Add embedded PNG texture modifier (#11498)

doc/lua_api.txt

@@ -628,6 +628,23 @@ Result is more like what you'd expect if you put a color on top of another
 color, meaning white surfaces get a lot of your new color while black parts
 don't change very much.
 
+#### `[png:<base64>`
+
+Embed a base64 encoded PNG image in the texture string.
+You can produce a valid string for this by calling
+`minetest.encode_base64(minetest.encode_png(tex))`,
+refer to the documentation of these functions for details.
+You can use this to send disposable images such as captchas
+to individual clients, or render things that would be too
+expensive to compose with `[combine:`.
+
+IMPORTANT: Avoid sending large images this way.
+This is not a replacement for asset files, do not use it to do anything
+that you could instead achieve by just using a file.
+In particular consider `minetest.dynamic_add_media` and test whether
+using other texture modifiers could result in a shorter string than
+embedding a whole image, this may vary by use case.
+
 Hardware coloring
 -----------------
 

games/devtest/mods/testnodes/textures.lua

@@ -102,12 +102,22 @@ local function gen_checkers(w, h, tile)
 end
 
 local fractal = mandelbrot(512, 512, 128)
+local frac_emb = mandelbrot(64, 64, 64)
 local checker = gen_checkers(512, 512, 32)
 
 local floor = math.floor
 local abs = math.abs
+local data_emb = {}
 local data_mb = {}
 local data_ck = {}
+for i=1, #frac_emb do
+	data_emb[i] = {
+		r = floor(abs(frac_emb[i] * 2 - 1) * 255),
+		g = floor(abs(1 - frac_emb[i]) * 255),
+		b = floor(frac_emb[i] * 255),
+		a = frac_emb[i] < 0.95 and 255 or 0,
+	}
+end
 for i=1, #fractal do
 	data_mb[i] = {
 		r = floor(fractal[i] * 255),
@@ -140,3 +150,24 @@ minetest.register_node("testnodes:generated_png_ck", {
 
 	groups = { dig_immediate = 2 },
 })
+
+local png_emb = "[png:" .. minetest.encode_base64(minetest.encode_png(64,64,data_emb))
+
+minetest.register_node("testnodes:generated_png_emb", {
+	description = S("Generated In-Band Mandelbrot PNG Test Node"),
+	tiles = { png_emb },
+
+	groups = { dig_immediate = 2 },
+})
+minetest.register_node("testnodes:generated_png_src_emb", {
+	description = S("Generated In-Band Source Blit Mandelbrot PNG Test Node"),
+	tiles = { png_emb .. "^testnodes_damage_neg.png" },
+
+	groups = { dig_immediate = 2 },
+})
+minetest.register_node("testnodes:generated_png_dst_emb", {
+	description = S("Generated In-Band Dest Blit Mandelbrot PNG Test Node"),
+	tiles = { "testnodes_generated_ck.png^" .. png_emb },
+
+	groups = { dig_immediate = 2 },
+})

src/client/tile.cpp

@@ -33,6 +33,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "imagefilters.h"
 #include "guiscalingfilter.h"
 #include "renderingengine.h"
+#include "util/base64.h"
 
 /*
 	A cache from texture name to texture path
@@ -1059,6 +1060,45 @@ static std::string unescape_string(const std::string &str, const char esc = '\\'
 	return out;
 }
 
+void blitBaseImage(video::IImage* &src, video::IImage* &dst)
+{
+	//infostream<<"Blitting "<<part_of_name<<" on base"<<std::endl;
+	// Size of the copied area
+	core::dimension2d<u32> dim = src->getDimension();
+	//core::dimension2d<u32> dim(16,16);
+	// Position to copy the blitted to in the base image
+	core::position2d<s32> pos_to(0,0);
+	// Position to copy the blitted from in the blitted image
+	core::position2d<s32> pos_from(0,0);
+	// Blit
+	/*image->copyToWithAlpha(baseimg, pos_to,
+			core::rect<s32>(pos_from, dim),
+			video::SColor(255,255,255,255),
+			NULL);*/
+
+	core::dimension2d<u32> dim_dst = dst->getDimension();
+	if (dim == dim_dst) {
+		blit_with_alpha(src, dst, pos_from, pos_to, dim);
+	} else if (dim.Width * dim.Height < dim_dst.Width * dim_dst.Height) {
+		// Upscale overlying image
+		video::IImage *scaled_image = RenderingEngine::get_video_driver()->
+			createImage(video::ECF_A8R8G8B8, dim_dst);
+		src->copyToScaling(scaled_image);
+
+		blit_with_alpha(scaled_image, dst, pos_from, pos_to, dim_dst);
+		scaled_image->drop();
+	} else {
+		// Upscale base image
+		video::IImage *scaled_base = RenderingEngine::get_video_driver()->
+			createImage(video::ECF_A8R8G8B8, dim);
+		dst->copyToScaling(scaled_base);
+		dst->drop();
+		dst = scaled_base;
+
+		blit_with_alpha(src, dst, pos_from, pos_to, dim);
+	}
+}
+
 bool TextureSource::generateImagePart(std::string part_of_name,
 		video::IImage *& baseimg)
 {
@@ -1122,41 +1162,7 @@ bool TextureSource::generateImagePart(std::string part_of_name,
 		// Else blit on base.
 		else
 		{
-			//infostream<<"Blitting "<<part_of_name<<" on base"<<std::endl;
-			// Size of the copied area
-			core::dimension2d<u32> dim = image->getDimension();
-			//core::dimension2d<u32> dim(16,16);
-			// Position to copy the blitted to in the base image
-			core::position2d<s32> pos_to(0,0);
-			// Position to copy the blitted from in the blitted image
-			core::position2d<s32> pos_from(0,0);
-			// Blit
-			/*image->copyToWithAlpha(baseimg, pos_to,
-					core::rect<s32>(pos_from, dim),
-					video::SColor(255,255,255,255),
-					NULL);*/
-
-			core::dimension2d<u32> dim_dst = baseimg->getDimension();
-			if (dim == dim_dst) {
-				blit_with_alpha(image, baseimg, pos_from, pos_to, dim);
-			} else if (dim.Width * dim.Height < dim_dst.Width * dim_dst.Height) {
-				// Upscale overlying image
-				video::IImage *scaled_image = RenderingEngine::get_video_driver()->
-					createImage(video::ECF_A8R8G8B8, dim_dst);
-				image->copyToScaling(scaled_image);
-
-				blit_with_alpha(scaled_image, baseimg, pos_from, pos_to, dim_dst);
-				scaled_image->drop();
-			} else {
-				// Upscale base image
-				video::IImage *scaled_base = RenderingEngine::get_video_driver()->
-					createImage(video::ECF_A8R8G8B8, dim);
-				baseimg->copyToScaling(scaled_base);
-				baseimg->drop();
-				baseimg = scaled_base;
-
-				blit_with_alpha(image, baseimg, pos_from, pos_to, dim);
-			}
+			blitBaseImage(image, baseimg);
 		}
 		//cleanup
 		image->drop();
@@ -1784,6 +1790,43 @@ bool TextureSource::generateImagePart(std::string part_of_name,
 			baseimg->drop();
 			baseimg = img;
 		}
+		/*
+			[png:base64
+			Decodes a PNG image in base64 form.
+			Use minetest.encode_png and minetest.encode_base64
+			to produce a valid string.
+		*/
+		else if (str_starts_with(part_of_name, "[png:")) {
+			Strfnd sf(part_of_name);
+			sf.next(":");
+			std::string png;
+			{
+				std::string blob = sf.next("");
+				if (!base64_is_valid(blob)) {
+					errorstream << "generateImagePart(): "
+								<< "malformed base64 in '[png'"
+								<< std::endl;
+					return false;
+				}
+				png = base64_decode(blob);
+			}
+
+			auto *device = RenderingEngine::get_raw_device();
+			auto *fs = device->getFileSystem();
+			auto *vd = device->getVideoDriver();
+			auto *memfile = fs->createMemoryReadFile(png.data(), png.size(), "__temp_png");
+			video::IImage* pngimg = vd->createImageFromFile(memfile);
+			memfile->drop();
+
+			if (baseimg) {
+				blitBaseImage(pngimg, baseimg);
+			} else {
+				core::dimension2d<u32> dim = pngimg->getDimension();
+				baseimg = driver->createImage(video::ECF_A8R8G8B8, dim);
+				pngimg->copyTo(baseimg);
+			}
+			pngimg->drop();
+		}
 		else
 		{
 			errorstream << "generateImagePart(): Invalid "