From 6e0913a3f77354eab2eeceba66db7d1750e22581 Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Sat, 19 Jul 2025 12:57:36 -0700
Subject: Avoid recomputing the iso space

---
 src/isogfx.c | 56 +++++++++++++++++++++++++++++---------------------------
 1 file changed, 29 insertions(+), 27 deletions(-)

(limited to 'src')

diff --git a/src/isogfx.c b/src/isogfx.c
index e182dff..0aaeb9d 100644
--- a/src/isogfx.c
+++ b/src/isogfx.c
@@ -32,6 +32,12 @@ typedef struct vec2 {
 // Renderer state.
 // -----------------------------------------------------------------------------
 
+typedef struct CoordSystem {
+  ivec2 o; // Origin.
+  ivec2 x;
+  ivec2 y;
+} CoordSystem;
+
 typedef struct Screen {
   int    width;
   int    height;
@@ -48,6 +54,7 @@ typedef struct SpriteInstance {
 
 typedef struct IsoGfx {
   Screen          screen;
+  CoordSystem     iso_space;
   double          last_animation_time;
   Tile            next_tile; // For procedurally-generated tiles.
   Tm_Map*         map;
@@ -109,6 +116,20 @@ static inline Pixel* screen_xy_mut(Screen* screen, int x, int y) {
   return (Pixel*)screen_xy_const_ref(screen, x, y);
 }
 
+/// Create the basis for the isometric coordinate system with origin and vectors
+/// expressed in the Cartesian system.
+static CoordSystem make_iso_coord_system(
+    const Tm_Map* const map, const Screen* const screen) {
+  assert(map);
+  assert(screen);
+  const ivec2 o = {screen->width / 2, 0};
+  const ivec2 x = {
+      .x = map->base_tile_width / 2, .y = map->base_tile_height / 2};
+  const ivec2 y = {
+      .x = -map->base_tile_width / 2, .y = map->base_tile_height / 2};
+  return (CoordSystem){o, x, y};
+}
+
 // -----------------------------------------------------------------------------
 // Renderer, world and tile management.
 // -----------------------------------------------------------------------------
@@ -212,6 +233,8 @@ void isogfx_make_world(IsoGfx* iso, const WorldDesc* desc) {
   *iso->tileset = (Ts_TileSet){
       .num_tiles = desc->num_tiles,
   };
+
+  iso->iso_space = make_iso_coord_system(iso->map, &iso->screen);
 }
 
 bool isogfx_load_world(IsoGfx* iso, const char* filepath) {
@@ -261,6 +284,8 @@ bool isogfx_load_world(IsoGfx* iso, const char* filepath) {
   assert(ts_validate_tileset(tileset));
   assert(tm_validate_map(map, tileset));
 
+  iso->iso_space = make_iso_coord_system(iso->map, &iso->screen);
+
   success = true;
 
 cleanup:
@@ -462,24 +487,6 @@ void isogfx_update(IsoGfx* iso, double t) {
 // Rendering and picking.
 // -----------------------------------------------------------------------------
 
-typedef struct CoordSystem {
-  ivec2 o; /// Origin.
-  ivec2 x;
-  ivec2 y;
-} CoordSystem;
-
-/// Create the basis for the isometric coordinate system with origin and vectors
-/// expressed in the Cartesian system.
-static CoordSystem make_iso_coord_system(const IsoGfx* iso) {
-  assert(iso);
-  const ivec2 o = {iso->screen.width / 2, 0};
-  const ivec2 x = {
-      .x = iso->map->base_tile_width / 2, .y = iso->map->base_tile_height / 2};
-  const ivec2 y = {
-      .x = -iso->map->base_tile_width / 2, .y = iso->map->base_tile_height / 2};
-  return (CoordSystem){o, x, y};
-}
-
 /// Get the screen position of the top diamond-corner of the tile at world
 /// (x,y).
 static ivec2 GetTileScreenOrigin(
@@ -582,8 +589,6 @@ static void draw_world(IsoGfx* iso) {
 
   memset(iso->screen.pixels, 0, W * H * sizeof(Pixel));
 
-  const CoordSystem iso_space = make_iso_coord_system(iso);
-
   const Tm_Layer* layer = tm_map_get_layer(iso->map, 0);
 
   // TODO: Culling.
@@ -594,7 +599,7 @@ static void draw_world(IsoGfx* iso) {
   for (int wy = 0; wy < iso->map->world_height; ++wy) {
     for (int wx = 0; wx < iso->map->world_width; ++wx) {
       const Tile  tile          = tm_layer_get_tile(iso->map, layer, wx, wy);
-      const ivec2 screen_origin = GetTileScreenOrigin(iso_space, wx, wy);
+      const ivec2 screen_origin = GetTileScreenOrigin(iso->iso_space, wx, wy);
       draw_tile(iso, screen_origin, tile);
     }
   }
@@ -620,15 +625,13 @@ static void draw_sprite(
 static void draw_sprites(IsoGfx* iso) {
   assert(iso);
 
-  const CoordSystem iso_space = make_iso_coord_system(iso);
-
   for (const SpriteInstance* sprite = iso->head_sprite; sprite;
        sprite                       = sprite->next) {
     const Ss_SpriteSheet* sheet = sprite->sheet;
     assert(sheet);
 
-    const ivec2 screen_origin =
-        GetTileScreenOrigin(iso_space, sprite->position.x, sprite->position.y);
+    const ivec2 screen_origin = GetTileScreenOrigin(
+        iso->iso_space, sprite->position.x, sprite->position.y);
     draw_sprite(iso, screen_origin, sprite, sheet);
   }
 }
@@ -646,8 +649,7 @@ void isogfx_draw_tile(IsoGfx* iso, int x, int y, Tile tile) {
   assert(x < iso->map->world_width);
   assert(y < iso->map->world_height);
 
-  const CoordSystem iso_space     = make_iso_coord_system(iso);
-  const ivec2       screen_origin = GetTileScreenOrigin(iso_space, x, y);
+  const ivec2 screen_origin = GetTileScreenOrigin(iso->iso_space, x, y);
   draw_tile(iso, screen_origin, tile);
 }
 
-- 
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