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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 "GrTHashCache.h"
#include "SkGr.h"
#include "SkTDArray.h"
#include "GrBinHashKey.h"
/**
* 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:
/**
* Descriptor struct which we'll use as a hash table key
**/
struct Desc {
Desc() { memset(this, 0, sizeof(*this)); }
uint16_t fWidth, fHeight, fRowHeight;
GrPixelConfig fConfig;
GrContext* fContext;
const uint32_t* asKey() const { return reinterpret_cast<const uint32_t*>(this); }
};
/**
* Try to find an atlas with the required parameters, creates a new one if necessary
*/
static GrTextureStripAtlas* GetAtlas(const Desc& desc);
~GrTextureStripAtlas();
/**
* 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(const SkBitmap& data);
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, vec2(x, y))
*
* Then when using the atlas we'd replace it with:
*
* texture2D(sampler, vec2(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 getVerticalScaleFactor(), is the y-scale of the row,
* relative to the height of the overall atlas texture.
*/
SkScalar getYOffset(int row) const { return SkIntToScalar(row) / fNumRows; }
SkScalar getVerticalScaleFactor() const { return SkIntToScalar(fDesc.fRowHeight) / fDesc.fHeight; }
GrContext* getContext() const { return fDesc.fContext; }
GrTexture* getTexture() const { return fTexture; }
private:
// 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 : public GrNoncopyable {
AtlasRow() : fKey(kEmptyAtlasRowKey), fLocks(0), fNext(NULL), fPrev(NULL) { }
// 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;
};
/**
* We'll only allow construction via the static GrTextureStripAtlas::GetAtlas
*/
GrTextureStripAtlas(Desc desc);
void lockTexture();
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 NULL 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 int compareKeys(const AtlasRow* lhs, const AtlasRow* rhs) {
return lhs->fKey - rhs->fKey;
}
#ifdef SK_DEBUG
void validate();
#endif
/**
* Clean up callback registered with GrContext. Allows this class to
* free up any allocated AtlasEntry and GrTextureStripAtlas objects
*/
static void CleanUp(const GrContext* context, void* info);
// Hash table entry for atlases
class AtlasEntry;
typedef GrTBinHashKey<AtlasEntry, sizeof(GrTextureStripAtlas::Desc)> AtlasHashKey;
class AtlasEntry : public ::GrNoncopyable {
public:
AtlasEntry() : fAtlas(NULL) {}
~AtlasEntry() { SkDELETE(fAtlas); }
int compare(const AtlasHashKey& key) const { return fKey.compare(key); }
AtlasHashKey fKey;
GrTextureStripAtlas* fAtlas;
};
static GrTHashTable<AtlasEntry, AtlasHashKey, 8>* gAtlasCache;
static GrTHashTable<AtlasEntry, AtlasHashKey, 8>* GetCache();
// We increment gCacheCount for each atlas
static int32_t gCacheCount;
// A unique ID for this texture (formed with: gCacheCount++), 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 int32_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;
GrTexture* fTexture;
// 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;
};
#endif
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