WritePng: Support transparent PNG images

Now matches exactly what Maniacs is saving

Author: Ghabry

src/bitmap.cpp

@@ -184,11 +184,19 @@ bool Bitmap::WritePNG(std::ostream& os) const {
 	auto format = PIXMAN_b8g8r8;
 #endif
 
+	if (GetTransparent()) {
+#ifdef WORDS_BIGENDIAN
+		format = PIXMAN_r8g8b8a8;
+#else
+		format = PIXMAN_a8b8g8r8;
+#endif
+	}
+
 	auto dst = PixmanImagePtr{pixman_image_create_bits(format, width, height, &data.front(), stride)};
 	pixman_image_composite32(PIXMAN_OP_SRC, bitmap.get(), NULL, dst.get(),
 							 0, 0, 0, 0, 0, 0, width, height);
 
-	return ImagePNG::Write(os, width, height, &data.front());
+	return ImagePNG::Write(os, width, height, &data.front(), GetTransparent());
 }
 
 size_t Bitmap::GetSize() const {

src/image_png.cpp

@@ -253,7 +253,7 @@ static void flush_stream(png_structp out_ptr) {
 	reinterpret_cast<Filesystem_Stream::OutputStream*>(png_get_io_ptr(out_ptr))->flush();
 }
 
-bool ImagePNG::Write(std::ostream& os, uint32_t width, uint32_t height, uint32_t* data) {
+bool ImagePNG::Write(std::ostream& os, uint32_t width, uint32_t height, uint32_t* data, bool transparent) {
 	png_structp write = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
 	if (!write) {
 		Output::Warning("Bitmap::WritePNG: error in png_create_write");
@@ -282,7 +282,7 @@ bool ImagePNG::Write(std::ostream& os, uint32_t width, uint32_t height, uint32_t
 	png_set_write_fn(write, &os, &write_data, &flush_stream);
 
 	png_set_IHDR(write, info, width, height, 8,
-				 PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
+				 transparent ? PNG_COLOR_TYPE_RGBA : PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
 				 PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
 	png_write_info(write, info);
 	png_write_image(write, ptrs);

src/image_png.h

@@ -25,7 +25,7 @@
 namespace ImagePNG {
 	bool Read(const void* buffer, bool transparent, ImageOut& output);
 	bool Read(Filesystem_Stream::InputStream& is, bool transparent, ImageOut& output);
-	bool Write(std::ostream& os, uint32_t width, uint32_t height, uint32_t* data);
+	bool Write(std::ostream& os, uint32_t width, uint32_t height, uint32_t* data, bool transparent);
 }
 
 #endif