From 4501207261be3b4685830feaa6d3a5b478c907cc Mon Sep 17 00:00:00 2001
From: davidovski <david@davidovski.xyz>
Date: Tue, 17 Oct 2023 20:18:43 +0100
Subject: implement curve collision

---
 go.mod    |   3 +-
 pengui.go | 112 +++++++++++++++++++++++++++++++++++++++++++++++++-------------
 2 files changed, 91 insertions(+), 24 deletions(-)

diff --git a/go.mod b/go.mod
index d1057e7..a18f943 100644
--- a/go.mod
+++ b/go.mod
@@ -2,9 +2,10 @@ module pengui
 
 go 1.18
 
+require github.com/hajimehoshi/ebiten/v2 v2.6.2
+
 require (
 	github.com/ebitengine/purego v0.5.0 // indirect
-	github.com/hajimehoshi/ebiten/v2 v2.6.2 // indirect
 	github.com/jezek/xgb v1.1.0 // indirect
 	golang.org/x/exp/shiny v0.0.0-20230817173708-d852ddb80c63 // indirect
 	golang.org/x/image v0.12.0 // indirect
diff --git a/pengui.go b/pengui.go
index 0c00862..79c8571 100644
--- a/pengui.go
+++ b/pengui.go
@@ -1,12 +1,14 @@
 package main
 
 import (
+	"image/color"
 	_ "image/png"
-    "image/color"
 	"log"
+	"math"
 
 	"github.com/hajimehoshi/ebiten/v2"
 	"github.com/hajimehoshi/ebiten/v2/ebitenutil"
+	"github.com/hajimehoshi/ebiten/v2/vector"
 )
 
 const screen_w, screen_h = 640, 480
@@ -18,13 +20,10 @@ type Penguin struct {
     xv, yv float64
 }
 
-var penguin Penguin
-
-func init() {
-    penguin = Penguin{
-        img: nil,
+func newPenguin() Penguin {
+    penguin := Penguin{
         x: screen_w / 2,
-        y: screen_h / 2,
+        y: 0,
         xv: 0,
         yv: 0,
     }
@@ -34,47 +33,106 @@ func init() {
 	if err != nil {
 		log.Fatal(err)
 	}
-}
 
-type Game struct{}
+    return penguin;
+}
 
-func drawPenguin(screen *ebiten.Image, penguin Penguin) {
+func (penguin *Penguin) draw(screen *ebiten.Image) {
     op := &ebiten.DrawImageOptions{}
 	op.GeoM.Translate(penguin.x, penguin.y)
     screen.DrawImage(penguin.img, op)
 }
 
-func updatePenguin(penguin *Penguin) {
-    penguin.x = penguin.x + penguin.xv
-    penguin.y = penguin.y + penguin.yv
+func (penguin *Penguin) drawBounds(screen *ebiten.Image) {
+    vector.StrokeRect(screen,
+        float32(penguin.x), float32(penguin.y),
+        float32(penguin.img.Bounds().Dx()), float32(penguin.img.Bounds().Dy()),
+        4, color.RGBA{0xcc, 0x66, 0x66, 0xff}, true)
+}
+
+func (penguin *Penguin) update(g *Game) {
+    if penguin.collideWithCurve(g.ground, penguin.xv, 0){
+        penguin.xv = 0
+        penguin.yv -= 4
+    } else {
+        penguin.x += penguin.xv
+        penguin.xv *= 0.9
+    }
+
+    if penguin.collideWithCurve(g.ground, 0, penguin.yv){
+        penguin.yv = 0
+    } else {
+        penguin.y += penguin.yv
+        penguin.yv += 0.9
+    }
+}
+
+func (p *Penguin) collideWithCurve(curve Curve, xv, yv float64) bool {
+    cy1 := curve(p.x + xv)
+    y1 := p.y + yv
+    y2 := p.y + yv + float64(p.img.Bounds().Dy())
+
+    if y1 < cy1 && cy1 < y2 {
+        return true
+    }
+
+    cy2 := curve(p.x + xv + float64(p.img.Bounds().Dx()))
+    if y1 < cy2 && cy2 < y2 {
+        return true
+    }
+
+    return false
+}
 
-    penguin.xv = penguin.xv / 2
-    penguin.yv = penguin.yv / 2
+func (g *Game) init() {
+    g.penguin = newPenguin()
+}
+
+type Curve func(x float64)(y float64)
+
+func (curve Curve) draw(dst *ebiten.Image, clr color.Color, width float32, resolution int, antialias bool) {
+    for x1 := 0; x1 < screen_w; x1 += resolution {
+        x2 := x1 + resolution
+        y1 := curve(float64(x1))
+        y2 := curve(float64(x2))
+
+        vector.StrokeLine(dst, float32(x1), float32(y1), float32(x2), float32(y2), width, color.RGBA{0x19, 0x19, 0x19, 0xff}, true)
+    }
+}
+
+type Game struct{
+    penguin Penguin
+    ground Curve
 }
 
 func (g *Game) Update() error {
     if ebiten.IsKeyPressed(ebiten.KeyArrowRight) {
-        penguin.xv = 4
+        g.penguin.xv = 4
     }
+
     if ebiten.IsKeyPressed(ebiten.KeyArrowLeft) {
-        penguin.xv = -4
+        g.penguin.xv = -4
     }
+
     if ebiten.IsKeyPressed(ebiten.KeyArrowUp) {
-        penguin.yv = -4
+        g.penguin.yv = -4
     }
+
     if ebiten.IsKeyPressed(ebiten.KeyArrowDown) {
-        penguin.yv = 4
+        g.penguin.yv = 4
     }
 
-    updatePenguin(&penguin)
-        
+    g.penguin.update(g)
+
 	return nil
 }
 
 func (g *Game) Draw(screen *ebiten.Image) {
     screen.Fill(color.RGBA{0xfe, 0xfe, 0xfe, 0xff})
 
-    drawPenguin(screen, penguin)
+    g.ground.draw(screen, color.RGBA{0x19, 0x19, 0x19, 0xff}, 4, 16, true);
+    g.penguin.draw(screen)
+    g.penguin.drawBounds(screen)
 }
 
 func (g *Game) Layout(outsideWidth, outsideHeight int) (screenWidth, screenHeight int) {
@@ -84,7 +142,15 @@ func (g *Game) Layout(outsideWidth, outsideHeight int) (screenWidth, screenHeigh
 func main() {
 	ebiten.SetWindowSize(640, 480)
 	ebiten.SetWindowTitle("penguin")
-	if err := ebiten.RunGame(&Game{}); err != nil {
+
+    game := Game{}
+
+    game.ground = func(x float64)(y float64) {
+        return 200-math.Pow((x - 320)/320, 3)+math.Pow((x-320), 2)/300
+    }
+
+    game.init()
+	if err := ebiten.RunGame(&game); err != nil {
 		log.Fatal(err)
 	}
 }
-- 
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