imiv: multi-backend CMake refactor

Refactor imiv CMake to support multiple renderer backends (Vulkan/Metal/OpenGL) enabled independently. Introduces OIIO_IMIV_DEFAULT_RENDERER (replacing deprecated OIIO_IMIV_RENDERER) and OIIO_IMIV_ENABLE_VULKAN/ENABLE_METAL/ENABLE_OPENGL (AUTO/ON/OFF) options, generates imiv_build_config.h, and sets IMIV_WITH_* compile defines. Improves Vulkan and glslang discovery (including explicit Vulkan SDK handling and MSVC CRT compatibility), conditionally enables backend-specific ImGui sources, and selects a sensible default backend when multiple backends are available. Adds imiv_backend.cpp/h and supporting docs/tools, a CTest option OIIO_IMIV_ADD_BACKEND_VERIFY_CTEST to run per-backend verification tests, and updates various regression test invocations to pass backend arguments and rename selection test to ux_actions_regression.

Author: ssh4net

src/imiv/CMakeLists.txt

@@ -0,0 +1,121 @@
+# imiv Verification
+
+Canonical cross-platform verifier:
+
+```bash
+python src/imiv/tools/imiv_backend_verify.py ...
+```
+
+Use the same runner everywhere. It selects the right regression set for the
+requested backend.
+
+Linux / WSL Vulkan:
+
+```bash
+python src/imiv/tools/imiv_backend_verify.py \
+  --backend vulkan \
+  --build-dir build_u \
+  --out-dir verify_vulkan \
+  --trace
+```
+
+Linux / WSL OpenGL:
+
+```bash
+python src/imiv/tools/imiv_backend_verify.py \
+  --backend opengl \
+  --build-dir build_u \
+  --out-dir verify_opengl \
+  --trace
+```
+
+macOS Metal:
+
+```bash
+python3 src/imiv/tools/imiv_backend_verify.py \
+  --backend metal \
+  --build-dir build \
+  --out-dir verify_metal \
+  --trace
+```
+
+macOS OpenGL:
+
+```bash
+python3 src/imiv/tools/imiv_backend_verify.py \
+  --backend opengl \
+  --build-dir build \
+  --out-dir verify_opengl \
+  --trace
+```
+
+macOS Vulkan, if MoltenVK is available:
+
+```bash
+python3 src/imiv/tools/imiv_backend_verify.py \
+  --backend vulkan \
+  --build-dir build \
+  --out-dir verify_vulkan \
+  --trace
+```
+
+Windows Vulkan:
+
+```bat
+python src\imiv\tools\imiv_backend_verify.py ^
+  --backend vulkan ^
+  --build-dir build ^
+  --config Debug ^
+  --out-dir verify_vulkan ^
+  --trace
+```
+
+Windows OpenGL:
+
+```bat
+python src\imiv\tools\imiv_backend_verify.py ^
+  --backend opengl ^
+  --build-dir build ^
+  --config Debug ^
+  --out-dir verify_opengl ^
+  --trace
+```
+
+If the build is already up to date, add:
+
+```text
+--skip-configure --skip-build
+```
+
+If you run through `uv` from the repo root, use:
+
+```bash
+uv run --no-project python src/imiv/tools/imiv_backend_verify.py ...
+```
+
+Optional backend-wide `ctest` entries from one multi-backend build:
+
+```bash
+cmake -S . -B build_u \
+  -D OIIO_IMIV_ENABLE_VULKAN=AUTO \
+  -D OIIO_IMIV_ENABLE_OPENGL=AUTO \
+  -D OIIO_IMIV_ENABLE_METAL=OFF \
+  -D OIIO_IMIV_DEFAULT_RENDERER=vulkan \
+  -D OIIO_IMIV_ADD_BACKEND_VERIFY_CTEST=ON
+```
+
+```bash
+ctest --test-dir build_u -N | rg imiv_backend_verify
+```
+
+Main output logs:
+
+- `verify_smoke.log`
+- `verify_ux.log`
+- `verify_screenshot.log`
+- `verify_sampling.log`
+- `verify_orientation.log`
+- `verify_ocio_missing.log`
+- `verify_ocio_config_source.log`
+- `verify_ocio_live.log`
+- `verify_ocio_live_display.log`

src/imiv/README.md

@@ -168,34 +168,17 @@ env_flag_is_truthy(const char* name)
 bool
 viewer_texture_has_gpu_lifetime(const RendererTexture& texture)
 {
-#if defined(IMIV_BACKEND_VULKAN_GLFW)
-    return texture.image != VK_NULL_HANDLE
-           || texture.source_image != VK_NULL_HANDLE
-           || texture.set != VK_NULL_HANDLE
-           || texture.nearest_mag_set != VK_NULL_HANDLE
-           || texture.pixelview_set != VK_NULL_HANDLE
-           || texture.upload_submit_pending || texture.preview_submit_pending;
-#else
-    (void)texture;
-    return false;
-#endif
+    return texture.backend != nullptr;
 }
 
 void
 quiesce_viewer_texture_lifetime(RendererState& renderer_state,
                                 const RendererTexture& texture)
 {
-#if defined(IMIV_BACKEND_VULKAN_GLFW)
-    if (renderer_state.device == VK_NULL_HANDLE
-        || !viewer_texture_has_gpu_lifetime(texture)) {
+    if (!viewer_texture_has_gpu_lifetime(texture))
         return;
-    }
-    VkResult err = vkDeviceWaitIdle(renderer_state.device);
-    check_vk_result(err);
-#else
-    (void)renderer_state;
-    (void)texture;
-#endif
+    std::string error_message;
+    renderer_wait_idle(renderer_state, error_message);
 }
 
 bool
@@ -677,9 +660,7 @@ close_current_image_action(RendererState& vk_state, ViewerState& viewer,
 {
     const std::string closing_path = viewer.image.path;
     const int closing_index        = viewer.current_path_index;
-#if defined(IMIV_BACKEND_VULKAN_GLFW)
     quiesce_viewer_texture_lifetime(vk_state, viewer.texture);
-#endif
     renderer_destroy_texture(vk_state, viewer.texture);
     remove_loaded_image_path(viewer, closing_path);
     if (!viewer.loaded_image_paths.empty()) {
@@ -847,10 +828,6 @@ capture_main_viewport_screenshot_action(RendererState& vk_state,
 
     int width  = std::max(0, vk_state.framebuffer_width);
     int height = std::max(0, vk_state.framebuffer_height);
-#if defined(IMIV_BACKEND_VULKAN_GLFW)
-    width  = std::max(width, vk_state.window_data.Width);
-    height = std::max(height, vk_state.window_data.Height);
-#endif
     if (width <= 0 || height <= 0) {
         viewer.last_error = "screenshot failed: main viewport size is invalid";
         return false;