go
new file mode 100644
index 0000000..ca605ce
--- /dev/null
+++ b/engine/draw.go
@@ -0,0 +1,127 @@
+package engine
+
+import (
+	"fmt"
+	"image/color"
+
+	"age_of_empires/ecs"
+	"age_of_empires/physics"
+	"age_of_empires/selection"
+
+	"github.com/hajimehoshi/ebiten/v2"
+	"github.com/hajimehoshi/ebiten/v2/text/v2"
+	"github.com/hajimehoshi/ebiten/v2/vector"
+)
+
+func (g *Game) font(size float64) *text.GoTextFace {
+	f := &text.GoTextFace{Source: g.FaceSource, Size: size}
+	f.SetVariation(text.MustParseTag("wght"), 500)
+	return f
+}
+
+func (g *Game) Draw(screen *ebiten.Image) {
+	sx, sy := ebiten.CursorPosition()
+	cursor := g.Camera.ScreenToWorld(sx, sy)
+	screenCursor := physics.Point{X: sx, Y: sy}
+	screen.Fill(soilColor)
+
+	camGeoM := g.Camera.GeoM()
+
+	required := ecs.CM_Image | ecs.CM_Position
+	for i, mask := range g.Mask {
+		if mask&required == required {
+			position := g.Position[i]
+			image := g.Image[i]
+			op := &ebiten.DrawImageOptions{}
+			op.GeoM.Translate(float64(position.X), float64(position.Y))
+			op.GeoM.Concat(camGeoM)
+			screen.DrawImage(image, op)
+			if mask&ecs.CM_Selectable == ecs.CM_Selectable {
+				selectable := g.Selectable[i]
+				if selectable.IsSelected {
+					opt := &ebiten.DrawImageOptions{}
+					opt.GeoM.Translate(float64(position.X-selection.HaloWidth/2), float64(position.Y-selection.HaloWidth/2))
+					opt.GeoM.Concat(camGeoM)
+					screen.DrawImage(selectable.Halo, opt)
+					if mask&ecs.CM_ResourceSource == ecs.CM_ResourceSource {
+						source := g.ResourceSource[i]
+						resourceText := fmt.Sprintf("%d", source.Remaining)
+						op := &text.DrawOptions{}
+						op.GeoM.Translate(float64(position.X+5), float64(position.Y+30))
+						op.GeoM.Concat(camGeoM)
+						op.ColorScale.ScaleWithColor(color.White)
+						text.Draw(screen, resourceText, g.font(40), op)
+					}
+					if mask&ecs.CM_Spawn == ecs.CM_Spawn {
+						spawn := g.Spawn[i]
+						spawnText := fmt.Sprintf("%d", len(spawn.Requests))
+						op := &text.DrawOptions{}
+						op.GeoM.Translate(float64(position.X+5), float64(position.Y+70))
+						op.GeoM.Concat(camGeoM)
+						op.ColorScale.ScaleWithColor(color.White)
+						text.Draw(screen, spawnText, g.font(40), op)
+						if spawn.SpawnTarget.Ok {
+							spawnTarget := spawn.SpawnTarget.Value
+							ssx, ssy := g.Camera.WorldToScreen(spawnTarget)
+							offset := 50 * float32(g.Camera.Zoom)
+							vector.DrawFilledCircle(screen, float32(ssx)+offset, float32(ssy)+offset, 30*float32(g.Camera.Zoom), Red, true)
+						}
+					}
+					if mask&ecs.CM_Move == ecs.CM_Move {
+						move := g.Move[i]
+						dx := image.Bounds().Dx() / 2
+						dy := image.Bounds().Dy() / 2
+						last := position
+						strokeW := 10.0 * float32(g.Camera.Zoom)
+						for _, point := range move.Path {
+							lsx, lsy := g.Camera.WorldToScreen(physics.Point{X: last.X + dx, Y: last.Y + dy})
+							psx, psy := g.Camera.WorldToScreen(physics.Point{X: point.X + dx, Y: point.Y + dy})
+							vector.StrokeLine(screen, float32(lsx), float32(lsy), float32(psx), float32(psy), strokeW, color.RGBA{256 * 3 / 16, 256 * 3 / 16, 256 * 3 / 16, 256 / 4}, true)
+							last = point
+						}
+					}
+				}
+			}
+		}
+	}
+	if g.GlobalSelection.IsActive(cursor) {
+		g.GlobalSelection.Draw(screen, screenCursor)
+	}
+
+	drawTopBanner(screen, g)
+
+	if len(g.GlobalSelection.Selected) > 0 {
+		drawBottomBanner(screen, g)
+	}
+}
+
+func drawTopBanner(screen *ebiten.Image, g *Game) {
+	screenBounds := screen.Bounds()
+	bannerHeight := float32(50)
+	vector.DrawFilledRect(screen, 0, 0, float32(screenBounds.Dx()), bannerHeight, color.White, true)
+	resourceText := fmt.Sprintf("Resources: %d", g.ResourceAmount)
+	op := &text.DrawOptions{}
+	op.GeoM.Translate(8, 6)
+	op.ColorScale.ScaleWithColor(color.Black)
+	text.Draw(screen, resourceText, g.font(30), op)
+}
+
+func drawBottomBanner(screen *ebiten.Image, g *Game) {
+	screenBounds := screen.Bounds()
+	bannerHeight := float32(40)
+	bannerTop := screenBounds.Dy() - int(bannerHeight)
+	vector.DrawFilledRect(screen, 0, float32(bannerTop), float32(screenBounds.Dx()), bannerHeight, color.White, true)
+
+	shortcuts := "[Right-click] Action  [Q] Patrol  [Esc] Deselect"
+	for _, i := range g.GlobalSelection.Selected {
+		if g.Mask[i]&ecs.CM_Spawn == ecs.CM_Spawn {
+			shortcuts += "  [S] Spawn unit"
+			break
+		}
+	}
+
+	op := &text.DrawOptions{}
+	op.GeoM.Translate(8, float64(float32(bannerTop)+6))
+	op.ColorScale.ScaleWithColor(color.Black)
+	text.Draw(screen, shortcuts, g.font(22), op)
+}