Show "transparent background" texture only behind actual texture in TexturePreview class + add borders for readability

editor/plugins/camera_3d_editor_plugin.cpp

@@ -91,6 +91,7 @@ Camera3DPreview::Camera3DPreview(Camera3D *p_camera) :
 	TextureRect *display = get_texture_display();
 	display->set_texture(sub_viewport->get_texture());
 	sub_viewport->connect("size_changed", callable_mp((CanvasItem *)display, &CanvasItem::queue_redraw));
+	sub_viewport->get_texture()->connect_changed(callable_mp((TexturePreview *)this, &Camera3DPreview::_update_texture_display_ratio));
 
 	ProjectSettings::get_singleton()->connect("settings_changed", callable_mp(this, &Camera3DPreview::_update_sub_viewport_size));
 	_update_sub_viewport_size();

editor/plugins/texture_editor_plugin.cpp

@@ -32,6 +32,8 @@
 
 #include "editor/editor_string_names.h"
 #include "editor/themes/editor_scale.h"
+#include "scene/gui/aspect_ratio_container.h"
+#include "scene/gui/color_rect.h"
 #include "scene/gui/label.h"
 #include "scene/gui/texture_rect.h"
 #include "scene/resources/animated_texture.h"
@@ -61,11 +63,25 @@ void TexturePreview::_notification(int p_what) {
 				metadata_label->add_theme_font_override(SceneStringName(font), metadata_label_font);
 			}
 
+			bg_rect->set_color(get_theme_color(SNAME("dark_color_2"), EditorStringName(Editor)));
 			checkerboard->set_texture(get_editor_theme_icon(SNAME("Checkerboard")));
+			cached_outline_color = get_theme_color(SNAME("extra_border_color_1"), EditorStringName(Editor));
 		} break;
 	}
 }
 
+void TexturePreview::_draw_outline() {
+	const float outline_width = Math::round(EDSCALE);
+	const Rect2 outline_rect = Rect2(Vector2(), texture_display->get_size()).grow(outline_width * 0.5);
+	texture_display->draw_rect(outline_rect, cached_outline_color, false, outline_width);
+}
+
+void TexturePreview::_update_texture_display_ratio() {
+	if (texture_display->get_texture().is_valid()) {
+		centering_container->set_ratio(texture_display->get_texture()->get_size().aspect());
+	}
+}
+
 void TexturePreview::_update_metadata_label_text() {
 	const Ref<Texture2D> texture = texture_display->get_texture();
 
@@ -124,25 +140,49 @@ void TexturePreview::_update_metadata_label_text() {
 }
 
 TexturePreview::TexturePreview(Ref<Texture2D> p_texture, bool p_show_metadata) {
+	set_custom_minimum_size(Size2(0.0, 256.0) * EDSCALE);
+
+	bg_rect = memnew(ColorRect);
+
+	add_child(bg_rect);
+
+	margin_container = memnew(MarginContainer);
+	const float outline_width = Math::round(EDSCALE);
+	margin_container->add_theme_constant_override("margin_right", outline_width);
+	margin_container->add_theme_constant_override("margin_top", outline_width);
+	margin_container->add_theme_constant_override("margin_left", outline_width);
+	margin_container->add_theme_constant_override("margin_bottom", outline_width);
+	add_child(margin_container);
+
+	centering_container = memnew(AspectRatioContainer);
+	margin_container->add_child(centering_container);
+
 	checkerboard = memnew(TextureRect);
+	checkerboard->set_expand_mode(TextureRect::EXPAND_IGNORE_SIZE);
 	checkerboard->set_stretch_mode(TextureRect::STRETCH_TILE);
 	checkerboard->set_texture_repeat(CanvasItem::TEXTURE_REPEAT_ENABLED);
-	checkerboard->set_custom_minimum_size(Size2(0.0, 256.0) * EDSCALE);
+	centering_container->add_child(checkerboard);
-	add_child(checkerboard);
 
 	texture_display = memnew(TextureRect);
 	texture_display->set_texture_filter(TEXTURE_FILTER_NEAREST_WITH_MIPMAPS);
 	texture_display->set_texture(p_texture);
-	texture_display->set_anchors_preset(TextureRect::PRESET_FULL_RECT);
-	texture_display->set_stretch_mode(TextureRect::STRETCH_KEEP_ASPECT_CENTERED);
 	texture_display->set_expand_mode(TextureRect::EXPAND_IGNORE_SIZE);
-	add_child(texture_display);
+	centering_container->add_child(texture_display);
+
+	texture_display->connect(SceneStringName(draw), callable_mp(this, &TexturePreview::_draw_outline));
+
+	if (p_texture.is_valid()) {
+		_update_texture_display_ratio();
+		p_texture->connect_changed(callable_mp(this, &TexturePreview::_update_texture_display_ratio));
+	}
 
 	if (p_show_metadata) {
 		metadata_label = memnew(Label);
 
+		if (p_texture.is_valid()) {
 			_update_metadata_label_text();
 			p_texture->connect_changed(callable_mp(this, &TexturePreview::_update_metadata_label_text));
+		}
 
 		// It's okay that these colors are static since the grid color is static too.
 		metadata_label->add_theme_color_override(SceneStringName(font_color), Color(1, 1, 1));

editor/plugins/texture_editor_plugin.h

@@ -36,6 +36,8 @@
 #include "scene/gui/margin_container.h"
 #include "scene/resources/texture.h"
 
+class AspectRatioContainer;
+class ColorRect;
 class TextureRect;
 
 class TexturePreview : public MarginContainer {
@@ -44,13 +46,20 @@ class TexturePreview : public MarginContainer {
 private:
 	TextureRect *texture_display = nullptr;
 
+	MarginContainer *margin_container = nullptr;
+	AspectRatioContainer *centering_container = nullptr;
+	ColorRect *bg_rect = nullptr;
 	TextureRect *checkerboard = nullptr;
 	Label *metadata_label = nullptr;
 
+	Color cached_outline_color;
+
+	void _draw_outline();
 	void _update_metadata_label_text();
 
 protected:
 	void _notification(int p_what);
+	void _update_texture_display_ratio();
 
 public:
 	TextureRect *get_texture_display();