feat(glfw): adapter and 1 MS/s streaming demo

adapters/glfw/CMakeLists.txt

@@ -0,0 +1,51 @@
+# The GLFW adapter: the reference host for the library. It owns the window, the
+# context and the loop, and translates GLFW's events into plot::input events.
+#
+# Dependency discovery follows the design spec's order: find_package first,
+# pkg-config next, FetchContent only when neither can supply GLFW (the last
+# resort, because it needs the network).
+set(plot_glfw_dep "")
+
+find_package(glfw3 3.3 QUIET)
+if(TARGET glfw)
+  set(plot_glfw_dep glfw)
+elseif(TARGET glfw3::glfw3)
+  set(plot_glfw_dep glfw3::glfw3)
+endif()
+
+if(NOT plot_glfw_dep)
+  find_package(PkgConfig QUIET)
+  if(PkgConfig_FOUND)
+    pkg_check_modules(GLFW_PC QUIET IMPORTED_TARGET glfw3)
+    if(TARGET PkgConfig::GLFW_PC)
+      set(plot_glfw_dep PkgConfig::GLFW_PC)
+    endif()
+  endif()
+endif()
+
+if(NOT plot_glfw_dep)
+  message(STATUS "plot: glfw3 not found via find_package or pkg-config; fetching it")
+  include(FetchContent)
+  set(GLFW_BUILD_DOCS OFF CACHE BOOL "" FORCE)
+  set(GLFW_BUILD_TESTS OFF CACHE BOOL "" FORCE)
+  set(GLFW_BUILD_EXAMPLES OFF CACHE BOOL "" FORCE)
+  set(GLFW_INSTALL OFF CACHE BOOL "" FORCE)
+  FetchContent_Declare(glfw
+    GIT_REPOSITORY https://github.com/glfw/glfw.git
+    GIT_TAG 3.4
+    GIT_SHALLOW TRUE)
+  FetchContent_MakeAvailable(glfw)
+  set(plot_glfw_dep glfw)
+endif()
+
+message(STATUS "plot: GLFW adapter dependency: ${plot_glfw_dep}")
+
+add_library(plot_glfw STATIC glfw_host.cpp)
+add_library(plot::glfw ALIAS plot_glfw)
+# The public include root is `adapters/`, so the header is reached as
+# <glfw/glfw_host.hpp> -- the toolkit's name first, like every other adapter's.
+target_include_directories(plot_glfw PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/..")
+# GLFW stays PRIVATE: the header forward-declares GLFWwindow and includes no GLFW
+# header, so a consumer of plot::glfw does not inherit the toolkit.
+target_link_libraries(plot_glfw PUBLIC plot::core PRIVATE ${plot_glfw_dep})
+plot_apply_warnings(plot_glfw)