maybe this is good?

libcygnet/include/cygnet/Renderer.h

@@ -15,6 +15,7 @@ struct RendererState;
 
 struct RenderChunk {
 	GLuint tex;
+	GLuint opacityTex;
 };
 
 struct RenderSprite {
@@ -48,8 +49,9 @@ public:
 	void modifyTile(TileID id, const void *data);
 
 	RenderChunk createChunk(
-			TileID tiles[SwanCommon::CHUNK_WIDTH * SwanCommon::CHUNK_HEIGHT]);
-	void modifyChunk(RenderChunk chunk, SwanCommon::Vec2i pos, TileID id);
+			TileID tiles[SwanCommon::CHUNK_WIDTH * SwanCommon::CHUNK_HEIGHT],
+			uint8_t opacities[SwanCommon::CHUNK_WIDTH * SwanCommon::CHUNK_HEIGHT]);
+	void modifyChunk(RenderChunk chunk, SwanCommon::Vec2i pos, TileID id, uint8_t opacity);
 	void destroyChunk(RenderChunk chunk);
 
 	RenderSprite createSprite(void *data, int width, int height, int fh);

libcygnet/src/Renderer.cc

@@ -662,9 +662,13 @@ void Renderer::modifyTile(TileID id, const void *data) {
 }
 
 RenderChunk Renderer::createChunk(
-		TileID tiles[SwanCommon::CHUNK_WIDTH * SwanCommon::CHUNK_HEIGHT]) {
+		TileID tiles[SwanCommon::CHUNK_WIDTH * SwanCommon::CHUNK_HEIGHT],
+		uint8_t opacities[SwanCommon::CHUNK_WIDTH * SwanCommon::CHUNK_HEIGHT]) {
 	RenderChunk chunk;
-	glGenTextures(1, &chunk.tex);
+	GLuint texes[2];
+	glGenTextures(2, texes);
+	chunk.tex = texes[0];
+	chunk.opacityTex = texes[1];
 	glCheck();
 
 	glActiveTexture(GL_TEXTURE0);
@@ -685,6 +689,7 @@ RenderChunk Renderer::createChunk(
 				GL_TEXTURE_2D, 0, GL_LUMINANCE_ALPHA,
 				SwanCommon::CHUNK_WIDTH, SwanCommon::CHUNK_HEIGHT,
 				0, GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, tiles);
+		glCheck();
 	} else if constexpr (std::endian::native == std::endian::big) {
 		uint8_t buf[SwanCommon::CHUNK_WIDTH * SwanCommon::CHUNK_HEIGHT * 2];
 		for (size_t y = 0; y < SwanCommon::CHUNK_HEIGHT; ++y) {
@@ -700,13 +705,20 @@ RenderChunk Renderer::createChunk(
 				GL_TEXTURE_2D, 0, GL_LUMINANCE_ALPHA,
 				SwanCommon::CHUNK_WIDTH, SwanCommon::CHUNK_HEIGHT,
 				0, GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, buf);
+		glCheck();
 	}
 
+	glBindTexture(GL_TEXTURE_2D, chunk.opacityTex);
+	glTexImage2D(
+			GL_TEXTURE_2D, 0, GL_LUMINANCE,
+			SwanCommon::CHUNK_WIDTH, SwanCommon::CHUNK_HEIGHT,
+			0, GL_LUMINANCE, GL_UNSIGNED_BYTE, opacities);
 	glCheck();
+
 	return chunk;
 }
 
-void Renderer::modifyChunk(RenderChunk chunk, SwanCommon::Vec2i pos, TileID id) {
+void Renderer::modifyChunk(RenderChunk chunk, SwanCommon::Vec2i pos, TileID id, uint8_t opacity) {
 	glActiveTexture(GL_TEXTURE0);
 	glBindTexture(GL_TEXTURE_2D, chunk.tex);
 	glCheck();
@@ -720,18 +732,24 @@ void Renderer::modifyChunk(RenderChunk chunk, SwanCommon::Vec2i pos, TileID id)
 		glTexSubImage2D(
 				GL_TEXTURE_2D, 0, pos.x, pos.y, 1, 1,
 				GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, &id);
+		glCheck();
 	} else if constexpr (std::endian::native == std::endian::big) {
 		uint8_t buf[] = { (uint8_t)(id & 0xff), (uint8_t)((id & 0xff00) >> 8) };
 		glTexSubImage2D(
 				GL_TEXTURE_2D, 0, pos.x, pos.y, 1, 1,
 				GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, buf);
+		glCheck();
 	}
 
-	glCheck();
+	glBindTexture(GL_TEXTURE_2D, chunk.opacityTex);
+	glTexSubImage2D(
+			GL_TEXTURE_2D, 0, pos.x, pos.y, 1, 1,
+			GL_LUMINANCE, GL_UNSIGNED_BYTE, &opacity);
 }
 
 void Renderer::destroyChunk(RenderChunk chunk) {
-	glDeleteTextures(1, &chunk.tex);
+	GLuint texes[] = {chunk.tex, chunk.opacityTex};
+	glDeleteTextures(2, texes);
 	glCheck();
 }
 

libswan/include/swan/Chunk.h

@@ -19,7 +19,8 @@ public:
 	using RelPos = TilePos;
 
 	static constexpr size_t DATA_SIZE =
-		CHUNK_WIDTH * CHUNK_HEIGHT * sizeof(Tile::ID);
+		CHUNK_WIDTH * CHUNK_HEIGHT * sizeof(Tile::ID) +
+		CHUNK_WIDTH * CHUNK_HEIGHT;
 
 	// What does this chunk want the world gen to do after a tick?
 	enum class TickAction {
@@ -35,13 +36,19 @@ public:
 		return (Tile::ID *)data_.get();
 	}
 
+	uint8_t *getOpacityData() {
+		assert(isActive());
+		return data_.get() + CHUNK_WIDTH * CHUNK_HEIGHT * sizeof(Tile::ID);
+	}
+
 	Tile::ID getTileID(RelPos pos) {
 		return getTileData()[pos.y * CHUNK_WIDTH + pos.x];
 	}
 
-	void setTileID(RelPos pos, Tile::ID id) {
+	void setTileID(RelPos pos, Tile::ID id, uint8_t opacity) {
 		getTileData()[pos.y * CHUNK_WIDTH + pos.x] = id;
-		changeList_.emplace_back(pos, id);
+		getOpacityData()[pos.y * CHUNK_WIDTH + pos.x] = opacity;
+		changeList_.emplace_back(pos, id, opacity);
 		isModified_ = true;
 	}
 
@@ -71,7 +78,7 @@ private:
 
 	std::unique_ptr<uint8_t[]> data_;
 	std::vector<std::pair<RelPos, float>> lights_;
-	std::vector<std::pair<RelPos, Tile::ID>> changeList_;
+	std::vector<std::tuple<RelPos, Tile::ID, uint8_t>> changeList_;
 
 	ssize_t compressedSize_ = -1; // -1 if not compressed, a positive number if compressed
 	Cygnet::RenderChunk renderChunk_;

libswan/src/Chunk.cc

@@ -118,11 +118,11 @@ void Chunk::draw(const Context &ctx, Cygnet::Renderer &rnd) {
 		return;
 
 	if (needChunkRender_) {
-		renderChunk_ = rnd.createChunk(getTileData());
+		renderChunk_ = rnd.createChunk(getTileData(), getOpacityData());
 		needChunkRender_ = false;
 	} else {
-		for (auto [pos, id]: changeList_) {
-			rnd.modifyChunk(renderChunk_, pos, id);
+		for (auto [pos, id, opacity]: changeList_) {
+			rnd.modifyChunk(renderChunk_, pos, id, opacity);
 		}
 	}
 

libswan/src/WorldPlane.cc

@@ -105,7 +105,7 @@ void WorldPlane::setTileID(TilePos pos, Tile::ID id) {
 	if (id != old) {
 		Tile &newTile = world_->getTileByID(id);
 		Tile &oldTile = world_->getTileByID(old);
-		chunk.setTileID(rp, id);
+		chunk.setTileID(rp, id, newTile.isSolid ? 255 : 0);
 
 		if (newTile.lightLevel != oldTile.lightLevel) {
 			if (oldTile.lightLevel > 0) {