core/SkMatrixUtils.h

/*
 * Copyright 2013 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkMatrixUtils_DEFINED
#define SkMatrixUtils_DEFINED

#include "SkMatrix.h"

/**
 *  Number of subpixel bits used in skia's bilerp.
 *  See SkBitmapProcState_procs.h and SkBitmapProcState_filter.h
 */
#define kSkSubPixelBitsForBilerp   4

/**
 *  Given a matrix and width/height, return true if the computed dst-rect would
 *  align such that there is a 1-to-1 coorspondence between src and dst pixels.
 *  This can be called by drawing code to see if drawBitmap can be turned into
 *  drawSprite (which is faster).
 *
 *  The src-rect is defined to be { 0, 0, width, height }
 *
 *  The "closeness" test is based on the subpixelBits parameter. Pass 0 for
 *  round-to-nearest behavior (e.g. nearest neighbor sampling). Pass the number
 *  of subpixel-bits to simulate filtering.
 */
bool SkTreatAsSprite(const SkMatrix&, int width, int height,
                     unsigned subpixelBits);

/**
 *  Calls SkTreatAsSprite() with default subpixelBits value to match Skia's
 *  filter-bitmap implementation (i.e. kSkSubPixelBitsForBilerp).
 */
static inline bool SkTreatAsSpriteFilter(const SkMatrix& matrix,
                                         int width, int height) {
    return SkTreatAsSprite(matrix, width, height, kSkSubPixelBitsForBilerp);
}

/** Decomposes the upper-left 2x2 of the matrix into a rotation, followed by a non-uniform scale,
    followed by another rotation. Returns true if successful.
    If the scale factors are uniform, then rotation1 will be 0.
    If there is a reflection, yScale will be negative.
    Returns false if the matrix is degenerate.
    */
bool SkDecomposeUpper2x2(const SkMatrix& matrix,
                         SkScalar* rotation0,
                         SkScalar* xScale, SkScalar* yScale,
                         SkScalar* rotation1);

#endif