From 5715968065256daa4c43d5365cf5e268d75e007a Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Tue, 26 Jul 2016 00:51:09 +0300
Subject: [PATCH] Implement a loader for BMP images

---
 source/graphics/bmploader.cpp   | 109 ++++++++++++++++++++++++++++++++
 source/graphics/bmploader.h     |  27 ++++++++
 source/graphics/imageloader.cpp |   2 +
 3 files changed, 138 insertions(+)
 create mode 100644 source/graphics/bmploader.cpp
 create mode 100644 source/graphics/bmploader.h

diff --git a/source/graphics/bmploader.cpp b/source/graphics/bmploader.cpp
new file mode 100644
index 0000000..71de507
--- /dev/null
+++ b/source/graphics/bmploader.cpp
@@ -0,0 +1,109 @@
+#include <msp/core/inttypes.h>
+#include "bmploader.h"
+
+using namespace std;
+
+namespace {
+
+void read_full(Msp::IO::Base &io, char *buffer, unsigned size)
+{
+	unsigned len = io.read(buffer, size);
+	if(len<size)
+		throw Msp::Graphics::bad_image_data("premature end of file");
+}
+
+template<typename T>
+T decode(const char *data)
+{
+	const Msp::UInt8 *udata = reinterpret_cast<const Msp::UInt8 *>(data);
+	T result = 0;
+	for(unsigned i=0; i<sizeof(T); ++i)
+		result |= udata[i]<<(i*8);
+	return result;
+}
+
+}
+
+namespace Msp {
+namespace Graphics {
+
+BmpLoader::BmpLoader(IO::Base &i, unsigned sb):
+	io(i),
+	sig_bytes(sb)
+{
+	// Image data location is stored at offset 10 and can't be skipped
+	if(sig_bytes>10)
+		throw invalid_argument("BmpLoader::BmpLoader");
+}
+
+bool BmpLoader::detect(const std::string &sig)
+{
+	static const char bmp_sig[] = "BM";
+	if(sig.size()<sizeof(bmp_sig))
+		return false;
+	return !sig.compare(0, 2, bmp_sig);
+}
+
+void BmpLoader::load(Image::Data &data)
+{
+	char bm_header[14];
+	read_full(io, bm_header+sig_bytes, sizeof(bm_header)-sig_bytes);
+
+	if(!sig_bytes && (bm_header[0]!='B' || bm_header[1]!='M'))
+		throw bad_image_data("bitmap header mismatch");
+
+	unsigned data_offset = decode<UInt32>(bm_header+10);
+
+	char dib_header[124];
+	read_full(io, dib_header, 12);
+	unsigned dib_length = min<unsigned>(decode<UInt32>(dib_header), sizeof(dib_header));
+	if(dib_length<40)
+		throw bad_image_data("DIB header too short (very old bmp file?)");
+
+	read_full(io, dib_header+12, dib_length-12);
+
+	data.width = decode<UInt32>(dib_header+4);
+	Int32 height = decode<UInt32>(dib_header+8);
+	data.height = abs(height);
+
+	unsigned color_planes = decode<UInt16>(dib_header+12);
+	if(color_planes!=1)
+		throw bad_image_data("color_planes!=1");
+	unsigned bits_per_pixel = decode<UInt16>(dib_header+14);
+	unsigned compression = decode<UInt32>(dib_header+16);
+	if(compression)
+		throw unsupported_image_format("compression not supported");
+
+	data.stride = (data.width*bits_per_pixel+31)/32*4;
+	switch(bits_per_pixel)
+	{
+	case 8:  data.fmt = COLOR_INDEX; break;
+	case 24: data.fmt = BGR; break;
+	case 32: data.fmt = BGRX; break;  // TODO is it BGRX or XBGR?
+	default: throw unsupported_image_format("bits per pixel value not supported");
+	}
+
+	unsigned skip = data_offset-sizeof(bm_header)-dib_length;
+	while(skip>0)
+	{
+		char buffer[1024];
+		unsigned size = min<unsigned>(sizeof(buffer), skip);
+		read_full(io, buffer, size);
+		skip -= size;
+	}
+
+	data.data = new char[data.stride*data.height];
+	if(height<0)
+	{
+		for(unsigned y=0; y<data.height; ++y)
+			read_full(io, data.data+(data.height-1-y)*data.stride, data.stride);
+	}
+	else
+	{
+		for(unsigned y=0; y<data.height; ++y)
+			read_full(io, data.data+y*data.stride, data.stride);
+	}
+}
+
+} // namespace Graphics
+} // namespace Msp
diff --git a/source/graphics/bmploader.h b/source/graphics/bmploader.h
new file mode 100644
index 0000000..db9af1d
--- /dev/null
+++ b/source/graphics/bmploader.h
@@ -0,0 +1,27 @@
+#ifndef MSP_GRAPHICS_BMPLOADER_H_
+#define MSP_GRAPHICS_BMPLOADER_H_
+
+#include <msp/graphics/imageloader.h>
+
+namespace Msp {
+namespace Graphics {
+
+class BmpLoader: public RegisteredImageLoader<BmpLoader>
+{
+private:
+	IO::Base &io;
+	unsigned sig_bytes;
+
+public:
+	BmpLoader(IO::Base &, unsigned = 0);
+
+	static unsigned get_signature_size() { return 2; }
+	static bool detect(const std::string &);
+
+	virtual void load(Image::Data &);
+};
+
+} // namespace Graphics
+} // namespace Msp
+
+#endif
diff --git a/source/graphics/imageloader.cpp b/source/graphics/imageloader.cpp
index fbba25c..965c7b3 100644
--- a/source/graphics/imageloader.cpp
+++ b/source/graphics/imageloader.cpp
@@ -1,6 +1,7 @@
 #include <msp/core/refptr.h>
 #include <msp/io/file.h>
 #include <msp/strings/format.h>
+#include "bmploader.h"
 #include "imageloader.h"
 #ifdef WITH_LIBPNG
 #include "png/pngloader.h"
@@ -48,6 +49,7 @@ ImageLoader *ImageLoader::open_file(const string &fn)
 
 ImageLoader *ImageLoader::open_io(IO::Seekable &io)
 {
+	(void)RegisteredImageLoader<BmpLoader>::reg;
 #ifdef WITH_LIBPNG
 	(void)RegisteredImageLoader<PngLoader>::reg;
 #endif
-- 
2.45.2