gecko-dev/gfx/thebes/gfxAlphaRecoverySSE2.cpp

/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "gfxAlphaRecovery.h"
#include "gfxImageSurface.h"
#include "nsDebug.h"
#include <emmintrin.h>

// This file should only be compiled on x86 and x64 systems.  Additionally,
// you'll need to compile it with -msse2 if you're using GCC on x86.

#if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_AMD64))
__declspec(align(16)) static uint32_t greenMaski[] = {0x0000ff00, 0x0000ff00,
                                                      0x0000ff00, 0x0000ff00};
__declspec(align(16)) static uint32_t alphaMaski[] = {0xff000000, 0xff000000,
                                                      0xff000000, 0xff000000};
#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
static uint32_t greenMaski[] __attribute__((aligned(16))) = {
    0x0000ff00, 0x0000ff00, 0x0000ff00, 0x0000ff00};
static uint32_t alphaMaski[] __attribute__((aligned(16))) = {
    0xff000000, 0xff000000, 0xff000000, 0xff000000};
#elif defined(__SUNPRO_CC) && (defined(__i386) || defined(__x86_64__))
#  pragma align 16(greenMaski, alphaMaski)
static uint32_t greenMaski[] = {0x0000ff00, 0x0000ff00, 0x0000ff00, 0x0000ff00};
static uint32_t alphaMaski[] = {0xff000000, 0xff000000, 0xff000000, 0xff000000};
#endif

bool gfxAlphaRecovery::RecoverAlphaSSE2(gfxImageSurface* blackSurf,
                                        const gfxImageSurface* whiteSurf) {
  mozilla::gfx::IntSize size = blackSurf->GetSize();

  if (size != whiteSurf->GetSize() ||
      (blackSurf->Format() != mozilla::gfx::SurfaceFormat::A8R8G8B8_UINT32 &&
       blackSurf->Format() != mozilla::gfx::SurfaceFormat::X8R8G8B8_UINT32) ||
      (whiteSurf->Format() != mozilla::gfx::SurfaceFormat::A8R8G8B8_UINT32 &&
       whiteSurf->Format() != mozilla::gfx::SurfaceFormat::X8R8G8B8_UINT32))
    return false;

  blackSurf->Flush();
  whiteSurf->Flush();

  unsigned char* blackData = blackSurf->Data();
  unsigned char* whiteData = whiteSurf->Data();

  if ((NS_PTR_TO_UINT32(blackData) & 0xf) !=
          (NS_PTR_TO_UINT32(whiteData) & 0xf) ||
      (blackSurf->Stride() - whiteSurf->Stride()) & 0xf) {
    // Cannot keep these in alignment.
    return false;
  }

  __m128i greenMask = _mm_load_si128((__m128i*)greenMaski);
  __m128i alphaMask = _mm_load_si128((__m128i*)alphaMaski);

  for (int32_t i = 0; i < size.height; ++i) {
    int32_t j = 0;
    // Loop single pixels until at 4 byte alignment.
    while (NS_PTR_TO_UINT32(blackData) & 0xf && j < size.width) {
      *((uint32_t*)blackData) =
          RecoverPixel(*reinterpret_cast<uint32_t*>(blackData),
                       *reinterpret_cast<uint32_t*>(whiteData));
      blackData += 4;
      whiteData += 4;
      j++;
    }
    // This extra loop allows the compiler to do some more clever registry
    // management and makes it about 5% faster than with only the 4 pixel
    // at a time loop.
    for (; j < size.width - 8; j += 8) {
      __m128i black1 = _mm_load_si128((__m128i*)blackData);
      __m128i white1 = _mm_load_si128((__m128i*)whiteData);
      __m128i black2 = _mm_load_si128((__m128i*)(blackData + 16));
      __m128i white2 = _mm_load_si128((__m128i*)(whiteData + 16));

      // Execute the same instructions as described in RecoverPixel, only
      // using an SSE2 packed saturated subtract.
      white1 = _mm_subs_epu8(white1, black1);
      white2 = _mm_subs_epu8(white2, black2);
      white1 = _mm_subs_epu8(greenMask, white1);
      white2 = _mm_subs_epu8(greenMask, white2);
      // Producing the final black pixel in an XMM register and storing
      // that is actually faster than doing a masked store since that
      // does an unaligned storage. We have the black pixel in a register
      // anyway.
      black1 = _mm_andnot_si128(alphaMask, black1);
      black2 = _mm_andnot_si128(alphaMask, black2);
      white1 = _mm_slli_si128(white1, 2);
      white2 = _mm_slli_si128(white2, 2);
      white1 = _mm_and_si128(alphaMask, white1);
      white2 = _mm_and_si128(alphaMask, white2);
      black1 = _mm_or_si128(white1, black1);
      black2 = _mm_or_si128(white2, black2);

      _mm_store_si128((__m128i*)blackData, black1);
      _mm_store_si128((__m128i*)(blackData + 16), black2);
      blackData += 32;
      whiteData += 32;
    }
    for (; j < size.width - 4; j += 4) {
      __m128i black = _mm_load_si128((__m128i*)blackData);
      __m128i white = _mm_load_si128((__m128i*)whiteData);

      white = _mm_subs_epu8(white, black);
      white = _mm_subs_epu8(greenMask, white);
      black = _mm_andnot_si128(alphaMask, black);
      white = _mm_slli_si128(white, 2);
      white = _mm_and_si128(alphaMask, white);
      black = _mm_or_si128(white, black);
      _mm_store_si128((__m128i*)blackData, black);
      blackData += 16;
      whiteData += 16;
    }
    // Loop single pixels until we're done.
    while (j < size.width) {
      *((uint32_t*)blackData) =
          RecoverPixel(*reinterpret_cast<uint32_t*>(blackData),
                       *reinterpret_cast<uint32_t*>(whiteData));
      blackData += 4;
      whiteData += 4;
      j++;
    }
    blackData += blackSurf->Stride() - j * 4;
    whiteData += whiteSurf->Stride() - j * 4;
  }

  blackSurf->MarkDirty();

  return true;
}

static int32_t ByteAlignment(int32_t aAlignToLog2, int32_t aX, int32_t aY = 0,
                             int32_t aStride = 1) {
  return (aX + aStride * aY) & ((1 << aAlignToLog2) - 1);
}

/*static*/ mozilla::gfx::IntRect gfxAlphaRecovery::AlignRectForSubimageRecovery(
    const mozilla::gfx::IntRect& aRect, gfxImageSurface* aSurface) {
  NS_ASSERTION(
      mozilla::gfx::SurfaceFormat::A8R8G8B8_UINT32 == aSurface->Format(),
      "Thebes grew support for non-ARGB32 COLOR_ALPHA?");
  static const int32_t kByteAlignLog2 = GoodAlignmentLog2();
  static const int32_t bpp = 4;
  static const int32_t pixPerAlign = (1 << kByteAlignLog2) / bpp;
  //
  // We're going to create a subimage of the surface with size
  // <sw,sh> for alpha recovery, and want a SIMD fast-path.  The
  // rect <x,y, w,h> /needs/ to be redrawn, but it might not be
  // properly aligned for SIMD.  So we want to find a rect <x',y',
  // w',h'> that's a superset of what needs to be redrawn but is
  // properly aligned.  Proper alignment is
  //
  //   BPP * (x' + y' * sw) \cong 0         (mod ALIGN)
  //   BPP * w'             \cong BPP * sw  (mod ALIGN)
  //
  // (We assume the pixel at surface <0,0> is already ALIGN'd.)
  // That rect (obviously) has to fit within the surface bounds, and
  // we should also minimize the extra pixels redrawn only for
  // alignment's sake.  So we also want
  //
  //  minimize <x',y', w',h'>
  //   0 <= x' <= x
  //   0 <= y' <= y
  //   w <= w' <= sw
  //   h <= h' <= sh
  //
  // This is a messy integer non-linear programming problem, except
  // ... we can assume that ALIGN/BPP is a very small constant.  So,
  // brute force is viable.  The algorithm below will find a
  // solution if one exists, but isn't guaranteed to find the
  // minimum solution.  (For SSE2, ALIGN/BPP = 4, so it'll do at
  // most 64 iterations below).  In what's likely the common case,
  // an already-aligned rectangle, it only needs 1 iteration.
  //
  // Is this alignment worth doing?  Recovering alpha will take work
  // proportional to w*h (assuming alpha recovery computation isn't
  // memory bound).  This analysis can lead to O(w+h) extra work
  // (with small constants).  In exchange, we expect to shave off a
  // ALIGN/BPP constant by using SIMD-ized alpha recovery.  So as
  // w*h diverges from w+h, the win factor approaches ALIGN/BPP.  We
  // only really care about the w*h >> w+h case anyway; others
  // should be fast enough even with the overhead.  (Unless the cost
  // of repainting the expanded rect is high, but in that case
  // SIMD-ized alpha recovery won't make a difference so this code
  // shouldn't be called.)
  //
  mozilla::gfx::IntSize surfaceSize = aSurface->GetSize();
  const int32_t stride = bpp * surfaceSize.width;
  if (stride != aSurface->Stride()) {
    NS_WARNING("Unexpected stride, falling back on slow alpha recovery");
    return aRect;
  }

  const int32_t x = aRect.X(), y = aRect.Y(), w = aRect.Width(),
                h = aRect.Height();
  const int32_t r = x + w;
  const int32_t sw = surfaceSize.width;
  const int32_t strideAlign = ByteAlignment(kByteAlignLog2, stride);

  // The outer two loops below keep the rightmost (|r| above) and
  // bottommost pixels in |aRect| fixed wrt <x,y>, to ensure that we
  // return only a superset of the original rect.  These loops
  // search for an aligned top-left pixel by trying to expand <x,y>
  // left and up by <dx,dy> pixels, respectively.
  //
  // Then if a properly-aligned top-left pixel is found, the
  // innermost loop tries to find an aligned stride by moving the
  // rightmost pixel rightward by dr.
  int32_t dx, dy, dr;
  for (dy = 0; (dy < pixPerAlign) && (y - dy >= 0); ++dy) {
    for (dx = 0; (dx < pixPerAlign) && (x - dx >= 0); ++dx) {
      if (0 != ByteAlignment(kByteAlignLog2, bpp * (x - dx), y - dy, stride)) {
        continue;
      }
      for (dr = 0; (dr < pixPerAlign) && (r + dr <= sw); ++dr) {
        if (strideAlign == ByteAlignment(kByteAlignLog2, bpp * (w + dr + dx))) {
          goto FOUND_SOLUTION;
        }
      }
    }
  }

  // Didn't find a solution.
  return aRect;

FOUND_SOLUTION:
  mozilla::gfx::IntRect solution =
      mozilla::gfx::IntRect(x - dx, y - dy, w + dr + dx, h + dy);
  MOZ_ASSERT(
      mozilla::gfx::IntRect(0, 0, sw, surfaceSize.height).Contains(solution),
      "'Solution' extends outside surface bounds!");
  return solution;
}