ichigo/engine/prisms.go

package engine

import (
	"encoding/gob"
	"fmt"
	"image"

	"drjosh.dev/gurgle/geom"
	"github.com/hajimehoshi/ebiten/v2"
)

var (
	_ interface {
		Identifier
		Collider
		Disabler
		Hider
		Prepper
		Transformer
	} = &PrismMap{}

	_ interface {
		Drawer
		Transformer
	} = &Prism{}
)

func init() {
	gob.Register(&PrismMap{})
	gob.Register(&Prism{})
}

// PrismMap is a generalised 3D tilemap/wallmap/etc.
type PrismMap struct {
	ID
	Disabled
	Hidden
	Ersatz        bool
	Map           map[geom.Int3]*Prism // pos -> prism
	DrawOrderBias image.Point          // dot with pos.XY() = bias value
	DrawOffset    image.Point          // offset applies to whole map
	PosToWorld    geom.IntMatrix3x4    // p.pos -> world voxelspace
	PrismSize     geom.Int3            // in world voxelspace units
	PrismTop      []image.Point        // polygon vertices anticlockwise, Y means Z
	Sheet         Sheet

	game      *Game
	pwinverse geom.RatMatrix3
}

func (m *PrismMap) CollidesWith(b geom.Box) bool {
	if m.Ersatz {
		return false
	}

	// To find the prisms need to test, we need to invert PosToWorld.

	// Step 1: subtract whatever the translation component of PosToWorld is,
	// reducing the rest of the problem to the 3x3 submatrix.
	rb := b.Sub(m.PosToWorld.Translation())
	// Step 2: invert the rest of the fucking matrix.
	// (Spoilers: I did this already in Prepare)
	rb.Min = m.pwinverse.IntApply(rb.Min)
	rb.Max = m.pwinverse.IntApply(rb.Max) //.Sub(Int3{1, 1, 1}))

	rb = rb.Canon() // inverse might flip the corners around...

	// Check neighboring prisms too because there's a fencepost somewhere here
	rb.Min = rb.Min.Sub(geom.Int3{X: 1, Y: 1, Z: 1})
	rb.Max = rb.Max.Add(geom.Int3{X: 1, Y: 1, Z: 1})

	var pp geom.Int3
	for pp.Z = rb.Min.Z; pp.Z <= rb.Max.Z; pp.Z++ {
		for pp.Y = rb.Min.Y; pp.Y <= rb.Max.Y; pp.Y++ {
			for pp.X = rb.Min.X; pp.X <= rb.Max.X; pp.X++ {
				// Is there a prism here?
				if _, found := m.Map[pp]; !found {
					continue
				}
				// Map it back to worldspace to get a bounding box for the prism
				wp := m.PosToWorld.Apply(pp)
				cb := geom.Box{Min: wp, Max: wp.Add(m.PrismSize)}
				if !b.Overlaps(cb) {
					continue
				}
				// Take into account the prism shape
				r := b.XZ().Sub(wp.XZ())
				if geom.PolygonRectOverlap(m.PrismTop, r) {
					return true
				}
			}
		}
	}

	/*
		// Here's the test-every-prism approach
		for pos := range m.Map {
			// Map it back to worldspace to get a bounding box for the prism
			wp := m.PosToWorld.Apply(pos)
			cb := Box{Min: wp, Max: wp.Add(m.PrismSize)}
			if !b.Overlaps(cb) {
				continue
			}
			// Take into account the prism shape
			r := b.XZ().Sub(wp.XZ())
			if geom.PolygonRectOverlap(m.PrismTop, r) {
				return true
			}
		}
	*/
	return false
}

func (m *PrismMap) Prepare(g *Game) error {
	m.game = g
	pwi, err := m.PosToWorld.ToRatMatrix3().Inverse()
	if err != nil {
		return fmt.Errorf("inverting PosToWorld: %w", err)
	}
	m.pwinverse = pwi
	for v, p := range m.Map {
		p.pos = v
		p.m = m
	}
	return nil
}

func (m *PrismMap) Scan() []interface{} {
	c := make([]interface{}, 1, len(m.Map)+1)
	c[0] = &m.Sheet
	for _, prism := range m.Map {
		c = append(c, prism)
	}
	return c
}

func (m *PrismMap) Transform() (opts ebiten.DrawImageOptions) {
	opts.GeoM.Translate(geom.CFloat(m.DrawOffset))
	return opts
}

type Prism struct {
	Cell int

	pos geom.Int3
	m   *PrismMap
}

func (p *Prism) Draw(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
	screen.DrawImage(p.m.Sheet.SubImage(p.Cell), opts)
}

func (p *Prism) DrawOrder() (int, int) {
	return p.m.PosToWorld.Apply(p.pos).Z,
		geom.Dot(p.pos.XY(), p.m.DrawOrderBias)
}

func (p *Prism) Transform() (opts ebiten.DrawImageOptions) {
	opts.GeoM.Translate(geom.CFloat(
		p.m.game.Projection.Project(p.m.PosToWorld.Apply(p.pos)),
	))
	return opts
}