Handle texture filtering sanely to avoid blurriness (#16034)

builtin/settingtypes.txt

@@ -2106,7 +2106,7 @@ world_aligned_mode (World-aligned textures mode) enum enable disable,enable,forc
 #    World-aligned textures may be scaled to span several nodes. However,
 #    the server may not send the scale you want, especially if you use
 #    a specially-designed texture pack; with this option, the client tries
-#    to determine the scale automatically basing on the texture size.
+#    to determine the scale automatically based on the texture size.
 #    See also texture_min_size.
 #    Warning: This option is EXPERIMENTAL!
 autoscale_mode (Autoscaling mode) enum disable disable,enable,force
@@ -2118,7 +2118,7 @@ autoscale_mode (Autoscaling mode) enum disable disable,enable,force
 #    This setting is ONLY applied if any of the mentioned filters are enabled.
 #    This is also used as the base node texture size for world-aligned
 #    texture autoscaling.
-texture_min_size (Base texture size) int 64 1 32768
+texture_min_size (Base texture size) int 192 192 16384
 
 #    Side length of a cube of map blocks that the client will consider together
 #    when generating meshes.

doc/lua_api.md

@@ -518,6 +518,15 @@ stripping out the file extension:
 
 Supported texture formats are PNG (`.png`), JPEG (`.jpg`) and Targa (`.tga`).
 
+Luanti generally uses nearest-neighbor upscaling for textures to preserve the crisp
+look of pixel art (low-res textures).
+Users can optionally enable bilinear and/or trilinear filtering. However, to avoid
+everything becoming blurry, textures smaller than 192px will either not be filtered,
+or will be upscaled to that minimum resolution first without filtering.
+
+This is subject to change to move more control to the Lua API, but you can rely on
+low-res textures not suddenly becoming filtered.
+
 Texture modifiers
 -----------------
 

src/client/content_cao.cpp

@@ -144,6 +144,31 @@ void SmoothTranslatorWrappedv3f::translate(f32 dtime)
 	Other stuff
 */
 
+static bool setMaterialTextureAndFilters(video::SMaterial &material,
+	const std::string &texturestring, ITextureSource *tsrc)
+{
+	bool use_trilinear_filter = g_settings->getBool("trilinear_filter");
+	bool use_bilinear_filter = g_settings->getBool("bilinear_filter");
+	bool use_anisotropic_filter = g_settings->getBool("anisotropic_filter");
+
+	video::ITexture *texture = tsrc->getTextureForMesh(texturestring);
+	if (!texture)
+		return false;
+
+	material.setTexture(0, texture);
+
+	// don't filter low-res textures, makes them look blurry
+	const core::dimension2d<u32> &size = texture->getOriginalSize();
+	if (std::min(size.Width, size.Height) < TEXTURE_FILTER_MIN_SIZE)
+		use_trilinear_filter = use_bilinear_filter = false;
+
+	material.forEachTexture([=] (auto &tex) {
+		setMaterialFilters(tex, use_bilinear_filter, use_trilinear_filter,
+				use_anisotropic_filter);
+	});
+	return true;
+}
+
 static void setBillboardTextureMatrix(scene::IBillboardSceneNode *bill,
 		float txs, float tys, int col, int row)
 {
@@ -1238,10 +1263,6 @@ void GenericCAO::updateTextures(std::string mod)
 {
 	ITextureSource *tsrc = m_client->tsrc();
 
-	bool use_trilinear_filter = g_settings->getBool("trilinear_filter");
-	bool use_bilinear_filter = g_settings->getBool("bilinear_filter");
-	bool use_anisotropic_filter = g_settings->getBool("anisotropic_filter");
-
 	m_previous_texture_modifier = m_current_texture_modifier;
 	m_current_texture_modifier = mod;
 
@@ -1254,12 +1275,7 @@ void GenericCAO::updateTextures(std::string mod)
 
 			video::SMaterial &material = m_spritenode->getMaterial(0);
 			material.MaterialType = m_material_type;
-			material.setTexture(0, tsrc->getTextureForMesh(texturestring));
-
-			material.forEachTexture([=] (auto &tex) {
-				setMaterialFilters(tex, use_bilinear_filter, use_trilinear_filter,
-						use_anisotropic_filter);
-			});
+			setMaterialTextureAndFilters(material, texturestring, tsrc);
 		}
 	}
 
@@ -1273,29 +1289,12 @@ void GenericCAO::updateTextures(std::string mod)
 				if (texturestring.empty())
 					continue; // Empty texture string means don't modify that material
 				texturestring += mod;
-				video::ITexture *texture = tsrc->getTextureForMesh(texturestring);
-				if (!texture) {
-					errorstream<<"GenericCAO::updateTextures(): Could not load texture "<<texturestring<<std::endl;
-					continue;
-				}
 
 				// Set material flags and texture
 				video::SMaterial &material = m_animated_meshnode->getMaterial(i);
 				material.MaterialType = m_material_type;
-				material.TextureLayers[0].Texture = texture;
 				material.BackfaceCulling = m_prop.backface_culling;
-
-				// don't filter low-res textures, makes them look blurry
-				// player models have a res of 64
-				const core::dimension2d<u32> &size = texture->getOriginalSize();
-				const u32 res = std::min(size.Height, size.Width);
-				use_trilinear_filter &= res > 64;
-				use_bilinear_filter &= res > 64;
-
-				material.forEachTexture([=] (auto &tex) {
-					setMaterialFilters(tex, use_bilinear_filter, use_trilinear_filter,
-							use_anisotropic_filter);
-				});
+				setMaterialTextureAndFilters(material, texturestring, tsrc);
 			}
 		}
 	}
@@ -1313,13 +1312,7 @@ void GenericCAO::updateTextures(std::string mod)
 				// Set material flags and texture
 				video::SMaterial &material = m_meshnode->getMaterial(i);
 				material.MaterialType = m_material_type;
-				material.setTexture(0, tsrc->getTextureForMesh(texturestring));
-				material.getTextureMatrix(0).makeIdentity();
-
-				material.forEachTexture([=] (auto &tex) {
-					setMaterialFilters(tex, use_bilinear_filter, use_trilinear_filter,
-							use_anisotropic_filter);
-				});
+				setMaterialTextureAndFilters(material, texturestring, tsrc);
 			}
 		} else if (m_prop.visual == OBJECTVISUAL_UPRIGHT_SPRITE) {
 			scene::IMesh *mesh = m_meshnode->getMesh();
@@ -1330,12 +1323,7 @@ void GenericCAO::updateTextures(std::string mod)
 				tname += mod;
 
 				auto &material = m_meshnode->getMaterial(0);
-				material.setTexture(0, tsrc->getTextureForMesh(tname));
-
-				material.forEachTexture([=] (auto &tex) {
-					setMaterialFilters(tex, use_bilinear_filter, use_trilinear_filter,
-							use_anisotropic_filter);
-				});
+				setMaterialTextureAndFilters(material, tname, tsrc);
 			}
 			{
 				std::string tname = "no_texture.png";
@@ -1346,12 +1334,7 @@ void GenericCAO::updateTextures(std::string mod)
 				tname += mod;
 
 				auto &material = m_meshnode->getMaterial(1);
-				material.setTexture(0, tsrc->getTextureForMesh(tname));
-
-				material.forEachTexture([=] (auto &tex) {
-					setMaterialFilters(tex, use_bilinear_filter, use_trilinear_filter,
-							use_anisotropic_filter);
-				});
+				setMaterialTextureAndFilters(material, tname, tsrc);
 			}
 			// Set mesh color (only if lighting is disabled)
 			if (m_prop.glow < 0)

src/client/imagesource.cpp

@@ -1479,21 +1479,28 @@ bool ImageSource::generateImagePart(std::string_view part_of_name,
 
 			/* Upscale textures to user's requested minimum size.  This is a trick to make
 			 * filters look as good on low-res textures as on high-res ones, by making
-			 * low-res textures BECOME high-res ones.  This is helpful for worlds that
+			 * low-res textures BECOME high-res ones. This is helpful for worlds that
 			 * mix high- and low-res textures, or for mods with least-common-denominator
 			 * textures that don't have the resources to offer high-res alternatives.
+			 *
+			 * Q: why not just enable/disable filtering depending on texture size?
+			 * A: large texture resolutions apparently allow getting rid of the Moire
+			 *    effect way better than anisotropic filtering alone could.
+			 *    see <https://github.com/luanti-org/luanti/issues/15604> and related
+			 *    linked discussions.
 			 */
 			const bool filter = m_setting_trilinear_filter || m_setting_bilinear_filter;
-			const s32 scaleto = filter ? g_settings->getU16("texture_min_size") : 1;
-			if (scaleto > 1) {
-				const core::dimension2d<u32> dim = baseimg->getDimension();
+			if (filter) {
+				const f32 scaleto = rangelim(g_settings->getU16("texture_min_size"),
+					TEXTURE_FILTER_MIN_SIZE, 16384);
 
-				/* Calculate scaling needed to make the shortest texture dimension
-				 * equal to the target minimum.  If e.g. this is a vertical frames
-				 * animation, the short dimension will be the real size.
+				/* Calculate integer-scaling needed to make the shortest texture
+				 * dimension equal to the target minimum. If this is e.g. a
+				 * vertical frames animation, the short dimension will be the real size.
 				 */
-				u32 xscale = scaleto / dim.Width;
-				u32 yscale = scaleto / dim.Height;
+				const auto &dim = baseimg->getDimension();
+				u32 xscale = std::ceil(scaleto / dim.Width);
+				u32 yscale = std::ceil(scaleto / dim.Height);
 				const s32 scale = std::max(xscale, yscale);
 
 				// Never downscale; only scale up by 2x or more.

src/client/wieldmesh.cpp

@@ -281,12 +281,11 @@ void WieldMeshSceneNode::setExtruded(const std::string &imagename,
 		material.MaterialType = m_material_type;
 		material.MaterialTypeParam = 0.5f;
 		material.BackfaceCulling = true;
-		// Enable bi/trilinear filtering only for high resolution textures
-		bool bilinear_filter = dim.Width > 32 && m_bilinear_filter;
-		bool trilinear_filter = dim.Width > 32 && m_trilinear_filter;
+		// don't filter low-res textures, makes them look blurry
+		bool f_ok = std::min(dim.Width, dim.Height) >= TEXTURE_FILTER_MIN_SIZE;
 		material.forEachTexture([=] (auto &tex) {
-			setMaterialFilters(tex, bilinear_filter, trilinear_filter,
-					m_anisotropic_filter);
+			setMaterialFilters(tex, m_bilinear_filter && f_ok,
+				m_trilinear_filter && f_ok, m_anisotropic_filter);
 		});
 		// mipmaps cause "thin black line" artifacts
 		material.UseMipMaps = false;

src/constants.h

@@ -99,3 +99,9 @@
 #define SCREENSHOT_MAX_SERIAL_TRIES 1000
 
 #define TTF_DEFAULT_FONT_SIZE (16)
+
+// Minimum texture size enforced/checked for enabling linear filtering
+// This serves as the minimum for `texture_min_size`.
+// The intent is to ensure that the rendering doesn't turn terribly blurry
+// when filtering is enabled.
+#define TEXTURE_FILTER_MIN_SIZE 192U

src/defaultsettings.cpp

@@ -246,7 +246,7 @@ void set_default_settings()
 	settings->setDefault("undersampling", "1");
 	settings->setDefault("world_aligned_mode", "enable");
 	settings->setDefault("autoscale_mode", "disable");
-	settings->setDefault("texture_min_size", "64");
+	settings->setDefault("texture_min_size", std::to_string(TEXTURE_FILTER_MIN_SIZE));
 	settings->setDefault("enable_fog", "true");
 	settings->setDefault("fog_start", "0.4");
 	settings->setDefault("3d_mode", "none");

src/nodedef.cpp

@@ -272,7 +272,8 @@ void TextureSettings::readSettings()
 	connected_glass                = g_settings->getBool("connected_glass");
 	translucent_liquids            = g_settings->getBool("translucent_liquids");
 	enable_minimap                 = g_settings->getBool("enable_minimap");
-	node_texture_size              = std::max<u16>(g_settings->getU16("texture_min_size"), 1);
+	node_texture_size              = rangelim(g_settings->getU16("texture_min_size"),
+		TEXTURE_FILTER_MIN_SIZE, 16384);
 	std::string leaves_style_str   = g_settings->get("leaves_style");
 	std::string world_aligned_mode_str = g_settings->get("world_aligned_mode");
 	std::string autoscale_mode_str = g_settings->get("autoscale_mode");