feat: size arena to ~80% of output with resize-aware grid

Store wl_output mode dimensions and compute the default logical window
size as 80% of the output divided by the active scale, with a fallback.
Grid dimensions continue to update on resize.

openspec/changes/arena-size/tasks.md

@@ -2,10 +2,10 @@
 
 ## 1. Output handling
 
-- [ ] 1.1 Store output mode dimensions in the output listener.
-- [ ] 1.2 Compute default logical window size as 80% of output divided by scale, with fallback.
+- [x] 1.1 Store output mode dimensions in the output listener.
+- [x] 1.2 Compute default logical window size as 80% of output divided by scale, with fallback.
 
 ## 2. Verification
 
-- [ ] 2.1 Build and run, verifying window is ~80% of screen.
-- [ ] 2.2 Resize window and verify grid updates.
+- [x] 2.1 Build and run, verifying window is ~80% of screen.
+- [x] 2.2 Resize window and verify grid updates.

wlgol.c

@@ -31,6 +31,8 @@ struct xdg_wm_base *xdg_shell;
 struct wl_seat *wl_seat;
 struct wl_output *wl_output = NULL;
 int output_scale_factor = 1;
+int output_width = 0;
+int output_height = 0;
 
 struct keyboard_data keyboard_data;
 struct pointer_data pointer_data;
@@ -83,7 +85,13 @@ struct wp_fractional_scale_v1 *fractional_scale = NULL;
 
 // output listener
 static void output_geometry_handler(void *data, struct wl_output *output, int32_t x, int32_t y, int32_t phys_w, int32_t phys_h, int32_t subpixel, const char *make, const char *model, int32_t transform) { (void)data;(void)output;(void)x;(void)y;(void)phys_w;(void)phys_h;(void)subpixel;(void)make;(void)model;(void)transform; }
-static void output_mode_handler(void *data, struct wl_output *output, uint32_t flags, int32_t width, int32_t height, int32_t refresh) { (void)data;(void)output;(void)flags;(void)width;(void)height;(void)refresh; }
+static void output_mode_handler(void *data, struct wl_output *output, uint32_t flags, int32_t width, int32_t height, int32_t refresh) {
+	(void)data;(void)output;(void)flags;(void)refresh;
+	if (width > 0 && height > 0) {
+		output_width = width;
+		output_height = height;
+	}
+}
 static void output_done_handler(void *data, struct wl_output *output) { (void)data;(void)output; }
 static void output_scale_handler(void *data, struct wl_output *output, int32_t factor) {
 	(void)data;(void)output;
@@ -426,12 +434,21 @@ int main(void)
 	wl_pointer_add_listener(pointer_data.pointer, &pointer_listener, &pointer_data);
 
 	canvas.fd = -1;
+	logical_width = 1024;
+	logical_height = 576;
 	grid_init(&grid, logical_width / 8, logical_height / 8);
 	grid.show_lines = 1;
 
 	// wait for the surface to be configured
 	wl_display_roundtrip(display);
 
+	if (output_width > 0 && output_height > 0 && current_scale > 0) {
+		logical_width = (int)(output_width * 0.8 / current_scale);
+		logical_height = (int)(output_height * 0.8 / current_scale);
+	}
+	if (logical_width < 8) logical_width = 8;
+	if (logical_height < 8) logical_height = 8;
+
 	/* initial scale may arrive via fractional/output after roundtrip */
 	if (fractional_manager && !fractional_scale) {
 		/* already created above */