Improve bloom effect (#12916)

* Remove the built-in exposure factor of 2.5
* Add physics-based bloom (https://learnopengl.com/Guest-Articles/2022/Phys.-Based-Bloom)
* Add luminance scaling for bloom layer to simulate HDR
* Add setting to control bloom strength

6 files changed, 58 insertions, 33 deletions

diff --git a/src/client/game.cpp b/src/client/game.cpp
index 5eb185f86..2f97b9b0c 100644
--- a/src/client/game.cpp
+++ b/src/client/game.cpp
@@ -432,6 +432,8 @@ class GameGlobalShaderConstantSetter : public IShaderConstantSetter
 	bool m_bloom_enabled;
 	CachedPixelShaderSetting<float> m_bloom_intensity_pixel;
 	float m_bloom_intensity;
+	CachedPixelShaderSetting<float> m_bloom_strength_pixel;
+	float m_bloom_strength;
 	CachedPixelShaderSetting<float> m_bloom_radius_pixel;
 	float m_bloom_radius;
 
@@ -444,8 +446,10 @@ public:
 			m_user_exposure_factor = g_settings->getFloat("exposure_factor", 0.1f, 10.0f);
 		if (name == "bloom_intensity")
 			m_bloom_intensity = g_settings->getFloat("bloom_intensity", 0.01f, 1.0f);
+		if (name == "bloom_strength_factor")
+			m_bloom_strength = RenderingEngine::BASE_BLOOM_STRENGTH * g_settings->getFloat("bloom_strength_factor", 0.1f, 10.0f);
 		if (name == "bloom_radius")
-			m_bloom_radius = g_settings->getFloat("bloom_radius", 1.0f, 64.0f);
+			m_bloom_radius = g_settings->getFloat("bloom_radius", 0.1f, 8.0f);
 	}
 
 	static void settingsCallback(const std::string &name, void *userdata)
@@ -479,17 +483,20 @@ public:
 		m_texel_size0("texelSize0"),
 		m_exposure_factor_pixel("exposureFactor"),
 		m_bloom_intensity_pixel("bloomIntensity"),
+		m_bloom_strength_pixel("bloomStrength"),
 		m_bloom_radius_pixel("bloomRadius")
 	{
 		g_settings->registerChangedCallback("enable_fog", settingsCallback, this);
 		g_settings->registerChangedCallback("exposure_factor", settingsCallback, this);
 		g_settings->registerChangedCallback("bloom_intensity", settingsCallback, this);
+		g_settings->registerChangedCallback("bloom_strength_factor", settingsCallback, this);
 		g_settings->registerChangedCallback("bloom_radius", settingsCallback, this);
 		m_fog_enabled = g_settings->getBool("enable_fog");
 		m_user_exposure_factor = g_settings->getFloat("exposure_factor", 0.1f, 10.0f);
 		m_bloom_enabled = g_settings->getBool("enable_bloom");
 		m_bloom_intensity = g_settings->getFloat("bloom_intensity", 0.01f, 1.0f);
-		m_bloom_radius = g_settings->getFloat("bloom_radius", 1.0f, 64.0f);
+		m_bloom_strength = RenderingEngine::BASE_BLOOM_STRENGTH * g_settings->getFloat("bloom_strength_factor", 0.1f, 10.0f);
+		m_bloom_radius = g_settings->getFloat("bloom_radius", 0.1f, 8.0f);
 	}
 
 	~GameGlobalShaderConstantSetter()
@@ -567,14 +574,15 @@ public:
 
 		m_texel_size0.set(m_texel_size0_values.data(), services);
 
-		float exposure_factor = RenderingEngine::DEFAULT_EXPOSURE_FACTOR * m_user_exposure_factor;
+		float exposure_factor = m_user_exposure_factor;
 		if (std::isnan(exposure_factor))
-			exposure_factor = RenderingEngine::DEFAULT_EXPOSURE_FACTOR;
+			exposure_factor = 1.0f;
 		m_exposure_factor_pixel.set(&exposure_factor, services);
 
 		if (m_bloom_enabled) {
 			m_bloom_intensity_pixel.set(&m_bloom_intensity, services);
 			m_bloom_radius_pixel.set(&m_bloom_radius, services);
+			m_bloom_strength_pixel.set(&m_bloom_strength, services);
 		}
 	}
 
diff --git a/src/client/render/pipeline.h b/src/client/render/pipeline.h
index 771c6f1d5..354624102 100644
--- a/src/client/render/pipeline.h
+++ b/src/client/render/pipeline.h
@@ -390,9 +390,10 @@ public:
 	 * @return RenderStep* Pointer to the created step for further configuration.
 	 */
 	template<typename T, typename... Args>
-	RenderStep *addStep(Args&&... args) {
+	T *addStep(Args&&... args) {
 		T* result = own(std::make_unique<T>(std::forward<Args>(args)...));
-		return addStep(result);
+		addStep(result);
+		return result;
 	}
 
 	RenderSource *getInput();
diff --git a/src/client/render/secondstage.cpp b/src/client/render/secondstage.cpp
index 860b277bd..ebc7e7411 100644
--- a/src/client/render/secondstage.cpp
+++ b/src/client/render/secondstage.cpp
@@ -115,8 +115,8 @@ RenderStep *addPostProcessing(RenderPipeline *pipeline, RenderStep *previousStep
 	static const u8 TEXTURE_COLOR = 0;
 	static const u8 TEXTURE_DEPTH = 1;
 	static const u8 TEXTURE_BLOOM = 2;
-	static const u8 TEXTURE_BLUR = 3;
-	static const u8 TEXTURE_BLUR_SECONDARY = 4;
+	static const u8 TEXTURE_BLOOM_DOWN = 10;
+	static const u8 TEXTURE_BLOOM_UP = 20;
 
 	buffer->setTexture(TEXTURE_COLOR, scale, "3d_render", color_format);
 	buffer->setTexture(TEXTURE_DEPTH, scale, "3d_depthmap", depth_format);
@@ -124,39 +124,56 @@ RenderStep *addPostProcessing(RenderPipeline *pipeline, RenderStep *previousStep
 	// attach buffer to the previous step
 	previousStep->setRenderTarget(pipeline->createOwned<TextureBufferOutput>(buffer, std::vector<u8> { TEXTURE_COLOR }, TEXTURE_DEPTH));
 
+	// shared variables
+	u32 shader_id;
+
 	// post-processing stage
 	// set up bloom
 	if (g_settings->getBool("enable_bloom")) {
 
-		buffer->setTexture(TEXTURE_BLUR, scale * 0.5, "blur", color_format);
-		buffer->setTexture(TEXTURE_BLOOM, scale * 0.5, "bloom", color_format);
-		u8 bloom_input_texture = TEXTURE_BLOOM;
-		
-		if (g_settings->getBool("enable_bloom_dedicated_texture")) {
-			buffer->setTexture(TEXTURE_BLUR_SECONDARY, scale * 0.5, "blur2", color_format);
-			bloom_input_texture = TEXTURE_BLUR_SECONDARY;
+
+		buffer->setTexture(TEXTURE_BLOOM, scale, "bloom", color_format);
+
+		const u8 MIPMAP_LEVELS = 4;
+		v2f downscale = scale * 0.5;
+		for (u8 i = 0; i < MIPMAP_LEVELS; i++) {
+			buffer->setTexture(TEXTURE_BLOOM_DOWN + i, downscale, std::string("bloom_down") + std::to_string(i), color_format);
+			buffer->setTexture(TEXTURE_BLOOM_UP + i, downscale, std::string("bloom_up") + std::to_string(i), color_format);
+			downscale *= 0.5;
 		}
 
 		// get bright spots
 		u32 shader_id = client->getShaderSource()->getShader("extract_bloom", TILE_MATERIAL_PLAIN, NDT_MESH);
 		RenderStep *extract_bloom = pipeline->addStep<PostProcessingStep>(shader_id, std::vector<u8> { TEXTURE_COLOR });
 		extract_bloom->setRenderSource(buffer);
-		extract_bloom->setRenderTarget(pipeline->createOwned<TextureBufferOutput>(buffer, bloom_input_texture));
-		// horizontal blur
-		shader_id = client->getShaderSource()->getShader("blur_h", TILE_MATERIAL_PLAIN, NDT_MESH);
-		RenderStep *blur_h = pipeline->addStep<PostProcessingStep>(shader_id, std::vector<u8> { bloom_input_texture });
-		blur_h->setRenderSource(buffer);
-		blur_h->setRenderTarget(pipeline->createOwned<TextureBufferOutput>(buffer, TEXTURE_BLUR));
-		// vertical blur
-		shader_id = client->getShaderSource()->getShader("blur_v", TILE_MATERIAL_PLAIN, NDT_MESH);
-		RenderStep *blur_v = pipeline->addStep<PostProcessingStep>(shader_id, std::vector<u8> { TEXTURE_BLUR });
-		blur_v->setRenderSource(buffer);
-		blur_v->setRenderTarget(pipeline->createOwned<TextureBufferOutput>(buffer, TEXTURE_BLOOM));
+		extract_bloom->setRenderTarget(pipeline->createOwned<TextureBufferOutput>(buffer, TEXTURE_BLOOM));
+
+		// downsample
+		shader_id = client->getShaderSource()->getShader("bloom_downsample", TILE_MATERIAL_PLAIN, NDT_MESH);
+		u8 source = TEXTURE_BLOOM;
+		for (u8 i = 0; i < MIPMAP_LEVELS; i++) {
+			auto step = pipeline->addStep<PostProcessingStep>(shader_id, std::vector<u8> { source });
+			step->setRenderSource(buffer);
+			step->setBilinearFilter(0, true);
+			step->setRenderTarget(pipeline->createOwned<TextureBufferOutput>(buffer, TEXTURE_BLOOM_DOWN + i));
+			source = TEXTURE_BLOOM_DOWN + i;
+		}
+
+		// upsample
+		shader_id = client->getShaderSource()->getShader("bloom_upsample", TILE_MATERIAL_PLAIN, NDT_MESH);
+		for (u8 i = MIPMAP_LEVELS - 1; i > 0; i--) {
+			auto step = pipeline->addStep<PostProcessingStep>(shader_id, std::vector<u8> { u8(TEXTURE_BLOOM_DOWN + i - 1), source });
+			step->setRenderSource(buffer);
+			step->setBilinearFilter(0, true);
+			step->setBilinearFilter(1, true);
+			step->setRenderTarget(pipeline->createOwned<TextureBufferOutput>(buffer, u8(TEXTURE_BLOOM_UP + i - 1)));
+			source = TEXTURE_BLOOM_UP + i - 1;
+		}
 	}
 
 	// final post-processing
-	u32 shader_id = client->getShaderSource()->getShader("second_stage", TILE_MATERIAL_PLAIN, NDT_MESH);
-	PostProcessingStep *effect = pipeline->createOwned<PostProcessingStep>(shader_id, std::vector<u8> { TEXTURE_COLOR, TEXTURE_BLOOM });
+	shader_id = client->getShaderSource()->getShader("second_stage", TILE_MATERIAL_PLAIN, NDT_MESH);
+	PostProcessingStep *effect = pipeline->createOwned<PostProcessingStep>(shader_id, std::vector<u8> { TEXTURE_COLOR, TEXTURE_BLOOM_UP });
 	pipeline->addStep(effect);
 	effect->setBilinearFilter(1, true); // apply filter to the bloom
 	effect->setRenderSource(buffer);
diff --git a/src/client/renderingengine.cpp b/src/client/renderingengine.cpp
index 9698b63bb..465e3fd4f 100644
--- a/src/client/renderingengine.cpp
+++ b/src/client/renderingengine.cpp
@@ -56,6 +56,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #endif
 
 RenderingEngine *RenderingEngine::s_singleton = nullptr;
+const float RenderingEngine::BASE_BLOOM_STRENGTH = 8.0f;
 
 
 static gui::GUISkin *createSkin(gui::IGUIEnvironment *environment,
diff --git a/src/client/renderingengine.h b/src/client/renderingengine.h
index e26171a44..b477da027 100644
--- a/src/client/renderingengine.h
+++ b/src/client/renderingengine.h
@@ -46,9 +46,7 @@ class RenderingCore;
 class RenderingEngine
 {
 public:
-	/// Default color factor before applying effects like bloom or tomemapping
-	/// this is derived from tonemapping code and tuned empirically
-	static constexpr float DEFAULT_EXPOSURE_FACTOR = 2.5f;
+	static const float BASE_BLOOM_STRENGTH;
 
 	RenderingEngine(IEventReceiver *eventReceiver);
 	~RenderingEngine();
diff --git a/src/defaultsettings.cpp b/src/defaultsettings.cpp
index 3274e1ff5..fb1130caa 100644
--- a/src/defaultsettings.cpp
+++ b/src/defaultsettings.cpp
@@ -273,9 +273,9 @@ void set_default_settings()
 	settings->setDefault("exposure_factor", "1.0");
 	settings->setDefault("enable_bloom", "false");
 	settings->setDefault("enable_bloom_debug", "false");
-	settings->setDefault("enable_bloom_dedicated_texture", "false");
+	settings->setDefault("bloom_strength_factor", "1.0");
 	settings->setDefault("bloom_intensity", "0.05");
-	settings->setDefault("bloom_radius", "16");
+	settings->setDefault("bloom_radius", "1");
 
 	// Effects Shadows
 	settings->setDefault("enable_dynamic_shadows", "false");