Use a shared copy of placeholder textures, tweak placeholder appearance

This reduces memory usage a bit in case multiple placeholders were
requested, e.g. when using multiple NoiseTextures with no noise property
defined.

The placeholder texture's appearance was also changed from a plain magenta
color to a checkerboard alternating between magenta and black pixels.
This makes it easier to spot when the placeholder texture ends up
being used in a complex scene (usually by accident).
The texture's dimensions remain identical to keep the physical size
identical in 2D.

servers/rendering/renderer_rd/storage_rd/texture_storage.cpp

@@ -518,6 +518,33 @@ TextureStorage::TextureStorage() {
 			rt_sdf.pipelines[i] = RD::get_singleton()->compute_pipeline_create(rt_sdf.shader.version_get_shader(rt_sdf.shader_version, i));
 		}
 	}
+
+	// Initialize texture placeholder data for the `texture_*_placeholder_initialize()` methods.
+
+	constexpr int placeholder_size = 4;
+	texture_2d_placeholder = Image::create_empty(placeholder_size, placeholder_size, false, Image::FORMAT_RGBA8);
+	// Draw a magenta/black checkerboard pattern.
+	for (int i = 0; i < placeholder_size * placeholder_size; i++) {
+		const int x = i % placeholder_size;
+		const int y = i / placeholder_size;
+		print_line(x, "\t", y);
+		texture_2d_placeholder->set_pixel(x, y, (x + y) % 2 == 0 ? Color(1, 0, 1) : Color(0, 0, 0));
+	}
+
+	texture_2d_array_placeholder.push_back(texture_2d_placeholder);
+
+	for (int i = 0; i < 6; i++) {
+		cubemap_placeholder.push_back(texture_2d_placeholder);
+	}
+
+	Ref<Image> texture_2d_placeholder_rotated;
+	texture_2d_placeholder_rotated.instantiate();
+	texture_2d_placeholder_rotated->copy_from(texture_2d_placeholder);
+	texture_2d_placeholder_rotated->rotate_90(CLOCKWISE);
+	for (int i = 0; i < 4; i++) {
+		// Alternate checkerboard pattern on odd layers (by using a copy that is rotated 90 degrees).
+		texture_3d_placeholder.push_back(i % 2 == 0 ? texture_2d_placeholder : texture_2d_placeholder_rotated);
+	}
 }
 
 TextureStorage::~TextureStorage() {
@@ -1365,46 +1392,19 @@ void TextureStorage::texture_proxy_update(RID p_texture, RID p_proxy_to) {
 
 //these two APIs can be used together or in combination with the others.
 void TextureStorage::texture_2d_placeholder_initialize(RID p_texture) {
-	//this could be better optimized to reuse an existing image , done this way
-	//for now to get it working
-	Ref<Image> image = Image::create_empty(4, 4, false, Image::FORMAT_RGBA8);
-	image->fill(Color(1, 0, 1, 1));
-
-	texture_2d_initialize(p_texture, image);
+	texture_2d_initialize(p_texture, texture_2d_placeholder);
 }
 
 void TextureStorage::texture_2d_layered_placeholder_initialize(RID p_texture, RS::TextureLayeredType p_layered_type) {
-	//this could be better optimized to reuse an existing image , done this way
-	//for now to get it working
-	Ref<Image> image = Image::create_empty(4, 4, false, Image::FORMAT_RGBA8);
-	image->fill(Color(1, 0, 1, 1));
-
-	Vector<Ref<Image>> images;
 	if (p_layered_type == RS::TEXTURE_LAYERED_2D_ARRAY) {
-		images.push_back(image);
+		texture_2d_layered_initialize(p_texture, texture_2d_array_placeholder, p_layered_type);
 	} else {
-		//cube
-		for (int i = 0; i < 6; i++) {
-			images.push_back(image);
-		}
+		texture_2d_layered_initialize(p_texture, cubemap_placeholder, p_layered_type);
 	}
-
-	texture_2d_layered_initialize(p_texture, images, p_layered_type);
 }
 
 void TextureStorage::texture_3d_placeholder_initialize(RID p_texture) {
-	//this could be better optimized to reuse an existing image , done this way
-	//for now to get it working
-	Ref<Image> image = Image::create_empty(4, 4, false, Image::FORMAT_RGBA8);
-	image->fill(Color(1, 0, 1, 1));
-
-	Vector<Ref<Image>> images;
-	//cube
-	for (int i = 0; i < 4; i++) {
-		images.push_back(image);
-	}
-
-	texture_3d_initialize(p_texture, Image::FORMAT_RGBA8, 4, 4, 4, false, images);
+	texture_3d_initialize(p_texture, Image::FORMAT_RGBA8, 4, 4, 4, false, texture_3d_placeholder);
 }
 
 Ref<Image> TextureStorage::texture_2d_get(RID p_texture) const {

servers/rendering/renderer_rd/storage_rd/texture_storage.h

@@ -520,6 +520,11 @@ class TextureStorage : public RendererTextureStorage {
 	virtual void texture_external_update(RID p_texture, int p_width, int p_height, uint64_t p_external_buffer) override;
 	virtual void texture_proxy_update(RID p_proxy, RID p_base) override;
 
+	Ref<Image> texture_2d_placeholder;
+	Vector<Ref<Image>> texture_2d_array_placeholder;
+	Vector<Ref<Image>> cubemap_placeholder;
+	Vector<Ref<Image>> texture_3d_placeholder;
+
 	//these two APIs can be used together or in combination with the others.
 	virtual void texture_2d_placeholder_initialize(RID p_texture) override;
 	virtual void texture_2d_layered_placeholder_initialize(RID p_texture, RenderingServer::TextureLayeredType p_layered_type) override;