core, viewer: add support for WebP output

WebP can be selected by passing `--image-format webp` on the command
line. For typical Minecraft worlds, this results in a size reduction of
10-15% without increasing processing time.

src/core/common.rs

@@ -7,6 +7,7 @@ use std::{
 };
 
 use anyhow::{Context, Result};
+use clap::ValueEnum;
 use indexmap::IndexSet;
 use regex::{Regex, RegexSet};
 use serde::{Deserialize, Serialize};
@@ -150,6 +151,8 @@ pub struct Config {
 	pub viewer_info_path: PathBuf,
 	/// Path of viewer entities file
 	pub viewer_entities_path: PathBuf,
+	/// Format of generated map tiles
+	pub image_format: ImageFormat,
 	/// Sign text filter patterns
 	pub sign_patterns: RegexSet,
 	/// Sign text transformation pattern
@@ -189,6 +192,7 @@ impl Config {
 			entities_path_final,
 			viewer_info_path,
 			viewer_entities_path,
+			image_format: args.image_format,
 			sign_patterns,
 			sign_transforms,
 		})
@@ -264,14 +268,39 @@ impl Config {
 		[&self.output_dir, Path::new(&dir)].iter().collect()
 	}
 
+	/// Returns the file extension for the configured image format
+	pub fn tile_extension(&self) -> &'static str {
+		match self.image_format {
+			ImageFormat::Png => "png",
+			ImageFormat::Webp => "webp",
+		}
+	}
+	/// Returns the configurured image format for the image library
+	pub fn tile_image_format(&self) -> image::ImageFormat {
+		match self.image_format {
+			ImageFormat::Png => image::ImageFormat::Png,
+			ImageFormat::Webp => image::ImageFormat::WebP,
+		}
+	}
+
 	/// Constructs the path of an output tile image
 	pub fn tile_path(&self, kind: TileKind, level: usize, coords: TileCoords) -> PathBuf {
-		let filename = coord_filename(coords, "png");
+		let filename = coord_filename(coords, self.tile_extension());
 		let dir = self.tile_dir(kind, level);
 		[Path::new(&dir), Path::new(&filename)].iter().collect()
 	}
 }
 
+/// Format of generated map tiles
+#[derive(Debug, Clone, Copy, Default, ValueEnum)]
+pub enum ImageFormat {
+	/// Generate PNG images
+	#[default]
+	Png,
+	/// Generate WebP images
+	Webp,
+}
+
 /// Copies a chunk image into a region tile
 pub fn overlay_chunk<I, J>(image: &mut I, chunk: &J, coords: ChunkCoords)
 where

src/core/metadata_writer.rs

@@ -61,6 +61,8 @@ struct Metadata<'t> {
 	spawn: Spawn,
 	/// Enabled MinedMap features
 	features: Features,
+	/// Format of generated map tiles
+	tile_extension: &'static str,
 }
 
 /// Viewer entity JSON data structure
@@ -205,6 +207,7 @@ impl<'a> MetadataWriter<'a> {
 			mipmaps: Vec::new(),
 			spawn: Self::spawn(&level_dat),
 			features,
+			tile_extension: self.config.tile_extension(),
 		};
 
 		for tile_map in self.tiles.iter() {

src/core/mod.rs

@@ -16,7 +16,7 @@ use anyhow::{Context, Result};
 use clap::Parser;
 use git_version::git_version;
 
-use common::Config;
+use common::{Config, ImageFormat};
 use metadata_writer::MetadataWriter;
 use region_processor::RegionProcessor;
 use tile_mipmapper::TileMipmapper;
@@ -47,6 +47,9 @@ pub struct Args {
 	/// Enable verbose messages
 	#[arg(short, long)]
 	pub verbose: bool,
+	/// Format of generated map tiles
+	#[arg(long, value_enum, default_value_t)]
+	pub image_format: ImageFormat,
 	/// Prefix for text of signs to show on the map
 	#[arg(long)]
 	pub sign_prefix: Vec<String>,

src/core/region_processor.rs

@@ -79,6 +79,8 @@ struct SingleRegionProcessor<'a> {
 	lightmap: image::GrayAlphaImage,
 	/// Processed entity intermediate data
 	entities: ProcessedEntities,
+	/// Format of generated map tiles
+	image_format: image::ImageFormat,
 	/// True if any unknown block or biome types were encountered during processing
 	has_unknown: bool,
 }
@@ -127,6 +129,7 @@ impl<'a> SingleRegionProcessor<'a> {
 			processed_region,
 			lightmap,
 			entities,
+			image_format: processor.config.tile_image_format(),
 			has_unknown: false,
 		})
 	}
@@ -179,7 +182,7 @@ impl<'a> SingleRegionProcessor<'a> {
 			self.input_timestamp,
 			|file| {
 				self.lightmap
-					.write_to(file, image::ImageFormat::Png)
+					.write_to(file, self.image_format)
 					.context("Failed to save image")
 			},
 		)

src/core/tile_mipmapper.rs

@@ -144,7 +144,7 @@ where
 		}
 
 		image
-			.write_to(file, image::ImageFormat::Png)
+			.write_to(file, self.config.tile_image_format())
 			.context("Failed to save image")
 	}
 }

src/core/tile_renderer.rs

@@ -304,7 +304,7 @@ impl<'a> TileRenderer<'a> {
 			processed_timestamp,
 			|file| {
 				image
-					.write_to(file, image::ImageFormat::Png)
+					.write_to(file, self.config.tile_image_format())
 					.context("Failed to save image")
 			},
 		)?;