[Fix] (DirectVulkan): advertise the GLSL 1.00-era ARB strings KWin gates on, and let a debug property pick the Android backend

MobileGL/ConfigLoader.cpp

@@ -6,6 +6,9 @@
 // SPDX-License-Identifier: LGPL-3.0-only
 // End of Source File Header
 
+#if defined(__ANDROID__)
+#include <sys/system_properties.h>
+#endif
 #include "Config.h"
 #if MOBILEGL_PIPE_PUSH
 // For kMGPipeSubsystemsMigratedAtP5e, the push build's PipePush default (the P2, P3a and P4a
@@ -302,6 +305,17 @@ namespace MobileGL::MG_ConfigLoader {
     inline void InitBackendType() {
         String backendTypeStr;
         QueryEnvVariable("MOBILEGL_BACKEND_TYPE", backendTypeStr, "DirectGLES");
+#if defined(__ANDROID__)
+        // An Android app that hosts the library sets the environment itself, before the library
+        // loads; the debug property is how a developer picks the backend for such a process
+        // without rebuilding it (`adb shell setprop debug.mobilegl.backend DirectVulkan`).
+        char property[PROP_VALUE_MAX] = {};
+        if (__system_property_get("debug.mobilegl.backend", property) > 0) {
+            MGLOG_I("Config: debug.mobilegl.backend=%s overrides MOBILEGL_BACKEND_TYPE=%s", property,
+                    backendTypeStr.c_str());
+            backendTypeStr = property;
+        }
+#endif
 #define ENTRY(backendType)                                                                                             \
     if (backendTypeStr == #backendType) {                                                                              \
         MG_Config::ActiveBackendType = BackendType::backendType;                                                       \

MobileGL/MG_Backend/DirectVulkan/BackendObject_DirectVulkan.cpp

@@ -565,6 +565,12 @@ namespace MobileGL::MG_Backend::DirectVulkan {
             V_OpenGL30, V_OpenGL31, V_OpenGL32, V_OpenGL33, V_OpenGL40, V_OpenGL41, V_OpenGL42, V_OpenGL43,
             V_OpenGL44, V_OpenGL45, V_OpenGL46,
             E_GL_ARB_draw_buffers_blend,
+            // The GLSL 1.00/1.10-era ARB trio plus NPOT textures: all core since GL 2.0 and
+            // trivially true for every context this backend claims (4.6). KWin 6's
+            // EglContext::checkSupported() gates desktop-GL compositing on exactly these four
+            // strings, so withholding them fails its renderer bring-up. Same block as DirectGLES.
+            E_GL_ARB_shader_objects, E_GL_ARB_vertex_shader, E_GL_ARB_fragment_shader,
+            E_GL_ARB_texture_non_power_of_two,
             E_GL_ARB_compute_shader, E_GL_ARB_shader_storage_buffer_object, E_GL_ARB_shader_image_load_store,
             E_GL_ARB_clear_buffer_object, E_GL_ARB_program_interface_query, E_GL_ARB_framebuffer_object, E_GL_ARB_draw_indirect,
             E_GL_ARB_multi_draw_indirect,