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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 first size_t is always the destination x coordinate.
* (If you need y, put it in your context.)
* - The second size_t is always tail: 0 when working on a full 4-pixel slab,
* or 1..3 when using only the bottom 1..3 lanes of each register.
* - 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.
*
* Sometimes arguments are 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 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().
*
* Most simple pipeline stages can use the SK_RASTER_STAGE macro to define a static EasyFn,
* which simplifies the user interface a bit:
* - the context pointer is available directly as the first parameter;
* - instead of manually calling a next() function, just modify registers in place.
*
* To add an EasyFn stage to the pipeline, call append<fn>() instead of append(&fn).
* It's a slight performance benefit to call last<fn>() for the last stage of a pipeline.
*/
// TODO: There may be a better place to stuff tail, e.g. in the bottom alignment bits of
// the Stage*. This mostly matters on 64-bit Windows where every register is precious.
class SkRasterPipeline {
public:
struct Stage;
using Fn = void(SK_VECTORCALL *)(Stage*, size_t, size_t, Sk4f,Sk4f,Sk4f,Sk4f,
Sk4f,Sk4f,Sk4f,Sk4f);
using EasyFn = void(void*, size_t, 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, size_t tail, 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,tail, 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, with perhaps one jagged tail step.
void run(size_t x, size_t n);
void run(size_t n) { this->run(0, n); }
// body() will only be called with tail=0, indicating it always works on a full 4 pixels.
// tail() will only be called with tail=1..3 to handle the jagged end of n%4 pixels.
void append(Fn body, Fn tail, const void* ctx = nullptr);
void append(Fn fn, const void* ctx = nullptr) { this->append(fn, fn, ctx); }
// Version of append that can be used with static EasyFn (see SK_RASTER_STAGE).
template <EasyFn fn>
void append(const void* ctx = nullptr) {
this->append(Body<fn,true>, Tail<fn,true>, ctx);
}
// If this is the last stage of the pipeline, last() is a bit faster than append().
template <EasyFn fn>
void last(const void* ctx = nullptr) {
this->append(Body<fn,false>, Tail<fn,false>, 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, size_t, Sk4f,Sk4f,Sk4f,Sk4f,
Sk4f,Sk4f,Sk4f,Sk4f);
template <EasyFn kernel, bool kCallNext>
static void SK_VECTORCALL Body(SkRasterPipeline::Stage* st, size_t x, size_t tail,
Sk4f r, Sk4f g, Sk4f b, Sk4f a,
Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
// Passing 0 lets the optimizer completely drop any "if (tail) {...}" code in kernel.
kernel(st->ctx<void*>(), x,0, r,g,b,a, dr,dg,db,da);
if (kCallNext) {
st->next(x,tail, r,g,b,a, dr,dg,db,da); // It's faster to pass tail here than 0.
}
}
template <EasyFn kernel, bool kCallNext>
static void SK_VECTORCALL Tail(SkRasterPipeline::Stage* st, size_t x, size_t tail,
Sk4f r, Sk4f g, Sk4f b, Sk4f a,
Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
#if defined(__clang__)
__builtin_assume(tail > 0); // This flourish lets Clang compile away any tail==0 code.
#endif
kernel(st->ctx<void*>(), x,tail, r,g,b,a, dr,dg,db,da);
if (kCallNext) {
st->next(x,tail, 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, size_t tail, \
Sk4f& r, Sk4f& g, Sk4f& b, Sk4f& a, \
Sk4f& dr, Sk4f& dg, Sk4f& db, Sk4f& da)
#endif//SkRasterPipeline_DEFINED
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