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, 19 insertions, 44 deletions

diff --git a/platform/x11/context_gl_x11.cpp b/platform/x11/context_gl_x11.cpp
index 5a239e326b..8c1869a1f1 100644
--- a/platform/x11/context_gl_x11.cpp
+++ b/platform/x11/context_gl_x11.cpp
@@ -116,9 +116,14 @@ Error ContextGL_X11::initialize() {
 	};
 
 	int fbcount;
-	GLXFBConfig fbconfig;
+	GLXFBConfig fbconfig = 0;
 	XVisualInfo *vi = NULL;
 
+	XSetWindowAttributes swa;
+	swa.event_mask = StructureNotifyMask;
+	swa.border_pixel = 0;
+	unsigned long valuemask = CWBorderPixel | CWColormap | CWEventMask;
+
 	if (OS::get_singleton()->is_layered_allowed()) {
 		GLXFBConfig *fbc = glXChooseFBConfig(x11_display, DefaultScreen(x11_display), visual_attribs_layered, &fbcount);
 		ERR_FAIL_COND_V(!fbc, ERR_UNCONFIGURED);
@@ -142,16 +147,10 @@ Error ContextGL_X11::initialize() {
 		}
 		ERR_FAIL_COND_V(!fbconfig, ERR_UNCONFIGURED);
 
-		XSetWindowAttributes swa;
-
-		swa.colormap = XCreateColormap(x11_display, RootWindow(x11_display, vi->screen), vi->visual, AllocNone);
-		swa.border_pixel = 0;
 		swa.background_pixmap = None;
 		swa.background_pixel = 0;
 		swa.border_pixmap = None;
-		swa.event_mask = StructureNotifyMask;
-
-		x11_window = XCreateWindow(x11_display, RootWindow(x11_display, vi->screen), 0, 0, OS::get_singleton()->get_video_mode().width, OS::get_singleton()->get_video_mode().height, 0, vi->depth, InputOutput, vi->visual, CWBorderPixel | CWColormap | CWEventMask | CWBackPixel, &swa);
+		valuemask |= CWBackPixel;
 
 	} else {
 		GLXFBConfig *fbc = glXChooseFBConfig(x11_display, DefaultScreen(x11_display), visual_attribs, &fbcount);
@@ -160,42 +159,21 @@ Error ContextGL_X11::initialize() {
 		vi = glXGetVisualFromFBConfig(x11_display, fbc[0]);
 
 		fbconfig = fbc[0];
-
-		XSetWindowAttributes swa;
-
-		swa.colormap = XCreateColormap(x11_display, RootWindow(x11_display, vi->screen), vi->visual, AllocNone);
-		swa.border_pixel = 0;
-		swa.event_mask = StructureNotifyMask;
-
-		x11_window = XCreateWindow(x11_display, RootWindow(x11_display, vi->screen), 0, 0, OS::get_singleton()->get_video_mode().width, OS::get_singleton()->get_video_mode().height, 0, vi->depth, InputOutput, vi->visual, CWBorderPixel | CWColormap | CWEventMask, &swa);
 	}
 
-	ERR_FAIL_COND_V(!x11_window, ERR_UNCONFIGURED);
-	set_class_hint(x11_display, x11_window);
-	XMapWindow(x11_display, x11_window);
-
-	int (*oldHandler)(Display *, XErrorEvent *) =
-			XSetErrorHandler(&ctxErrorHandler);
+	int (*oldHandler)(Display *, XErrorEvent *) = XSetErrorHandler(&ctxErrorHandler);
 
 	switch (context_type) {
-		case GLES_2_0_COMPATIBLE:
 		case OLDSTYLE: {
+
 			p->glx_context = glXCreateContext(x11_display, vi, 0, GL_TRUE);
+			ERR_FAIL_COND_V(!p->glx_context, ERR_UNCONFIGURED);
 		} break;
-		/*
-		case ContextType::GLES_2_0_COMPATIBLE: {
-
-			static int context_attribs[] = {
-				GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
-				GLX_CONTEXT_MINOR_VERSION_ARB, 0,
-				None
-			};
+		case GLES_2_0_COMPATIBLE: {
 
-			p->glx_context = glXCreateContextAttribsARB(x11_display, fbconfig, NULL, true, context_attribs);
-			ERR_EXPLAIN("Could not obtain an OpenGL 3.0 context!");
+			p->glx_context = glXCreateNewContext(x11_display, fbconfig, GLX_RGBA_TYPE, 0, true);
 			ERR_FAIL_COND_V(!p->glx_context, ERR_UNCONFIGURED);
 		} break;
-		*/
 		case GLES_3_0_COMPATIBLE: {
 
 			static int context_attribs[] = {
@@ -207,24 +185,22 @@ Error ContextGL_X11::initialize() {
 			};
 
 			p->glx_context = glXCreateContextAttribsARB(x11_display, fbconfig, NULL, true, context_attribs);
-			ERR_EXPLAIN("Could not obtain an OpenGL 3.3 context!");
 			ERR_FAIL_COND_V(ctxErrorOccurred || !p->glx_context, ERR_UNCONFIGURED);
 		} break;
 	}
 
+	swa.colormap = XCreateColormap(x11_display, RootWindow(x11_display, vi->screen), vi->visual, AllocNone);
+	x11_window = XCreateWindow(x11_display, RootWindow(x11_display, vi->screen), 0, 0, OS::get_singleton()->get_video_mode().width, OS::get_singleton()->get_video_mode().height, 0, vi->depth, InputOutput, vi->visual, valuemask, &swa);
+
+	ERR_FAIL_COND_V(!x11_window, ERR_UNCONFIGURED);
+	set_class_hint(x11_display, x11_window);
+	XMapWindow(x11_display, x11_window);
+
 	XSync(x11_display, False);
 	XSetErrorHandler(oldHandler);
 
 	glXMakeCurrent(x11_display, x11_window, p->glx_context);
 
-	/*
-	glWrapperInit(wrapper_get_proc_address);
-	glFlush();
-
-	glXSwapBuffers(x11_display,x11_window);
-*/
-	//glXMakeCurrent(x11_display, None, NULL);
-
 	XFree(vi);
 
 	return OK;
@@ -297,7 +273,6 @@ ContextGL_X11::ContextGL_X11(::Display *p_x11_display, ::Window &p_x11_window, c
 ContextGL_X11::~ContextGL_X11() {
 	release_current();
 	glXDestroyContext(x11_display, p->glx_context);
-
 	memdelete(p);
 }