bool DisplayListBoundsCalculator::paint_nops_on_transparency()

in display_list/display_list_utils.cc [616:690]

• 47 lines of code
• 35 McCabe index (conditional complexity)

bool DisplayListBoundsCalculator::paint_nops_on_transparency() {
  // SkImageFilter::canComputeFastBounds tests for transparency behavior
  // This test assumes that the blend mode checked down below will
  // NOP on transparent black.
  if (image_filter_ && !image_filter_->canComputeFastBounds()) {
    return false;
  }

  // We filter the transparent black that is used for the background of a
  // saveLayer and make sure it returns transparent black. If it does, then
  // the color filter will leave all area surrounding the contents of the
  // save layer untouched out to the edge of the output surface.
  // This test assumes that the blend mode checked down below will
  // NOP on transparent black.
  if (color_filter_ &&
      color_filter_->filterColor(SK_ColorTRANSPARENT) != SK_ColorTRANSPARENT) {
    return false;
  }

  if (!blend_mode_) {
    return false;  // can we query other blenders for this?
  }
  // Unusual blendmodes require us to process a saved layer
  // even with operations outisde the clip.
  // For example, DstIn is used by masking layers.
  // https://code.google.com/p/skia/issues/detail?id=1291
  // https://crbug.com/401593
  switch (blend_mode_.value()) {
    // For each of the following transfer modes, if the source
    // alpha is zero (our transparent black), the resulting
    // blended pixel is not necessarily equal to the original
    // destination pixel.
    // Mathematically, any time in the following equations where
    // the result is not d assuming source is 0
    case SkBlendMode::kClear:     // r = 0
    case SkBlendMode::kSrc:       // r = s
    case SkBlendMode::kSrcIn:     // r = s * da
    case SkBlendMode::kDstIn:     // r = d * sa
    case SkBlendMode::kSrcOut:    // r = s * (1-da)
    case SkBlendMode::kDstATop:   // r = d*sa + s*(1-da)
    case SkBlendMode::kModulate:  // r = s*d
      return false;
      break;

    // And in these equations, the result must be d if the
    // source is 0
    case SkBlendMode::kDst:         // r = d
    case SkBlendMode::kSrcOver:     // r = s + (1-sa)*d
    case SkBlendMode::kDstOver:     // r = d + (1-da)*s
    case SkBlendMode::kDstOut:      // r = d * (1-sa)
    case SkBlendMode::kSrcATop:     // r = s*da + d*(1-sa)
    case SkBlendMode::kXor:         // r = s*(1-da) + d*(1-sa)
    case SkBlendMode::kPlus:        // r = min(s + d, 1)
    case SkBlendMode::kScreen:      // r = s + d - s*d
    case SkBlendMode::kOverlay:     // multiply or screen, depending on dest
    case SkBlendMode::kDarken:      // rc = s + d - max(s*da, d*sa),
                                    // ra = kSrcOver
    case SkBlendMode::kLighten:     // rc = s + d - min(s*da, d*sa),
                                    // ra = kSrcOver
    case SkBlendMode::kColorDodge:  // brighten destination to reflect source
    case SkBlendMode::kColorBurn:   // darken destination to reflect source
    case SkBlendMode::kHardLight:   // multiply or screen, depending on source
    case SkBlendMode::kSoftLight:   // lighten or darken, depending on source
    case SkBlendMode::kDifference:  // rc = s + d - 2*(min(s*da, d*sa)),
                                    // ra = kSrcOver
    case SkBlendMode::kExclusion:   // rc = s + d - two(s*d), ra = kSrcOver
    case SkBlendMode::kMultiply:    // r = s*(1-da) + d*(1-sa) + s*d
    case SkBlendMode::kHue:         // ra = kSrcOver
    case SkBlendMode::kSaturation:  // ra = kSrcOver
    case SkBlendMode::kColor:       // ra = kSrcOver
    case SkBlendMode::kLuminosity:  // ra = kSrcOver
      return true;
      break;
  }
}