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A demo recorder: --record-pad writes what --pad reads

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One byte a frame, in exactly the format the player takes, so a recording
needs no conversion and there is no second format to keep in step. That
symmetry is the feature, and it makes the strongest form of the claim
testable: a recording is made OF a playback, and the bytes coming out have
to be the bytes that went in.

It exists because some inputs cannot sensibly be written by hand. Flying a
lander from one base to another is a few hundred frames of steering that
has to arrive somewhere eight cells wide, and several attempts at
authoring one got within two columns and no closer. That is a piloting
exercise rather than a test. Playing it once and keeping what happened is
the answer.

A BYTE FOR EVERY FRAME, written inside the loop that advances the
recordings rather than after it, so a machine that jumped several frames
at once still writes one for each. A recording is a timeline: one that
skipped the frames nobody looked at would play back faster than it was
flown.

What is recorded is what the DEVICE WOULD REPORT, not the live state - a
recording of a playback that wrote the live state would be a file of
noughts. And it is flushed as it goes, because a recording is usually
stopped by whoever is playing rather than by the program ending, and a
demo lost to a buffer is a demo flown twice.

Tests/replay.sh is where this and whatever follows it are checked. Twelve
scripts now.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
This commit is contained in:
Anachronaut
2026-09-03 12:38:43 -04:00
co-authored by Claude Opus 5
parent caf5e1f99d
commit a163c670d0
8 changed files with 186 additions and 3 deletions
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Source/Emulator/utility.c
+11 -1
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@@ -38,6 +38,10 @@ void printHelp(const char *programName) {
printf(" again for the next pad. A byte is the buttons held:\n");
printf(" 1 right, 2 left, 4 down, 8 up, 16 A, 32 B, 64 start,\n");
printf(" 128 select.\n");
printf(" -Y, --record-pad FILE\n");
printf(" Write what a controller held, one byte a frame, in the\n");
printf(" format --pad reads. Given again for the next pad. Play a\n");
printf(" thing once and keep what happened.\n");
printf(" -N, --sound FILE Save every sample the machine made, as raw signed 16 bit\n");
printf(" at 48kHz. What --screen is for a picture: the only way to\n");
printf(" check a sound on a machine with no speaker.\n");
@@ -57,6 +61,7 @@ uint8_t parseOptions(int argc, char *argv[], EmulatorOptions *options) {
{"keyboard", required_argument, 0, 'K'},
{"sound", required_argument, 0, 'N'},
{"pad", required_argument, 0, 'P'},
{"record-pad", required_argument, 0, 'Y'},
{"help", no_argument, 0, 'h'},
{0, 0, 0, 0 }
};
@@ -76,7 +81,7 @@ uint8_t parseOptions(int argc, char *argv[], EmulatorOptions *options) {
*options = (EmulatorOptions){0};
// Parse options
while ((opt = getopt_long(argc, argv, "dc:fhD:WL:S:K:N:R:P:", long_options, &option_index)) != -1) {
while ((opt = getopt_long(argc, argv, "dc:fhD:WL:S:K:N:R:P:Y:", long_options, &option_index)) != -1) {
switch (opt) {
case 'd':
options->debug = 1;
@@ -136,6 +141,11 @@ uint8_t parseOptions(int argc, char *argv[], EmulatorOptions *options) {
case 'N':
options->sound = optarg;
break;
case 'Y':
if (options->padRecordCount < PAD_DRIVE_COUNT) {
options->padRecord[options->padRecordCount++] = optarg;
}
break;
case 'P':
// Fills the pads in turn, the same way --disk fills the drives, so the first
// one named is pad nought and the machine has as many as were asked for.