ordoor/internal/scenario/draw.go

package scenario

import (
	"fmt"
	"image"
	"sort"

	"github.com/hajimehoshi/ebiten"
	"github.com/hajimehoshi/ebiten/ebitenutil"
)

type CartPt struct {
	X float64
	Y float64
}

type IsoPt struct {
	X float64
	Y float64
}

func (s *Scenario) Update(screenX, screenY int) error {
	s.tick += 1

	x, y := ebiten.CursorPosition()
	screenPos := CartPt{
		X: float64(s.Viewpoint.X + x),
		Y: float64(s.Viewpoint.Y + y),
	}

	s.selectedCell = screenPos.ToISO()

	// TODO: zoom support will need a camera
	// FIXME: adjust for Z level

	return nil
}

func (s *Scenario) Draw(screen *ebiten.Image) error {
	// Bounds clipping
	// http://www.java-gaming.org/index.php?topic=24922.0
	// https://stackoverflow.com/questions/892811/drawing-isometric-game-worlds
	// https://gamedev.stackexchange.com/questions/25896/how-do-i-find-which-isometric-tiles-are-inside-the-cameras-current-view

	sw, sh := screen.Size()

	topLeft := CartPt{
		X: float64(s.Viewpoint.X - 2*cellWidth), // Ensure all visible cells are rendered
		Y: float64(s.Viewpoint.Y - 2*cellHeight),
	}.ToISO()

	bottomRight := CartPt{
		X: float64(s.Viewpoint.X + sw + 2*cellHeight),
		Y: float64(s.Viewpoint.Y + sh + 5*cellHeight), // Z dimension requires it
	}.ToISO()

	// X+Y is constant for all tiles in a column
	// X-Y is constant for all tiles in a row
	// However, the drawing order is odd unless we reorder explicitly.
	toDraw := []IsoPt{}
	for a := int(topLeft.X + topLeft.Y); a <= int(bottomRight.X+bottomRight.Y); a++ {
		for b := int(topLeft.X - topLeft.Y); b <= int(bottomRight.X-bottomRight.Y); b++ {
			if b&1 != a&1 {
				continue
			}

			pt := IsoPt{X: float64((a + b) / 2), Y: float64((a - b) / 2)}
			ipt := image.Pt(int(pt.X), int(pt.Y))

			if !ipt.In(s.area.Rect) {
				continue
			}
			toDraw = append(toDraw, pt)
		}
	}

	sort.Slice(toDraw, func(i, j int) bool {
		iPix := toDraw[i].ToCart()
		jPix := toDraw[j].ToCart()

		if iPix.Y < jPix.Y {
			return true
		}

		if iPix.Y == jPix.Y {
			return iPix.X < jPix.X
		}

		return false
	})

	counter := map[string]int{}
	for _, pt := range toDraw {
		for z := 0; z <= s.ZIdx; z++ {
			if err := s.renderCell(int(pt.X), int(pt.Y), z, screen, counter); err != nil {
				return err
			}
		}
	}

	//log.Printf("%#+v", counter)

	// Finally, draw cursor chrome
	spr, err := s.specials.Sprite(0)
	if err != nil {
		return err
	}

	op := ebiten.DrawImageOptions{}
	op.GeoM = s.geoForCoords(int(s.selectedCell.X), int(s.selectedCell.Y), 0)
	op.GeoM.Translate(-cellWidthHalf, -cellHeightHalf)

	if err := screen.DrawImage(spr.Image, &op); err != nil {
		return err
	}

	sx, sy := op.GeoM.Apply(0, 0)
	ebitenutil.DebugPrintAt(screen, fmt.Sprintf("(%.0f,%.0f)", s.selectedCell.X, s.selectedCell.Y), int(sx), int(sy))

	return nil
}

func (s *Scenario) geoForCoords(x, y, z int) ebiten.GeoM {
	geo := ebiten.GeoM{}
	geo.Translate(-float64(s.Viewpoint.X), -float64(s.Viewpoint.Y))

	pix := IsoPt{X: float64(x), Y: float64(y)}.ToCart()
	geo.Translate(pix.X, pix.Y)

	// Taking the Z index away *seems* to draw the object in the correct place.
	// FIXME: There are some artifacts, investigate more
	geo.Translate(0.0, -float64(z*48.0)) // offset for Z index

	return geo
}

func (s *Scenario) renderCell(x, y, z int, screen *ebiten.Image, counter map[string]int) error {
	sprites, err := s.area.SpritesForCell(x, y, z)
	if err != nil {
		return err
	}

	// TODO: iso.Scale(e.state.zoom, e.state.zoom) // apply current zoom factor
	iso := s.geoForCoords(x, y, z)

	// FIXME: this fixed offset is found in jungtil.obj. Drawing with it
	// means we put everywhere where the iso->pix conversion expects, but
	// it's a bit nasty. Is there a better way?
	iso.Translate(-209, -332)

	for _, spr := range sprites {
		//		if _, ok := counter[spr.ID]; !ok {
		//			counter[spr.ID] = 0
		//		}
		//		counter[spr.ID] = counter[spr.ID] + 1
		op := ebiten.DrawImageOptions{GeoM: iso}

		op.GeoM.Translate(float64(spr.Rect.Min.X), float64(spr.Rect.Min.Y))

		if err := screen.DrawImage(spr.Image, &op); err != nil {
			return err
		}
	}

	return nil
}

const (
	cellWidth  = 128
	cellHeight = 64

	cellWidthHalf  = cellWidth / 2
	cellHeightHalf = cellHeight / 2
)

func (p CartPt) ToISO() IsoPt {
	return IsoPt{
		X: (p.Y / cellHeight) + (p.X / cellWidth),
		Y: (p.Y / cellHeight) - (p.X / cellWidth),
	}
}

func (p IsoPt) ToCart() CartPt {
	return CartPt{
		X: (p.X - p.Y) * cellWidthHalf,
		Y: (p.X + p.Y) * cellHeightHalf,
	}
}

/*
// Doesn't take the camera or Z level into account
func cellToPix(pt image.Point) image.Point {
	return image.Pt(
		(pt.X-pt.Y)*cellWidthHalf,
		(pt.X+pt.Y)*cellHeightHalf,
	)
}

// Doesn't take the camera or Z level into account
func pixToCell(pt image.Point) image.Point {
	fX := pt.X
	fY := pt.Y
	return image.Pt(
//		(pt.X / cellWidthHalf  +  pt.Y / cellHeightHalf) / 2,
//		(pt.Y / cellHeightHalf - (pt.Y / cellWidthHalf)) / 2,
//		int(fY/cellHeight+fX/(cellWidth*2)),
//		int(fY/cellHeight-fX/(cellWidth*2)),
		//int((fY / cellHeight) + (fX / cellWidth)),
		//int((-fX / cellWidth) + (fY / cellHeight)),


	)
}*/