From 73553cb8b0babf88d5b9febac350720a30396a8d Mon Sep 17 00:00:00 2001
From: Nick Thomas <me@ur.gs>
Date: Tue, 31 Dec 2019 01:38:39 +0000
Subject: [PATCH] Bounds checking

---
 Makefile             |  4 +--
 cmd/view-map/main.go | 80 ++++++++++++++++++++++++++++----------------
 2 files changed, 53 insertions(+), 31 deletions(-)

diff --git a/Makefile b/Makefile
index 2628ded..1a2853e 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
-srcfiles = Makefile $(shell find . -iname *.go)
+srcfiles = Makefile go.mod $(shell find . -iname *.go)
 
-GOBUILD ?= go build
+GOBUILD ?= go build -tags ebitengl
 
 all: loader palette-idx view-obj view-map view-menu view-minimap view-set wh40k
 
diff --git a/cmd/view-map/main.go b/cmd/view-map/main.go
index bf94138..52bd222 100644
--- a/cmd/view-map/main.go
+++ b/cmd/view-map/main.go
@@ -80,7 +80,7 @@ func main() {
 
 	state := state{
 		zoom:   1.0,
-		origin: image.Point{0, -3000}, // FIXME: haxxx
+		origin: image.Point{0, 3000}, // FIXME: haxxx
 	}
 	env := &env{
 		gameMap:   gameMap,
@@ -97,10 +97,10 @@ func main() {
 
 	// TODO: click to view cell data
 
-	win.OnKeyUp(ebiten.KeyLeft, env.changeOrigin(+64, +0))
-	win.OnKeyUp(ebiten.KeyRight, env.changeOrigin(-64, +0))
-	win.OnKeyUp(ebiten.KeyUp, env.changeOrigin(+0, +64))
-	win.OnKeyUp(ebiten.KeyDown, env.changeOrigin(+0, -64))
+	win.OnKeyUp(ebiten.KeyLeft, env.changeOrigin(-64, +0))
+	win.OnKeyUp(ebiten.KeyRight, env.changeOrigin(+64, +0))
+	win.OnKeyUp(ebiten.KeyUp, env.changeOrigin(+0, -64))
+	win.OnKeyUp(ebiten.KeyDown, env.changeOrigin(+0, +64))
 	win.OnMouseWheel(env.changeZoom)
 
 	for i := 0; i <= 6; i++ {
@@ -148,20 +148,42 @@ func (e *env) getSprite(palette []string, ref maps.ObjRef) (*conv.Sprite, error)
 }
 
 func (e *env) Draw(screen *ebiten.Image) error {
-	// TODO: we should be able to perform bounds clipping on these
-	minX := int(e.gameMap.MinWidth)
-	maxX := int(e.gameMap.MaxWidth)
-	minY := int(e.gameMap.MinLength)
-	maxY := int(e.gameMap.MaxLength)
-	minZ := 0
-	maxZ := int(e.state.zIdx) + 1
+	// 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
 
-	for z := minZ; z < maxZ; z++ {
-		for y := minY; y < maxY; y++ {
-			for x := minX; x < maxX; x++ {
-				if err := e.renderCell(x, y, z, screen); err != nil {
-					return err
-				}
+	sw, sh := screen.Size()
+
+	topLeftX, topLeftY := pixToCell(
+		float64(e.state.origin.X),
+		float64(e.state.origin.Y),
+	)
+	topLeftX -= 1 // Otherwise we miss half a cell on alternate rows on the left
+
+	bottomRightX, bottomRightY := pixToCell(
+		float64(e.state.origin.X+sw),
+		float64(e.state.origin.Y+sh),
+	)
+
+	// X+Y is constant for all tiles in a column
+	// X-Y is constant for all tiles in a row
+	for a := int(topLeftX + topLeftY); a <= int(bottomRightX+bottomRightY); a++ {
+		for b := int(topLeftX - topLeftY); b <= int(bottomRightX-bottomRightY); b++ {
+			if b&1 != a&1 {
+				continue
+			}
+
+			x := (a + b) / 2
+			y := (a - b) / 2
+
+			if x < int(e.gameMap.MinWidth) || x >= int(e.gameMap.MaxWidth) ||
+				y < int(e.gameMap.MinLength) || y >= int(e.gameMap.MaxLength) {
+				continue
+			}
+
+			for z := 0; z <= e.state.zIdx; z++ {
+				e.renderCell(x, y, z, screen)
 			}
 		}
 	}
@@ -171,7 +193,6 @@ func (e *env) Draw(screen *ebiten.Image) error {
 
 func (e *env) renderCell(x, y, z int, screen *ebiten.Image) error {
 	var sprites []*conv.Sprite
-
 	cell := e.gameMap.Cells.At(x, y, z)
 
 	if spr, err := e.getSprite(e.set.Palette, cell.Surface); err != nil {
@@ -198,16 +219,17 @@ func (e *env) renderCell(x, y, z int, screen *ebiten.Image) error {
 		sprites = append(sprites, spr)
 	}
 
+	iso := ebiten.GeoM{}
+	iso.Translate(-float64(e.state.origin.X), -float64(e.state.origin.Y))
+
+	fx, fy := cellToPix(float64(x), float64(y))
+	iso.Translate(fx, fy)
+
 	// Taking the Z index away *seems* to draw the object in the correct place.
 	// FIXME: There are some artifacts, investigate more
-	fx, fy := cellToPix(float64(x), float64(y))
-	fx += float64(e.state.origin.X)
-	fy += float64(e.state.origin.Y)
+	iso.Translate(0.0, -float64(z*48.0)) // offset for Z index
 
-	iso := ebiten.GeoM{}
-	iso.Translate(fx, fy)
-	iso.Translate(0.0, -float64(z*48.0))  // offset for Z index
-	iso.Scale(e.state.zoom, e.state.zoom) // apply current zoom factor
+	// TODO: iso.Scale(e.state.zoom, e.state.zoom) // apply current zoom factor
 
 	for _, sprite := range sprites {
 		if err := screen.DrawImage(sprite.Image, &ebiten.DrawImageOptions{GeoM: iso}); err != nil {
@@ -236,9 +258,9 @@ func (e *env) setZIdx(to int) func() {
 	}
 }
 
-var (
-	cellWidth  = 64.0
-	cellHeight = 64.0
+const (
+	cellWidth  = 64
+	cellHeight = 64
 )
 
 // Doesn't take the camera or Z level into account