barneshut/main.go

package main

// veja:
// The relationship between chaos, fractal and physics
// https://www.youtube.com/watch?v=C5Jkgvw-Z6E

import (
	// "fmt"
	"fmt"
	"math"
	"math/rand"
	"strconv"

	// "math/rand"

	rl "github.com/gen2brain/raylib-go/raylib"
)


type quadnode struct {
    topleft, bottomright rl.Vector2
    magnet *magnet
    parent *quadnode
    nodes []*quadnode
}

func newQuadTree() *quadnode {
    return &quadnode{
        topleft: rl.NewVector2(0, 0),
        bottomright: rl.NewVector2(windowWidth, windowHeight),
        nodes: nil,
    }
}

func (q *quadnode) subdivide() {
    halfX := q.bottomright.X/2 
    halfY := q.bottomright.X/2 

    q.nodes = []*quadnode{
        {
            topleft: q.topleft,
            bottomright: rl.Vector2{X: halfX, Y: halfY},
            parent: q,
        },
        {
            topleft: rl.Vector2{X: halfX, Y: q.topleft.Y},
            bottomright: rl.Vector2{X: q.bottomright.X, Y: halfY},
            parent: q,
        },
        {
            topleft: rl.Vector2{X: q.topleft.X, Y: halfY},
            bottomright: rl.Vector2{X: halfX, Y: q.bottomright.Y},
            parent: q,
        },
        {
            topleft: rl.Vector2{X: halfX, Y: halfY},
            bottomright: q.bottomright,
            parent: q,
        },
    }
}

func (q *quadnode) drawBoundaries() {
    if q.nodes == nil {
        return
    }
    for _, node := range q.nodes {
        node.drawBoundaries()
        size := rl.Vector2Subtract(node.bottomright, node.topleft)
        rl.DrawRectangleLines(
            int32(node.topleft.X), int32(node.topleft.Y), 
            int32(size.X), int32(size.Y),
            rl.Green,
        )
    }
}

type magnet struct {
    pos rl.Vector2
    speed rl.Vector2
    color rl.Color
    mass float32
    radius float32
}

// type ball struct {
//     pos rl.Vector2
//     originGrid rl.Vector2
//     radius float32
//     speed rl.Vector2
//     steps int
// }

// parâmetros
const initalMagnetCount = 10
const windowWidth = 700
const windowHeight = 700
const magnetRadius = 5 
const gravConst float32 = 10

func tick(magnets []*magnet) {

    for _, a := range magnets {
        for _, b := range magnets {
            if a == b { continue }
            // não creio que isso esteja certo porem isso quaqueja que nem um pato
            direction := rl.Vector2Normalize(rl.Vector2Subtract(a.pos, b.pos))
            distance := rl.Vector2Distance(a.pos, b.pos)
            distanceSquared := math.Pow(float64(distance), 2)
            force := gravConst / float32(distanceSquared)
            acceleration := rl.Vector2Scale(direction, force)

            if distance < magnetRadius*2 {
                continue
            } 
            // f = m * a 
            forceA := rl.Vector2Scale(acceleration, a.mass)
            forceB := rl.Vector2Scale(acceleration, b.mass)
            a.speed = rl.Vector2Add(a.speed, rl.Vector2Negate(forceB))
            b.speed = rl.Vector2Add(b.speed, forceA)

        }
    }

    for _, magnet := range magnets {
        magnet.pos = rl.Vector2Add(magnet.pos, magnet.speed)
    }
}

func (m *magnet) update(magnets []*magnet) {
    magnetsPull := rl.Vector2{}

    for _, magnet := range magnets {
        if m == magnet { continue }

        direction := rl.Vector2Normalize(rl.Vector2Subtract(m.pos, magnet.pos))
        distance := rl.Vector2Distance(magnet.pos, m.pos)
        if (distance < magnetRadius*2 + 10) {
            direction = rl.Vector2Negate(direction)
            // continue
        }
        distanceSquared := math.Pow(float64(distance), 2)
        force := gravConst / float32(distanceSquared)

        acceleration := rl.Vector2Scale(direction, -force)

        magnetsPull = rl.Vector2Add(magnetsPull, acceleration)
    }

    m.speed = rl.Vector2Add(m.speed, magnetsPull)
    newPos := rl.Vector2Add(m.speed, m.pos)

    // x, y := insideArea(newPos)    
    // if !x { newPos.X = -newPos.X; m.speed.X = 0 }
    // if !y { newPos.Y = -newPos.Y; m.speed.Y = 0 }

    m.pos = newPos
}

func newMagnet(x, y, mass float32) *magnet {
    newMagnet := magnet{
        pos: rl.Vector2{X: x, Y: y},
        color: rl.NewColor(
            uint8(rand.Int()),
            uint8(rand.Int()),
            uint8(rand.Int()),
            255,
        ),
        mass: mass,
        radius: mass,
    }
    return &newMagnet
}

func randomMagnets(n int) []*magnet {
    var magnets []*magnet

    for i := 0; i < n; i++ {
        x := float32(rand.Intn(windowWidth - 100) + 50)
        y := float32(rand.Intn(windowHeight - 100) + 50)
        magnets = append(magnets, newMagnet(x, y, 1))
    }

    return magnets
}

func main() {
	rl.InitWindow(
        windowWidth, windowHeight, 
        "barnes hut",
    )
	defer rl.CloseWindow()
	rl.SetTargetFPS(60)

    magnets := randomMagnets(initalMagnetCount)

    quadtree := newQuadTree()
    quadtree.subdivide()
    quadtree.nodes[0].subdivide()

    pause := true

	for !rl.WindowShouldClose() {

		rl.BeginDrawing()
		rl.ClearBackground(rl.Black)
        rl.DrawFPS(0, 0)
        rl.DrawText(strconv.Itoa(len(magnets)), 0, 20, 20, rl.White)
        if pause {
            rl.DrawText("pausado (E)", 0, 40, 20, rl.White)
        }

        {
            if rl.IsKeyPressed(rl.KeyR) {
                magnets = randomMagnets(initalMagnetCount)
            }
            if rl.IsKeyPressed(rl.KeyW) {
                magnets = append(magnets, randomMagnets(100)...)
            }
            if rl.IsKeyPressed(rl.KeyE) {
                pause = !pause
            }
            if rl.IsKeyPressed(rl.KeySpace) {
                mouse := rl.GetMousePosition()
                magnets = append(magnets, newMagnet(mouse.X, mouse.Y, 50))
            }
        }

        if !pause {
            tick(magnets)
        }

        quadtree.drawBoundaries()

        for _, magnet := range magnets {
            rl.DrawCircleV(magnet.pos, magnet.radius+1, rl.White)
            rl.DrawCircleV(magnet.pos, magnet.radius, magnet.color)
        }

        rl.EndDrawing()
	}

    fmt.Println("hello world")

}