Function ReadHeightmapPNG

src/heightmap.cpp:141–199

* Reads the heightmap and/or size of the heightmap from a PNG file. * If map == nullptr only the size of the PNG is read, otherwise a map * with greyscale pixels is allocated and assigned to *map. */

 * with greyscale pixels is allocated and assigned to *map.
 */
static bool ReadHeightmapPNG(std::string_view filename, uint *x, uint *y, std::vector<uint8_t> *map)
{
	png_structp png_ptr = nullptr;
	png_infop info_ptr  = nullptr;

	auto fp = FioFOpenFile(filename, "rb", HEIGHTMAP_DIR);
	if (!fp.has_value()) {
		ShowErrorMessage(GetEncodedString(STR_ERROR_PNGMAP), GetEncodedString(STR_ERROR_PNGMAP_FILE_NOT_FOUND), WL_ERROR);
		return false;
	}

	png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);
	if (png_ptr == nullptr) {
		ShowErrorMessage(GetEncodedString(STR_ERROR_PNGMAP), GetEncodedString(STR_ERROR_PNGMAP_MISC), WL_ERROR);
		return false;
	}

	info_ptr = png_create_info_struct(png_ptr);
	if (info_ptr == nullptr || setjmp(png_jmpbuf(png_ptr))) {
		ShowErrorMessage(GetEncodedString(STR_ERROR_PNGMAP), GetEncodedString(STR_ERROR_PNGMAP_MISC), WL_ERROR);
		png_destroy_read_struct(&png_ptr, &info_ptr, nullptr);
		return false;
	}

	png_init_io(png_ptr, *fp);

	/* Allocate memory and read image, without alpha or 16-bit samples
	 * (result is either 8-bit indexed/greyscale or 24-bit RGB) */
	png_set_packing(png_ptr);
	png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_PACKING | PNG_TRANSFORM_STRIP_ALPHA | PNG_TRANSFORM_STRIP_16, nullptr);

	/* Maps of wrong colour-depth are not used.
	 * (this should have been taken care of by stripping alpha and 16-bit samples on load) */
	if ((png_get_channels(png_ptr, info_ptr) != 1) && (png_get_channels(png_ptr, info_ptr) != 3) && (png_get_bit_depth(png_ptr, info_ptr) != 8)) {
		ShowErrorMessage(GetEncodedString(STR_ERROR_PNGMAP), GetEncodedString(STR_ERROR_PNGMAP_IMAGE_TYPE), WL_ERROR);
		png_destroy_read_struct(&png_ptr, &info_ptr, nullptr);
		return false;
	}

	uint width = png_get_image_width(png_ptr, info_ptr);
	uint height = png_get_image_height(png_ptr, info_ptr);

	if (!IsValidHeightmapDimension(width, height)) {
		ShowErrorMessage(GetEncodedString(STR_ERROR_PNGMAP), GetEncodedString(STR_ERROR_HEIGHTMAP_TOO_LARGE), WL_ERROR);
		png_destroy_read_struct(&png_ptr, &info_ptr, nullptr);
		return false;
	}

	if (map != nullptr) {
		map->resize(static_cast<size_t>(width) * height);
		ReadHeightmapPNGImageData(*map, png_ptr, info_ptr);
	}

	*x = width;
	*y = height;

	png_destroy_read_struct(&png_ptr, &info_ptr, nullptr);
	return true;