SkPdf: smaller color serialization

src/pdf/SkPDFUtils.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkData.h"
 #include "SkGeometry.h"
@@ skipping 233 matching lines @@
     SkString resourceName = SkPDFResourceDict::getResourceName(
             SkPDFResourceDict::kPattern_ResourceType,
             objectIndex);
     content->writeText("/Pattern CS/Pattern cs/");
     content->writeText(resourceName.c_str());
     content->writeText(" SCN/");
     content->writeText(resourceName.c_str());
     content->writeText(" scn\n");
 }
 
+size_t SkPDFUtils::ColorToDecimal(uint8_t value, char result[5]) {
+    if (value == 255 || value == 0) {
+        result[0] = value ? '1' : '0';
+        result[1] = '\0';
+        return 1;
+    }
+    int x = (((1000 << 20) / 255) * value + (1 << 19)) >> 20;
+    // ((int)(0.5 + (1000.0 / 255.0) * value) == x);

[tomhudson, 2016/07/15 19:20:18]

Not sure what the comment is doing here - it's mostly a literal restatement of
the line above?

After a fair amount of thought, I'm still not confident I know what you intend
by the <<20.

[hal.canary, 2016/07/15 19:46:42]

To make this more clear, I am switching to SkFixed.

+    result[0] = '.';
+    for (int i = 3; i > 0; --i) {
+        result[i] = '0' + x % 10;
+        x /= 10;
+    }
+    int j;
+    for (j = 3; j > 1; --j) {

[tomhudson, 2016/07/15 19:20:17]

Trimming off trailing zeroes? Is this important?

[hal.canary, 2016/07/15 19:46:42]

it's cheap to do here, and everyone wants smaller PDFs.

+        if (result[j] != '0') {
+            break;
+        }
+    }
+    result[j + 1] = '\0';
+    return j + 1;
+}
+
 void SkPDFUtils::AppendScalar(SkScalar value, SkWStream* stream) {
     char result[kMaximumFloatDecimalLength];
     size_t len = SkPDFUtils::FloatToDecimal(SkScalarToFloat(value), result);
     SkASSERT(len < kMaximumFloatDecimalLength);
     stream->write(result, len);
 }
 
 /** Write a string into result, includeing a terminating '\0' (for
     unit testing).  Return strlen(result) (for SkWStream::write) The
     resulting string will be in the form /[-]?([0-9]*.)?[0-9]+/ and
@@ skipping 142 matching lines @@
             uint8_t c = static_cast<uint8_t>(cin[i]);
             static const char gHex[] = "0123456789ABCDEF";
             char hexValue[2];
             hexValue[0] = gHex[(c >> 4) & 0xF];
             hexValue[1] = gHex[ c       & 0xF];
             wStream->write(hexValue, 2);
         }
         wStream->writeText(">");
     }
 }