Merge pull request #92 from davidgiven/d64

Add write-only support for D64 disk images.

doc/disk-c64.md

@@ -23,7 +23,7 @@ computer](https://ilesj.wordpress.com/2014/05/14/1541-why-so-complicated/) of
 300 bytes per second (!). (The drive itself could transfer data reasonably
 quickly.)
 
-A standard 1541 disk has 35 tracks of 17 to 20 sectors, each 256 bytes long.
+A standard 1541 disk has 35 tracks of 17 to 21 sectors, each 256 bytes long.
 
 Reading discs
 -------------
@@ -34,15 +34,14 @@ Just do:
 fluxengine read c64
 ```
 
-You should end up with an `c64.img` which is 187136 bytes long (for a normal
-1541 disk).
+You should end up with an `c64.d64` file which is 174848 bytes long. You can
+load this straight into a Commodore 64 emulator such as
+[VICE](http://vice-emu.sourceforge.net/).
 
-**Big warning!** The image may not work in an emulator. Commodore 64 disk images are
+**Big warning!** Commodore 64 disk images are
 complicated due to the way the tracks are different sizes and the odd sector
-size. FluxEngine chooses to store them in a simple 256 x 20 x 35 layout,
-with holes where missing sectors should be. This was easiest. If anyone can
-suggest a better way, please [get in
-touch](https://github.com/davidgiven/fluxengine/issues/new).
+size, so you need the special D64 or LDBS output formats to represent them
+sensibly. Don't use IMG unless you know what you're doing.
 
 Useful references
 -----------------

doc/using.md

@@ -148,6 +148,15 @@ based on the extension:
     it doesn't store a lot of the more esoteric LDBS features like format
     types, timings, and data rates.
 
+  - `.d64`: the venerable Commodore 64 disk image format as used by the 1540,
+    1541, etc. This is a special-purpose format due to the weird layout of
+    1540 disks and while you can use this for non-Commodore disks the result
+    will be gibberish. Use this to image Commodore 64 disks and load the
+    result into an emulator.
+
+    FluxEngine's D64 support is currently limited to write only. It will work
+    with up to 40 logical tracks.
+
 ### High density disks
 
 High density disks use a different magnetic medium to low and double density

lib/imagewriter/d64imagewriter.cc

@@ -0,0 +1,64 @@
+#include "globals.h"
+#include "image.h"
+#include "flags.h"
+#include "dataspec.h"
+#include "sector.h"
+#include "sectorset.h"
+#include "imagewriter/imagewriter.h"
+#include "fmt/format.h"
+#include "ldbs.h"
+#include <algorithm>
+#include <iostream>
+#include <fstream>
+
+static int sectors_per_track(int track)
+{
+    if (track < 17)
+        return 21;
+    if (track < 24)
+        return 19;
+    if (track < 30)
+        return 18;
+    return 17;
+}
+
+class D64ImageWriter : public ImageWriter
+{
+public:
+	D64ImageWriter(const SectorSet& sectors, const ImageSpec& spec):
+		ImageWriter(sectors, spec)
+	{}
+
+	void writeImage()
+	{
+		std::cout << "writing D64 triangular image\n";
+
+		std::ofstream outputFile(spec.filename, std::ios::out | std::ios::binary);
+		if (!outputFile.is_open())
+			Error() << "cannot open output file";
+
+        uint32_t offset = 0;
+		for (int track = 0; track < 40; track++)
+		{
+            int sectorCount = sectors_per_track(track);
+            for (int sectorId = 0; sectorId < sectorCount; sectorId++)
+            {
+                const auto& sector = sectors.get(track, 0, sectorId);
+                if (sector)
+                {
+                    outputFile.seekp(offset);
+                    outputFile.write((const char*) sector->data.cbegin(), 256);
+                }
+
+                offset += 256;
+            }
+		}
+    }
+};
+
+std::unique_ptr<ImageWriter> ImageWriter::createD64ImageWriter(
+	const SectorSet& sectors, const ImageSpec& spec)
+{
+    return std::unique_ptr<ImageWriter>(new D64ImageWriter(sectors, spec));
+}
+

lib/imagewriter/imagewriter.cc

@@ -22,6 +22,8 @@ std::unique_ptr<ImageWriter> ImageWriter::create(const SectorSet& sectors, const
         return createImgImageWriter(sectors, spec);
 	else if (ends_with(filename, ".ldbs"))
 		return createLDBSImageWriter(sectors, spec);
+	else if (ends_with(filename, ".d64"))
+		return createD64ImageWriter(sectors, spec);
 
     Error() << "unrecognised image filename extension";
     return std::unique_ptr<ImageWriter>();

lib/imagewriter/imagewriter.h

@@ -18,6 +18,8 @@ private:
 		const SectorSet& sectors, const ImageSpec& spec);
     static std::unique_ptr<ImageWriter> createLDBSImageWriter(
 		const SectorSet& sectors, const ImageSpec& spec);
+    static std::unique_ptr<ImageWriter> createD64ImageWriter(
+		const SectorSet& sectors, const ImageSpec& spec);
 
 public:
 	virtual void adjustGeometry();

mkninja.sh

@@ -139,6 +139,7 @@ buildlibrary libfmt.a \
 buildlibrary libbackend.a \
 	lib/imagereader/imagereader.cc \
 	lib/imagereader/imgimagereader.cc \
+	lib/imagewriter/d64imagewriter.cc \
 	lib/imagewriter/imagewriter.cc \
 	lib/imagewriter/imgimagewriter.cc \
 	lib/imagewriter/ldbsimagewriter.cc \

src/fe-readc64.cc

@@ -16,7 +16,7 @@ static FlagGroup flags { &readerFlags };
 int mainReadC64(int argc, const char* argv[])
 {
 	setReaderDefaultSource(":t=0-79x2:s=0");
-	setReaderDefaultOutput("c64.img");
+	setReaderDefaultOutput("c64.d64");
     setReaderRevolutions(2);
     flags.parseFlags(argc, argv);