menu_view: make texture handling more robust

This patch improves the robustness of menu_view when encounting missing
textures, which can happen during development when using styled buttons
and frames. With the patch, menu_view outputs diagnostic messages,
pinpointing the problem.

The patch also updates the texture handling to use the 'File_content'
utility and the VFS for obtaining PNG images.

Issue #3629

repos/gems/include/gems/png_image.h

@@ -78,7 +78,7 @@ class Png_image
 					_assert_non_null<Read_struct_failed>(
 						png_create_read_struct(PNG_LIBPNG_VER_STRING, 0, 0, 0));
 
-				Read_struct(void *data) : data((png_bytep)data)
+				Read_struct(void const *data) : data((png_bytep)data)
 				{
 					png_set_read_fn(png_ptr, this, callback);
 				}
@@ -174,7 +174,7 @@ class Png_image
 		 * \throw Info_failed
 		 */
 		Png_image(Genode::Ram_allocator &ram, Genode::Region_map &rm,
-		          Genode::Allocator &alloc, void *data)
+		          Genode::Allocator &alloc, void const *data)
 		:
 			_ram(ram), _rm(rm), _alloc(alloc), _read_struct(data)
 		{ }

repos/gems/src/app/menu_view/button_widget.h

@@ -110,6 +110,9 @@ struct Menu_view::Button_widget : Widget, Animator::Item
 		_children.for_each([&] (Widget const &child) {
 			child_min_size = child.min_size(); });
 
+		if (!_curr_texture)
+			return child_min_size;
+
 		/* don't get smaller than the background texture */
 		Area const texture_size = _curr_texture->size();
 
@@ -123,7 +126,7 @@ struct Menu_view::Button_widget : Widget, Animator::Item
 	{
 		static Scratch_surface scratch(_factory.alloc);
 
-		Area const texture_size = _curr_texture->size();
+		Area const texture_size = _curr_texture ? _curr_texture->size() : Area(0, 0);
 		Rect const texture_rect(Point(0, 0), texture_size);
 
 		/*
@@ -133,6 +136,9 @@ struct Menu_view::Button_widget : Widget, Animator::Item
 
 		scratch.apply([&] (Surface<Opaque_pixel> &pixel, Surface<Additive_alpha> &alpha) {
 
+			if (!_curr_texture)
+				return;
+
 			if (_prev_texture && animated()) {
 
 				int const blend = _blend >> 8;

repos/gems/src/app/menu_view/frame_widget.h

@@ -64,11 +64,13 @@ struct Menu_view::Frame_widget : Widget
 	          Surface<Pixel_alpha8> &alpha_surface,
 	          Point at) const override
 	{
-		Icon_painter::paint(pixel_surface, Rect(at, _animated_geometry.area()),
-		                    *texture, 255);
+		if (texture) {
+			Icon_painter::paint(pixel_surface, Rect(at, _animated_geometry.area()),
+			                    *texture, 255);
 
-		Icon_painter::paint(alpha_surface, Rect(at, _animated_geometry.area()),
-		                    *texture, 255);
+			Icon_painter::paint(alpha_surface, Rect(at, _animated_geometry.area()),
+			                    *texture, 255);
+		}
 
 		_draw_children(pixel_surface, alpha_surface, at);
 	}

repos/gems/src/app/menu_view/style_database.h

@@ -78,21 +78,28 @@ class Menu_view::Style_database
 		struct Texture_entry : List<Texture_entry>::Element
 		{
 			Path             const path;
-			::File                 png_file;
+			File_content           png_file;
 			Png_image              png_image;
 			Texture<Pixel_rgb888> &texture;
 
+			void const *_png_data()
+			{
+				void const *result = nullptr;
+				png_file.bytes([&] (char const *ptr, size_t) { result = ptr; });
+				return result;
+			}
+
 			/**
 			 * Constructor
 			 *
 			 * \throw Reading_failed
 			 */
-			Texture_entry(Ram_allocator &ram, Region_map &rm,
-			              Allocator &alloc, Path const &path)
+			Texture_entry(Ram_allocator &ram, Region_map &rm, Allocator &alloc,
+			              Directory const &dir, Path const &path)
 			:
 				path(path),
-				png_file(path.string(), alloc),
-				png_image(ram, rm, alloc, png_file.data<void>()),
+				png_file(alloc, dir, path.string(), File_content::Limit{256*1024}),
+				png_image(ram, rm, alloc, _png_data()),
 				texture(*png_image.texture<Pixel_rgb888>())
 			{ }
 		};
@@ -153,7 +160,7 @@ class Menu_view::Style_database
 			typedef String<64> Style;
 			Style const style = node.attribute_value("style", Style("default"));
 
-			return Path("/styles/", node.type(), "/", style, "/", name, ".png");
+			return Path(node.type(), "/", style, "/", name, ".png");
 		}
 
 		/*
@@ -205,12 +212,12 @@ class Menu_view::Style_database
 			 */
 			try {
 				Texture_entry *e = new (_alloc)
-					Texture_entry(_ram, _rm, _alloc, path.string());
+					Texture_entry(_ram, _rm, _alloc, _styles_dir, path.string());
 
 				_textures.insert(e);
 				return &e->texture;
 
-			} catch (Reading_failed) {
+			} catch (...) {
 				warning("could not read texture data from file \"", path.string(), "\"");
 				return nullptr;
 			}