Fall back to GLES2 if GLES3 is not working

This adds a static is_viable() method to all rasterizers which has to be
called before initializing the rasterizer. This allows us to check what
rasterizer to use in OS::initialize together with the GL context
initialization.

This commit also adds a new project setting
"rendering/quality/driver/driver_fallback" which allows the creator of a
project to specify whether or not fallback to GLES2 is allowed. This
setting is ignored for the editor so the editor will always open even if
the project itself cannot run. This will hopefully reduce confusion for
users downloading projects from the internet.

We also no longer crash when GLES3 is not functioning on a platform.

This fixes #15324

1 files changed, 70 insertions, 18 deletions

diff --git a/platform/uwp/os_uwp.cpp b/platform/uwp/os_uwp.cpp
index 8549a44ce5..b6c3dcf9e0 100644
--- a/platform/uwp/os_uwp.cpp
+++ b/platform/uwp/os_uwp.cpp
@@ -187,12 +187,78 @@ Error OSUWP::initialize(const VideoMode &p_desired, int p_video_driver, int p_au
 	main_loop = NULL;
 	outside = true;
 
+	ContextEGL::Driver opengl_api_type = ContextEGL::GLES_2_0;
+
 	if (p_video_driver == VIDEO_DRIVER_GLES2) {
-		gl_context = memnew(ContextEGL(window, ContextEGL::GLES_2_0));
-	} else {
-		gl_context = memnew(ContextEGL(window, ContextEGL::GLES_3_0));
+		opengl_api_type = ContextEGL::GLES_2_0;
+	}
+
+	bool gl_initialization_error = false;
+
+	gl_context = NULL;
+	while (!gl_context) {
+		gl_context = memnew(ContextEGL(window, opengl_api_type));
+
+		if (gl_context->initialize() != OK) {
+			memdelete(gl_context);
+			gl_context = NULL;
+
+			if (GLOBAL_GET("rendering/quality/driver/driver_fallback") == "Best") {
+				if (p_video_driver == VIDEO_DRIVER_GLES2) {
+					gl_initialization_error = true;
+					break;
+				}
+
+				p_video_driver = VIDEO_DRIVER_GLES2;
+				opengl_api_type = ContextEGL::GLES_2_0;
+			} else {
+				gl_initialization_error = true;
+				break;
+			}
+		}
+	}
+
+	while (true) {
+		if (opengl_api_type == ContextEGL::GLES_3_0) {
+			if (RasterizerGLES3::is_viable() == OK) {
+				RasterizerGLES3::register_config();
+				RasterizerGLES3::make_current();
+				break;
+			} else {
+				if (GLOBAL_GET("rendering/quality/driver/driver_fallback") == "Best" || editor) {
+					p_video_driver = VIDEO_DRIVER_GLES2;
+					opengl_api_type = ContextEGL::GLES_2_0;
+					continue;
+				} else {
+					gl_initialization_error = true;
+					break;
+				}
+			}
+		}
+
+		if (opengl_api_type == ContextEGL::GLES_2_0) {
+			if (RasterizerGLES2::is_viable() == OK) {
+				RasterizerGLES2::register_config();
+				RasterizerGLES2::make_current();
+				break;
+			} else {
+				gl_initialization_error = true;
+				break;
+			}
+		}
+	}
+
+	if (gl_initialization_error) {
+		OS::get_singleton()->alert("Your video card driver does not support any of the supported OpenGL versions.\n"
+								   "Please update your drivers or if you have a very old or integrated GPU upgrade it.",
+				"Unable to initialize Video driver");
+		return ERR_UNAVAILABLE;
 	}
-	gl_context->initialize();
+
+	video_driver_index = p_video_driver;
+	gl_context->make_current();
+	gl_context->set_use_vsync(video_mode.use_vsync);
+
 	VideoMode vm;
 	vm.width = gl_context->get_window_width();
 	vm.height = gl_context->get_window_height();
@@ -230,19 +296,6 @@ Error OSUWP::initialize(const VideoMode &p_desired, int p_video_driver, int p_au
 
 	set_video_mode(vm);
 
-	gl_context->make_current();
-
-	if (p_video_driver == VIDEO_DRIVER_GLES2) {
-		RasterizerGLES2::register_config();
-		RasterizerGLES2::make_current();
-	} else {
-		RasterizerGLES3::register_config();
-		RasterizerGLES3::make_current();
-	}
-	gl_context->set_use_vsync(vm.use_vsync);
-
-	video_driver_index = p_video_driver;
-
 	visual_server = memnew(VisualServerRaster);
 	// FIXME: Reimplement threaded rendering? Or remove?
 	/*
@@ -253,7 +306,6 @@ Error OSUWP::initialize(const VideoMode &p_desired, int p_video_driver, int p_au
 	*/
 
 	visual_server->init();
-
 	input = memnew(InputDefault);
 
 	joypad = ref new JoypadUWP(input);