From 66612995734f0cef9ebd595763a00590f4dddf8b Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Sat, 27 Feb 2021 19:44:17 +0300
Subject: [PATCH] Support reading grayscale pngs

---
 libs/gfx/include/psemek/gfx/pixmap.hpp |  1 +
 libs/gfx/source/png.cpp                | 34 ++++++++++++++++++--------
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/libs/gfx/include/psemek/gfx/pixmap.hpp b/libs/gfx/include/psemek/gfx/pixmap.hpp
index 353a6e69..02babf58 100644
--- a/libs/gfx/include/psemek/gfx/pixmap.hpp
+++ b/libs/gfx/include/psemek/gfx/pixmap.hpp
@@ -24,5 +24,6 @@ namespace psemek::gfx
 	void write_ppm(pixmap_rgb const & p, std::ostream & os);
 
 	pixmap_rgba read_png(std::istream & is);
+	pixmap_monochrome read_png_monochrome(std::istream & is);
 
 }
diff --git a/libs/gfx/source/png.cpp b/libs/gfx/source/png.cpp
index 80199aef..6bd63cb2 100644
--- a/libs/gfx/source/png.cpp
+++ b/libs/gfx/source/png.cpp
@@ -3,14 +3,13 @@
 #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)
+	template <typename Pixel>
+	basic_pixmap<Pixel> read_png_impl(std::istream & is, png_byte expected_color_type)
 	{
 		png_error_ptr error = [](png_structp, png_const_charp str)
 		{
@@ -52,17 +51,22 @@ namespace psemek::gfx
 		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 (color_type != expected_color_type)
+			throw std::runtime_error("PNG color type not supported");
 
-		if (bit_depth != 8)
-			throw std::runtime_error("PNG bit depths other than 8 are not supported");
+		if (bit_depth == 16)
+			png_set_strip_16(png);
 
-		pixmap_rgba result({width, height});
+		if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
+			png_set_expand_gray_1_2_4_to_8(png);
+
+		png_read_update_info(png, info);
+
+		basic_pixmap<Pixel> 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");
+		if (row_bytes != width * sizeof(Pixel))
+			throw std::runtime_error("PNG row bytes mismatch");
 
 		for (std::uint32_t i = 0; i < height; ++i)
 			png_read_row(png, reinterpret_cast<png_bytep>(result.data() + i * width), nullptr);
@@ -70,4 +74,14 @@ namespace psemek::gfx
 		return result;
 	}
 
+	pixmap_rgba read_png(std::istream & is)
+	{
+		return read_png_impl<color_rgba>(is, PNG_COLOR_TYPE_RGBA);
+	}
+
+	pixmap_monochrome read_png_monochrome(std::istream & is)
+	{
+		return read_png_impl<std::uint8_t>(is, PNG_COLOR_TYPE_GRAY);
+	}
+
 }