Hard-coded undersampling.

Adds uniform undersampling for the 3D rendered scene. GUI elements
are not undersampled, resulting in better playability for users
with low-performance platforms with readable fonts and formspecs.

The undersampling setting can be set to 0 (disabled), 2, 3, 4 pixels
which translates into a resolution reduction of x4, x9 or x16, and
is significant.

1 files changed, 40 insertions, 7 deletions

diff --git a/src/drawscene.cpp b/src/drawscene.cpp
index 663c8828c..421b96f12 100644
--- a/src/drawscene.cpp
+++ b/src/drawscene.cpp
@@ -459,10 +459,37 @@ void draw_pageflip_3d_mode(Camera& camera, bool show_hud,
 #endif
 }
 
-void draw_plain(Camera &camera, bool show_hud, Hud &hud,
-		video::IVideoDriver *driver, bool draw_wield_tool,
-		Client &client, gui::IGUIEnvironment *guienv)
+// returns (size / coef), rounded upwards
+inline int scaledown(int coef, int size)
 {
+	return (size + coef - 1) / coef;
+}
+
+void draw_plain(Camera &camera, bool show_hud,
+		Hud &hud, video::IVideoDriver *driver,
+		scene::ISceneManager *smgr, const v2u32 &screensize,
+		bool draw_wield_tool, Client &client, gui::IGUIEnvironment *guienv,
+		video::SColor skycolor)
+{
+	// Undersampling-specific stuff
+	static video::ITexture *image = NULL;
+	static v2u32 last_pixelated_size = v2u32(0, 0);
+	int undersampling = g_settings->getU16("undersampling");
+	v2u32 pixelated_size;
+	v2u32 dest_size;
+	if (undersampling > 0) {
+		pixelated_size = v2u32(scaledown(undersampling, screensize.X),
+				scaledown(undersampling, screensize.Y));
+		dest_size = v2u32(undersampling * pixelated_size.X, undersampling * pixelated_size.Y);
+		if (pixelated_size != last_pixelated_size) {
+			init_texture(driver, pixelated_size, &image, "mt_drawimage_img1");
+			last_pixelated_size = pixelated_size;
+		}
+		driver->setRenderTarget(image, true, true, skycolor);
+	}
+
+	// Render
+	smgr->drawAll();
 	driver->setTransform(video::ETS_WORLD, core::IdentityMatrix);
 	if (show_hud) {
 		hud.drawSelectionMesh();
@@ -470,10 +497,18 @@ void draw_plain(Camera &camera, bool show_hud, Hud &hud,
 			camera.drawWieldedTool();
 		}
 	}
+
+	// Upscale lowres render
+	if (undersampling > 0) {
+		driver->setRenderTarget(0, true, true);
+		driver->draw2DImage(image,
+				irr::core::rect<s32>(0, 0, dest_size.X, dest_size.Y),
+				irr::core::rect<s32>(0, 0, pixelated_size.X, pixelated_size.Y));
+	}
 }
 
 void draw_scene(video::IVideoDriver *driver, scene::ISceneManager *smgr,
-		Camera &camera, Client& client, LocalPlayer *player, Hud &hud,
+		Camera &camera, Client &client, LocalPlayer *player, Hud &hud,
 		Minimap &mapper, gui::IGUIEnvironment *guienv,
 		const v2u32 &screensize, const video::SColor &skycolor,
 		bool show_hud, bool show_minimap)
@@ -496,8 +531,6 @@ void draw_scene(video::IVideoDriver *driver, scene::ISceneManager *smgr,
 
 	const std::string &draw_mode = g_settings->get("3d_mode");
 
-	smgr->drawAll();
-
 	if (draw_mode == "anaglyph")
 	{
 		draw_anaglyph_3d_mode(camera, show_hud, hud, driver,
@@ -531,7 +564,7 @@ void draw_scene(video::IVideoDriver *driver, scene::ISceneManager *smgr,
 	}
 	else {
 		draw_plain(camera, show_hud, hud, driver,
-				draw_wield_tool, client, guienv);
+				smgr, screensize, draw_wield_tool, client, guienv, skycolor);
 	}
 
 	/*