SkPDF: Remove some unused glyphs from fallback fonts

This makes the /Widths and the /Differences arrays smaller.

Example diff in output PDF (lines are wrapped for easy viewing):

 <</Type /Font
 /Subtype /Type3
 /FontMatrix [.00100000005 0 0 -.00100000005 0 0]
 /FirstChar 0
-/LastChar 255
+/LastChar 118
 /FontBBox [23 228 669 -694]
 /CIDToGIDMap /Identity
 /ToUnicode 8 0 R
-/Widths [280 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
-525 0 0 0 525 0 0 0 0 525 525 525 525 0 0 0 0 0 0 525 0 0 0 0 0 0 0 0
-0 0 0 0 0 525 0 525 0 0 0 525 0 0 0 0 0 0 0 0 0 0 0 525 0 0 0 0 0 0
-525 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 525 0 0 0 0 0 0 0 525
-0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
-0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
-0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
-0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
+/Widths [280 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
+525 0 0 0 525 0 0 0 0 525 525 525 525 0 0 0 0 0 0 525 0 0 0 0 0 0 0 0
+0 0 0 0 0 525 0 525 0 0 0 525 0 0 0 0 0 0 0 0 0 0 0 525 0 0 0 0 0 0
+525 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 525 0 0 0 0 0 0 0
+525]
 /Encoding <</Type /Encoding
-/Differences [0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
-/g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g1D
-/g0 /g0 /g0 /g21 /g0 /g0 /g0 /g0 /g26 /g27 /g28 /g29 /g0 /g0 /g0 /g0
-/g0 /g0 /g30 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g3E
-/g0 /g40 /g0 /g0 /g0 /g44 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
-/g50 /g0 /g0 /g0 /g0 /g0 /g0 /g57 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
-/g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g6E /g0 /g0 /g0
-/g0 /g0 /g0 /g0 /g76 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
-/g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
-/g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
-/g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
-/g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
-/g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
-/g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
-/g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
-/g0 /g0 /g0 /g0 /g0 /g0]>>
+/Differences [0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
+/g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g1D
+/g0 /g0 /g0 /g21 /g0 /g0 /g0 /g0 /g26 /g27 /g28 /g29 /g0 /g0 /g0 /g0
+/g0 /g0 /g30 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g3E
+/g0 /g40 /g0 /g0 /g0 /g44 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
+/g50 /g0 /g0 /g0 /g0 /g0 /g0 /g57 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0
+/g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g0 /g6E /g0 /g0 /g0
+/g0 /g0 /g0 /g0 /g76]>>
 /CharProcs <</g0 9 0 R
 /g1D 10 0 R
 /g21 11 0 R
.......

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2287393002

Review-Url: https://codereview.chromium.org/2287393002

1 files changed, 6 insertions, 1 deletions

diff --git a/src/pdf/SkPDFFont.cpp b/src/pdf/SkPDFFont.cpp
index d7ef8123a2..53a0c02ed0 100644
--- a/src/pdf/SkPDFFont.cpp
+++ b/src/pdf/SkPDFFont.cpp
@@ -167,7 +167,7 @@ const SkAdvancedTypefaceMetrics* SkPDFFont::GetMetrics(SkTypeface* typeface,
     if (!metrics) {
         metrics = sk_make_sp<SkAdvancedTypefaceMetrics>();
         metrics->fLastGlyphID = SkToU16(count - 1);
-    } 
+    }
     SkASSERT(metrics->fLastGlyphID == SkToU16(count - 1));
     return *canon->fTypefaceMetrics.set(id, metrics.release());
 }
@@ -603,6 +603,11 @@ static void add_type3_font_info(SkPDFCanon* canon,
                                 SkGlyphID firstGlyphID,
                                 SkGlyphID lastGlyphID) {
     SkASSERT(lastGlyphID >= firstGlyphID);
+    // Remove unused glyphs at the end of the range.
+    // Keep the lastGlyphID >= firstGlyphID invariant true.
+    while (lastGlyphID > firstGlyphID && !subset.has(lastGlyphID)) {
+        --lastGlyphID;
+    }
     SkASSERT(emSize > 0.0f);
     SkAutoGlyphCache cache = vector_cache(typeface, emSize);
     font->insertName("Subtype", "Type3");