OSYSTEM: Add Stretch Mode API

backends/graphics/graphics.h

@@ -53,6 +53,13 @@ public:
 	};
 	virtual bool setShader(int id) { return false; }
 	virtual int getShader() const { return 0; }
+	virtual const OSystem::GraphicsMode *getSupportedStretchModes() const {
+		static const OSystem::GraphicsMode noStretchModes[] = {{"NONE", "Normal", 0}, {nullptr, nullptr, 0 }};
+		return noStretchModes;
+	}
+	virtual int getDefaultStretchMode() const { return 0; }
+	virtual bool setStretchMode(int mode) { return false; }
+	virtual int getStretchMode() const { return 0; }
 
 #ifdef USE_RGB_COLOR
 	virtual Graphics::PixelFormat getScreenFormat() const = 0;

backends/modular-backend.cpp

@@ -93,6 +93,22 @@ int ModularBackend::getShader() const {
 	return _graphicsManager->getShader();
 }
 
+const OSystem::GraphicsMode *ModularBackend::getSupportedStretchModes() const {
+	return _graphicsManager->getSupportedStretchModes();
+}
+
+int ModularBackend::getDefaultStretchMode() const {
+	return _graphicsManager->getDefaultStretchMode();
+}
+
+bool ModularBackend::setStretchMode(int mode) {
+	return _graphicsManager->setStretchMode(mode);
+}
+
+int ModularBackend::getStretchMode() const {
+	return _graphicsManager->getStretchMode();
+}
+
 void ModularBackend::resetGraphicsScale() {
 	_graphicsManager->resetGraphicsScale();
 }

backends/modular-backend.h

@@ -69,6 +69,10 @@ public:
 	virtual const GraphicsMode *getSupportedShaders() const override;
 	virtual int getShader() const override;
 	virtual bool setShader(int id) override;
+	virtual const GraphicsMode *getSupportedStretchModes() const override;
+	virtual int getDefaultStretchMode() const override;
+	virtual bool setStretchMode(int mode) override;
+	virtual int getStretchMode() const override;
 	virtual void resetGraphicsScale() override;
 #ifdef USE_RGB_COLOR
 	virtual Graphics::PixelFormat getScreenFormat() const override;

common/system.cpp

@@ -121,6 +121,27 @@ bool OSystem::setGraphicsMode(const char *name) {
 	return false;
 }
 
+bool OSystem::setStretchMode(const char *name) {
+	if (!name)
+		return false;
+
+	// Special case for the 'default' filter
+	if (!scumm_stricmp(name, "default")) {
+		return setStretchMode(getDefaultStretchMode());
+	}
+
+	const GraphicsMode *sm = getSupportedStretchModes();
+
+	while (sm->name) {
+		if (!scumm_stricmp(sm->name, name)) {
+			return setStretchMode(sm->id);
+		}
+		sm++;
+	}
+
+	return false;
+}
+
 void OSystem::fatalError() {
 	quit();
 	exit(1);

common/system.h

@@ -606,6 +606,56 @@ public:
 	 */
 	virtual int getShader() const { return 0; }
 
+	/**
+	 * Retrieve a list of all stretch modes supported by this backend.
+	 * It is completely up to the backend maintainer to decide what is
+	 * appropriate here and what not.
+	 * The list is terminated by an all-zero entry.
+	 * @return a list of supported stretch modes
+	 */
+	virtual const GraphicsMode *getSupportedStretchModes() const {
+		static const GraphicsMode noStretchModes[] = {{"NONE", "Normal", 0}, {nullptr, nullptr, 0 }};
+		return noStretchModes;
+	}
+
+	/**
+	 * Return the ID of the 'default' stretch mode. What exactly this means
+	 * is up to the backend. This mode is set by the client code when no user
+	 * overrides are present (i.e. if no custom stretch mode is selected via
+	 * the command line or a config file).
+	 *
+	 * @return the ID of the 'default' graphics mode
+	 */
+	virtual int getDefaultStretchMode() const { return 0; }
+
+	/**
+	 * Switch to the specified stretch mode. If switching to the new mode
+	 * failed, this method returns false.
+	 *
+	 * @param mode	the ID of the new graphics mode
+	 * @return true if the switch was successful, false otherwise
+	 */
+	virtual bool setStretchMode(int mode) { return false; }
+
+	/**
+	 * Switch to the stretch mode with the given name. If 'name' is unknown,
+	 * or if switching to the new mode failed, this method returns false.
+	 *
+	 * @param name	the name of the new stretch mode
+	 * @return true if the switch was successful, false otherwise
+	 * @note This is implemented via the setStretchMode(int) method, as well
+	 *       as getSupportedStretchModes() and getDefaultStretchMode().
+	 *       In particular, backends do not have to overload this!
+	 */
+	bool setStretchMode(const char *name);
+
+	/**
+	 * Determine which stretch mode is currently active.
+	 * @return the ID of the active stretch mode
+	 */
+	virtual int getStretchMode() const { return 0; }
+
+
 	/**
 	 * Set the size and color format of the virtual screen. Typical sizes include:
 	 *  - 320x200 (e.g. for most SCUMM games, and Simon)
@@ -695,7 +745,8 @@ public:
 		kTransactionModeSwitchFailed = (1 << 2),	/**< Failed switching the GFX graphics mode (setGraphicsMode) */
 		kTransactionSizeChangeFailed = (1 << 3),	/**< Failed switching the screen dimensions (initSize) */
 		kTransactionFormatNotSupported = (1 << 4),	/**< Failed setting the color format */
-		kTransactionFilteringFailed = (1 << 5)		/**< Failed setting the filtering mode */
+		kTransactionFilteringFailed = (1 << 5),		/**< Failed setting the filtering mode */
+		kTransactionStretchModeSwitchFailed = (1 << 6)	/**< Failed setting the stretch mode */
 	};
 
 	/**