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* Copyright 2012 Google Inc.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef GrTextureStripAtlas_DEFINED
#define GrTextureStripAtlas_DEFINED
#include "SkBitmap.h"
#include "SkGr.h"
#include "SkOpts.h"
#include "SkRefCnt.h"
#include "SkTDArray.h"
#include "SkTDynamicHash.h"
#include "SkTypes.h"
class GrSurfaceContext;
class GrTextureProxy;
* Maintains a single large texture whose rows store many textures of a small fixed height,
* stored in rows across the x-axis such that we can safely wrap/repeat them horizontally.
class GrTextureStripAtlas : public SkRefCnt {
* Descriptor struct which we'll use as a hash table key
struct Desc {
Desc() { sk_bzero(this, sizeof(*this)); }
GrPixelConfig fConfig;
uint16_t fWidth, fHeight, fRowHeight;
uint16_t fUnusedPadding;
bool operator==(const Desc& other) const {
return 0 == memcmp(this, &other, sizeof(Desc));
* Add a texture to the atlas
* @param data Bitmap data to copy into the row
* @return The row index we inserted into, or -1 if we failed to find an open row. The caller
* is responsible for calling unlockRow() with this row index when it's done with it.
int lockRow(GrContext*, const SkBitmap&);
* This is intended to be used when cloning a processor that already holds a lock. It is
* assumed that the row already has at least one lock.
void lockRow(int row);
void unlockRow(int row);
* These functions help turn an integer row index in [0, 1, 2, ... numRows] into a scalar y
* texture coordinate in [0, 1] that we can use in a shader.
* If a regular texture access without using the atlas looks like:
* texture2D(sampler, float2(x, y))
* Then when using the atlas we'd replace it with:
* texture2D(sampler, float2(x, yOffset + y * scaleFactor))
* Where yOffset, returned by getYOffset(), is the offset to the start of the row within the
* atlas and scaleFactor, returned by getNormalizedTexelHeight, is the normalized height of
* one texel row.
SkScalar getYOffset(int row) const { return SkIntToScalar(row) / fNumRows; }
SkScalar getNormalizedTexelHeight() const { return fNormalizedYHeight; }
sk_sp<GrTextureProxy> asTextureProxyRef() const;
friend class GrTextureStripAtlasManager; // for ctor
static uint32_t CreateUniqueID();
// Key to indicate an atlas row without any meaningful data stored in it
const static uint32_t kEmptyAtlasRowKey = 0xffffffff;
* The state of a single row in our cache, next/prev pointers allow these to be chained
* together to represent LRU status
struct AtlasRow : ::SkNoncopyable {
AtlasRow() : fKey(kEmptyAtlasRowKey), fLocks(0), fNext(nullptr), fPrev(nullptr) { }
// GenerationID of the bitmap that is represented by this row, 0xffffffff means "empty"
uint32_t fKey;
// How many times this has been locked (0 == unlocked)
int32_t fLocks;
// We maintain an LRU linked list between unlocked nodes with these pointers
AtlasRow* fNext;
AtlasRow* fPrev;
* Only the GrTextureStripAtlasManager is allowed to create GrTextureStripAtlases
GrTextureStripAtlas(const Desc& desc);
void lockTexture(GrContext*);
void unlockTexture();
* Initialize our LRU list (if one already exists, clear it and start anew)
void initLRU();
* Grabs the least recently used free row out of the LRU list, returns nullptr if no rows
* are free.
AtlasRow* getLRU();
void appendLRU(AtlasRow* row);
void removeFromLRU(AtlasRow* row);
* Searches the key table for a key and returns the index if found; if not found, it returns
* the bitwise not of the index at which we could insert the key to maintain a sorted list.
int searchByKey(uint32_t key);
* Compare two atlas rows by key, so we can sort/search by key
static bool KeyLess(const AtlasRow& lhs, const AtlasRow& rhs) {
return lhs.fKey < rhs.fKey;
#ifdef SK_DEBUG
void validate();
// A unique ID for this atlas, so we can be sure that if we
// get a texture back from the texture cache, that it's the same one we last used.
const uint32_t fCacheKey;
// Total locks on all rows (when this reaches zero, we can unlock our texture)
int32_t fLockedRows;
const Desc fDesc;
const uint16_t fNumRows;
sk_sp<GrSurfaceContext> fTexContext;
SkScalar fNormalizedYHeight;
// Array of AtlasRows which store the state of all our rows. Stored in a contiguous array, in
// order that they appear in our texture, this means we can subtract this pointer from a row
// pointer to get its index in the texture, and can save storing a row number in AtlasRow.
AtlasRow* fRows;
// Head and tail for linked list of least-recently-used rows (front = least recently used).
// Note that when a texture is locked, it gets removed from this list until it is unlocked.
AtlasRow* fLRUFront;
AtlasRow* fLRUBack;
// A list of pointers to AtlasRows that currently contain cached images, sorted by key
SkTDArray<AtlasRow*> fKeyTable;
class GrTextureStripAtlasManager {
GrTextureStripAtlasManager() {}
void abandon();
* Try to find an atlas with the required parameters, creates a new one if necessary
sk_sp<GrTextureStripAtlas> refAtlas(const GrTextureStripAtlas::Desc&);
void deleteAllAtlases();
// Hash table entry for atlases
class AtlasEntry : public ::SkNoncopyable {
AtlasEntry(const GrTextureStripAtlas::Desc& desc, sk_sp<GrTextureStripAtlas> atlas)
: fDesc(desc)
, fAtlas(std::move(atlas)) {
~AtlasEntry() { }
// for SkTDynamicHash
static const GrTextureStripAtlas::Desc& GetKey(const AtlasEntry& entry) {
return entry.fDesc;
static uint32_t Hash(const GrTextureStripAtlas::Desc& desc) {
return SkOpts::hash(&desc, sizeof(GrTextureStripAtlas::Desc));
const GrTextureStripAtlas::Desc fDesc;
sk_sp<GrTextureStripAtlas> fAtlas;
typedef SkTDynamicHash<AtlasEntry, GrTextureStripAtlas::Desc> AtlasHash;
AtlasHash fAtlasCache;