SkPdf: smaller color serialization

SkPDFUtils now has a special function (SkPDFUtils::AppendColorComponent)
just for writing out (color/255) as a decimal with three digits of
precision.

SkPDFUnion now has a type to represent a color component.  It holds a
utint_8, but calls into AppendColorComponent to serialize.

Added a unit test that tests all possible input values.
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2151863003

Review-Url: https://codereview.chromium.org/2151863003

1 files changed, 9 insertions, 0 deletions

diff --git a/src/pdf/SkPDFUtils.h b/src/pdf/SkPDFUtils.h
index 3ddd3d0933..a9194f2e72 100644
--- a/src/pdf/SkPDFUtils.h
+++ b/src/pdf/SkPDFUtils.h
@@ -57,6 +57,15 @@ void DrawFormXObject(int objectIndex, SkWStream* content);
 void ApplyGraphicState(int objectIndex, SkWStream* content);
 void ApplyPattern(int objectIndex, SkWStream* content);
 
+// Converts (value / 255.0) with three significant digits of accuracy.
+// Writes value as string into result.  Returns strlen() of result.
+size_t ColorToDecimal(uint8_t value, char result[5]);
+inline void AppendColorComponent(uint8_t value, SkWStream* wStream) {
+    char buffer[5];
+    size_t len = SkPDFUtils::ColorToDecimal(value, buffer);
+    wStream->write(buffer, len);
+}
+
 // 3 = '-', '.', and '\0' characters.
 // 9 = number of significant digits
 // abs(FLT_MIN_10_EXP) = number of zeros in FLT_MIN