Fix multiwindow support in GLES3 for X11, Windows, and MacOS.

Instead of updating all viewports, then blitting all viewports
to the backbuffer, then swapping all buffers, we run through
all viewports and render, blit, and swap backbuffer before
going to the next viewport.

drivers/gles3/rasterizer_gles3.cpp

@@ -280,11 +280,6 @@ void RasterizerGLES3::_blit_render_target_to_screen(RID p_render_target, Display
 	GLES3::RenderTarget *rt = texture_storage->get_render_target(p_render_target);
 	ERR_FAIL_COND(!rt);
 
-	// TODO: do we need a keep 3d linear option?
-
-	// Make sure we are drawing to the right context.
-	DisplayServer::get_singleton()->gl_window_make_current(p_screen);
-
 	if (rt->external.fbo != 0) {
 		glBindFramebuffer(GL_READ_FRAMEBUFFER, rt->external.fbo);
 	} else {
@@ -298,9 +293,6 @@ void RasterizerGLES3::_blit_render_target_to_screen(RID p_render_target, Display
 
 // is this p_screen useless in a multi window environment?
 void RasterizerGLES3::blit_render_targets_to_screen(DisplayServer::WindowID p_screen, const BlitToScreen *p_render_targets, int p_amount) {
-	// All blits are going to the system framebuffer, so just bind once.
-	glBindFramebuffer(GL_FRAMEBUFFER, GLES3::TextureStorage::system_fbo);
-
 	for (int i = 0; i < p_amount; i++) {
 		const BlitToScreen &blit = p_render_targets[i];
 

platform/linuxbsd/gl_manager_x11.cpp

@@ -256,7 +256,11 @@ void GLManager_X11::release_current() {
 	if (!_current_window) {
 		return;
 	}
-	glXMakeCurrent(_x_windisp.x11_display, None, nullptr);
+
+	if (!glXMakeCurrent(_x_windisp.x11_display, None, nullptr)) {
+		ERR_PRINT("glXMakeCurrent failed");
+	}
+	_current_window = nullptr;
 }
 
 void GLManager_X11::window_make_current(DisplayServer::WindowID p_window_id) {
@@ -276,7 +280,9 @@ void GLManager_X11::window_make_current(DisplayServer::WindowID p_window_id) {
 
 	const GLDisplay &disp = get_display(win.gldisplay_id);
 
-	glXMakeCurrent(disp.x11_display, win.x11_window, disp.context->glx_context);
+	if (!glXMakeCurrent(disp.x11_display, win.x11_window, disp.context->glx_context)) {
+		ERR_PRINT("glXMakeCurrent failed");
+	}
 
 	_internal_set_current_window(&win);
 }
@@ -290,13 +296,12 @@ void GLManager_X11::make_current() {
 		return;
 	}
 	const GLDisplay &disp = get_current_display();
-	glXMakeCurrent(_x_windisp.x11_display, _x_windisp.x11_window, disp.context->glx_context);
+	if (!glXMakeCurrent(_x_windisp.x11_display, _x_windisp.x11_window, disp.context->glx_context)) {
+		ERR_PRINT("glXMakeCurrent failed");
+	}
 }
 
 void GLManager_X11::swap_buffers() {
-	// NO NEED TO CALL SWAP BUFFERS for each window...
-	// see https://www.khronos.org/registry/OpenGL-Refpages/gl2.1/xhtml/glXSwapBuffers.xml
-
 	if (!_current_window) {
 		return;
 	}
@@ -315,13 +320,6 @@ void GLManager_X11::swap_buffers() {
 		}
 	}
 
-	//	print_line("\tswap_buffers");
-
-	// only for debugging without drawing anything
-	//	glClearColor(Math::randf(), 0, 1, 1);
-	//glClear(GL_COLOR_BUFFER_BIT);
-
-	//const GLDisplay &disp = get_current_display();
 	glXSwapBuffers(_x_windisp.x11_display, _x_windisp.x11_window);
 }
 

platform/macos/gl_manager_macos_legacy.mm

@@ -167,9 +167,8 @@ void GLManager_MacOS::make_current() {
 }
 
 void GLManager_MacOS::swap_buffers() {
-	for (const KeyValue<DisplayServer::WindowID, GLWindow> &E : windows) {
-		[E.value.context flushBuffer];
-	}
+	GLWindow &win = windows[current_window];
+	[win.context flushBuffer];
 }
 
 void GLManager_MacOS::window_update(DisplayServer::WindowID p_window_id) {

platform/windows/gl_manager_windows.cpp

@@ -289,12 +289,7 @@ void GLManager_Windows::make_current() {
 }
 
 void GLManager_Windows::swap_buffers() {
-	// on other platforms, OpenGL swaps buffers for all windows (on all displays, really?)
-	// Windows swaps buffers on a per-window basis
-	// REVISIT: this could be structurally bad, should we have "dirty" flags then?
-	for (KeyValue<DisplayServer::WindowID, GLWindow> &entry : _windows) {
-		SwapBuffers(entry.value.hDC);
-	}
+	SwapBuffers(_current_window->hDC);
 }
 
 Error GLManager_Windows::initialize() {

servers/rendering/renderer_viewport.cpp

@@ -714,7 +714,14 @@ void RendererViewport::draw_viewports() {
 					blit_to_screen_list[vp->viewport_to_screen] = Vector<BlitToScreen>();
 				}
 
-				blit_to_screen_list[vp->viewport_to_screen].push_back(blit);
+				if (OS::get_singleton()->get_current_rendering_driver_name() == "opengl3") {
+					Vector<BlitToScreen> blit_to_screen_vec;
+					blit_to_screen_vec.push_back(blit);
+					RSG::rasterizer->blit_render_targets_to_screen(vp->viewport_to_screen, blit_to_screen_vec.ptr(), 1);
+					RSG::rasterizer->end_frame(true);
+				} else {
+					blit_to_screen_list[vp->viewport_to_screen].push_back(blit);
+				}
 			}
 		}
 

servers/rendering/rendering_server_default.cpp

@@ -91,7 +91,10 @@ void RenderingServerDefault::_draw(bool p_swap_buffers, double frame_step) {
 	RSG::viewport->draw_viewports();
 	RSG::canvas_render->update();
 
-	RSG::rasterizer->end_frame(p_swap_buffers);
+	if (OS::get_singleton()->get_current_rendering_driver_name() != "opengl3") {
+		// Already called for gl_compatibility renderer.
+		RSG::rasterizer->end_frame(p_swap_buffers);
+	}
 
 	XRServer *xr_server = XRServer::get_singleton();
 	if (xr_server != nullptr) {