From 08d646931187b30211f725a7e794a2efb1c02332 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Sat, 27 Feb 2021 19:09:14 +0300
Subject: [PATCH] Support png image loading

---
 libs/gfx/include/psemek/gfx/pixmap.hpp |  2 +
 libs/gfx/source/png.cpp                | 73 ++++++++++++++++++++++++++
 2 files changed, 75 insertions(+)
 create mode 100644 libs/gfx/source/png.cpp

diff --git a/libs/gfx/include/psemek/gfx/pixmap.hpp b/libs/gfx/include/psemek/gfx/pixmap.hpp
index c0624175..353a6e69 100644
--- a/libs/gfx/include/psemek/gfx/pixmap.hpp
+++ b/libs/gfx/include/psemek/gfx/pixmap.hpp
@@ -23,4 +23,6 @@ namespace psemek::gfx
 	void write_pgm(pixmap_monochrome const & p, std::ostream & os);
 	void write_ppm(pixmap_rgb const & p, std::ostream & os);
 
+	pixmap_rgba read_png(std::istream & is);
+
 }
diff --git a/libs/gfx/source/png.cpp b/libs/gfx/source/png.cpp
new file mode 100644
index 00000000..80199aef
--- /dev/null
+++ b/libs/gfx/source/png.cpp
@@ -0,0 +1,73 @@
+#include <psemek/gfx/pixmap.hpp>
+
+#include <psemek/log/log.hpp>
+#include <psemek/util/at_scope_exit.hpp>
+
+#include <vector>
+
+#include <png.h>
+
+namespace psemek::gfx
+{
+
+	pixmap_rgba read_png(std::istream & is)
+	{
+		png_error_ptr error = [](png_structp, png_const_charp str)
+		{
+			throw std::runtime_error(str);
+		};
+
+		png_error_ptr warn = [](png_structp, png_const_charp str)
+		{
+			log::warning() << str;
+		};
+
+		auto png = png_create_read_struct(PNG_LIBPNG_VER_STRING, nullptr, error, warn);
+		if (!png) throw std::runtime_error("png_create_read_struct returned null");
+
+		png_set_error_fn(png, nullptr, error, warn);
+
+		png_infop info = nullptr;
+		png_infop end_info = nullptr;
+
+		[[maybe_unused]] auto png_dtor = util::at_scope_exit([&]{
+			png_destroy_read_struct(&png, &info, &end_info);
+		});
+
+		info = png_create_info_struct(png);
+		if (!info) throw std::runtime_error("png_create_info_struct returned null");
+
+		end_info = png_create_info_struct(png);
+		if (!end_info) throw std::runtime_error("png_create_info_struct returned null");
+
+		png_rw_ptr read = [](png_structp png, png_bytep ptr, size_t count){
+			reinterpret_cast<std::istream *>(png_get_io_ptr(png))->read(reinterpret_cast<char *>(ptr), count);
+		};
+		png_set_read_fn(png, &is, read);
+
+		png_read_info(png, info);
+
+		auto const width = png_get_image_width(png, info);
+		auto const height = png_get_image_height(png, info);
+		auto const color_type = png_get_color_type(png, info);
+		auto const bit_depth = png_get_bit_depth(png, info);
+
+		if (color_type != PNG_COLOR_TYPE_RGBA)
+			throw std::runtime_error("PNG color types other than RGBA are not supported");
+
+		if (bit_depth != 8)
+			throw std::runtime_error("PNG bit depths other than 8 are not supported");
+
+		pixmap_rgba result({width, height});
+
+		auto const row_bytes = png_get_rowbytes(png, info);
+		if (row_bytes != width * 4)
+			throw std::runtime_error("PNG row bytes is wrong");
+
+		for (std::uint32_t i = 0; i < height; ++i)
+			png_read_row(png, reinterpret_cast<png_bytep>(result.data() + i * width), nullptr);
+
+		return result;
+	}
+
+}