From 65425f5b2edd9069854883a636eb3e0b2d390ca0 Mon Sep 17 00:00:00 2001
From: veclavtalica <veclavtalica@poto.cafe>
Date: Wed, 25 Sep 2024 18:01:50 +0300
Subject: [PATCH] twn_textures.c: stream-based texture load

---
 src/twn_textures.c | 49 ++++++++++++++++++++++++++++++++++------------
 1 file changed, 37 insertions(+), 12 deletions(-)

diff --git a/src/twn_textures.c b/src/twn_textures.c
index eba5ac4..f9325c0 100644
--- a/src/twn_textures.c
+++ b/src/twn_textures.c
@@ -14,27 +14,55 @@
 
 #include <stdbool.h>
 
+typedef struct {
+    SDL_RWops *rwops;
+    size_t size;
+    size_t position;
+} TextureLoadingContext;
+
+
+static int load_read_callback(void *user, char *data, int size) {
+    TextureLoadingContext *context = user;
+    int read = (int)SDL_RWread(context->rwops, data, 1, size);
+    context->position += read;
+    if (read == 0)
+        CRY_SDL( "Error in streamed texture load.");
+    return read;
+}
+
+static void load_skip_callback(void *user, int n) {
+    TextureLoadingContext *context = user;
+    context->position += n;
+    Sint64 result = SDL_RWseek(context->rwops, n, RW_SEEK_CUR);
+    SDL_assert_always(result != -1);
+}
+
+static int load_eof_callback(void *user) {
+    TextureLoadingContext *context = user;
+    return context->position == context->size;
+}
 
 static SDL_Surface *image_to_surface(const char *path) {
     SDL_RWops *handle = PHYSFSRWOPS_openRead(path);
     if (handle == NULL)
         goto ERR_CANNOT_OPEN_FILE;
 
-    /* TODO: try using callbacks so that no loading of whole files is needed */
-    size_t file_size;
-    void *file_mem = SDL_LoadFile_RW(handle, &file_size, 0);
-    SDL_FreeRW(handle);
+    TextureLoadingContext context = {
+        .rwops = handle,
+        .size = SDL_RWsize(handle),
+    };
 
-    if (!file_mem)
-        goto ERR_CANNOT_ALLOCATE_MEM;
+    stbi_io_callbacks callbacks = {
+        .read = load_read_callback,
+        .skip = load_skip_callback,
+        .eof = load_eof_callback,
+    };
 
     int width, height, channels;
-    void *image_mem = stbi_load_from_memory(file_mem, (int)file_size, &width, &height, &channels, 0);
+    void *image_mem = stbi_load_from_callbacks(&callbacks, &context, &width, &height, &channels, 0);
     if (!image_mem)
         goto ERR_CANNOT_READ_IMAGE;
 
-    SDL_free(file_mem);
-
     Uint32 rmask, gmask, bmask, amask;
 
     #if SDL_BYTEORDER == SDL_BIG_ENDIAN
@@ -65,9 +93,6 @@ ERR_CANNOT_CREATE_SURFACE:
     stbi_image_free(image_mem);
 
 ERR_CANNOT_READ_IMAGE:
-    SDL_free(file_mem);
-
-ERR_CANNOT_ALLOCATE_MEM:
 ERR_CANNOT_OPEN_FILE:
     CRY(path, "Failed to load image. Aborting...");
     die_abruptly();