render: draw fullscreen views properly

- use a solid black background
- only draw the overlay layer

river/render.zig

@@ -46,23 +46,37 @@ pub fn renderOutput(output: *Output) void {
     _ = c.clock_gettime(c.CLOCK_MONOTONIC, &now);
 
     // wlr_output_attach_render makes the OpenGL context current.
-    if (!c.wlr_output_attach_render(output.wlr_output, null)) {
+    if (!c.wlr_output_attach_render(output.wlr_output, null)) return;
-        return;
+
-    }
     // The "effective" resolution can change if you rotate your outputs.
     var width: c_int = undefined;
     var height: c_int = undefined;
     c.wlr_output_effective_resolution(output.wlr_output, &width, &height);
+
     // Begin the renderer (calls glViewport and some other GL sanity checks)
     c.wlr_renderer_begin(wlr_renderer, width, height);
 
+    // Find the first visible fullscreen view in the stack if there is one
+    var it = ViewStack(View).iterator(output.views.first, output.current_focused_tags);
+    const fullscreen_view = while (it.next()) |node| {
+        if (node.view.current.fullscreen) break &node.view;
+    } else null;
+
+    // If we have a fullscreen view to render, render it.
+    if (fullscreen_view) |view| {
+        // Always clear with solid black for fullscreen
+        c.wlr_renderer_clear(wlr_renderer, &[_]f32{ 0, 0, 0, 1 });
+        renderView(output.*, view, &now);
+        if (build_options.xwayland) renderXwaylandUnmanaged(output.*, &now);
+    } else {
+        // No fullscreen view, so render normal layers/views
         c.wlr_renderer_clear(wlr_renderer, &config.background_color);
 
         renderLayer(output.*, output.layers[c.ZWLR_LAYER_SHELL_V1_LAYER_BACKGROUND], &now);
         renderLayer(output.*, output.layers[c.ZWLR_LAYER_SHELL_V1_LAYER_BOTTOM], &now);
 
         // The first view in the list is "on top" so iterate in reverse.
-    var it = ViewStack(View).reverseIterator(output.views.last, output.current_focused_tags);
+        it = ViewStack(View).reverseIterator(output.views.last, output.current_focused_tags);
         while (it.next()) |node| {
             const view = &node.view;
 
@@ -93,12 +107,12 @@ pub fn renderOutput(output: *Output) void {
             renderBorders(output.*, view, &now);
         }
 
-    // Render xwayland unmanged views
+        if (build_options.xwayland) renderXwaylandUnmanaged(output.*, &now);
-    if (build_options.xwayland) {
-        renderXwaylandUnmanaged(output.*, &now);
-    }
 
         renderLayer(output.*, output.layers[c.ZWLR_LAYER_SHELL_V1_LAYER_TOP], &now);
+    }
+
+    // The overlay layer is rendered in both fullscreen and normal cases
     renderLayer(output.*, output.layers[c.ZWLR_LAYER_SHELL_V1_LAYER_OVERLAY], &now);
 
     // Hardware cursors are rendered by the GPU on a separate plane, and can be