refactor: call_gfx_find_and_load takes &CStr instead of *const u8

The high-level sprite lookup helper now accepts &CStr directly,
moving the pointer cast inside the function. Callers pass c"name"
without .as_ptr().cast().

Lower-level functions (gfx_dir_find_entry, gfx_resource_create,
DDDisplay vtable methods) keep *const u8 since they're called from
FFI hooks or thin vtable wrappers.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/openwa-core/src/display/gradient.rs

@@ -113,8 +113,7 @@ pub(crate) unsafe fn compute_complex_gradient(
     let mut palette = PaletteContext::new();
 
     // Step 1: Load gradient.img
-    let gradient_sprite =
-        call_gfx_find_and_load(land_layer, c"gradient.img".as_ptr().cast(), layer3_ctx);
+    let gradient_sprite = call_gfx_find_and_load(land_layer, c"gradient.img", layer3_ctx);
     if gradient_sprite.is_null() {
         return;
     }
@@ -143,8 +142,7 @@ pub(crate) unsafe fn compute_complex_gradient(
 
     // Step 3: If heights match, also set gradient_image_2
     if target_rows == gradient_height {
-        let gradient2 =
-            call_gfx_find_and_load(land_layer, c"gradient.img".as_ptr().cast(), layer3_ctx);
+        let gradient2 = call_gfx_find_and_load(land_layer, c"gradient.img", layer3_ctx);
         (*ddgame).gradient_image_2 = gradient2;
     }
 

crates/openwa-core/src/engine/ddgame.rs

@@ -1264,8 +1264,7 @@ unsafe fn init_graphics_and_resources(
 
         if s_var1 < 0x61 && level_height == 0x2B8 {
             // Simple gradient: load gradient.img directly
-            let gradient =
-                call_gfx_find_and_load(land_layer, c"gradient.img".as_ptr().cast(), layer3_ctx);
+            let gradient = call_gfx_find_and_load(land_layer, c"gradient.img", layer3_ctx);
             (*ddgame).gradient_image = gradient;
         } else {
             compute_complex_gradient(ddgame, land_layer, layer3_ctx, s_var1);
@@ -1276,8 +1275,7 @@ unsafe fn init_graphics_and_resources(
             let layer2_ctx = DDDisplay::set_active_layer((*ddgame).display, 2);
             // In the original, fill.img uses piStack_126c which the decompiler
             // shows was set from piVar3 (water_layer from landscape+0xB38).
-            let fill_sprite =
-                call_gfx_find_and_load(water_layer, c"fill.img".as_ptr().cast(), layer2_ctx);
+            let fill_sprite = call_gfx_find_and_load(water_layer, c"fill.img", layer2_ctx);
             if !fill_sprite.is_null() {
                 // Get pixel value: fill_sprite->vtable[4](0, 0)
                 let fill_vt = *(fill_sprite as *const *const u32);

crates/openwa-core/src/render/gfx_dir.rs

@@ -378,10 +378,11 @@ pub unsafe fn gfx_resource_create(gfx_dir: *mut u8, name: *const u8, output: *mu
 #[cfg(target_arch = "x86")]
 pub(crate) unsafe fn call_gfx_find_and_load(
     gfx_dir: *mut u8,
-    name: *const u8,
+    name: &core::ffi::CStr,
     display_ctx: *mut u8,
 ) -> *mut u8 {
-    let entry = gfx_dir_find_entry(name, gfx_dir);
+    let name_ptr = name.as_ptr() as *const u8;
+    let entry = gfx_dir_find_entry(name_ptr, gfx_dir);
 
     if !entry.is_null() {
         // Try cached load: gfx_dir->vtable[2](entry->field_4)
@@ -399,7 +400,7 @@ pub(crate) unsafe fn call_gfx_find_and_load(
     }
 
     // Fallback: load image directly
-    call_gfx_load_and_wrap(gfx_dir, name, display_ctx)
+    call_gfx_load_and_wrap(gfx_dir, name_ptr, display_ctx)
 }
 
 /// Helper: load image via GfxDir__LoadImage + wrap as DisplayGfx.