Add GLES2 2D renderer + Linux display manager

First implementation with Linux display manager.

- Add single-threaded mode for EditorResourcePreview (needed for OpenGL).

Co-authored-by: clayjohn <claynjohn@gmail.com>
Co-authored-by: Fabio Alessandrelli <fabio.alessandrelli@gmail.com>

SConstruct

@@ -15,6 +15,8 @@ from collections import OrderedDict
 # Local
 import methods
 import glsl_builders
+import gles_builders
+from platform_methods import run_in_subprocess
 
 # Scan possible build platforms
 
@@ -706,6 +708,26 @@ if selected_platform in platform_list:
     }
     env.Append(BUILDERS=GLSL_BUILDERS)
 
+    if not env["platform"] == "server":  # FIXME: detect GLES3
+        env.Append(
+            BUILDERS={
+                "GLES3_GLSL": env.Builder(
+                    action=run_in_subprocess(gles_builders.build_gles3_headers),
+                    suffix="glsl.gen.h",
+                    src_suffix=".glsl",
+                )
+            }
+        )
+        env.Append(
+            BUILDERS={
+                "GLES2_GLSL": env.Builder(
+                    action=run_in_subprocess(gles_builders.build_gles2_headers),
+                    suffix="glsl.gen.h",
+                    src_suffix=".glsl",
+                )
+            }
+        )
+
     scons_cache_path = os.environ.get("SCONS_CACHE")
     if scons_cache_path != None:
         CacheDir(scons_cache_path)

core/os/os.h

@@ -68,6 +68,11 @@ class OS {
 	bool restart_on_exit = false;
 	List<String> restart_commandline;
 
+	// for the user interface we keep a record of the current display driver
+	// so we can retrieve the rendering drivers available
+	int _display_driver_id = -1;
+	String _current_rendering_driver_name = "";
+
 protected:
 	void _set_logger(CompositeLogger *p_logger);
 
@@ -81,20 +86,29 @@ class OS {
 		RENDER_SEPARATE_THREAD
 	};
 
+	enum RenderMainThreadMode {
+		RENDER_MAIN_THREAD_ONLY,
+		RENDER_ANY_THREAD,
+	};
+
 protected:
 	friend class Main;
 	// Needed by tests to setup command-line args.
 	friend int test_main(int argc, char *argv[]);
 
 	HasServerFeatureCallback has_server_feature_callback = nullptr;
 	RenderThreadMode _render_thread_mode = RENDER_THREAD_SAFE;
+	RenderMainThreadMode _render_main_thread_mode = RENDER_ANY_THREAD;
 
 	// Functions used by Main to initialize/deinitialize the OS.
 	void add_logger(Logger *p_logger);
 
 	virtual void initialize() = 0;
 	virtual void initialize_joypads() = 0;
 
+	void set_current_rendering_driver_name(String p_driver_name) { _current_rendering_driver_name = p_driver_name; }
+	void set_display_driver_id(int p_display_driver_id) { _display_driver_id = p_display_driver_id; }
+
 	virtual void set_main_loop(MainLoop *p_main_loop) = 0;
 	virtual void delete_main_loop() = 0;
 
@@ -110,6 +124,9 @@ class OS {
 
 	static OS *get_singleton();
 
+	String get_current_rendering_driver_name() const { return _current_rendering_driver_name; }
+	int get_display_driver_id() const { return _display_driver_id; }
+
 	void print_error(const char *p_function, const char *p_file, int p_line, const char *p_code, const char *p_rationale, bool p_editor_notify = false, Logger::ErrorType p_type = Logger::ERR_ERROR);
 	void print(const char *p_format, ...) _PRINTF_FORMAT_ATTRIBUTE_2_3;
 	void printerr(const char *p_format, ...) _PRINTF_FORMAT_ATTRIBUTE_2_3;
@@ -241,6 +258,8 @@ class OS {
 	virtual uint64_t get_free_static_memory() const;
 
 	RenderThreadMode get_render_thread_mode() const { return _render_thread_mode; }
+	RenderMainThreadMode get_render_main_thread_mode() const { return _render_main_thread_mode; }
+	void set_render_main_thread_mode(RenderMainThreadMode p_thread_mode) { _render_main_thread_mode = p_thread_mode; }
 
 	virtual String get_locale() const;
 	String get_locale_language() const;

drivers/SCsub

@@ -25,6 +25,11 @@ SConscript("winmidi/SCsub")
 # Graphics drivers
 if env["vulkan"]:
     SConscript("vulkan/SCsub")
+    SConscript("gles2/SCsub")
+    SConscript("gles_common/SCsub")
+    SConscript("gl_context/SCsub")
+else:
+    SConscript("dummy/SCsub")
 
 # Core dependencies
 SConscript("png/SCsub")

drivers/gl_context/SCsub

@@ -0,0 +1,23 @@
+#!/usr/bin/env python
+
+Import("env")
+
+if env["platform"] in ["haiku", "osx", "windows", "linuxbsd"]:
+    # Thirdparty source files
+    thirdparty_dir = "#thirdparty/glad/"
+    thirdparty_sources = [
+        "glad.c",
+    ]
+    thirdparty_sources = [thirdparty_dir + file for file in thirdparty_sources]
+
+    env.Prepend(CPPPATH=[thirdparty_dir])
+
+    env.Append(CPPDEFINES=["GLAD_ENABLED"])
+    env.Append(CPPDEFINES=["GLES_OVER_GL"])
+
+    env_thirdparty = env.Clone()
+    env_thirdparty.disable_warnings()
+    env_thirdparty.add_source_files(env.drivers_sources, thirdparty_sources)
+
+# Godot source files
+env.add_source_files(env.drivers_sources, "*.cpp")

drivers/gles2/SCsub

@@ -0,0 +1,7 @@
+#!/usr/bin/env python
+
+Import("env")
+
+env.add_source_files(env.drivers_sources, "*.cpp")
+
+SConscript("shaders/SCsub")