examples/triangles: Draw polygons

examples/triangles/main.go

@@ -24,6 +24,7 @@ import (
 
 	"github.com/hajimehoshi/ebiten"
 	"github.com/hajimehoshi/ebiten/ebitenutil"
+	"github.com/hajimehoshi/ebiten/inpututil"
 )
 
 const (
@@ -41,19 +42,21 @@ func init() {
 
 var (
 	vertices []ebiten.Vertex
-	indices  []uint16
+
+	numVerticesToDraw     = 10
+	prevNumVerticesToDraw = 0
 )
 
-func init() {
+func genVertices(num int) []ebiten.Vertex {
 	const (
-		num     = 120
 		centerX = screenWidth / 2
 		centerY = screenHeight / 2
 		r       = 160
 	)
 
+	vs := []ebiten.Vertex{}
 	for i := 0; i < num; i++ {
-		theta := float64(i) / num * 2 * math.Pi
+		theta := float64(i) / float64(num) * 2 * math.Pi
 		cr := float32(0)
 		cg := float32(0)
 		cb := float32(0)
@@ -75,7 +78,7 @@ func init() {
 		if 0 <= i && i < num/3 {
 			cb = 2 - 2*float32(i)/float32(num/3)
 		}
-		vertices = append(vertices, ebiten.Vertex{
+		vs = append(vs, ebiten.Vertex{
 			DstX:   float32(r*math.Cos(theta)) + centerX,
 			DstY:   float32(r*math.Sin(theta)) + centerY,
 			SrcX:   0,
@@ -87,7 +90,7 @@ func init() {
 		})
 	}
 
-	vertices = append(vertices, ebiten.Vertex{
+	vs = append(vs, ebiten.Vertex{
 		DstX:   centerX,
 		DstY:   centerY,
 		SrcX:   0,
@@ -97,19 +100,42 @@ func init() {
 		ColorB: 1,
 		ColorA: 1,
 	})
-	for i := 0; i < num; i++ {
+
-		indices = append(indices, uint16(i), uint16(i+1)%num, num)
+	return vs
-	}
 }
 
 func update(screen *ebiten.Image) error {
+	if inpututil.IsKeyJustPressed(ebiten.KeyLeft) {
+		numVerticesToDraw--
+		if numVerticesToDraw < 1 {
+			numVerticesToDraw = 1
+		}
+	}
+	if inpututil.IsKeyJustPressed(ebiten.KeyRight) {
+		numVerticesToDraw++
+		if numVerticesToDraw > 120 {
+			numVerticesToDraw = 120
+		}
+	}
+
+	if prevNumVerticesToDraw != numVerticesToDraw || len(vertices) == 0 {
+		vertices = genVertices(numVerticesToDraw)
+		prevNumVerticesToDraw = numVerticesToDraw
+	}
+
 	if ebiten.IsDrawingSkipped() {
 		return nil
 	}
 
 	op := &ebiten.DrawTrianglesOptions{}
+	indices := []uint16{}
+	for i := 0; i < numVerticesToDraw; i++ {
+		indices = append(indices, uint16(i), uint16(i+1)%uint16(numVerticesToDraw), uint16(numVerticesToDraw))
+	}
 	screen.DrawTriangles(vertices, indices, emptyImage, op)
-	ebitenutil.DebugPrint(screen, fmt.Sprintf("TPS: %0.2f", ebiten.CurrentTPS()))
+
+	msg := fmt.Sprintf("TPS: %0.2f\nVertices: %d\nPress <- or -> to change the number of the vertices", ebiten.CurrentTPS(), numVerticesToDraw)
+	ebitenutil.DebugPrint(screen, msg)
 	return nil
 }