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Compare file contents with old data before writing

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Do not writeoutput files when their content hasn't changed. This saves
time for incremental generation (as compressing a PNG takes much longer
than decompressing it) and avoids modification timestamp updates that
might trigger subsequent generation steps.
This commit is contained in:
Matthias Schiffer 2020-06-20 15:01:52 +02:00
parent ef69a34034
commit 3ec83c8cf8
Signed by: neocturne
GPG key ID: 16EF3F64CB201D9C
1 changed files with 31 additions and 11 deletions
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42
src/MinedMap.cpp
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@ -164,15 +164,29 @@ static void writeStamp(const std::string &filename, int64_t v) {
}
}
static void writeImage(const std::string &output, const uint8_t *data, PNG::Format format, int64_t t) {
static bool writeImage(const std::string &output, const uint8_t *data, PNG::Format format, int64_t t) {
const std::string tmpfile = output + ".tmp";
try {
PNG::write(tmpfile.c_str(), data, DIM, DIM, format);
size_t len = PNG::formatBytes(format)*DIM*DIM;
bool changed = true;
if (std::rename(tmpfile.c_str(), output.c_str()) < 0) {
std::fprintf(stderr, "Unable to save %s: %s\n", output.c_str(), std::strerror(errno));
std::remove(tmpfile.c_str());
try {
std::unique_ptr<uint8_t[]> old(new uint8_t[len]);
PNG::read(output.c_str(), old.get(), DIM, DIM, format);
if (std::memcmp(data, old.get(), len) == 0)
changed = false;
} catch (const std::exception& ex) {
}
try {
if (changed) {
PNG::write(tmpfile.c_str(), data, DIM, DIM, format);
if (std::rename(tmpfile.c_str(), output.c_str()) < 0) {
std::fprintf(stderr, "Unable to save %s: %s\n", output.c_str(), std::strerror(errno));
std::remove(tmpfile.c_str());
}
}
writeStamp(output, t);
@ -180,6 +194,8 @@ static void writeImage(const std::string &output, const uint8_t *data, PNG::Form
std::remove(tmpfile.c_str());
throw;
}
return changed;
}
static int64_t getModTime(const std::string &file) {
@ -257,7 +273,8 @@ static void makeBiome(const std::string &regiondir, const std::string &outputdir
if (!checkRegion(intime, output))
return;
std::printf("Generating %s from %s...\n", output.c_str(), input.c_str());
std::printf("Generating %s from %s... ", output.c_str(), input.c_str());
std::fflush(stdout);
try {
std::unique_ptr<uint8_t[]> biomemap(new uint8_t[DIM*DIM]);
@ -267,7 +284,8 @@ static void makeBiome(const std::string &regiondir, const std::string &outputdir
addChunkBiome(biomemap.get(), X, Z, chunk);
});
writeImage(output, biomemap.get(), PNG::GRAY, intime);
bool changed = writeImage(output, biomemap.get(), PNG::GRAY, intime);
std::printf("%s.\n", changed ? "done" : "unchanged");
} catch (const std::exception& ex) {
std::fprintf(stderr, "Failed to generate %s: %s\n", output.c_str(), ex.what());
}
@ -304,7 +322,8 @@ static void makeMap(const std::string &regiondir, const std::string &outputdir,
if (!checkRegion(intime, output))
return;
std::printf("Generating %s from %s...\n", output.c_str(), input.c_str());
std::printf("Generating %s from %s... ", output.c_str(), input.c_str());
std::fflush(stdout);
try {
std::unique_ptr<uint8_t[]> biomemaps[3][3];
@ -328,8 +347,9 @@ static void makeMap(const std::string &regiondir, const std::string &outputdir,
addChunk(image.get(), lightmap.get(), X, Z, chunk, biomemaps);
});
writeImage(output, reinterpret_cast<const uint8_t*>(image.get()), PNG::RGB_ALPHA, intime);
writeImage(output_light, lightmap.get(), PNG::GRAY_ALPHA, intime);
bool changed = writeImage(output, reinterpret_cast<const uint8_t*>(image.get()), PNG::RGB_ALPHA, intime);
changed = writeImage(output_light, lightmap.get(), PNG::GRAY_ALPHA, intime) || changed;
std::printf("%s.\n", changed ? "done" : "unchanged");
} catch (const std::exception& ex) {
std::fprintf(stderr, "Failed to generate %s: %s\n", output.c_str(), ex.what());
}