gpu_helper: dual-path Vulkan init with runtime API-level branch

[Copilot]

On Android 10 (API 29), static Vulkan linking crashes at vkCreateInstance. The fix is dynamic loading via dlopen/dlsym, but applying it unconditionally diverges unnecessarily from upstream. This PR restores the upstream static path for API > 29 and gates the dynamic-load fix behind a runtime check.

Changes

• Runtime branch — Java_com_winlator_core_GPUHelper_vkGetDeviceExtensions now calls android_get_device_api_level() and dispatches to one of two static helpers:

  if (android_get_device_api_level() <= 29)
      return vkGetDeviceExtensions_dynamic(env);
  return vkGetDeviceExtensions_static(env);

• vkGetDeviceExtensions_dynamic (API ≤ 29) — resolves vkCreateInstance, vkEnumeratePhysicalDevices, vkEnumerateDeviceExtensionProperties, vkDestroyInstance via dlsym; populates a full VkApplicationInfo; cleans up (vkDestroyInstance + dlclose) on every exit path; releases JNI local refs in the loop; null-checks all allocations and JNI calls.

• vkGetDeviceExtensions_static (API > 29) — upstream code verbatim; only change is the return type jlong → jobjectArray.

• Return type fix — the JNI entry point and both helpers now return jobjectArray instead of jlong, matching the Java declaration public static native String[] vkGetDeviceExtensions().

• make_empty_array helper — shared by both paths; includes a null guard on FindClass.

• New includes — <dlfcn.h>, <string.h>, <android/api-level.h>.

Original prompt

Context

The file app/src/main/cpp/winlator/gpu_helper.c was modified in commit 5476493f5d87b251772a95213396de9d2dde1872 to fix a crash on Android 10 (API 29) by switching from static Vulkan linking to dynamic loading via dlopen/dlsym. However, the goal is to minimize changes to the upstream code (from utkarshdalal/GameNative) and only apply the dynamic-load fix where it's actually needed.

Required Changes

Restructure app/src/main/cpp/winlator/gpu_helper.c so that:

1. A runtime API-level check determines which code path runs, using android_get_device_api_level() from <android/api-level.h>.

2. For API ≤ 29: Use the dynamic-loading implementation (the fix from commit 5476493), which:

   • Loads libvulkan.so at runtime via dlopen/dlsym
   • Provides a fully populated VkApplicationInfo with VK_API_VERSION_1_0
   • Properly cleans up with vkDestroyInstance and dlclose on all code paths
   • Releases JNI local refs in the extension name loop
   • Has comprehensive null checks

3. For API > 29: Use the original upstream code from utkarshdalal/GameNative, preserved as-is. The original upstream code for reference is:

#include <jni.h>
#include <vulkan/vulkan.h>
#include <stdlib.h>

JNIEXPORT jlong JNICALL
Java_com_winlator_core_GPUHelper_vkGetDeviceExtensions(JNIEnv *env, jclass clazz)
{
    VkInstance instance;
    VkResult   res;

    VkInstanceCreateInfo ci = { .sType = VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO };
    res = vkCreateInstance(&ci, NULL, &instance);
    if (res != VK_SUCCESS) goto make_empty_array;

    uint32_t pdCount = 0;
    res = vkEnumeratePhysicalDevices(instance, &pdCount, NULL);
    if (res != VK_SUCCESS || pdCount == 0) goto make_empty_array;

    pdCount = 1;                        /* original code asks for only one */
    VkPhysicalDevice pd;
    res = vkEnumeratePhysicalDevices(instance, &pdCount, &pd);
    if (!(res == VK_SUCCESS || res == VK_INCOMPLETE)) goto make_empty_array;

    uint32_t extCount = 0;
    res = vkEnumerateDeviceExtensionProperties(pd, NULL, &extCount, NULL);
    if (res != VK_SUCCESS || extCount == 0) goto make_empty_array;

    VkExtensionProperties *ext =
            calloc(extCount, sizeof(VkExtensionProperties));
    res = vkEnumerateDeviceExtensionProperties(pd, NULL, &extCount, ext);
    if (res != VK_SUCCESS) { free(ext); goto make_empty_array; }

    jclass stringCls = (*env)->FindClass(env, "java/lang/String");
    jobjectArray arr =
            (*env)->NewObjectArray(env, (jsize)extCount, stringCls, NULL);

    for (jsize i = 0; i < (jsize)extCount; ++i)
    {
        jstring js = (*env)->NewStringUTF(env, ext[i].extensionName);
        (*env)->SetObjectArrayElement(env, arr, i, js);
    }
    free(ext);
    return (jlong)arr;

    make_empty_array:
    {
        jclass stringCls = (*env)->FindClass(env, "java/lang/String");
        jobjectArray empty = (*env)->NewObjectArray(env, 0, stringCls, NULL);
        return (jlong)empty;
    }
}

4. The JNI entry point Java_com_winlator_core_GPUHelper_vkGetDeviceExtensions should have its return type changed from jlong to jobjectArray (this is mandatory on ALL paths because the Java declaration is public static native String[] vkGetDeviceExtensions() — returning jlong is undefined behavior). The entry point should simply branch:

JNIEXPORT jobjectArray JNICALL
Java_com_winlator_core_GPUHelper_vkGetDeviceExtensions(JNIEnv *env, jclass clazz)
{
    (void)clazz;
    if (android_get_device_api_level() <= 29) {
        return vkGetDeviceExtensions_dynamic(env);
    }
    return vkGetDeviceExtensions_static(env);
}

5. The structure should be:

   • A make_empty_array() helper at the top
   • static jobjectArray vkGetDeviceExtensions_dynamic(JNIEnv *env) — the dynamic-load fix for API ≤ 29
   • static jobjectArray vkGetDeviceExtensions_static(JNIEnv *env) — the original upstream code (with only the jlong → jobjectArray return type fix applied)
   • The JNI entry point that branches based on android_get_device_api_level()

6. Required includes: <jni.h>, <vulkan/vulkan.h>, <stdlib.h>, <dlfcn.h>, <string.h>, <android/api-level.h>

Important Notes

• The base for this PR should be the current state of the file (which is the dynamic-load version from commit 5476493). The PR needs to restructure it into the two-path approach described above.
• Keep the upstream static path as close to the original as possible — the only change should be the return type from jlong to jobjectArray and corresponding return statements.

This pull request was created from Copilot chat.

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