magnets/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"

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


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

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

// parâmetros
const windowWidth = 700
const windowHeight = 700
const gridDivision = 4
const verticalGrids = windowHeight/gridDivision
const horizontalGrids = windowWidth/gridDivision
const magnetsDistance float32 = 80
const magnetRadius = 10 
const gravConst float32 = 50
const magnetsAngle = 30
const luminance = false
const hideBalls = true
const hideMagnets = false
var startingBallSpeed = rl.Vector2{X: 0, Y: 0} // joga a bola em alguma diração 
// antes que ela comece a ser atraida pelos ímãs
var cameraOffset = rl.Vector2{X: 0, Y: 0}

func (ball *ball) update(magnets []magnet) (bool, rl.Color) {
    magnetsPull := rl.Vector2{}

    for _, magnet := range magnets {
        direction := rl.Vector2Normalize(
            rl.Vector2Subtract(ball.pos, magnet.pos),
        )
        distance := rl.Vector2Distance(magnet.pos, ball.pos)
        distanceSquared := math.Pow(float64(distance), 2)
        force := gravConst / float32(distanceSquared)

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

        magnetsPull = rl.Vector2Add(magnetsPull, acceleration)
    }

    ball.speed = rl.Vector2Add(ball.speed, magnetsPull)
    ball.pos = rl.Vector2Add(ball.speed, ball.pos)

    // verificar se bola parou em cima de um ímã
    for _, magnet := range magnets {

        distance := rl.Vector2Distance(ball.pos, magnet.pos)

        insideMagnet := distance < magnet.radius /* + ball.radius */
        // atRest := math.Abs(float64(rl.Vector2Length(ball.speed))) < 0.01

        if insideMagnet /* && atRest */ {
            if luminance { magnet.color.A = uint8(ball.steps) }
            return true, magnet.color
        }
    }
    return false, rl.NewColor(0, 0, 0, 0)
}

// var colors = []rl.Color{
//     rl.Red, rl.Green, rl.Blue, rl.Yellow, rl.NewColor(0, 255, 255, 255), 
//     rl.Magenta, rl.White,
// }

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

    magnets := []magnet{
        {
            color: rl.Red,
            radius: magnetRadius,
            // force: magnetForce,
        },
        {
            color: rl.Gray,
            radius: magnetRadius,
            // force: magnetForce,
        },
        {
            color: rl.White,
            radius: magnetRadius,
            // force: magnetForce,
        },
        {
            color: rl.Yellow,
            radius: magnetRadius,
            // force: magnetForce,
        },
        {
            color: rl.Magenta,
            radius: magnetRadius,
            // force: magnetForce,
        },
    }

    // posiciona imas em volta de um circulo
    xCenter := float32(windowWidth / 2) + cameraOffset.X
    yCenter := float32(windowHeight / 2) + cameraOffset.Y
    for i := range magnets {
        angle := 2.0 * math.Pi * float64(i) / float64(len(magnets)) + magnetsAngle

        magnets[i].pos = rl.Vector2{
            X: float32(math.Cos(angle)) * magnetsDistance + xCenter,
            Y: float32(math.Sin(angle)) * magnetsDistance + yCenter,
        }
    }
    

    grid := make([][]rl.Color, verticalGrids)
    for i := range grid {
        grid[i] = make([]rl.Color, horizontalGrids)
        for j := range grid[i] {
            grid[i][j] = rl.Black
        }
    }

    // ball := ball{
    //     pos: rl.Vector2{0, 0},
    //     originGrid: rl.Vector2{X: 0, Y: 0},
    // }
    //
    gridSize := rl.Vector2{
        X: float32(windowWidth / int32(verticalGrids)),
        Y: float32(windowHeight / int32(horizontalGrids)),
    }

    var fallingBall []*ball

    var fallingBallOrder []rl.Vector2
    for y := range grid {
        for x := range grid[y] {
            fallingBallOrder = append(fallingBallOrder, rl.Vector2{
                X: float32(x),
                Y: float32(y),
            })
        }
    }
    // rand.Shuffle(len(fallingBallOrder), func(i, j int) {
    //     fallingBallOrder[i], fallingBallOrder[j] = 
    //     fallingBallOrder[j], fallingBallOrder[i]
    // })

    for _, randomGrid := range fallingBallOrder {
        x := randomGrid.X * gridSize.X + gridSize.X/2
        y := randomGrid.Y * gridSize.Y + gridSize.Y/2
        fallingBall = append(fallingBall, &ball{
            pos: rl.Vector2{X: x, Y: y},
            speed: startingBallSpeed,
            radius: magnetRadius/2,
            originGrid: randomGrid,
        })
    }

	for !rl.WindowShouldClose() {
		rl.BeginDrawing()
		rl.ClearBackground(rl.Black)

        for y := range grid {
            for x := range grid[y] {
                pos := rl.Vector2{
                    X: gridSize.X * float32(x),
                    Y: gridSize.Y * float32(y),
                }
                rl.DrawRectangleV(pos, gridSize, grid[y][x])
            }
        }
        if !hideMagnets {
            for i := range magnets {
                rl.DrawCircleV(magnets[i].pos, magnetRadius+2, rl.Black)
                rl.DrawCircleV(magnets[i].pos, magnetRadius, magnets[i].color)
            }
        }

        if len(fallingBall) == 0 {
            rl.EndDrawing()
            continue
        } 


        for i := 0; i < len(fallingBall); i++ {
            ball := fallingBall[i]

            if !hideBalls {
                // rl.DrawCircleV(
                //     ball.pos, ball.radius/2+1, rl.Black,
                // )
                // rl.DrawCircleV(
                //     ball.pos, ball.radius/2, 
                //     rl.NewColor(100, 100, 100, 255),
                // )
                // bolas são difíceis de se calcular =/
                rl.DrawRectangleV(
                    rl.Vector2{X: ball.pos.X-1, Y: ball.pos.Y-1 }, 
                    rl.Vector2{X: ball.radius+1, Y: ball.radius+1}, 
                    rl.Black,
                )
                rl.DrawRectangleV(
                    ball.pos, rl.Vector2{X: ball.radius, Y: ball.radius}, 
                    rl.NewColor(100, 100, 100, 255),
                )
            }
            if hit, color := ball.update(magnets); hit {
                x := ball.originGrid.X
                y := ball.originGrid.Y
                grid[int(y)][int(x)] = color
                // remover bola
                fallingBall[i] = fallingBall[len(fallingBall)-1]
                fallingBall = fallingBall[:len(fallingBall)-1]
            }
            ball.steps += 1
        }

        // fmt.Println("foo")

        rl.EndDrawing()
	}

    fmt.Println("hello world")

}