Implement Texture Atlases

assets.cpp

@@ -13,16 +13,32 @@ static constexpr uint8_t FRUITS_DATA[] = {
 #embed "fruits.jpg"
 };
 
-void init_assets(flecs::world &world) {
-  auto *renderer = world.get<SdlHandles>()->renderer;
-
-  auto *background_iostream =
-      SDL_IOFromConstMem(BACKGROUND_DATA, sizeof(BACKGROUND_DATA));
-  SDL_Texture *background =
-      IMG_LoadTexture_IO(renderer, background_iostream, false);
-  if (background == nullptr) {
+SDL_Texture *load_texture(uint8_t const *data, size_t size,
+                          SDL_Renderer *renderer) {
+  auto *iostream = SDL_IOFromConstMem(data, size);
+  SDL_Texture *texture = IMG_LoadTexture_IO(renderer, iostream, false);
+  if (texture == nullptr) {
     spdlog::error("Failed to load SDL texture!\nCause: {}", SDL_GetError());
   }
 
-  world.set<SpriteAssets>(SpriteAssets{.background = background});
+  return texture;
+}
+
+void init_assets(flecs::world &world) {
+  auto *renderer = world.get<SdlHandles>()->renderer;
+
+  auto *background =
+      load_texture(BACKGROUND_DATA, sizeof(BACKGROUND_DATA), renderer);
+  TextureAtlasLayout background_layout = {
+      .width = 866, .height = 510, .rows = 1, .columns = 1};
+
+  auto *fruits = load_texture(FRUITS_DATA, sizeof(FRUITS_DATA), renderer);
+  TextureAtlasLayout fruits_layout = {
+      .width = 16, .height = 16, .rows = 6, .columns = 38};
+
+  world.set<TextureAssets>(TextureAssets{
+      .background = Texture{.sdl_texture = background,
+                            .texture_atlas_layout = background_layout},
+      .fruits = Texture{.sdl_texture = fruits,
+                        .texture_atlas_layout = fruits_layout}});
 }

assets.hpp

@@ -3,9 +3,21 @@
 #include <SDL3/SDL.h>
 #include <flecs.h>
 
-struct SpriteAssets {
-  SDL_Texture *background;
-  SDL_Texture *fruits;
+struct TextureAtlasLayout {
+  uint16_t width;
+  uint16_t height;
+  uint8_t rows;
+  uint8_t columns;
+};
+
+struct Texture {
+  SDL_Texture *sdl_texture;
+  TextureAtlasLayout texture_atlas_layout;
+};
+
+struct TextureAssets {
+  Texture background;
+  Texture fruits;
 };
 
 void init_assets(flecs::world &world);

main.cpp

@@ -1,6 +1,7 @@
 #include "assets.hpp"
-#include "sdl_types.hpp"
 #include "input.hpp"
+#include "sdl_types.hpp"
+#include "sprite.hpp"
 
 #include <SDL3/SDL.h>
 #include <SDL3/SDL_error.h>
@@ -43,6 +44,42 @@ int main() {
   world.set<ButtonInput>(ButtonInput{});
   world.set<SdlHandles>(SdlHandles{.window = window, .renderer = renderer});
   init_assets(world);
+  auto *texture_assets = world.get<TextureAssets>();
+
+  world.entity("Sprite1")
+      .set<Position>(Position{.x = 0, .y = 0})
+      .set<Sprite>(
+          Sprite{.texture = &texture_assets->fruits, .texture_atlas_index = 0});
+
+  world.entity("Sprite2")
+      .set<Position>(Position{.x = 32, .y = 32})
+      .set<Sprite>(
+          Sprite{.texture = &texture_assets->fruits, .texture_atlas_index = 5});
+
+  flecs::system sys =
+      world
+          .system<SdlHandles const, Position const, Sprite const>(
+              "RenderSprites")
+          .term_at(0)
+          .singleton()
+          .each([](flecs::entity e, SdlHandles const &sdl_handles,
+                   Position const &pos, Sprite const &sprite) {
+            TextureAtlasLayout layout = sprite.texture->texture_atlas_layout;
+            uint8_t row = sprite.texture_atlas_index / layout.columns;
+            uint8_t column = sprite.texture_atlas_index % layout.columns;
+            SDL_FRect srcrect{static_cast<float>(column * layout.width),
+                              static_cast<float>(row * layout.height),
+                              static_cast<float>(layout.width),
+                              static_cast<float>(layout.height)};
+
+            SDL_FRect dstrect{static_cast<float>(pos.x),
+                              static_cast<float>(pos.y),
+                              static_cast<float>(layout.width),
+                              static_cast<float>(layout.height)};
+
+            SDL_RenderTexture(sdl_handles.renderer, sprite.texture->sdl_texture,
+                              &srcrect, &dstrect);
+          });
 
   bool exit_gameloop = false;
   while (!exit_gameloop) {
@@ -84,8 +121,9 @@ int main() {
 
     // Render
     SDL_RenderClear(renderer);
-    SDL_RenderTexture(renderer, world.get<SpriteAssets>()->background, nullptr,
+    SDL_RenderTexture(renderer, texture_assets->background.sdl_texture, nullptr,
                       nullptr);
+    world.progress();
     SDL_RenderPresent(renderer);
   }
 

sprite.hpp

@@ -0,0 +1,12 @@
+#pragma once
+
+#include "assets.hpp"
+
+#include <SDL3/SDL.h>
+#include <cstdint>
+#include <optional>
+
+struct Sprite {
+  Texture const *texture;
+  uint16_t texture_atlas_index;
+};