SkPDF: unify drawText and drawPosText

src/pdf/SkPDFDevice.cpp

Index: src/pdf/SkPDFDevice.cpp
diff --git a/src/pdf/SkPDFDevice.cpp b/src/pdf/SkPDFDevice.cpp
index f3ede3524d1fba25caf1a59e8669df9e9bfbf28a..290c1c4f565ae0f02e6ffc47bdbd5af72554766b 100644
--- a/src/pdf/SkPDFDevice.cpp
+++ b/src/pdf/SkPDFDevice.cpp
@@ -76,77 +76,6 @@ static SkPaint calculate_text_paint(const SkPaint& paint) {
     return result;
 }
 
-// Stolen from measure_text in SkDraw.cpp and then tweaked.
-static void align_text(const SkPaint& paint,
-                       const uint16_t* glyphs, size_t len,
-                       SkScalar* x, SkScalar* y) {
-    if (paint.getTextAlign() == SkPaint::kLeft_Align) {
-        return;
-    }
-    SkScalar advance = paint.measureText(glyphs, len * sizeof(uint16_t));
-    if (paint.getTextAlign() == SkPaint::kCenter_Align) {
-        advance *= 0.5f;
-    }
-    if (paint.isVerticalText()) {
-        *y -= advance;
-    } else {
-        *x -= advance;
-    }
-}
-
-static int max_glyphid_for_typeface(SkTypeface* typeface) {
-    SkAutoResolveDefaultTypeface autoResolve(typeface);
-    typeface = autoResolve.get();
-    return typeface->countGlyphs() - 1;
-}
-
-typedef SkAutoSTMalloc<128, uint16_t> SkGlyphStorage;
-
-static int force_glyph_encoding(const SkPaint& paint, const void* text,
-                                size_t len, SkGlyphStorage* storage,
-                                const uint16_t** glyphIDs) {
-    // Make sure we have a glyph id encoding.
-    if (paint.getTextEncoding() != SkPaint::kGlyphID_TextEncoding) {
-        int numGlyphs = paint.textToGlyphs(text, len, nullptr);
-        storage->reset(numGlyphs);
-        paint.textToGlyphs(text, len, storage->get());
-        *glyphIDs = storage->get();
-        return numGlyphs;
-    }
-
-    // For user supplied glyph ids we need to validate them.
-    SkASSERT((len & 1) == 0);
-    int numGlyphs = SkToInt(len / 2);
-    const uint16_t* input = static_cast<const uint16_t*>(text);
-
-    int maxGlyphID = max_glyphid_for_typeface(paint.getTypeface());
-    int validated;
-    for (validated = 0; validated < numGlyphs; ++validated) {
-        if (input[validated] > maxGlyphID) {
-            break;
-        }
-    }
-    if (validated >= numGlyphs) {
-        *glyphIDs = static_cast<const uint16_t*>(text);
-        return numGlyphs;
-    }
-
-    // Silently drop anything out of range.
-    storage->reset(numGlyphs);
-    if (validated > 0) {
-        memcpy(storage->get(), input, validated * sizeof(uint16_t));
-    }
-
-    for (int i = validated; i < numGlyphs; ++i) {
-        storage->get()[i] = input[i];
-        if (input[i] > maxGlyphID) {
-            storage->get()[i] = 0;
-        }
-    }
-    *glyphIDs = storage->get();
-    return numGlyphs;
-}
-
 static void set_text_transform(SkScalar x, SkScalar y, SkScalar textSkewX,
                                SkWStream* content) {
     // Flip the text about the x-axis to account for origin swap and include
@@ -1027,50 +956,22 @@ void SkPDFDevice::drawImageRect(const SkDraw& draw,
     SkASSERT(false);
 }
 
-//  Create a PDF string. Maximum length (in bytes) is 65,535.
-//  @param input     A string value.
-//  @param len       The length of the input array.
-//  @param wideChars True iff the upper byte in each uint16_t is
-//                   significant and should be encoded and not
-//                   discarded.  If true, the upper byte is encoded
-//                   first.  Otherwise, we assert the upper byte is
-//                   zero.
-static void write_wide_string(SkDynamicMemoryWStream* wStream,
-                              const uint16_t* input,
-                              size_t len,
-                              bool wideChars) {
-    if (wideChars) {
-        SkASSERT(2 * len < 65535);
-        wStream->writeText("<");
-        for (size_t i = 0; i < len; i++) {
-            SkPDFUtils::WriteUInt16BE(wStream, input[i]);
-        }
-        wStream->writeText(">");
-    } else {
-        SkASSERT(len <= 65535);
-        SkAutoMalloc buffer(len);  // Remove every other byte.
-        uint8_t* ptr = (uint8_t*)buffer.get();
-        for (size_t i = 0; i < len; i++) {
-            SkASSERT(0 == input[i] >> 8);
-            ptr[i] = static_cast<uint8_t>(input[i]);
-        }
-        SkPDFUtils::WriteString(wStream, (char*)buffer.get(), len);
-    }
-}
-
 namespace {
 class GlyphPositioner {
 public:
     GlyphPositioner(SkDynamicMemoryWStream* content,
                     SkScalar textSkewX,
-                    bool wideChars)
+                    bool wideChars,
+                    bool defaultPositioning,
+                    SkPoint origin)
         : fContent(content)
         , fCurrentMatrixX(0.0f)
         , fCurrentMatrixY(0.0f)
         , fXAdvance(0.0f)
         , fWideChars(wideChars)
-        , fInText(false) {
-        set_text_transform(0.0f, 0.0f, textSkewX, fContent);
+        , fInText(false)
+        , fDefaultPositioning(defaultPositioning) {
+        set_text_transform(origin.x(), origin.y(), textSkewX, fContent);
     }
     ~GlyphPositioner() { SkASSERT(!fInText);  /* flush first */ }
     void flush() {
@@ -1082,6 +983,7 @@ public:
     void setWideChars(bool wideChars) {
         if (fWideChars != wideChars) {
             SkASSERT(!fInText);
+            SkASSERT(fWideChars == wideChars);
             fWideChars = wideChars;
         }
     }
@@ -1089,17 +991,20 @@ public:
                     SkScalar y,
                     SkScalar advanceWidth,
                     uint16_t glyph) {
-        SkScalar xPosition = x - fCurrentMatrixX;
-        SkScalar yPosition = y - fCurrentMatrixY;
-        if (xPosition != fXAdvance || yPosition != 0) {
-            this->flush();
-            SkPDFUtils::AppendScalar(xPosition, fContent);
-            fContent->writeText(" ");
-            SkPDFUtils::AppendScalar(-yPosition, fContent);
-            fContent->writeText(" Td ");
-            fCurrentMatrixX = x;
-            fCurrentMatrixY = y;
-            fXAdvance = 0;
+        if (!fDefaultPositioning) {
+            SkScalar xPosition = x - fCurrentMatrixX;
+            SkScalar yPosition = y - fCurrentMatrixY;
+            if (xPosition != fXAdvance || yPosition != 0) {
+                this->flush();
+                SkPDFUtils::AppendScalar(xPosition, fContent);
+                fContent->writeText(" ");
+                SkPDFUtils::AppendScalar(-yPosition, fContent);
+                fContent->writeText(" Td ");
+                fCurrentMatrixX = x;
+                fCurrentMatrixY = y;
+                fXAdvance = 0;
+            }
+            fXAdvance += advanceWidth;
         }
         if (!fInText) {
             fContent->writeText("<");
@@ -1111,7 +1016,6 @@ public:
             SkASSERT(0 == glyph >> 8);
             SkPDFUtils::WriteUInt8(fContent, static_cast<uint8_t>(glyph));
         }
-        fXAdvance += advanceWidth;
     }
 
 private:
@@ -1121,6 +1025,7 @@ private:
     SkScalar fXAdvance;
     bool fWideChars;
     bool fInText;
+    const bool fDefaultPositioning;
 };
 }  // namespace
 
@@ -1129,11 +1034,10 @@ static void draw_transparent_text(SkPDFDevice* device,
                                   const void* text, size_t len,
                                   SkScalar x, SkScalar y,
                                   const SkPaint& srcPaint) {
-
     SkPaint transparent;
     if (!SkPDFFont::CanEmbedTypeface(transparent.getTypeface(),
                                      device->getCanon())) {
-        SkDEBUGFAIL("default typeface should be embeddable");
+        SkDebugf("SkPDF: default typeface should be embeddable");
         return;  // Avoid infinite loop in release.
     }
     transparent.setTextSize(srcPaint.getTextSize());
@@ -1147,6 +1051,8 @@ static void draw_transparent_text(SkPDFDevice* device,
             srcPaint.glyphsToUnichars(
                     (const uint16_t*)text, SkToInt(glyphCount), &unichars[0]);
             transparent.setTextEncoding(SkPaint::kUTF32_TextEncoding);
+            // TODO(halcanary): deal with case where default typeface
+            // does not have glyphs for these unicode code points.
             device->drawText(d, &unichars[0],
                              glyphCount * sizeof(SkUnichar),
                              x, y, transparent);
@@ -1163,158 +1069,161 @@ static void draw_transparent_text(SkPDFDevice* device,
     }
 }
 
-
-void SkPDFDevice::drawText(const SkDraw& d, const void* text, size_t len,
-                           SkScalar x, SkScalar y, const SkPaint& srcPaint) {
-    if (!SkPDFFont::CanEmbedTypeface(srcPaint.getTypeface(), fDocument->canon())) {
-        // https://bug.skia.org/3866
-        SkPath path;
-        srcPaint.getTextPath(text, len, x, y, &path);
-        this->drawPath(d, path, srcPaint, &SkMatrix::I(), true);
-        // Draw text transparently to make it copyable/searchable/accessable.
-        draw_transparent_text(this, d, text, len, x, y, srcPaint);
-        return;
-    }
-    SkPaint paint = srcPaint;
-    replace_srcmode_on_opaque_paint(&paint);
-
-    NOT_IMPLEMENTED(paint.getMaskFilter() != nullptr, false);
-    if (paint.getMaskFilter() != nullptr) {
+void SkPDFDevice::internalDrawText(
+        const SkDraw& d, const void* sourceText, size_t sourceByteCount,
+        const SkScalar pos[], SkTextBlob::GlyphPositioning positioning,
+        SkPoint offset, const SkPaint& srcPaint) {
+    NOT_IMPLEMENTED(srcPaint.getMaskFilter() != nullptr, false);
+    if (srcPaint.getMaskFilter() != nullptr) {
         // Don't pretend we support drawing MaskFilters, it makes for artifacts
         // making text unreadable (e.g. same text twice when using CSS shadows).
         return;
     }
-    SkPaint textPaint = calculate_text_paint(paint);
-    ScopedContentEntry content(this, d, textPaint, true);
-    if (!content.entry()) {
+    SkPaint paint = calculate_text_paint(srcPaint);
+    replace_srcmode_on_opaque_paint(&paint);
+    if (!paint.getTypeface()) {
+        paint.setTypeface(SkTypeface::MakeDefault());
+    }
+    SkTypeface* typeface = paint.getTypeface();
+    if (!typeface) {
+        SkDebugf("SkPDF: SkTypeface::MakeDefault() returned nullptr.\n");
         return;
     }
-
-    SkGlyphStorage storage(0);
-    const uint16_t* glyphIDs = nullptr;
-    int numGlyphs = force_glyph_encoding(paint, text, len, &storage, &glyphIDs);
-    textPaint.setTextEncoding(SkPaint::kGlyphID_TextEncoding);
-
-    align_text(textPaint, glyphIDs, numGlyphs, &x, &y);
-    content.entry()->fContent.writeText("BT\n");
-    set_text_transform(x, y, textPaint.getTextSkewX(),
-                       &content.entry()->fContent);
-    int consumedGlyphCount = 0;
-
-    SkTDArray<uint16_t> glyphIDsCopy(glyphIDs, numGlyphs);
-
-    SkPDFGlyphSetMap* fontGlyphUsage = fDocument->getGlyphUsage();
-
-    while (numGlyphs > consumedGlyphCount) {
-        if (!this->updateFont(textPaint, glyphIDs[consumedGlyphCount], content.entry())) {
-            SkDebugf("SkPDF: Font error.");
-            content.entry()->fContent.writeText("ET\n%SkPDF: Font error.\n");
-            return;
-        }
-        SkPDFFont* font = content.entry()->fState.fFont;
-
-        int availableGlyphs = font->glyphsToPDFFontEncoding(
-                glyphIDsCopy.begin() + consumedGlyphCount,
-                numGlyphs - consumedGlyphCount);
-        fontGlyphUsage->noteGlyphUsage(
-                font,  glyphIDsCopy.begin() + consumedGlyphCount,
-                availableGlyphs);
-        write_wide_string(&content.entry()->fContent,
-                          glyphIDsCopy.begin() + consumedGlyphCount,
-                          availableGlyphs, font->multiByteGlyphs());
-        consumedGlyphCount += availableGlyphs;
-        content.entry()->fContent.writeText(" Tj\n");
+    int typefaceGlyphCount = typeface->countGlyphs();
+    if (typefaceGlyphCount < 1) {
+        SkDebugf("SkPDF: SkTypeface has no glyphs.\n");
+        return;
     }
-    content.entry()->fContent.writeText("ET\n");
-}
-
-void SkPDFDevice::drawPosText(const SkDraw& d, const void* text, size_t len,
-                              const SkScalar pos[], int scalarsPerPos,
-                              const SkPoint& offset, const SkPaint& srcPaint) {
-    if (!SkPDFFont::CanEmbedTypeface(srcPaint.getTypeface(), fDocument->canon())) {
-        const SkPoint* positions = reinterpret_cast<const SkPoint*>(pos);
-        SkAutoTMalloc<SkPoint> positionsBuffer;
-        if (2 != scalarsPerPos) {
-            int glyphCount = srcPaint.textToGlyphs(text, len, NULL);
-            positionsBuffer.reset(glyphCount);
-            for (int  i = 0; i < glyphCount; ++i) {
-                positionsBuffer[i].set(pos[i], 0.0f);
-            }
-            positions = &positionsBuffer[0];
-        }
-        SkPath path;
-        srcPaint.getPosTextPath(text, len, positions, &path);
-        SkMatrix matrix;
-        matrix.setTranslate(offset);
-        this->drawPath(d, path, srcPaint, &matrix, true);
+    if (!SkPDFFont::CanEmbedTypeface(typeface, fDocument->canon())) {
+        SkPath path; // https://bug.skia.org/3866
+        paint.getTextPath(sourceText, sourceByteCount,
+                          offset.x(), offset.y(), &path);
+        this->drawPath(d, path, srcPaint, &SkMatrix::I(), true);
         // Draw text transparently to make it copyable/searchable/accessable.
-        draw_transparent_text(
-                this, d, text, len, offset.x() + positions[0].x(),
-                offset.y() + positions[0].y(), srcPaint);
+        draw_transparent_text(this, d, sourceText, sourceByteCount,
+                              offset.x(), offset.y(), paint);
         return;
     }
+    // Always make a copy (1) to validate user-input glyphs and
+    // (2) because we may modify the glyphs in place (for
+    // single-byte-glyph-id PDF fonts).
+    int glyphCount = paint.textToGlyphs(sourceText, sourceByteCount, nullptr);
+    if (glyphCount <= 0) { return; }
+    SkAutoSTMalloc<128, SkGlyphID> glyphStorage(SkToSizeT(glyphCount));
+    SkGlyphID* glyphs = glyphStorage.get();
+    (void)paint.textToGlyphs(sourceText, sourceByteCount, glyphs);
+    if (paint.getTextEncoding() == SkPaint::kGlyphID_TextEncoding) {
+        // Validate user-input glyphs.
+        SkGlyphID maxGlyphID = SkToU16(typefaceGlyphCount - 1);
+        for (int i = 0; i < glyphCount; ++i) {
+            glyphs[i] = SkTMin(maxGlyphID, glyphs[i]);
+        }
+    } else {
+        paint.setTextEncoding(SkPaint::kGlyphID_TextEncoding);
+    }
 
-    SkPaint paint = srcPaint;
-    replace_srcmode_on_opaque_paint(&paint);
+    bool defaultPositioning = (positioning == SkTextBlob::kDefault_Positioning);
+    SkAutoGlyphCache glyphCache(paint, nullptr, nullptr);
 
-    NOT_IMPLEMENTED(paint.getMaskFilter() != nullptr, false);
-    if (paint.getMaskFilter() != nullptr) {
-        // Don't pretend we support drawing MaskFilters, it makes for artifacts
-        // making text unreadable (e.g. same text twice when using CSS shadows).
-        return;
+    SkPaint::Align alignment = paint.getTextAlign();
+    bool verticalText = paint.isVerticalText();
+    if (defaultPositioning && alignment != SkPaint::kLeft_Align) {
+        SkScalar advance{0};
+        for (int i = 0; i < glyphCount; ++i) {
+            advance += glyphCache->getGlyphIDAdvance(glyphs[i]).fAdvanceX;
+        }
+        SkScalar m = alignment == SkPaint::kCenter_Align
+            ? 0.5f * advance : advance;
+        offset -= verticalText ? SkPoint{0, m} : SkPoint{m, 0};
     }
-    SkASSERT(1 == scalarsPerPos || 2 == scalarsPerPos);
-    SkPaint textPaint = calculate_text_paint(paint);
-    ScopedContentEntry content(this, d, textPaint, true);
+    ScopedContentEntry content(this, d, paint, true);
     if (!content.entry()) {
         return;
     }
-
-    SkGlyphStorage storage(0);
-    const uint16_t* glyphIDs = nullptr;
-    size_t numGlyphs = force_glyph_encoding(paint, text, len, &storage, &glyphIDs);
-    textPaint.setTextEncoding(SkPaint::kGlyphID_TextEncoding);
-    SkAutoGlyphCache autoGlyphCache(textPaint, nullptr, nullptr);
-
-    content.entry()->fContent.writeText("BT\n");
-    if (!this->updateFont(textPaint, glyphIDs[0], content.entry())) {
+    SkDynamicMemoryWStream* out = &content.entry()->fContent;
+    out->writeText("BT\n");
+    if (!this->updateFont(paint, glyphs[0], content.entry())) {
         SkDebugf("SkPDF: Font error.");
-        content.entry()->fContent.writeText("ET\n%SkPDF: Font error.\n");
+        out->writeText("ET\n%SkPDF: Font error.\n");
         return;
     }
-    GlyphPositioner glyphPositioner(&content.entry()->fContent,
-                                    textPaint.getTextSkewX(),
-                                    content.entry()->fState.fFont->multiByteGlyphs());
+    SkPDFFont* font = content.entry()->fState.fFont;
+    GlyphPositioner glyphPositioner(out,
+                                    paint.getTextSkewX(),
+                                    font->multiByteGlyphs(),
+                                    defaultPositioning,
+                                    offset);
     SkPDFGlyphSetMap* fontGlyphUsage = fDocument->getGlyphUsage();
-    for (size_t i = 0; i < numGlyphs; i++) {
-        SkPDFFont* font = content.entry()->fState.fFont;
-        uint16_t encodedValue = glyphIDs[i];
-        SkScalar advanceWidth = autoGlyphCache->getGlyphIDAdvance(encodedValue).fAdvanceX;
-        if (font->glyphsToPDFFontEncoding(&encodedValue, 1) != 1) {
-            // The current pdf font cannot encode the current glyph.
-            // Try to get a pdf font which can encode the current glyph.
+    const SkGlyphID* const glyphsEnd = glyphs + glyphCount;
+
+    while (glyphs < glyphsEnd) {
+        font = content.entry()->fState.fFont;
+        int stretch = font->multiByteGlyphs()
+            ? SkToInt(glyphsEnd - glyphs)
+            : font->glyphsToPDFFontEncodingCount(glyphs, SkToInt(glyphsEnd - glyphs));
+        SkASSERT(glyphs + stretch <= glyphsEnd);
+        if (stretch < 1) {
+            SkASSERT(!font->multiByteGlyphs());
+            // The current pdf font cannot encode the next glyph.
+            // Try to get a pdf font which can encode the next glyph.
             glyphPositioner.flush();
-            if (!this->updateFont(textPaint, glyphIDs[i], content.entry())) {
+            if (!this->updateFont(paint, *glyphs, content.entry())) {
                 SkDebugf("SkPDF: Font error.");
-                content.entry()->fContent.writeText("ET\n%SkPDF: Font error.\n");
+                out->writeText("ET\n%SkPDF: Font error.\n");
                 return;
             }
             font = content.entry()->fState.fFont;
             glyphPositioner.setWideChars(font->multiByteGlyphs());
-            if (font->glyphsToPDFFontEncoding(&encodedValue, 1) != 1) {
+            // try again
+            stretch = font->glyphsToPDFFontEncodingCount(glyphs,
+                                                         SkToInt(glyphsEnd - glyphs));
+            if (stretch < 1) {
                 SkDEBUGFAIL("PDF could not encode glyph.");
-                continue;
+                glyphPositioner.flush();
+                out->writeText("ET\n%SkPDF: Font encoding error.\n");
+                return;
+            }
+        }
+        fontGlyphUsage->noteGlyphUsage(font, glyphs, stretch);
+        if (defaultPositioning) {
+            (void)font->glyphsToPDFFontEncoding(glyphs, SkToInt(glyphsEnd - glyphs));
+            while (stretch-- > 0) {
+                glyphPositioner.writeGlyph(0, 0, 0, *glyphs);
+                ++glyphs;
+            }
+        } else {
+            while (stretch-- > 0) {
+                SkScalar advance = glyphCache->getGlyphIDAdvance(*glyphs).fAdvanceX;
+                SkScalar x = *pos++;
+                // evaluate x and y in order!
+                SkScalar y = SkTextBlob::kFull_Positioning == positioning ? *pos++ : 0;
+                SkPoint xy{x, y};
+                if (alignment != SkPaint::kLeft_Align) {
+                    SkScalar m = alignment == SkPaint::kCenter_Align
+                        ? 0.5f * advance : advance;
+                    xy -= verticalText ? SkPoint{0, m} : SkPoint{m, 0};
+                }
+                (void)font->glyphsToPDFFontEncoding(glyphs, 1);
+                glyphPositioner.writeGlyph(xy.x(), xy.y(), advance, *glyphs);
+                ++glyphs;
             }
         }
-        fontGlyphUsage->noteGlyphUsage(font, &encodedValue, 1);
-        SkScalar x = offset.x() + pos[i * scalarsPerPos];
-        SkScalar y = offset.y() + (2 == scalarsPerPos ? pos[i * scalarsPerPos + 1] : 0);
-        align_text(textPaint, glyphIDs + i, 1, &x, &y);
-
-        glyphPositioner.writeGlyph(x, y, advanceWidth, encodedValue);
     }
-    glyphPositioner.flush();  // Must flush before ending text object.
-    content.entry()->fContent.writeText("ET\n");
+    glyphPositioner.flush();
+    out->writeText("ET\n");
+}
+
+void SkPDFDevice::drawText(const SkDraw& d, const void* text, size_t len,
+                           SkScalar x, SkScalar y, const SkPaint& paint) {
+    this->internalDrawText(d, text, len, nullptr, SkTextBlob::kDefault_Positioning,
+                           SkPoint{x, y}, paint);
+}
+
+void SkPDFDevice::drawPosText(const SkDraw& d, const void* text, size_t len,
+                              const SkScalar pos[], int scalarsPerPos,
+                              const SkPoint& offset, const SkPaint& paint) {
+    this->internalDrawText(d, text, len, pos, (SkTextBlob::GlyphPositioning)scalarsPerPos,
+                           offset, paint);
 }
 
 void SkPDFDevice::drawVertices(const SkDraw& d, SkCanvas::VertexMode,