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/*
* Copyright 2016 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkRasterPipeline_DEFINED
#define SkRasterPipeline_DEFINED
#include "SkNx.h"
#include "SkTArray.h"
#include "SkTypes.h"
/**
* SkRasterPipeline provides a cheap way to chain together a pixel processing pipeline.
*
* It's particularly designed for situations where the potential pipeline is extremely
* combinatoric: {N dst formats} x {M source formats} x {K mask formats} x {C transfer modes} ...
* No one wants to write specialized routines for all those combinations, and if we did, we'd
* end up bloating our code size dramatically. SkRasterPipeline stages can be chained together
* at runtime, so we can scale this problem linearly rather than combinatorically.
*
* Each stage is represented by a function conforming to a common interface, SkRasterPipeline::Fn,
* and by an arbitrary context pointer. Fn's arguments, and sometimes custom calling convention,
* are designed to maximize the amount of data we can pass along the pipeline cheaply.
* On many machines all arguments stay in registers the entire time.
*
* The meaning of the arguments to Fn are sometimes fixed...
* - The Stage* always represents the current stage, mainly providing access to ctx().
* - The size_t is always the destination x coordinate. If you need y, put it in your context.
* - By the time the shader's done, the first four vectors should hold source red,
* green, blue, and alpha, up to 4 pixels' worth each.
*
* ...and sometimes flexible:
* - In the shader, the first four vectors can be used for anything, e.g. sample coordinates.
* - The last four vectors are scratch registers that can be used to communicate between
* stages; transfer modes use these to hold the original destination pixel components.
*
* On some platforms the last four vectors are slower to work with than the other arguments.
*
* When done mutating its arguments and/or context, a stage can either:
* 1) call st->next() with its mutated arguments, chaining to the next stage of the pipeline; or
* 2) return, indicating the pipeline is complete for these pixels.
*
* Some obvious stages that typically return are those that write a color to a destination pointer,
* but any stage can short-circuit the rest of the pipeline by returning instead of calling next().
*
* TODO: explain EasyFn and SK_RASTER_STAGE
*/
class SkRasterPipeline {
public:
struct Stage;
using Fn = void(SK_VECTORCALL *)(Stage*, size_t, Sk4f,Sk4f,Sk4f,Sk4f,
Sk4f,Sk4f,Sk4f,Sk4f);
using EasyFn = void(void*, size_t, Sk4f&, Sk4f&, Sk4f&, Sk4f&,
Sk4f&, Sk4f&, Sk4f&, Sk4f&);
struct Stage {
template <typename T>
T ctx() { return static_cast<T>(fCtx); }
void SK_VECTORCALL next(size_t x, Sk4f v0, Sk4f v1, Sk4f v2, Sk4f v3,
Sk4f v4, Sk4f v5, Sk4f v6, Sk4f v7) {
// Stages are logically a pipeline, and physically are contiguous in an array.
// To get to the next stage, we just increment our pointer to the next array element.
fNext(this+1, x, v0,v1,v2,v3, v4,v5,v6,v7);
}
// It makes next() a good bit cheaper if we hold the next function to call here,
// rather than logically simpler choice of the function implementing this stage.
Fn fNext;
void* fCtx;
};
SkRasterPipeline();
// Run the pipeline constructed with append(), walking x through [x,x+n),
// generally in 4 pixel steps, but sometimes 1 pixel at a time.
void run(size_t x, size_t n);
void run(size_t n) { this->run(0, n); }
// Use this append() if your stage is sensitive to the number of pixels you're working with:
// - body will always be called for a full 4 pixels
// - tail will always be called for a single pixel
// Typically this is only an essential distintion for stages that read or write memory.
void append(Fn body, const void* body_ctx,
Fn tail, const void* tail_ctx);
// Most stages don't actually care if they're working on 4 or 1 pixel.
void append(Fn fn, const void* ctx = nullptr) {
this->append(fn, ctx, fn, ctx);
}
// Most 4 pixel or 1 pixel variants share the same context pointer.
void append(Fn body, Fn tail, const void* ctx = nullptr) {
this->append(body, ctx, tail, ctx);
}
// Versions of append that can be used with static EasyFns (see SK_RASTER_STAGE).
template <EasyFn body, EasyFn tail>
void append(const void* body_ctx, const void* tail_ctx) {
this->append(Easy<body>, body_ctx,
Easy<tail>, tail_ctx);
}
template <EasyFn fn>
void append(const void* ctx = nullptr) { this->append<fn, fn>(ctx, ctx); }
template <EasyFn body, EasyFn tail>
void append(const void* ctx = nullptr) { this->append<body, tail>(ctx, ctx); }
// Append all stages to this pipeline.
void extend(const SkRasterPipeline&);
private:
using Stages = SkSTArray<10, Stage, /*MEM_COPY=*/true>;
// This no-op default makes fBodyStart and fTailStart unconditionally safe to call,
// and is always the last stage's fNext as a sort of safety net to make sure even a
// buggy pipeline can't walk off its own end.
static void SK_VECTORCALL JustReturn(Stage*, size_t, Sk4f,Sk4f,Sk4f,Sk4f,
Sk4f,Sk4f,Sk4f,Sk4f);
template <EasyFn kernel>
static void SK_VECTORCALL Easy(SkRasterPipeline::Stage* st, size_t x,
Sk4f r, Sk4f g, Sk4f b, Sk4f a,
Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
kernel(st->ctx<void*>(), x, r,g,b,a, dr,dg,db,da);
st->next(x, r,g,b,a, dr,dg,db,da);
}
Stages fBody,
fTail;
Fn fBodyStart = &JustReturn,
fTailStart = &JustReturn;
};
// These are always static, and we _really_ want them to inline.
// If you find yourself wanting a non-inline stage, write a SkRasterPipeline::Fn directly.
#define SK_RASTER_STAGE(name) \
static SK_ALWAYS_INLINE void name(void* ctx, size_t x, \
Sk4f& r, Sk4f& g, Sk4f& b, Sk4f& a, \
Sk4f& dr, Sk4f& dg, Sk4f& db, Sk4f& da)
#endif//SkRasterPipeline_DEFINED
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