SkPDF: more accurate (float) colors from paint

Does not yet affect colors from gradient shaders.

Serialize colors with 4 digits of accuracy, not 3.

Resulting PDFs are usually slightly larger, but render the same when
rendered into an 8-bit buffer.

Change-Id: I64336f3a1f34021f9ddb723bd8a16d51ddfea0f4
Reviewed-on: https://skia-review.googlesource.com/c/161141
Commit-Queue: Hal Canary <halcanary@google.com>
Auto-Submit: Hal Canary <halcanary@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>

src/pdf/SkPDFDevice.cpp

@@ -148,13 +148,13 @@ static void transform_shader(SkPaint* paint, const SkMatrix& ctm) {
     }
 }
 
-static void emit_pdf_color(SkColor color, SkWStream* result) {
-    SkASSERT(SkColorGetA(color) == 0xFF);  // We handle alpha elsewhere.
-    SkPDFUtils::AppendColorComponent(SkColorGetR(color), result);
+static void emit_pdf_color(SkColor4f color, SkWStream* result) {
+    SkASSERT(color.fA == 1);  // We handle alpha elsewhere.
+    SkPDFUtils::AppendColorComponentF(color.fR, result);
     result->writeText(" ");
-    SkPDFUtils::AppendColorComponent(SkColorGetG(color), result);
+    SkPDFUtils::AppendColorComponentF(color.fG, result);
     result->writeText(" ");
-    SkPDFUtils::AppendColorComponent(SkColorGetB(color), result);
+    SkPDFUtils::AppendColorComponentF(color.fB, result);
     result->writeText(" ");
 }
 
@@ -165,7 +165,7 @@ void remove_color_filter(SkPaint* paint) {
         if (SkShader* shader = paint->getShader()) {
             paint->setShader(shader->makeWithColorFilter(paint->refColorFilter()));
         } else {
-            paint->setColor(cf->filterColor(paint->getColor()));
+            paint->setColor4f(cf->filterColor4f(paint->getColor4f(), nullptr), nullptr);
         }
         paint->setColorFilter(nullptr);
     }
@@ -1699,13 +1699,13 @@ void SkPDFDevice::populateGraphicStateEntryFromPaint(
     entry->fMatrix = matrix;
     entry->fClipStackGenID = clipStack ? clipStack->getTopmostGenID()
                                        : SkClipStack::kWideOpenGenID;
-    entry->fColor = SkColorSetA(paint.getColor(), 0xFF);
+    SkColor4f color = paint.getColor4f();
+    entry->fColor = {color.fR, color.fG, color.fB, 1};
     entry->fShaderIndex = -1;
 
     // PDF treats a shader as a color, so we only set one or the other.
     sk_sp<SkPDFObject> pdfShader;
     SkShader* shader = paint.getShader();
-    SkColor color = paint.getColor();
     if (shader) {
         if (SkShader::kColor_GradientType == shader->asAGradient(nullptr)) {
             // We don't have to set a shader just for a color.
@@ -1715,8 +1715,9 @@ void SkPDFDevice::populateGraphicStateEntryFromPaint(
             gradientInfo.fColorOffsets = nullptr;
             gradientInfo.fColorCount = 1;
             SkAssertResult(shader->asAGradient(&gradientInfo) == SkShader::kColor_GradientType);
-            entry->fColor = SkColorSetA(gradientColor, 0xFF);
-            color = gradientColor;
+            color = SkColor4f::FromColor(gradientColor);
+            entry->fColor ={color.fR, color.fG, color.fB, 1};
+
         } else {
             // PDF positions patterns relative to the initial transform, so
             // we need to apply the current transform to the shader parameters.
@@ -1744,11 +1745,11 @@ void SkPDFDevice::populateGraphicStateEntryFromPaint(
     }
 
     sk_sp<SkPDFDict> newGraphicState;
-    if (color == paint.getColor()) {
+    if (color == paint.getColor4f()) {
         newGraphicState = SkPDFGraphicState::GetGraphicStateForPaint(fDocument->canon(), paint);
     } else {
         SkPaint newPaint = paint;
-        newPaint.setColor(color);
+        newPaint.setColor4f(color, nullptr);
         newGraphicState = SkPDFGraphicState::GetGraphicStateForPaint(fDocument->canon(), newPaint);
     }
     entry->fGraphicStateIndex = find_or_add(&fGraphicStateResources, std::move(newGraphicState));
@@ -1839,7 +1840,7 @@ void SkPDFDevice::internalDrawImageRect(SkKeyedImage imageSubset,
         // In the case of alpha images with shaders, the shader's coordinate
         // system is the image's coordiantes.
         tmpPaint.setShader(sk_ref_sp(paint.getShader()));
-        tmpPaint.setColor(paint.getColor());
+        tmpPaint.setColor4f(paint.getColor4f(), nullptr);
         canvas->clear(0x00000000);
         canvas->drawImage(imageSubset.image().get(), 0, 0, &tmpPaint);
         paint.setShader(nullptr);

src/pdf/SkPDFDevice.h

@@ -123,7 +123,7 @@ public:
     struct GraphicStateEntry {
         SkMatrix fMatrix = SkMatrix::I();
         uint32_t fClipStackGenID = SkClipStack::kWideOpenGenID;
-        SkColor fColor = SK_ColorBLACK;
+        SkColor4f fColor = {0, 0, 0, 1};
         SkScalar fTextScaleX = 1;  // Zero means we don't care what the value is.
         SkPaint::Style fTextFill = SkPaint::kFill_Style;  // Only if TextScaleX is non-zero.
         int fShaderIndex = -1;

src/pdf/SkPDFUtils.cpp

@@ -244,21 +244,16 @@ void SkPDFUtils::ApplyPattern(int objectIndex, SkWStream* content) {
     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 = 0.5 + (1000.0 / 255.0) * value;
-    int x = SkFixedRoundToInt((SK_Fixed1 * 1000 / 255) * value);
+// return "x/pow(10, places)", given 0<x<pow(10, places)
+// result points to places+2 chars.
+static size_t print_permil_as_decimal(int x, char* result, unsigned places) {
     result[0] = '.';
-    for (int i = 3; i > 0; --i) {
+    for (int i = places; i > 0; --i) {
         result[i] = '0' + x % 10;
         x /= 10;
     }
     int j;
-    for (j = 3; j > 1; --j) {
+    for (j = places; j > 1; --j) {
         if (result[j] != '0') {
             break;
         }
@@ -268,6 +263,36 @@ size_t SkPDFUtils::ColorToDecimal(uint8_t value, char result[5]) {
 }
 
 
+static constexpr int int_pow(int base, unsigned exp, int acc = 1) {
+  return exp < 1 ? acc
+                 : int_pow(base * base,
+                           exp / 2,
+                           (exp % 2) ? acc * base : acc);
+}
+
+
+size_t SkPDFUtils::ColorToDecimalF(float value, char result[kFloatColorDecimalCount + 2]) {
+    static constexpr int kFactor = int_pow(10, kFloatColorDecimalCount);
+    int x = sk_float_round2int(value * kFactor);
+    if (x >= kFactor || x <= 0) {  // clamp to 0-1
+        result[0] = x > 0 ? '1' : '0';
+        result[1] = '\0';
+        return 1;
+    }
+    return print_permil_as_decimal(x, result, kFloatColorDecimalCount);
+}
+
+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 = 0.5 + (1000.0 / 255.0) * value;
+    int x = SkFixedRoundToInt((SK_Fixed1 * 1000 / 255) * value);
+    return print_permil_as_decimal(x, result, 3);
+}
+
 bool SkPDFUtils::InverseTransformBBox(const SkMatrix& matrix, SkRect* bbox) {
     SkMatrix inverse;
     if (!matrix.invert(&inverse)) {

src/pdf/SkPDFUtils.h

@@ -66,11 +66,19 @@ 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]);
+
+static constexpr unsigned kFloatColorDecimalCount = 4;
+size_t ColorToDecimalF(float value, char result[kFloatColorDecimalCount + 2]);
 inline void AppendColorComponent(uint8_t value, SkWStream* wStream) {
     char buffer[5];
     size_t len = SkPDFUtils::ColorToDecimal(value, buffer);
     wStream->write(buffer, len);
 }
+inline void AppendColorComponentF(float value, SkWStream* wStream) {
+    char buffer[kFloatColorDecimalCount + 2];
+    size_t len = SkPDFUtils::ColorToDecimalF(value, buffer);
+    wStream->write(buffer, len);
+}
 
 inline void AppendScalar(SkScalar value, SkWStream* stream) {
     char result[kMaximumSkFloatToDecimalLength];