Add Metal preview and OpenGL selection regression

Add a CPU-driven Metal preview implementation and an OpenGL selection regression test. Metal: implement RendererTextureBackendState, build RGBA float pixels via OpenImageIO, generate preview pixels with exposure/gamma/offset, color modes, orientation and heatmap, create/upload RGBA32Float Metal textures, manage texture lifecycle and expose ImGui texture refs; also set CAMetalLayer framebufferOnly and minor cleanup. Tests/docs: add imiv_opengl_selection_regression.py and wire it into CMake to run when OpenGL is enabled; update imiv_backends.md to reflect OpenGL partial feature coverage and Metal development status. This enables immediate preview/testing on macOS while GPU-native Metal preview pipeline remains planned.

Author: ssh4net

src/imiv/CMakeLists.txt

@@ -1043,6 +1043,23 @@ if (TARGET imiv
         imiv_selection_regression PROPERTIES
             LABELS "imiv;gui"
             TIMEOUT 360)
+
+    if (_imiv_renderer_is_opengl)
+        add_test (
+            NAME imiv_opengl_selection_regression
+            COMMAND
+                "${Python3_EXECUTABLE}"
+                "${CMAKE_CURRENT_SOURCE_DIR}/tools/imiv_opengl_selection_regression.py"
+                --bin "$<TARGET_FILE:imiv>"
+                --cwd "$<TARGET_FILE_DIR:imiv>"
+                --oiiotool "$<TARGET_FILE:oiiotool>"
+                --env-script "${CMAKE_BINARY_DIR}/imiv_env.sh"
+                --out-dir "${CMAKE_BINARY_DIR}/imiv_captures/opengl_selection_regression")
+        set_tests_properties (
+            imiv_opengl_selection_regression PROPERTIES
+                LABELS "imiv;imiv_opengl;gui"
+                TIMEOUT 360)
+    endif ()
 elseif (TARGET imiv
         AND OIIO_BUILD_TESTS
         AND BUILD_TESTING)

src/imiv/imiv_backends.md

@@ -67,14 +67,14 @@ Legend:
 |---|---|---|---|
 | App bootstrap and main window | Yes | Yes | Yes |
 | Dear ImGui backend | Yes | Yes | Yes |
-| Direct image upload | Yes | Yes | No |
-| Preview rendering | Yes | Yes | No |
-| Exposure / gamma / offset | Yes | Yes | No |
-| Channel / luma / heatmap modes | Yes | Yes | No |
-| Orientation-aware preview | Yes | Yes | No |
-| Linear / nearest preview sampling | Yes | Yes | No |
-| Pixel closeup window | Yes | Yes | No |
-| Area Sample / selection UI | Yes | Yes | No |
+| Direct image upload | Yes | Yes | Partial |
+| Preview rendering | Yes | Yes | Partial |
+| Exposure / gamma / offset | Yes | Yes | Partial |
+| Channel / luma / heatmap modes | Yes | Yes | Partial |
+| Orientation-aware preview | Yes | Yes | Partial |
+| Linear / nearest preview sampling | Yes | Yes | Partial |
+| Pixel closeup window | Yes | Yes | Partial |
+| Area Sample / selection UI | Yes | Yes | Partial |
 | Drag and drop | Yes | Yes | Yes |
 | Screenshot / readback | Yes | Yes | No |
 | OCIO display/view | Yes | Yes | No |
@@ -145,8 +145,6 @@ Current design:
 
 Current gaps:
 
-- no live OCIO display/view update regression equivalent to Vulkan yet
-- no dedicated OpenGL selection/interaction regression target yet
 - no Metal-equivalent backend parity to compare against
 
 Current coverage:
@@ -158,19 +156,21 @@ Current coverage:
 - OCIO config selection and builtin/global/user fallback
 - OCIO GLSL preview path
 - OpenGL-only screenshot smoke regression
+- OpenGL live OCIO update regressions
+- OpenGL selection regression target
 
 OCIO notes:
 
 - startup preflight for OpenGL now validates the OCIO runtime/config path
   without using Vulkan SPIR-V compilation
-- OpenGL OCIO regressions currently rely on the shared config/fallback tests,
-  not the Vulkan-only runtime-glslang live-update tests
+- OpenGL OCIO regressions now include dedicated live view/display switching
+  coverage without relying on Vulkan runtime glslang
 
 ## Metal
 
 Status:
 
-- `Skeleton`
+- `Development`
 
 Implementation:
 
@@ -182,20 +182,29 @@ Current scope:
 - Metal device / command queue creation
 - CAMetalLayer setup
 - Dear ImGui Metal backend hookup
+- CPU preview generation uploaded into Metal textures
+- basic preview controls through the shared renderer contract
 
 Current gaps:
 
-- no image upload
-- no preview rendering
 - no screenshot/readback
 - no OCIO path
+- no GPU-native Metal preview pipeline yet
 
 Planned direction:
 
 - use backend-native Metal rendering
 - do not try to reuse Vulkan pipeline code directly
 - OCIO should later use OCIO MSL output, not the Vulkan shader path
 
+Important constraints:
+
+- the current Metal path is a bring-up path for immediate macOS verification,
+  not the final performance path
+- Dear ImGui Metal currently samples textures linearly, so nearest/closeup
+  behavior is only partial until Metal-specific sampler control or a dedicated
+  closeup preview path is added
+
 ## Feature Mapping Rules
 
 These should stay consistent across backends where the feature exists.