Revert "Do not use delta-encoding across block boundaries"

This reverts commit 7ed0d6f2e8.

This was intended as a possible fix for problems with the HL-L2300D
(#4), but it didn't help. And it worsens compression.

src/block.h

@@ -24,38 +24,35 @@
 
 class block {
  public:
-  block(): block_size_(0) {
+  block(): line_bytes_(0) {
     lines_.reserve(max_lines_per_block_);
   }
 
   bool empty() const {
-    return block_size_ == 0;
-  }
-
-  bool full() const {
-    return lines_.size() == max_lines_per_block_;
+    return line_bytes_ == 0;
   }
 
   void add_line(std::vector<uint8_t> &&line) {
     assert(!line.empty());
     assert(line_fits(line.size()));
-    block_size_ += line.size();
+    line_bytes_ += line.size();
     lines_.emplace_back(line);
   }
 
-  bool line_fits(unsigned line_size) const {
-    return !full() && block_size_ + line_size < max_block_size_;
+  bool line_fits(unsigned size) {
+    return lines_.size() != max_lines_per_block_
+      && line_bytes_ + size < max_block_size_;
   }
 
   void flush(FILE *f) {
     if (!empty()) {
       fprintf(f, "%dw%c%c",
-              block_size_ + 2, 0,
+              line_bytes_ + 2, 0,
               static_cast<int>(lines_.size()));
       for (auto &line : lines_) {
         fwrite(line.data(), 1, line.size(), f);
       }
-      block_size_ = 0;
+      line_bytes_ = 0;
       lines_.clear();
     }
   }
@@ -65,7 +62,7 @@ class block {
   static const unsigned max_lines_per_block_ = 128;
 
   std::vector<std::vector<uint8_t>> lines_;
-  int block_size_;
+  int line_bytes_;
 };
 
 #endif  // BLOCK_H

src/job.cc

@@ -91,31 +91,24 @@ void job::encode_page(const page_params &page_params,
     write_page_header();
   }
 
-  fputs("\033*b1030m", out_);
-
   std::vector<uint8_t> line(linesize);
   std::vector<uint8_t> reference(linesize);
   block block;
 
-  for (int i = 0; i < lines && nextline(line); ++i) {
-    if (block.empty()) {
-      // Beginning of a new block, do not apply delta-encoding.
-      block.add_line(encode_line(line));
-    } else {
-      // In the middle of a block, try delta-encoding.
-      std::vector<uint8_t> encoded = encode_line(line, reference);
-      if (block.line_fits(encoded.size())) {
-        // Ok, there's enough room for another line.
-        block.add_line(std::move(encoded));
-      } else {
-        // Oops, the line didn't fit. Start a new block.
-        block.flush(out_);
-        block.add_line(encode_line(line));
-      }
-    }
-    if (block.full()) {
+  if (!nextline(line)) {
+    return;
+  }
+  block.add_line(encode_line(line));
+  std::swap(line, reference);
+
+  fputs("\033*b1030m", out_);
+
+  for (int i = 1; i < lines && nextline(line); ++i) {
+    std::vector<uint8_t> encoded = encode_line(line, reference);
+    if (!block.line_fits(encoded.size())) {
       block.flush(out_);
     }
+    block.add_line(std::move(encoded));
     std::swap(line, reference);
   }