STARK: Optionally use linear filtering when rendering backgrounds

engines/stark/detection.cpp

@@ -297,7 +297,8 @@ static const ADFileBasedFallback fileBasedFallback[] = {
 	{NULL, {NULL}}
 };*/
 
-#define GAMEOPTION_ASSETS_MOD GUIO_GAMEOPTIONS1
+#define GAMEOPTION_ASSETS_MOD       GUIO_GAMEOPTIONS1
+#define GAMEOPTION_LINEAR_FILTERING GUIO_GAMEOPTIONS2
 
 static const ADExtraGuiOptionsMap optionsList[] = {
 	{
@@ -309,6 +310,15 @@ static const ADExtraGuiOptionsMap optionsList[] = {
 			true
 		}
 	},
+	{
+		GAMEOPTION_LINEAR_FILTERING,
+		{
+			_s("Enable linear filtering of the backgrounds images"),
+			_s("When linear filtering is enabled the background graphics are smoother in full screen mode, at the cost of some details."),
+			"use_linear_filtering",
+			true
+		}
+	},
 
 	AD_EXTRA_GUI_OPTIONS_TERMINATOR
 };
@@ -317,7 +327,7 @@ class StarkMetaEngine : public AdvancedMetaEngine {
 public:
 	StarkMetaEngine() : AdvancedMetaEngine(gameDescriptions, sizeof(ADGameDescription), starkGames, optionsList) {
 		_singleId = "stark";
-		_guiOptions = GUIO2(GUIO_NOMIDI, GAMEOPTION_ASSETS_MOD);
+		_guiOptions = GUIO3(GUIO_NOMIDI, GAMEOPTION_ASSETS_MOD, GAMEOPTION_LINEAR_FILTERING);
 	}
 
 	const char *getName() const override {

engines/stark/formats/xmg.cpp

@@ -198,10 +198,10 @@ XMGDecoder::Block XMGDecoder::processYCrCb() {
 XMGDecoder::Block XMGDecoder::processTrans() {
 	Block block;
 
-	block.a1 = _transColor;
-	block.a2 = _transColor;
-	block.b1 = _transColor;
-	block.b2 = _transColor;
+	block.a1 = 0;
+	block.a2 = 0;
+	block.b1 = 0;
+	block.b2 = 0;
 
 	return block;
 }
@@ -214,24 +214,32 @@ XMGDecoder::Block XMGDecoder::processRGB() {
 	color += _stream->readByte() << 16;
 	if (color != _transColor)
 		color += 255 << 24;
+	else
+		color = 0;
 	block.a1 = color;
 
 	color = _stream->readUint16LE();
 	color += _stream->readByte() << 16;
 	if (color != _transColor)
 		color += 255 << 24;
+	else
+		color = 0;
 	block.a2 = color;
 
 	color = _stream->readUint16LE();
 	color += _stream->readByte() << 16;
 	if (color != _transColor)
 		color += 255 << 24;
+	else
+		color = 0;
 	block.b1 = color;
 
 	color = _stream->readUint16LE();
 	color += _stream->readByte() << 16;
 	if (color != _transColor)
 		color += 255 << 24;
+	else
+		color = 0;
 	block.b2 = color;
 
 	return block;

engines/stark/formats/xmg.h

@@ -65,6 +65,11 @@ private:
 
 	Common::ReadStream *_stream;
 
+	/**
+	 * The transparency color in the RGB and transparency blocks.
+	 * In the output surface, the transparent color is black with zero
+	 * alpha. So the images are effectively pre-multiplied alpha.
+	 */
 	uint32 _transColor;
 };
 

engines/stark/gfx/opengls.cpp

@@ -162,7 +162,11 @@ void OpenGLSDriver::start2DMode() {
 	// Enable alpha blending
 	glEnable(GL_BLEND);
 	//glBlendEquation(GL_FUNC_ADD); // It's the default
-	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+
+	// This blend mode prevents color fringes due to filtering.
+	// It requires the textures to have their color values pre-multiplied
+	// with their alpha value. This is the "Premultiplied Alpha" technique.
+	glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
 
 	glDisable(GL_DEPTH_TEST);
 	glDepthMask(GL_FALSE);

engines/stark/gfx/opengltexture.cpp

@@ -78,6 +78,23 @@ void OpenGlTexture::update(const Graphics::Surface *surface, const byte *palette
 	updateLevel(0, surface, palette);
 }
 
+void OpenGlTexture::setSamplingFilter(Texture::SamplingFilter filter) {
+	assert(_levelCount == 0);
+
+	switch (filter) {
+	case kNearest:
+		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+		break;
+	case kLinear:
+		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+		break;
+	default:
+		warning("Unhandled sampling filter %d", filter);
+	}
+}
+
 void OpenGlTexture::setLevelCount(uint32 count) {
 	_levelCount = count;
 

engines/stark/gfx/opengltexture.h

@@ -41,6 +41,7 @@ public:
 	// Texture API
 	void bind() const override;
 	void update(const Graphics::Surface *surface, const byte *palette = nullptr) override;
+	void setSamplingFilter(SamplingFilter filter) override;
 	void setLevelCount(uint32 count) override;
 	void addLevel(uint32 level, const Graphics::Surface *surface, const byte *palette = nullptr) override;
 

engines/stark/gfx/texture.h

@@ -40,12 +40,20 @@ public:
 	Texture();
 	virtual ~Texture();
 
+	enum SamplingFilter {
+		kNearest,
+		kLinear
+	};
+
 	/** Make the texture active */
 	virtual void bind() const = 0;
 
 	/** Define or update the texture pixel data */
 	virtual void update(const Graphics::Surface *surface, const byte *palette = nullptr) = 0;
 
+	/** Set the filter used when sampling the texture */
+	virtual void setSamplingFilter(SamplingFilter filter) = 0;
+
 	/**
 	 * Define the total number of levels of details
 	 *

engines/stark/services/settings.cpp

@@ -88,4 +88,8 @@ bool Settings::isAssetsModEnabled() const {
 	return ConfMan.getBool("enable_assets_mod");
 }
 
+Gfx::Texture::SamplingFilter Settings::getImageSamplingFilter() const {
+	return ConfMan.getBool("use_linear_filtering") ? Gfx::Texture::kLinear : Gfx::Texture::kNearest;
+}
+
 } // End of namespace Stark

engines/stark/services/settings.h

@@ -25,6 +25,7 @@
 
 #include "common/config-manager.h"
 
+#include "engines/stark/gfx/texture.h"
 #include "engines/stark/services/services.h"
 
 struct ADGameDescription;
@@ -97,6 +98,9 @@ public:
 	/** Should the game try to load external replacement assets? */
 	bool isAssetsModEnabled() const;
 
+	/** Should linear filtering be used when sampling the background image textures? */
+	Gfx::Texture::SamplingFilter getImageSamplingFilter() const;
+
 private:
 	Audio::Mixer *_mixer;
 	bool _hasLowRes;

engines/stark/services/userinterface.cpp

@@ -255,7 +255,7 @@ Screen *UserInterface::getScreenByName(Screen::Name screenName) const {
 }
 
 bool UserInterface::isInGameScreen() const {
-	return _currentScreen->getName() == Screen::kScreenGame;
+	return _currentScreen && (_currentScreen->getName() == Screen::kScreenGame);
 }
 
 bool UserInterface::isInSaveLoadMenuScreen() const {

engines/stark/ui/world/fmvscreen.cpp

@@ -45,6 +45,8 @@ FMVScreen::FMVScreen(Gfx::Driver *gfx, Cursor *cursor) :
 	_decoder->setSoundType(Audio::Mixer::kSFXSoundType);
 
 	_texture = _gfx->createTexture();
+	_texture->setSamplingFilter(StarkSettings->getImageSamplingFilter());
+
 	_surfaceRenderer = _gfx->createSurfaceRenderer();
 }
 

engines/stark/visual/effects/effect.cpp

@@ -27,6 +27,8 @@
 #include "engines/stark/gfx/driver.h"
 #include "engines/stark/gfx/surfacerenderer.h"
 #include "engines/stark/gfx/texture.h"
+#include "engines/stark/services/services.h"
+#include "engines/stark/services/settings.h"
 
 namespace Stark {
 
@@ -40,6 +42,7 @@ VisualEffect::VisualEffect(VisualType type, const Common::Point &size, Gfx::Driv
 	_surface->create(size.x, size.y, Gfx::Driver::getRGBAPixelFormat());
 
 	_texture = _gfx->createTexture(_surface);
+	_texture->setSamplingFilter(StarkSettings->getImageSamplingFilter());
 
 	_surfaceRenderer = _gfx->createSurfaceRenderer();
 }

engines/stark/visual/explodingimage.cpp

@@ -31,6 +31,7 @@
 
 #include "engines/stark/services/global.h"
 #include "engines/stark/services/services.h"
+#include "engines/stark/services/settings.h"
 
 namespace Stark {
 
@@ -57,7 +58,9 @@ void VisualExplodingImage::initFromSurface(const Graphics::Surface *surface) {
 	// Decode the XMG
 	_surface = new Graphics::Surface();
 	_surface->copyFrom(*surface);
+
 	_texture = _gfx->createTexture(_surface);
+	_texture->setSamplingFilter(StarkSettings->getImageSamplingFilter());
 
 	// Create an explosion unit for each pixel in the surface
 	_units.resize(_surface->w * _surface->h);

engines/stark/visual/flashingimage.cpp

@@ -31,6 +31,7 @@
 
 #include "engines/stark/services/global.h"
 #include "engines/stark/services/services.h"
+#include "engines/stark/services/settings.h"
 
 namespace Stark {
 
@@ -55,6 +56,7 @@ void VisualFlashingImage::initFromSurface(const Graphics::Surface *surface) {
 	assert(!_texture);
 
 	_texture = _gfx->createTexture(surface);
+	_texture->setSamplingFilter(StarkSettings->getImageSamplingFilter());
 }
 
 void VisualFlashingImage::updateFadeLevel() {

engines/stark/visual/image.cpp

@@ -29,6 +29,8 @@
 #include "engines/stark/gfx/driver.h"
 #include "engines/stark/gfx/surfacerenderer.h"
 #include "engines/stark/gfx/texture.h"
+#include "engines/stark/services/services.h"
+#include "engines/stark/services/settings.h"
 
 namespace Stark {
 
@@ -61,6 +63,7 @@ void VisualImageXMG::load(Common::ReadStream *stream) {
 	// Decode the XMG
 	_surface = Formats::XMGDecoder::decode(stream);
 	_texture = _gfx->createTexture(_surface);
+	_texture->setSamplingFilter(StarkSettings->getImageSamplingFilter());
 
 	_originalWidth  = _surface->w;
 	_originalHeight = _surface->h;
@@ -81,7 +84,7 @@ bool VisualImageXMG::loadPNG(Common::SeekableReadStream *stream) {
 
 	_surface = pngDecoder.getSurface()->convertTo(Gfx::Driver::getRGBAPixelFormat());
 	_texture = _gfx->createTexture(_surface);
-	_texture->setSamplingFilter(Gfx::Texture::kLinear);
+	_texture->setSamplingFilter(StarkSettings->getImageSamplingFilter());
 
 	return true;
 }

engines/stark/visual/smacker.cpp

@@ -27,6 +27,7 @@
 #include "engines/stark/gfx/texture.h"
 #include "engines/stark/scene.h"
 #include "engines/stark/services/services.h"
+#include "engines/stark/services/settings.h"
 
 #include "common/str.h"
 #include "common/archive.h"
@@ -63,6 +64,7 @@ void VisualSmacker::load(Common::SeekableReadStream *stream) {
 	rewind();
 
 	_texture = _gfx->createTexture();
+	_texture->setSamplingFilter(StarkSettings->getImageSamplingFilter());
 
 	update();
 }

engines/stark/visual/text.cpp

@@ -140,6 +140,8 @@ void VisualText::createTexture() {
 
 	// Create a texture from the surface
 	_texture = _gfx->createTexture(&surface);
+	_texture->setSamplingFilter(Gfx::Texture::kNearest);
+
 	surface.free();
 }