doctorlectro/entity/player.go

package entity

import (
	"time"

	"github.com/hajimehoshi/ebiten/v2"

	"github.com/jakecoffman/cp"

	"code.rocketnine.space/tslocum/doctorlectro/world"

	"code.rocketnine.space/tslocum/doctorlectro/asset"

	"code.rocketnine.space/tslocum/doctorlectro/component"
	"code.rocketnine.space/tslocum/gohan"
)

const (
	playerVelocity        = 40.0
	playerGroundAccelTime = 0.1
	playerGroundAccel     = playerVelocity / playerGroundAccelTime
	playerAirAccelTime    = 0.25
	playerAirAccel        = playerVelocity / playerAirAccelTime
	fallVelocity          = 900.0
)

func NewPlayer() gohan.Entity {

	playerBody := world.Space.AddBody(cp.NewBody(4, cp.INFINITY))
	playerBody.SetPosition(cp.Vector{0, 0})
	playerBody.SetVelocityUpdateFunc(playerUpdateVelocity)

	x1, y1 := 1.0, 1.0
	x2, y2 := 15.0, 15.0

	playerShape := world.Space.AddShape(cp.NewBox2(playerBody, cp.BB{x1, y2, x2, y1}, 0))
	playerShape.SetElasticity(0)
	playerShape.SetFriction(0)

	world.PlayerBody = playerBody
	world.PlayerShape = playerShape

	player := gohan.NewEntity()

	player.AddComponent(&component.Position{
		Body: world.PlayerBody,
	})

	player.AddComponent(&component.Velocity{})

	player.AddComponent(&component.Sprite{
		Frames:    asset.PlayerIdleFrames,
		FrameTime: 150 * time.Millisecond,
		NumFrames: len(asset.PlayerIdleFrames),
		OffsetY:   -10,
	})

	player.AddComponent(&component.Player{})

	return player
}

func playerUpdateVelocity(body *cp.Body, gravity cp.Vector, damping, dt float64) {
	jumpState := false

	// Grab the grounding normal from last frame
	groundNormal := cp.Vector{}
	/*world.PlayerBody.EachArbiter(func(arb *cp.Arbiter) {
		n := arb.Normal().Neg()

		if n.Y > groundNormal.Y {
			groundNormal = n
		}
	})*/

	grounded := groundNormal.Y > 0
	if groundNormal.Y < 0 {
		//remainingBoost = 0
	}

	// Do a normal-ish update
	boost := jumpState // && remainingBoost > 0
	var g cp.Vector
	if !boost {
		g = gravity
	}
	body.UpdateVelocity(g, damping, dt)

	xDir := 0.0
	if ebiten.IsKeyPressed(ebiten.KeyA) {
		xDir -= 1
		world.LastWalkDirL = false
	}
	if ebiten.IsKeyPressed(ebiten.KeyD) { // TODO
		xDir += 1
		world.LastWalkDirL = true
	}

	// Target horizontal speed for air/ground control
	targetVx := playerVelocity * xDir

	// Update the surface velocity and friction
	// Note that the "feet" move in the opposite direction of the player.
	surfaceV := cp.Vector{-targetVx, 0}
	world.PlayerShape.SetSurfaceV(surfaceV)
	if grounded {
		world.PlayerShape.SetFriction(playerGroundAccel / world.Gravity)
	} else {
		world.PlayerShape.SetFriction(0)
	}

	// Apply air control if not grounded
	if !grounded {
		v := world.PlayerBody.Velocity()
		world.PlayerBody.SetVelocity(cp.LerpConst(v.X, targetVx, playerAirAccel*dt), v.Y)
	}

	v := body.Velocity()
	body.SetVelocity(v.X, cp.Clamp(v.Y, -fallVelocity, cp.INFINITY))
}