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Factor out a single PNG-reading function to encapsulate the libpng API (#1765)
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Rangi
+216
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// SPDX-License-Identifier: MIT
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#include "gfx/png.hpp"
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#include <png.h>
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#include "gfx/main.hpp"
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#include "gfx/rgba.hpp"
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#include "gfx/warning.hpp"
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struct Input {
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char const *filename;
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std::streambuf &file;
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Input(char const *filename_, std::streambuf &file_) : filename(filename_), file(file_) {}
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};
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[[noreturn]]
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static void handleError(png_structp png, char const *msg) {
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Input const &input = *reinterpret_cast<Input *>(png_get_error_ptr(png));
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fatal("Error reading PNG image (\"%s\"): %s", input.filename, msg);
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}
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static void handleWarning(png_structp png, char const *msg) {
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Input const &input = *reinterpret_cast<Input *>(png_get_error_ptr(png));
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warnx("In PNG image (\"%s\"): %s", input.filename, msg);
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}
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static void readData(png_structp png, png_bytep data, size_t length) {
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Input &input = *reinterpret_cast<Input *>(png_get_io_ptr(png));
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std::streamsize expectedLen = length;
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std::streamsize nbBytesRead = input.file.sgetn(reinterpret_cast<char *>(data), expectedLen);
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if (nbBytesRead != expectedLen) {
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fatal(
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"Error reading PNG image (\"%s\"): file too short (expected at least %zd more "
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"bytes after reading %zu)",
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input.filename,
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length - nbBytesRead,
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static_cast<size_t>(input.file.pubseekoff(0, std::ios_base::cur))
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);
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}
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}
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Png::Png(char const *filename, std::streambuf &file) {
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Input input(filename, file);
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options.verbosePrint(Options::VERB_LOG_ACT, "Reading PNG file \"%s\"\n", input.filename);
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std::array<unsigned char, 8> pngHeader;
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if (input.file.sgetn(reinterpret_cast<char *>(pngHeader.data()), pngHeader.size())
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!= static_cast<std::streamsize>(pngHeader.size()) // Not enough bytes?
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|| png_sig_cmp(pngHeader.data(), 0, pngHeader.size()) != 0) {
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fatal("PNG file (\"%s\") is not a valid PNG image!", input.filename); // LCOV_EXCL_LINE
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}
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options.verbosePrint(Options::VERB_INTERM, "PNG header signature is OK\n");
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png_structp png = png_create_read_struct(
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PNG_LIBPNG_VER_STRING, static_cast<png_voidp>(&input), handleError, handleWarning
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);
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if (!png) {
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fatal("Failed to create PNG read structure: %s", strerror(errno)); // LCOV_EXCL_LINE
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}
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png_infop info = png_create_info_struct(png);
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Defer destroyPng{[&] { png_destroy_read_struct(&png, info ? &info : nullptr, nullptr); }};
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if (!info) {
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fatal("Failed to create PNG info structure: %s", strerror(errno)); // LCOV_EXCL_LINE
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}
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png_set_read_fn(png, &input, readData);
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png_set_sig_bytes(png, pngHeader.size());
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// Process all chunks up to but not including the image data
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png_read_info(png, info);
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int bitDepth, colorType, interlaceType;
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png_get_IHDR(
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png, info, &width, &height, &bitDepth, &colorType, &interlaceType, nullptr, nullptr
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);
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pixels.resize(static_cast<size_t>(width) * static_cast<size_t>(height));
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auto colorTypeName = [](int type) {
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switch (type) {
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case PNG_COLOR_TYPE_GRAY:
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return "grayscale";
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case PNG_COLOR_TYPE_GRAY_ALPHA:
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return "grayscale + alpha";
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case PNG_COLOR_TYPE_PALETTE:
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return "palette";
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case PNG_COLOR_TYPE_RGB:
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return "RGB";
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case PNG_COLOR_TYPE_RGB_ALPHA:
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return "RGB + alpha";
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default:
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return "unknown color type";
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}
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};
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auto interlaceTypeName = [](int type) {
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switch (type) {
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case PNG_INTERLACE_NONE:
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return "not interlaced";
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case PNG_INTERLACE_ADAM7:
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return "interlaced (Adam7)";
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default:
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return "unknown interlace type";
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}
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};
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options.verbosePrint(
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Options::VERB_INTERM,
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"PNG image: %" PRIu32 "x%" PRIu32 " pixels, %dbpp %s, %s\n",
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width,
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height,
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bitDepth,
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colorTypeName(colorType),
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interlaceTypeName(interlaceType)
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);
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int nbColors = 0;
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png_colorp embeddedPal = nullptr;
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if (png_get_PLTE(png, info, &embeddedPal, &nbColors) != 0) {
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int nbTransparentEntries = 0;
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png_bytep transparencyPal = nullptr;
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if (png_get_tRNS(png, info, &transparencyPal, &nbTransparentEntries, nullptr)) {
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assume(nbTransparentEntries <= nbColors);
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}
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for (int i = 0; i < nbColors; ++i) {
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png_color const &color = embeddedPal[i];
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palette.emplace_back(
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color.red,
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color.green,
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color.blue,
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transparencyPal && i < nbTransparentEntries ? transparencyPal[i] : 0xFF
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);
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}
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options.verbosePrint(
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Options::VERB_INTERM, "Embedded PNG palette has %d colors: [", nbColors
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);
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for (int i = 0; i < nbColors; ++i) {
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if (i > 0) {
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options.verbosePrint(Options::VERB_INTERM, ", ");
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}
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options.verbosePrint(Options::VERB_INTERM, "#%08x", palette[i].toCSS());
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}
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options.verbosePrint(Options::VERB_INTERM, "]\n");
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} else {
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options.verbosePrint(Options::VERB_INTERM, "No embedded PNG palette\n");
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}
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// Set up transformations to turn everything into RGBA8888 for simplicity of handling
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// Convert grayscale to RGB
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switch (colorType & ~PNG_COLOR_MASK_ALPHA) {
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case PNG_COLOR_TYPE_GRAY:
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png_set_gray_to_rgb(png); // This also converts tRNS to alpha
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break;
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case PNG_COLOR_TYPE_PALETTE:
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png_set_palette_to_rgb(png);
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break;
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}
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if (png_get_valid(png, info, PNG_INFO_tRNS)) {
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// If we read a tRNS chunk, convert it to alpha
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png_set_tRNS_to_alpha(png);
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} else if (!(colorType & PNG_COLOR_MASK_ALPHA)) {
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// Otherwise, if we lack an alpha channel, default to full opacity
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png_set_add_alpha(png, 0xFFFF, PNG_FILLER_AFTER);
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}
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// Scale 16bpp back to 8 (we don't need all of that precision anyway)
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if (bitDepth == 16) {
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png_set_scale_16(png);
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} else if (bitDepth < 8) {
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png_set_packing(png);
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}
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// Deinterlace rows so they can trivially be read in order
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if (interlaceType != PNG_INTERLACE_NONE) {
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png_set_interlace_handling(png);
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}
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// Update `info` with the transformations
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png_read_update_info(png, info);
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// These shouldn't have changed
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assume(png_get_image_width(png, info) == width);
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assume(png_get_image_height(png, info) == height);
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// These should have changed, however
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assume(png_get_color_type(png, info) == PNG_COLOR_TYPE_RGBA);
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assume(png_get_bit_depth(png, info) == 8);
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// Now that metadata has been read, we can read the image data
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std::vector<png_byte> image(width * height * 4);
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std::vector<png_bytep> rowPtrs(height);
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for (uint32_t y = 0; y < height; ++y) {
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rowPtrs[y] = image.data() + y * width * 4;
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}
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png_read_image(png, rowPtrs.data());
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// We don't care about chunks after the image data (comments, etc.)
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png_read_end(png, nullptr);
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// Finally, process the image data from RGBA8888 bytes into `Rgba` colors
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for (uint32_t y = 0; y < height; ++y) {
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for (uint32_t x = 0; x < width; ++x) {
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uint32_t idx = y * width + x;
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uint32_t off = idx * 4;
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pixels[idx] = Rgba(image[off], image[off + 1], image[off + 2], image[off + 3]);
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}
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}
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}
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