Function ReadHeightmapBMPImageData

src/heightmap.cpp:207–255

* The BMP Heightmap loader. */

 * The BMP Heightmap loader.
 */
static void ReadHeightmapBMPImageData(std::span<uint8_t> map, const BmpInfo &info, const BmpData &data)
{
	uint8_t gray_palette[256];

	if (!data.palette.empty()) {
		bool all_gray = true;

		if (info.palette_size != 2) {
			for (uint i = 0; i < info.palette_size && (info.palette_size != 16 || all_gray); i++) {
				all_gray &= data.palette[i].r == data.palette[i].g && data.palette[i].r == data.palette[i].b;
				gray_palette[i] = RGBToGreyscale(data.palette[i].r, data.palette[i].g, data.palette[i].b);
			}

			/**
			 * For a non-gray palette of size 16 we assume that
			 * the order of the palette determines the height;
			 * the first entry is the sea (level 0), the second one
			 * level 1, etc.
			 */
			if (info.palette_size == 16 && !all_gray) {
				for (uint i = 0; i < info.palette_size; i++) {
					gray_palette[i] = 256 * i / info.palette_size;
				}
			}
		} else {
			/**
			 * For a palette of size 2 we assume that the order of the palette determines the height;
			 * the first entry is the sea (level 0), the second one is the land (level 1)
			 */
			gray_palette[0] = 0;
			gray_palette[1] = 16;
		}
	}

	/* Read the raw image data and convert in 8-bit greyscale */
	for (uint y = 0; y < info.height; y++) {
		uint8_t *pixel = &map[y * static_cast<size_t>(info.width)];
		const uint8_t *bitmap = &data.bitmap[y * static_cast<size_t>(info.width) * (info.bpp == 24 ? 3 : 1)];

		for (uint x = 0; x < info.width; x++) {
			if (info.bpp != 24) {
				*pixel++ = gray_palette[*bitmap++];
			} else {
				*pixel++ = RGBToGreyscale(*bitmap, *(bitmap + 1), *(bitmap + 2));
				bitmap += 3;
			}
		}
	}
}

/**
 * Reads the heightmap and/or size of the heightmap from a BMP file.