Module: Gsplat::Backend::RubyTileCompositor

Defined in:
lib/gsplat/backend/ruby/tile_compositor.rb

Overview

Vectorized per-tile alpha compositing kernel.

Class Method Summary collapse

Class Method Details

.composite(means2d, conics, colors, opacities, flatten_ids, range_start, range_end, pixels_x, pixels_y) ⇒ Object

rubocop:disable Metrics/AbcSize, Metrics/ParameterLists



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# File 'lib/gsplat/backend/ruby/tile_compositor.rb', line 10

def composite(means2d, conics, colors, opacities, flatten_ids, range_start, range_end,
              pixels_x, pixels_y)
  # rubocop:enable Metrics/ParameterLists
  pixel_count = pixels_x.size
  channel_count = colors.shape[-1]
  transmittance = means2d.class.ones(pixel_count)
  composited = means2d.class.zeros(pixel_count, channel_count)
  last_ids = Numo::Int32.zeros(pixel_count)
  active = Numo::Bit.ones(pixel_count)
  (range_start...range_end).each do |intersection_index|
    gaussian_index = flatten_ids[intersection_index]
    delta_x = means2d[gaussian_index, 0] - pixels_x
    delta_y = means2d[gaussian_index, 1] - pixels_y
    sigma = (0.5 * (
      (conics[gaussian_index, 0] * (delta_x**2)) +
      (conics[gaussian_index, 2] * (delta_y**2))
    )) + (conics[gaussian_index, 1] * delta_x * delta_y)
    alpha = opacities[gaussian_index] * Numo::NMath.exp(-sigma)
    above_clamp = alpha.gt(RubyAccumulate::ALPHA_CLAMP)
    alpha[above_clamp] = RubyAccumulate::ALPHA_CLAMP if above_clamp.any?
    candidate = active & sigma.ge(0) & alpha.ge(RubyAccumulate::ALPHA_SKIP)
    next_transmittance = transmittance * (1 - alpha)
    accepted = candidate & next_transmittance.gt(RubyAccumulate::TRANSMITTANCE_STOP)
    if accepted.any?
      contribution = means2d.class.zeros(pixel_count)
      contribution[accepted] = (alpha * transmittance)[accepted]
      composited += contribution.reshape(pixel_count, 1) *
                    colors[gaussian_index, true].reshape(1, channel_count)
      transmittance[accepted] = next_transmittance[accepted]
      last_ids[accepted] = intersection_index
    end
    terminating = candidate & next_transmittance.le(RubyAccumulate::TRANSMITTANCE_STOP)
    active[terminating] = 0 if terminating.any?
    break unless active.any?
  end
  [composited, transmittance, last_ids]
end