Speed up terrain generation

worldgen-c/include/worldgen.h

@@ -7,6 +7,7 @@
 
 #define CHUNK_SIZE 16
 #define CHUNK_HEIGHT 256
+#define WORLDGEN_HEIGHT_CACHE_SIZE 32768
 
 	enum BlockId {
 		BLOCK_BEDROCK = 0,
@@ -64,6 +65,13 @@ typedef struct {
 	uint16_t blocks[CHUNK_HEIGHT][CHUNK_SIZE][CHUNK_SIZE];
 } chunk_data;
 
+typedef struct {
+	int x;
+	int z;
+	int value;
+	uint8_t valid;
+} worldgen_height_cache_entry;
+
 typedef struct {
 	simplex_noise noise;
 	int sea_level;
@@ -75,6 +83,7 @@ typedef struct {
 	size_t trail_segment_cap;
 	int prepass_done;
 	int prepass_min_x, prepass_max_x, prepass_min_z, prepass_max_z;
+	worldgen_height_cache_entry height_cache[WORLDGEN_HEIGHT_CACHE_SIZE];
 } worldgen_ctx;
 
 void worldgen_init(worldgen_ctx *ctx, int world_seed, int sea_level, int snow_line);