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* Copyright 2006 The Android Open Source Project
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef SkScalerContext_DEFINED
#define SkScalerContext_DEFINED
#include <memory>
#include "SkFont.h"
#include "SkFontTypes.h"
#include "SkGlyph.h"
#include "SkMacros.h"
#include "SkMask.h"
#include "SkMaskFilter.h"
#include "SkMaskGamma.h"
#include "SkMatrix.h"
#include "SkPaint.h"
#include "SkStrikeInterface.h"
#include "SkSurfacePriv.h"
#include "SkTypeface.h"
#include "SkWriteBuffer.h"
class SkAutoDescriptor;
class SkDescriptor;
class SkMaskFilter;
class SkPathEffect;
class SkScalerContext;
class SkScalerContext_DW;
enum SkScalerContextFlags : uint32_t {
kNone = 0,
kFakeGamma = 1 << 0,
kBoostContrast = 1 << 1,
kFakeGammaAndBoostContrast = kFakeGamma | kBoostContrast,
enum SkAxisAlignment : uint32_t {
* To allow this to be forward-declared, it must be its own typename, rather
* than a nested struct inside SkScalerContext (where it started).
* SkScalerContextRec must be dense, and all bytes must be set to a know quantity because this
* structure is used to calculate a checksum.
struct SkScalerContextRec {
uint32_t fFontID;
SkScalar fTextSize, fPreScaleX, fPreSkewX;
SkScalar fPost2x2[2][2];
SkScalar fFrameWidth, fMiterLimit;
//These describe the parameters to create (uniquely identify) the pre-blend.
uint32_t fLumBits;
uint8_t fDeviceGamma; //2.6, (0.0, 4.0) gamma, 0.0 for sRGB
uint8_t fPaintGamma; //2.6, (0.0, 4.0) gamma, 0.0 for sRGB
uint8_t fContrast; //0.8+1, [0.0, 1.0] artificial contrast
const uint8_t fReservedAlign{0};
SkScalar getDeviceGamma() const {
return SkIntToScalar(fDeviceGamma) / (1 << 6);
void setDeviceGamma(SkScalar dg) {
SkASSERT(0 <= dg && dg < SkIntToScalar(4));
fDeviceGamma = SkScalarFloorToInt(dg * (1 << 6));
SkScalar getPaintGamma() const {
return SkIntToScalar(fPaintGamma) / (1 << 6);
void setPaintGamma(SkScalar pg) {
SkASSERT(0 <= pg && pg < SkIntToScalar(4));
fPaintGamma = SkScalarFloorToInt(pg * (1 << 6));
SkScalar getContrast() const {
return SkIntToScalar(fContrast) / ((1 << 8) - 1);
void setContrast(SkScalar c) {
SkASSERT(0 <= c && c <= SK_Scalar1);
fContrast = SkScalarRoundToInt(c * ((1 << 8) - 1));
* Causes the luminance color to be ignored, and the paint and device
* gamma to be effectively 1.0
void ignoreGamma() {
* Causes the luminance color and contrast to be ignored, and the
* paint and device gamma to be effectively 1.0.
void ignorePreBlend() {
uint8_t fMaskFormat;
uint8_t fStrokeJoin : 4;
uint8_t fStrokeCap : 4;
uint16_t fFlags;
// Warning: when adding members note that the size of this structure
// must be a multiple of 4. SkDescriptor requires that its arguments be
// multiples of four and this structure is put in an SkDescriptor in
// SkPaint::MakeRecAndEffects.
SkString dump() const {
SkString msg;
msg.appendf(" textsize %g prescale %g preskew %g post [%g %g %g %g]\n",
fTextSize, fPreScaleX, fPreSkewX, fPost2x2[0][0],
fPost2x2[0][1], fPost2x2[1][0], fPost2x2[1][1]);
msg.appendf(" frame %g miter %g format %d join %d cap %d flags %#hx\n",
fFrameWidth, fMiterLimit, fMaskFormat, fStrokeJoin, fStrokeCap, fFlags);
msg.appendf(" lum bits %x, device gamma %d, paint gamma %d contrast %d\n", fLumBits,
fDeviceGamma, fPaintGamma, fContrast);
return msg;
void getMatrixFrom2x2(SkMatrix*) const;
void getLocalMatrix(SkMatrix*) const;
void getSingleMatrix(SkMatrix*) const;
/** The kind of scale which will be applied by the underlying port (pre-matrix). */
enum PreMatrixScale {
kFull_PreMatrixScale, // The underlying port can apply both x and y scale.
kVertical_PreMatrixScale, // The underlying port can only apply a y scale.
kVerticalInteger_PreMatrixScale // The underlying port can only apply an integer y scale.
* Compute useful matrices for use with sizing in underlying libraries.
* There are two kinds of text size, a 'requested/logical size' which is like asking for size
* '12' and a 'real' size which is the size after the matrix is applied. The matrices produced
* by this method are based on the 'real' size. This method effectively finds the total device
* matrix and decomposes it in various ways.
* The most useful decomposition is into 'scale' and 'remaining'. The 'scale' is applied first
* and then the 'remaining' to fully apply the total matrix. This decomposition is useful when
* the text size ('scale') may have meaning apart from the total matrix. This is true when
* hinting, and sometimes true for other properties as well.
* The second (optional) decomposition is of 'remaining' into a non-rotational part
* 'remainingWithoutRotation' and a rotational part 'remainingRotation'. The 'scale' is applied
* first, then 'remainingWithoutRotation', then 'remainingRotation' to fully apply the total
* matrix. This decomposition is helpful when only horizontal metrics can be trusted, so the
* 'scale' and 'remainingWithoutRotation' will be handled by the underlying library, but
* the final rotation 'remainingRotation' will be handled manually.
* The 'total' matrix is also (optionally) available. This is useful in cases where the
* underlying library will not be used, often when working directly with font data.
* The parameters 'scale' and 'remaining' are required, the other pointers may be nullptr.
* @param preMatrixScale the kind of scale to extract from the total matrix.
* @param scale the scale extracted from the total matrix (both values positive).
* @param remaining apply after scale to apply the total matrix.
* @param remainingWithoutRotation apply after scale to apply the total matrix sans rotation.
* @param remainingRotation apply after remainingWithoutRotation to apply the total matrix.
* @param total the total matrix.
* @return false if the matrix was singular. The output will be valid but not invertible.
bool computeMatrices(PreMatrixScale preMatrixScale,
SkVector* scale, SkMatrix* remaining,
SkMatrix* remainingWithoutRotation = nullptr,
SkMatrix* remainingRotation = nullptr,
SkMatrix* total = nullptr);
SkAxisAlignment computeAxisAlignmentForHText() const;
inline SkFontHinting getHinting() const;
inline void setHinting(SkFontHinting);
SkMask::Format getFormat() const {
return static_cast<SkMask::Format>(fMaskFormat);
SkColor getLuminanceColor() const {
return fLumBits;
// setLuminanceColor forces the alpha to be 0xFF because the blitter that draws the glyph
// will apply the alpha from the paint. Don't apply the alpha twice.
void setLuminanceColor(SkColor c);
// TODO: remove
friend class SkScalerContext;
//The following typedef hides from the rest of the implementation the number of
//most significant bits to consider when creating mask gamma tables. Two bits
//per channel was chosen as a balance between fidelity (more bits) and cache
//sizes (fewer bits). Three bits per channel was chosen when #303942; (used by
//the Chrome UI) turned out too green.
typedef SkTMaskGamma<3, 3, 3> SkMaskGamma;
class SkScalerContext {
enum Flags {
kFrameAndFill_Flag = 0x0001,
kUnused = 0x0002,
kEmbeddedBitmapText_Flag = 0x0004,
kEmbolden_Flag = 0x0008,
kSubpixelPositioning_Flag = 0x0010,
kForceAutohinting_Flag = 0x0020, // Use auto instead of bytcode hinting if hinting.
// together, these two flags resulting in a two bit value which matches
// up with the SkPaint::Hinting enum.
kHinting_Shift = 7, // to shift into the other flags above
kHintingBit1_Flag = 0x0080,
kHintingBit2_Flag = 0x0100,
// Pixel geometry information.
// only meaningful if fMaskFormat is kLCD16
kLCD_Vertical_Flag = 0x0200, // else Horizontal
kLCD_BGROrder_Flag = 0x0400, // else RGB order
// Generate A8 from LCD source (for GDI and CoreGraphics).
// only meaningful if fMaskFormat is kA8
kGenA8FromLCD_Flag = 0x0800, // could be 0x200 (bit meaning dependent on fMaskFormat)
// computed values
enum {
kHinting_Mask = kHintingBit1_Flag | kHintingBit2_Flag,
SkScalerContext(sk_sp<SkTypeface>, const SkScalerContextEffects&, const SkDescriptor*);
virtual ~SkScalerContext();
SkTypeface* getTypeface() const { return fTypeface.get(); }
SkMask::Format getMaskFormat() const {
return (SkMask::Format)fRec.fMaskFormat;
bool isSubpixel() const {
return SkToBool(fRec.fFlags & kSubpixelPositioning_Flag);
bool isVertical() const { return false; }
unsigned getGlyphCount() { return this->generateGlyphCount(); }
void getAdvance(SkGlyph*);
void getMetrics(SkGlyph*);
void getImage(const SkGlyph&);
bool SK_WARN_UNUSED_RESULT getPath(SkPackedGlyphID, SkPath*);
void getFontMetrics(SkFontMetrics*);
/** Return the size in bytes of the associated gamma lookup table
static size_t GetGammaLUTSize(SkScalar contrast, SkScalar paintGamma, SkScalar deviceGamma,
int* width, int* height);
/** Get the associated gamma lookup table. The 'data' pointer must point to pre-allocated
* memory, with size in bytes greater than or equal to the return value of getGammaLUTSize().
* If the lookup table hasn't been initialized (e.g., it's linear), this will return false.
static bool GetGammaLUTData(SkScalar contrast, SkScalar paintGamma, SkScalar deviceGamma,
uint8_t* data);
static void MakeRecAndEffects(const SkFont& font, const SkPaint& paint,
const SkSurfaceProps& surfaceProps,
SkScalerContextFlags scalerContextFlags,
const SkMatrix& deviceMatrix,
SkScalerContextRec* rec,
SkScalerContextEffects* effects);
// If we are creating rec and effects from a font only, then there is no device around either.
static void MakeRecAndEffectsFromFont(const SkFont& font,
SkScalerContextRec* rec,
SkScalerContextEffects* effects) {
SkPaint paint;
return MakeRecAndEffects(
font, paint, SkSurfaceProps(SkSurfaceProps::kLegacyFontHost_InitType),
SkScalerContextFlags::kNone, SkMatrix::I(), rec, effects);
static SkDescriptor* MakeDescriptorForPaths(SkFontID fontID,
SkAutoDescriptor* ad);
static SkDescriptor* AutoDescriptorGivenRecAndEffects(
const SkScalerContextRec& rec,
const SkScalerContextEffects& effects,
SkAutoDescriptor* ad);
static std::unique_ptr<SkDescriptor> DescriptorGivenRecAndEffects(
const SkScalerContextRec& rec,
const SkScalerContextEffects& effects);
static void DescriptorBufferGiveRec(const SkScalerContextRec& rec, void* buffer);
static bool CheckBufferSizeForRec(const SkScalerContextRec& rec,
const SkScalerContextEffects& effects,
size_t size);
static SkMaskGamma::PreBlend GetMaskPreBlend(const SkScalerContextRec& rec);
const SkScalerContextRec& getRec() const { return fRec; }
SkScalerContextEffects getEffects() const {
return { fPathEffect.get(), fMaskFilter.get() };
* Return the axis (if any) that the baseline for horizontal text should land on.
* As an example, the identity matrix will return kX_SkAxisAlignment
SkAxisAlignment computeAxisAlignmentForHText() const;
static SkDescriptor* CreateDescriptorAndEffectsUsingPaint(
const SkFont&, const SkPaint&, const SkSurfaceProps&,
SkScalerContextFlags scalerContextFlags,
const SkMatrix& deviceMatrix, SkAutoDescriptor* ad,
SkScalerContextEffects* effects);
SkScalerContextRec fRec;
/** Generates the contents of glyph.fAdvanceX and glyph.fAdvanceY if it can do so quickly.
* Returns true if it could, false otherwise.
virtual bool generateAdvance(SkGlyph* glyph) = 0;
/** Generates the contents of glyph.fWidth, fHeight, fTop, fLeft,
* as well as fAdvanceX and fAdvanceY if not already set.
* TODO: fMaskFormat is set by getMetrics later; cannot be set here.
virtual void generateMetrics(SkGlyph* glyph) = 0;
/** Generates the contents of glyph.fImage.
* When called, glyph.fImage will be pointing to a pre-allocated,
* uninitialized region of memory of size glyph.computeImageSize().
* This method may change glyph.fMaskFormat if the new image size is
* less than or equal to the old image size.
* Because glyph.computeImageSize() will determine the size of fImage,
* generateMetrics will be called before generateImage.
virtual void generateImage(const SkGlyph& glyph) = 0;
/** Sets the passed path to the glyph outline.
* If this cannot be done the path is set to empty;
* @return false if this glyph does not have any path.
virtual bool SK_WARN_UNUSED_RESULT generatePath(SkGlyphID glyphId, SkPath* path) = 0;
/** Retrieves font metrics. */
virtual void generateFontMetrics(SkFontMetrics*) = 0;
/** Returns the number of glyphs in the font. */
virtual unsigned generateGlyphCount() = 0;
void forceGenerateImageFromPath() { fGenerateImageFromPath = true; }
void forceOffGenerateImageFromPath() { fGenerateImageFromPath = false; }
friend class RandomScalerContext; // For debug purposes
static SkScalerContextRec PreprocessRec(const SkTypeface& typeface,
const SkScalerContextEffects& effects,
const SkDescriptor& desc);
// never null
sk_sp<SkTypeface> fTypeface;
// optional objects, which may be null
sk_sp<SkPathEffect> fPathEffect;
sk_sp<SkMaskFilter> fMaskFilter;
// if this is set, we draw the image from a path, rather than
// calling generateImage.
bool fGenerateImageFromPath;
/** Returns false if the glyph has no path at all. */
bool internalGetPath(SkPackedGlyphID id, SkPath* devPath);
// SkMaskGamma::PreBlend converts linear masks to gamma correcting masks.
// Visible to subclasses so that generateImage can apply the pre-blend directly.
const SkMaskGamma::PreBlend fPreBlend;
#define kRec_SkDescriptorTag SkSetFourByteTag('s', 'r', 'e', 'c')
#define kEffects_SkDescriptorTag SkSetFourByteTag('e', 'f', 'c', 't')
SkFontHinting SkScalerContextRec::getHinting() const {
unsigned hint = (fFlags & SkScalerContext::kHinting_Mask) >>
return static_cast<SkFontHinting>(hint);
void SkScalerContextRec::setHinting(SkFontHinting hinting) {
fFlags = (fFlags & ~SkScalerContext::kHinting_Mask) |
(static_cast<unsigned>(hinting) << SkScalerContext::kHinting_Shift);