renderer: make overlay features configurable

src/renderer/Overlay.zig

@@ -1,3 +1,15 @@
+/// The debug overlay that can be drawn on top of the terminal
+/// during the rendering process.
+///
+/// This is implemented by doing all the drawing on the CPU via z2d,
+/// since the debug overlay isn't that common, z2d is pretty fast, and
+/// it simplifies our implementation quite a bit by not relying on us
+/// having a bunch of shaders that we have to write per-platform.
+///
+/// Initialize the overlay, apply features with `applyFeatures`, then
+/// get the resulting image with `pendingImage` to upload to the GPU.
+/// This works in concert with `renderer.image.State` to simplify. Draw
+/// it on the GPU as an image composited on top of the terminal output.
 const Overlay = @This();
 
 const std = @import("std");
@@ -15,6 +27,11 @@ surface: z2d.Surface,
 /// Cell size information so we can map grid coordinates to pixels.
 cell_size: CellSize,
 
+/// The set of available features and their configuration.
+pub const Feature = union(enum) {
+    highlight_hyperlinks,
+};
+
 pub const InitError = Allocator.Error || error{
     // The terminal dimensions are invalid to support an overlay.
     // Either too small or too big.
@@ -60,12 +77,28 @@ pub fn pendingImage(self: *const Overlay) Image.Pending {
     };
 }
 
+/// Apply the given features to this overlay. This will draw on top of
+/// any pre-existing content in the overlay.
+pub fn applyFeatures(
+    self: *Overlay,
+    alloc: Allocator,
+    state: *const terminal.RenderState,
+    features: []const Feature,
+) void {
+    for (features) |f| switch (f) {
+        .highlight_hyperlinks => self.highlightHyperlinks(
+            alloc,
+            state,
+        ),
+    };
+}
+
 /// Add rectangles around contiguous hyperlinks in the render state.
 ///
 /// Note: this currently doesn't take into account unique hyperlink IDs
 /// because the render state doesn't contain this. This will be added
 /// later.
-pub fn highlightHyperlinks(
+fn highlightHyperlinks(
     self: *Overlay,
     alloc: Allocator,
     state: *const terminal.RenderState,

src/renderer/generic.zig

@@ -2207,9 +2207,28 @@ pub fn Renderer(comptime GraphicsAPI: type) type {
             }
         }
 
-        fn rebuildOverlay(self: *Self, alloc: Allocator) Overlay.InitError!Overlay {
+        /// Build the overlay as configured. Returns null if there is no
+        /// overlay currently configured.
+        fn rebuildOverlay(
+            self: *Self,
+            alloc: Allocator,
+        ) Overlay.InitError!?Overlay {
+            // Right now, the debug overlay is turned on and configured by
+            // modifying these and recompiling. In the future, we will expose
+            // all of this at runtime via the inspector.
+            const features: []const Overlay.Feature = &.{
+                //.highlight_hyperlinks,
+            };
+
+            // If we have no features enabled, don't build an overlay.
+            if (features.len == 0) return null;
+
             var overlay: Overlay = try .init(alloc, self.size);
-            overlay.highlightHyperlinks(alloc, &self.terminal_state);
+            overlay.applyFeatures(
+                alloc,
+                &self.terminal_state,
+                features,
+            );
             return overlay;
         }