feat: Finished and added tests for palette implementation

world/palette.go

@@ -5,47 +5,82 @@ package world
 //
 // This palette is unique to each section, and allows ranges of blocks to be
 // changed in constant time, with the downside of having to "compact" the palette
-type SectionPalette []BlockID
+type SectionPalette struct {
+	ids map[PaletteIndex]BlockID
+}
 
-// `Compact` removes all duplicate states from a palette and returns a new palette
-func (p SectionPalette) Compact() SectionPalette {
-	ids := make(map[BlockID]bool)
+func NewSectionPalette() SectionPalette {
+	return SectionPalette{
+		ids: make(map[PaletteIndex]BlockID),
+	}
+}
+
+// `Compact` removes all duplicate states from a palette and returns if the
+// palette was modified
+func (p *SectionPalette) Compact() bool {
+	newIds := make(map[BlockID]PaletteIndex)
+
+	var wasResized bool
 
 	// Filter out the duplicate block ids
-	for _, blockId := range p {
-		ids[blockId] = true
+	for index, blockId := range p.ids {
+		newIds[blockId] = index
 	}
 
-	var np SectionPalette
-
-	for blockId := range ids {
-		np = append(np, blockId)
+	// If there was not a resize, return instantly
+	if len(newIds) != len(p.ids) {
+		wasResized = true
+	} else {
+		return false
 	}
 
-	return np
+	ids := make(map[PaletteIndex]BlockID)
+
+	for blockId, index := range newIds {
+		ids[index] = blockId
+	}
+
+	p.ids = ids
+
+	return wasResized
 }
 
 // `IndexFor` returns the palette index for a specified block id
 //
 // If the block id does not exist, it is placed in the palette and the index
 // is returned
-func (p SectionPalette) IndexFor(state BlockID) PaletteIndex {
+func (p *SectionPalette) IndexFor(state BlockID) PaletteIndex {
+	var maxIndex PaletteIndex
+
 	// If the state is already in the palette, return it
-	for index, blockId := range p {
+	for index, blockId := range p.ids {
+		if index > maxIndex {
+			maxIndex = index
+		}
+
 		if state == blockId {
 			return PaletteIndex(index)
 		}
 	}
 
 	// Otherwise, insert it into the palette and return the index
-	p = append(p, state)
+	p.ids[maxIndex+1] = state
 
-	return PaletteIndex(len(p) - 1)
+	return maxIndex + 1
 }
 
 // `State` returns the state for a palette's index
 func (p SectionPalette) State(index PaletteIndex) BlockID {
-	return p[index]
+	return p.ids[index]
+}
+
+// `ReplaceIndex` replaces the block state at the given palette' index
+//
+// This function is used to quickly zero a section with a given block state in
+// constant time, and should not be used for any other purpose. Otherwise, set
+// the block state within the section to the result of `IndexFor`.
+func (p *SectionPalette) ReplaceIndex(index PaletteIndex, state BlockID) {
+	p.ids[index] = state
 }
 
 type PaletteIndex byte

world/palette_test.go

@@ -0,0 +1,64 @@
+package world
+
+import (
+	"runtime/debug"
+	"testing"
+)
+
+func newPaletteWith(ids []BlockID) *SectionPalette {
+	p := NewSectionPalette()
+
+	for _, id := range ids {
+		p.IndexFor(id)
+	}
+
+	return &p
+}
+
+func checkPaletteEqual(t *testing.T, p *SectionPalette, index PaletteIndex, expected BlockID) {
+	if p.State(index) != expected {
+		debug.PrintStack()
+		t.Fatalf("Expected to get state %v at index %v, got %v", expected, index, p.State(index))
+	}
+}
+
+func TestInsertPalette(t *testing.T) {
+	p := NewSectionPalette()
+
+	ids := []BlockID{Empty, Generic}
+
+	for _, id := range ids {
+		index := p.IndexFor(id)
+		if id != p.State(index) {
+			t.Fatalf("Fetching index for id %v: got index %v which returned %v", id, index, p.State(index))
+		}
+	}
+}
+
+func TestReplaceCompactPalettte(t *testing.T) {
+	p := newPaletteWith([]BlockID{Empty, Generic})
+
+	zeroIndex := p.IndexFor(Empty)
+	checkPaletteEqual(t, p, zeroIndex, Empty)
+
+	// Zero out the chunk
+	genIndex := p.IndexFor(Generic)
+	checkPaletteEqual(t, p, genIndex, Generic)
+	p.ReplaceIndex(genIndex, Empty)
+
+	// Check that everything now returns zero
+	checkPaletteEqual(t, p, zeroIndex, Empty)
+	checkPaletteEqual(t, p, genIndex, Empty)
+
+	// Test for compaction
+	wasCompacted := p.Compact()
+	if !wasCompacted {
+		t.Fatalf("Palette should have been compacted")
+	}
+
+	// Test to see that we don't compact again
+	wasCompacted = p.Compact()
+	if wasCompacted {
+		t.Fatalf("Palette should have not been compacted again")
+	}
+}