Only allow a single render interface, remove the ability to set per-c…

…ontext render interfaces [breaking change]

Now, only a single render interface can be set, and it must be set globally before the call to Rml::Initialise. Furthermore, the render interface cannot be changed while the library is initialised, and must live until after the call to Rml::Shutdown. If these conditions are not met, the library will submit error messages to the user in most cases.

This change is motivated by several reasons:

- The feature added considerable complexity, since several types of render state needed to store their state per render interface.
- This complexity would have become more pronounced with upcoming changes for advanced render effects.
- It was easy to make bugs where render resources (e.g. textures) would be freed in the wrong render interface.
- It was difficult to test for the presence of the above bugs.
- No tests existed already, it is very likely that bugs were already present.

Include/RmlUi/Core/Context.h

@@ -42,7 +42,6 @@ class Stream;
 class ContextInstancer;
 class ElementDocument;
 class EventListener;
-class RenderInterface;
 class DataModel;
 class DataModelConstructor;
 class DataTypeRegister;
@@ -247,9 +246,6 @@ class RMLUICORE_API Context : public ScriptInterface {
 	/// @param[in] speed_factor A factor for adjusting the final smooth scrolling speed, must be strictly positive, defaults to 1.0.
 	void SetDefaultScrollBehavior(ScrollBehavior scroll_behavior, float speed_factor);
 
-	/// Gets the context's render interface.
-	/// @return The render interface the context renders through.
-	RenderInterface* GetRenderInterface() const;
 	/// Gets the current clipping region for the render traversal
 	/// @param[out] origin The clipping origin
 	/// @param[out] dimensions The clipping dimensions
@@ -373,8 +369,6 @@ class RMLUICORE_API Context : public ScriptInterface {
 	// itself can't be part of it.
 	ElementSet drag_hover_chain;
 
-	// The render interface this context renders through.
-	RenderInterface* render_interface;
 	Vector2i clip_origin;
 	Vector2i clip_dimensions;
 
@@ -426,7 +420,6 @@ class RMLUICORE_API Context : public ScriptInterface {
 	static void SendEvents(const ElementSet& old_items, const ElementSet& new_items, EventId id, const Dictionary& parameters);
 
 	friend class Rml::Element;
-	friend RMLUICORE_API Context* CreateContext(const String&, Vector2i, RenderInterface*);
 };
 
 } // namespace Rml

Include/RmlUi/Core/Core.h

@@ -66,9 +66,7 @@ RMLUICORE_API void SetSystemInterface(SystemInterface* system_interface);
 /// Returns RmlUi's system interface.
 RMLUICORE_API SystemInterface* GetSystemInterface();
 
-/// Sets the interface through which all rendering requests are made. This is not required to be called, but if it is
-/// it must be called before Initialise(). If no render interface is specified, then all contexts must have a custom
-/// render interface.
+/// Sets the interface through which all rendering requests are made. This must be called before Initialise().
 /// @param[in] render_interface A non-owning pointer to the render interface implementation.
 /// @lifetime The interface must be kept alive until after the call to Rml::Shutdown.
 RMLUICORE_API void SetRenderInterface(RenderInterface* render_interface);
@@ -94,11 +92,8 @@ RMLUICORE_API FontEngineInterface* GetFontEngineInterface();
 /// Creates a new element context.
 /// @param[in] name The new name of the context. This must be unique.
 /// @param[in] dimensions The initial dimensions of the new context.
-/// @param[in] render_interface The custom render interface to use, or nullptr to use the default.
-/// @lifetime If specified, the render interface must be kept alive until after the call to Rml::Shutdown. Alternatively, the render interface can be
-///           destroyed after all contexts it belongs to have been destroyed and a subsequent call has been made to Rml::ReleaseTextures.
 /// @return A non-owning pointer to the new context, or nullptr if the context could not be created.
-RMLUICORE_API Context* CreateContext(const String& name, Vector2i dimensions, RenderInterface* render_interface = nullptr);
+RMLUICORE_API Context* CreateContext(const String& name, Vector2i dimensions);
 /// Removes and destroys a context.
 /// @param[in] name The name of the context to remove.
 /// @return True if name is a valid context, false otherwise.
@@ -154,8 +149,7 @@ RMLUICORE_API EventId RegisterEventType(const String& type, bool interruptible,
 /// Returns a list of source URLs to textures in all loaded documents.
 RMLUICORE_API StringList GetTextureSourceList();
 /// Forces all texture handles loaded and generated by RmlUi to be released.
-/// @param[in] render_interface Release all textures belonging to the given interface, or nullptr to release all textures in all interfaces.
-RMLUICORE_API void ReleaseTextures(RenderInterface* render_interface = nullptr);
+RMLUICORE_API void ReleaseTextures();
 /// Forces all compiled geometry handles generated by RmlUi to be released.
 RMLUICORE_API void ReleaseCompiledGeometry();
 /// Releases unused font textures and rendered glyphs to free up memory, and regenerates actively used fonts.

Include/RmlUi/Core/Element.h

@@ -60,7 +60,6 @@ class InlineLevelBox;
 class ReplacedBox;
 class PropertiesIteratorView;
 class PropertyDictionary;
-class RenderInterface;
 class StyleSheet;
 class StyleSheetContainer;
 class TransformState;
@@ -584,10 +583,6 @@ class RMLUICORE_API Element : public ScriptInterface, public EnableObserverPtr<E
 	DataModel* GetDataModel() const;
 	//@}
 
-	/// Gets the render interface owned by this element's context.
-	/// @return The element's context's render interface.
-	RenderInterface* GetRenderInterface();
-
 	/// Sets the instancer to use for releasing this element.
 	/// @param[in] instancer Instancer to set on this element.
 	void SetInstancer(ElementInstancer* instancer);

Include/RmlUi/Core/ElementUtilities.h

@@ -36,7 +36,6 @@ namespace Rml {
 
 class Box;
 class Context;
-class RenderInterface;
 namespace Style {
 	class ComputedValues;
 }
@@ -100,8 +99,7 @@ class RMLUICORE_API ElementUtilities {
 	static bool SetClippingRegion(Element* element, Context* context = nullptr);
 	/// Applies the clip region from the render interface to the renderer
 	/// @param[in] context The context to read the clip region from
-	/// @param[in] render_interface The render interface to update.
-	static void ApplyActiveClipRegion(Context* context, RenderInterface* render_interface);
+	static void ApplyActiveClipRegion(Context* context);
 
 	/// Formats the contents of an element. This does not need to be called for ordinary elements, but can be useful
 	/// for non-DOM elements of custom elements.
@@ -124,9 +122,9 @@ class RMLUICORE_API ElementUtilities {
 	static bool PositionElement(Element* element, Vector2f offset, PositionAnchor anchor);
 
 	/// Applies an element's accumulated transform matrix, determined from its and ancestor's `perspective' and `transform' properties.
-	/// Note: All calls to RenderInterface::SetTransform must go through here.
-	/// @param[in] element		The element whose transform to apply.
+	/// @param[in] element The element whose transform to apply.
 	/// @return true if a render interface is available to set the transform.
+	/// @note All calls to RenderInterface::SetTransform must go through here.
 	static bool ApplyTransform(Element& element);
 
 	/// Creates data views and data controllers if a data model applies to the element.

Include/RmlUi/Core/Geometry.h

@@ -37,7 +37,6 @@ namespace Rml {
 
 class Context;
 class Element;
-class RenderInterface;
 struct Texture;
 using GeometryDatabaseHandle = uint32_t;
 
@@ -49,8 +48,7 @@ using GeometryDatabaseHandle = uint32_t;
 
 class RMLUICORE_API Geometry {
 public:
-	Geometry(Element* host_element = nullptr);
-	Geometry(Context* host_context);
+	Geometry();
 
 	Geometry(const Geometry&) = delete;
 	Geometry& operator=(const Geometry&) = delete;
@@ -60,10 +58,6 @@ class RMLUICORE_API Geometry {
 
 	~Geometry();
 
-	/// Set the host element for this geometry; this should be passed in the constructor if possible.
-	/// @param[in] host_element The new host element for the geometry.
-	void SetHostElement(Element* host_element);
-
 	/// Attempts to compile the geometry if appropriate, then renders the geometry, compiled if it can.
 	/// @param[in] translation The translation of the geometry.
 	void Render(Vector2f translation);
@@ -92,12 +86,6 @@ class RMLUICORE_API Geometry {
 	// Move members from another geometry.
 	void MoveFrom(Geometry& other) noexcept;
 
-	// Returns the host context's render interface.
-	RenderInterface* GetRenderInterface();
-
-	Context* host_context = nullptr;
-	Element* host_element = nullptr;
-
 	Vector<Vertex> vertices;
 	Vector<int> indices;
 	const Texture* texture = nullptr;

Include/RmlUi/Core/RenderInterface.h

@@ -37,8 +37,6 @@
 
 namespace Rml {
 
-class Context;
-
 /**
     The abstract base class for application-specific rendering implementation. Your application must provide a concrete
     implementation of this class and install it through Rml::SetRenderInterface() in order for anything to be rendered.
@@ -112,15 +110,6 @@ class RMLUICORE_API RenderInterface : public NonCopyMoveable {
 	/// is submitted. Then it expects the renderer to use an identity matrix or otherwise omit the multiplication with the transform.
 	/// @param[in] transform The new transform to apply, or nullptr if no transform applies to the current element.
 	virtual void SetTransform(const Matrix4f* transform);
-
-	/// Get the context currently being rendered. This is only valid during RenderGeometry,
-	/// CompileGeometry, RenderCompiledGeometry, EnableScissorRegion and SetScissorRegion.
-	Context* GetContext() const;
-
-private:
-	Context* context;
-
-	friend class Rml::Context;
 };
 
 } // namespace Rml

Include/RmlUi/Core/Texture.h

@@ -68,14 +68,12 @@ struct RMLUICORE_API Texture {
 	/// Returns the texture's source name. This is usually the name of the file the texture was loaded from.
 	/// @return The name of the this texture's source. This will be the empty string if this texture is not loaded.
 	const String& GetSource() const;
-	/// Returns the texture's handle.
-	/// @param[in] The render interface that is requesting the handle.
-	/// @return The texture's handle. This will be nullptr if the texture isn't loaded.
-	TextureHandle GetHandle(RenderInterface* render_interface) const;
-	/// Returns the texture's dimensions.
-	/// @param[in] The render interface that is requesting the dimensions.
-	/// @return The texture's dimensions. This will be (0, 0) if the texture isn't loaded.
-	Vector2i GetDimensions(RenderInterface* render_interface) const;
+	/// Returns the texture's handle, will attempt to load the texture as necessary.
+	/// @return The texture's handle. This will be 0 if the texture cannot be loaded.
+	TextureHandle GetHandle() const;
+	/// Returns the texture's dimensions, will attempt to load the texture as necessary.
+	/// @return The texture's dimensions. This will be (0, 0) if the texture cannot be loaded.
+	Vector2i GetDimensions() const;
 
 	/// Returns true if the texture points to the same underlying resource.
 	bool operator==(const Texture&) const;

Samples/invaders/src/DecoratorDefender.cpp

@@ -27,6 +27,7 @@
  */
 
 #include "DecoratorDefender.h"
+#include <RmlUi/Core/Core.h>
 #include <RmlUi/Core/Element.h>
 #include <RmlUi/Core/GeometryUtilities.h>
 #include <RmlUi/Core/Math.h>
@@ -59,9 +60,9 @@ void DecoratorDefender::RenderElement(Rml::Element* element, Rml::DecoratorDataH
 	Rml::Vector2f size = element->GetBox().GetSize(Rml::Box::PADDING);
 	Rml::Math::SnapToPixelGrid(position, size);
 
-	if (Rml::RenderInterface* render_interface = element->GetRenderInterface())
+	if (Rml::RenderInterface* render_interface = ::Rml::GetRenderInterface())
 	{
-		Rml::TextureHandle texture = GetTexture(image_index)->GetHandle(render_interface);
+		Rml::TextureHandle texture = GetTexture(image_index)->GetHandle();
 		Rml::Colourb color = element->GetProperty<Rml::Colourb>("color");
 
 		Rml::Vertex vertices[4];

Samples/invaders/src/DecoratorStarfield.cpp

@@ -106,10 +106,6 @@ void DecoratorStarfield::RenderElement(Rml::Element* element, Rml::DecoratorData
 	const float dp_ratio = Rml::ElementUtilities::GetDensityIndependentPixelRatio(element);
 	const float point_size = Rml::Math::RoundUp(2.f * dp_ratio);
 
-	Rml::RenderInterface* render_interface = element->GetRenderInterface();
-	if (!render_interface)
-		return;
-
 	int num_stars = 0;
 
 	for (size_t i = 0; i < star_field->star_layers.size(); i++)

Samples/invaders/src/Game.cpp

@@ -144,7 +144,7 @@ void Game::Render(float dp_ratio)
 	if (defender_lives <= 0)
 		return;
 
-	Rml::TextureHandle texture_handle = texture.GetHandle(Rml::GetRenderInterface());
+	Rml::TextureHandle texture_handle = texture.GetHandle();
 
 	// Render all available shields
 	for (int i = 0; i < NUM_SHIELDS; i++)

Samples/luainvaders/src/DecoratorDefender.cpp

@@ -27,6 +27,7 @@
  */
 
 #include "DecoratorDefender.h"
+#include <RmlUi/Core/Core.h>
 #include <RmlUi/Core/Element.h>
 #include <RmlUi/Core/GeometryUtilities.h>
 #include <RmlUi/Core/Math.h>
@@ -59,9 +60,9 @@ void DecoratorDefender::RenderElement(Rml::Element* element, Rml::DecoratorDataH
 	Rml::Vector2f size = element->GetBox().GetSize(Rml::Box::PADDING);
 	Rml::Math::SnapToPixelGrid(position, size);
 
-	if (Rml::RenderInterface* render_interface = element->GetRenderInterface())
+	if (Rml::RenderInterface* render_interface = ::Rml::GetRenderInterface())
 	{
-		Rml::TextureHandle texture = GetTexture(image_index)->GetHandle(render_interface);
+		Rml::TextureHandle texture = GetTexture(image_index)->GetHandle();
 		Rml::Colourb color = element->GetProperty<Rml::Colourb>("color");
 
 		Rml::Vertex vertices[4];

Samples/luainvaders/src/DecoratorStarfield.cpp

@@ -106,10 +106,6 @@ void DecoratorStarfield::RenderElement(Rml::Element* element, Rml::DecoratorData
 	const float dp_ratio = Rml::ElementUtilities::GetDensityIndependentPixelRatio(element);
 	const float point_size = Rml::Math::RoundUp(2.f * dp_ratio);
 
-	Rml::RenderInterface* render_interface = element->GetRenderInterface();
-	if (!render_interface)
-		return;
-
 	int num_stars = 0;
 
 	for (size_t i = 0; i < star_field->star_layers.size(); i++)

Samples/luainvaders/src/Game.cpp

@@ -142,7 +142,7 @@ void Game::Render(float dp_ratio)
 	if (defender_lives <= 0)
 		return;
 
-	Rml::TextureHandle texture_handle = texture.GetHandle(Rml::GetRenderInterface());
+	Rml::TextureHandle texture_handle = texture.GetHandle();
 
 	// Render all available shields
 	for (int i = 0; i < NUM_SHIELDS; i++)

Source/Core/Context.cpp

@@ -60,9 +60,6 @@ Context::Context(const String& name) :
 {
 	instancer = nullptr;
 
-	// Initialise this to nullptr; this will be set in Rml::CreateContext().
-	render_interface = nullptr;
-
 	root = Factory::InstanceElement(nullptr, "*", "#root", XMLAttributes());
 	root->SetId(name);
 	root->SetOffset(Vector2f(0, 0), nullptr);
@@ -117,8 +114,6 @@ Context::~Context()
 	cursor_proxy.reset();
 
 	instancer = nullptr;
-
-	render_interface = nullptr;
 }
 
 const String& Context::GetName() const
@@ -223,12 +218,7 @@ bool Context::Render()
 {
 	RMLUI_ZoneScoped;
 
-	RenderInterface* render_interface = GetRenderInterface();
-	if (render_interface == nullptr)
-		return false;
-
-	render_interface->context = this;
-	ElementUtilities::ApplyActiveClipRegion(this, render_interface);
+	ElementUtilities::ApplyActiveClipRegion(this);
 
 	root->Render();
 
@@ -243,8 +233,6 @@ bool Context::Render()
 		cursor_proxy->Render();
 	}
 
-	render_interface->context = nullptr;
-
 	return true;
 }
 
@@ -867,11 +855,6 @@ void Context::SetDefaultScrollBehavior(ScrollBehavior scroll_behavior, float spe
 	scroll_controller->SetDefaultScrollBehavior(scroll_behavior, speed_factor);
 }
 
-RenderInterface* Context::GetRenderInterface() const
-{
-	return render_interface;
-}
-
 bool Context::GetActiveClipRegion(Vector2i& origin, Vector2i& dimensions) const
 {
 	if (clip_dimensions.x < 0 || clip_dimensions.y < 0)