Refactor: factorize WGPU init code for 3D tests

Extracted duplicate WGPU initialization boilerplate from test_3d_physics,
test_3d_render, and test_mesh into shared helper (test_3d_helpers).

**Changes:**
- New: src/tests/common/test_3d_helpers.{h,cc} (~120 LOC)
- Removed ~280 LOC of duplicate init_wgpu() implementations
- Net savings: -141 LOC

**Benefits:**
- Single source of truth for surface+device initialization
- Eliminates cross-compile #ifdef duplication
- Easier maintenance for callback API changes

All 34 tests pass.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 100 insertions, 0 deletions

diff --git a/src/tests/common/test_3d_helpers.cc b/src/tests/common/test_3d_helpers.cc
new file mode 100644
index 0000000..13e1cfe
--- /dev/null
+++ b/src/tests/common/test_3d_helpers.cc
@@ -0,0 +1,100 @@
+// This file is part of the 64k demo project.
+// Common WGPU initialization for 3D visual tests with surfaces.
+
+#include "test_3d_helpers.h"
+#include <cstdio>
+#include <cstdlib>
+
+WgpuSurfaceContext init_wgpu_with_surface(PlatformState* platform_state) {
+  WgpuSurfaceContext ctx = {};
+
+  WGPUInstance instance = wgpuCreateInstance(nullptr);
+  if (!instance) {
+    fprintf(stderr, "Failed to create WGPU instance.\n");
+    exit(1);
+  }
+
+  ctx.surface = platform_create_wgpu_surface(instance, platform_state);
+  if (!ctx.surface) {
+    fprintf(stderr, "Failed to create WGPU surface.\n");
+    exit(1);
+  }
+
+  WGPURequestAdapterOptions adapter_opts = {};
+  adapter_opts.compatibleSurface = ctx.surface;
+  adapter_opts.powerPreference = WGPUPowerPreference_HighPerformance;
+
+#if defined(DEMO_CROSS_COMPILE_WIN32)
+  auto on_adapter = [](WGPURequestAdapterStatus status, WGPUAdapter adapter,
+                       const char* message, void* userdata) {
+    if (status == WGPURequestAdapterStatus_Success) {
+      *(WGPUAdapter*)userdata = adapter;
+    }
+  };
+  wgpuInstanceRequestAdapter(instance, &adapter_opts, on_adapter, &ctx.adapter);
+#else
+  auto on_adapter = [](WGPURequestAdapterStatus status, WGPUAdapter adapter,
+                       WGPUStringView message, void* userdata, void* user2) {
+    (void)user2;
+    if (status == WGPURequestAdapterStatus_Success) {
+      *(WGPUAdapter*)userdata = adapter;
+    }
+  };
+  WGPURequestAdapterCallbackInfo adapter_cb = {};
+  adapter_cb.mode = WGPUCallbackMode_WaitAnyOnly;
+  adapter_cb.callback = on_adapter;
+  adapter_cb.userdata1 = &ctx.adapter;
+  wgpuInstanceRequestAdapter(instance, &adapter_opts, adapter_cb);
+#endif
+
+  while (!ctx.adapter) {
+    platform_wgpu_wait_any(instance);
+  }
+
+  WGPUDeviceDescriptor device_desc = {};
+
+#if defined(DEMO_CROSS_COMPILE_WIN32)
+  auto on_device = [](WGPURequestDeviceStatus status, WGPUDevice device,
+                      const char* message, void* userdata) {
+    if (status == WGPURequestDeviceStatus_Success) {
+      *(WGPUDevice*)userdata = device;
+    }
+  };
+  wgpuAdapterRequestDevice(ctx.adapter, &device_desc, on_device, &ctx.device);
+#else
+  auto on_device = [](WGPURequestDeviceStatus status, WGPUDevice device,
+                      WGPUStringView message, void* userdata, void* user2) {
+    (void)user2;
+    if (status == WGPURequestDeviceStatus_Success) {
+      *(WGPUDevice*)userdata = device;
+    }
+  };
+  WGPURequestDeviceCallbackInfo device_cb = {};
+  device_cb.mode = WGPUCallbackMode_WaitAnyOnly;
+  device_cb.callback = on_device;
+  device_cb.userdata1 = &ctx.device;
+  wgpuAdapterRequestDevice(ctx.adapter, &device_desc, device_cb);
+#endif
+
+  while (!ctx.device) {
+    platform_wgpu_wait_any(instance);
+  }
+
+  ctx.queue = wgpuDeviceGetQueue(ctx.device);
+
+  WGPUSurfaceCapabilities caps = {};
+  wgpuSurfaceGetCapabilities(ctx.surface, ctx.adapter, &caps);
+  ctx.format = caps.formats[0];
+
+  WGPUSurfaceConfiguration config = {};
+  config.device = ctx.device;
+  config.format = ctx.format;
+  config.usage = WGPUTextureUsage_RenderAttachment;
+  config.width = platform_state->width;
+  config.height = platform_state->height;
+  config.presentMode = WGPUPresentMode_Fifo;
+  config.alphaMode = WGPUCompositeAlphaMode_Opaque;
+  wgpuSurfaceConfigure(ctx.surface, &config);
+
+  return ctx;
+}