From 417c6f0080ca3af0e259535f28040374cbf8bd48 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Sun, 5 Feb 2023 00:33:53 +0300
Subject: [PATCH] Support more PNG color types

---
 libs/gfx/source/png.cpp | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/libs/gfx/source/png.cpp b/libs/gfx/source/png.cpp
index 76bd5dcd..24d6c9f9 100644
--- a/libs/gfx/source/png.cpp
+++ b/libs/gfx/source/png.cpp
@@ -9,7 +9,7 @@ namespace psemek::gfx
 {
 
 	template <typename Pixel>
-	basic_pixmap<Pixel> read_png_impl(io::istream & is, png_byte expected_color_type)
+	basic_pixmap<Pixel> read_png_impl(io::istream & is, bool monochrome)
 	{
 		png_error_ptr error = [](png_structp, png_const_charp str)
 		{
@@ -51,15 +51,21 @@ 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 != expected_color_type)
-			throw std::runtime_error("PNG color type not supported");
-
 		if (bit_depth == 16)
 			png_set_strip_16(png);
 
+		if (monochrome && color_type != PNG_COLOR_TYPE_GRAY)
+			throw std::runtime_error("invalid color type for monochrome PNG");
+
+		if (color_type == PNG_COLOR_TYPE_PALETTE)
+			png_set_palette_to_rgb(png);
+
 		if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
 			png_set_expand_gray_1_2_4_to_8(png);
 
+		if (color_type == PNG_COLOR_TYPE_RGB)
+			png_set_add_alpha(png, 0xff, PNG_FILLER_AFTER);
+
 		png_read_update_info(png, info);
 
 		basic_pixmap<Pixel> result({width, height});
@@ -76,12 +82,12 @@ namespace psemek::gfx
 
 	pixmap_rgba read_png(io::istream && is)
 	{
-		return read_png_impl<color_rgba>(is, PNG_COLOR_TYPE_RGBA);
+		return read_png_impl<color_rgba>(is, false);
 	}
 
 	pixmap_monochrome read_png_monochrome(io::istream && is)
 	{
-		return read_png_impl<std::uint8_t>(is, PNG_COLOR_TYPE_GRAY);
+		return read_png_impl<std::uint8_t>(is, true);
 	}
 
 }