Module: Rgltf::AccessorReader

Defined in:
lib/rgltf/accessor_reader.rb

Constant Summary collapse

COMPONENT_TYPES = 
{
  5120 => { sym: :i8, size: 1, pack: 'c', min: -128, max: 127 },
  5121 => { sym: :u8, size: 1, pack: 'C', min: 0, max: 255 },
  5122 => { sym: :i16, size: 2, pack: 's<', min: -32_768, max: 32_767 },
  5123 => { sym: :u16, size: 2, pack: 'S<', min: 0, max: 65_535 },
  5125 => { sym: :u32, size: 4, pack: 'L<', min: 0, max: 4_294_967_295 },
  5126 => { sym: :f32, size: 4, pack: 'e' }
}.freeze
COMPONENTS_BY_SYMBOL = 
COMPONENT_TYPES.to_h { |number, info| [info[:sym], info.merge(number:)] }.freeze
ELEMENT_COUNTS = 
{
  'SCALAR' => 1, 'VEC2' => 2, 'VEC3' => 3, 'VEC4' => 4,
  'MAT2' => 4, 'MAT3' => 9, 'MAT4' => 16
}.freeze
MATRIX_DIMENSIONS = 
{ 'MAT2' => 2, 'MAT3' => 3, 'MAT4' => 4 }.freeze

Class Method Summary collapse

Class Method Details

.align4(value) ⇒ Object 



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# File 'lib/rgltf/accessor_reader.rb', line 138

def align4(value)
  (value + 3) & ~3
end

.append_element(output, bytes, start, type, component_size, storage_size) ⇒ Object 



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# File 'lib/rgltf/accessor_reader.rb', line 84

def append_element(output, bytes, start, type, component_size, storage_size)
  dimension = MATRIX_DIMENSIONS[type]
  unless dimension && component_size < 4
    output << bytes.byteslice(start, storage_size)
    return
  end

  column_size = dimension * component_size
  column_stride = align4(column_size)
  dimension.times { |column| output << bytes.byteslice(start + (column * column_stride), column_size) }
end

.apply_sparse(base, accessor, element_size) ⇒ Object 



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# File 'lib/rgltf/accessor_reader.rb', line 96

def apply_sparse(base, accessor, element_size)
  sparse = accessor.sparse
  indices_info = COMPONENTS_BY_SYMBOL.fetch(sparse.indices.component_type)
  index_bytes = extract(
    sparse.indices.buffer_view,
    sparse.indices.byte_offset,
    sparse.count,
    'SCALAR',
    indices_info[:size],
    indices_info[:size]
  )
  indices = index_bytes.unpack("#{indices_info[:pack]}*")

  component_size = COMPONENTS_BY_SYMBOL.fetch(accessor.component_type)[:size]
  values = extract(
    sparse.values.buffer_view,
    sparse.values.byte_offset,
    sparse.count,
    accessor.type,
    component_size,
    element_size
  )

  output = base.dup
  indices.each_with_index do |target, sparse_index|
    raise FormatError, "sparse accessor index #{target} is out of range" if target >= accessor.count

    output[target * element_size, element_size] = values.byteslice(sparse_index * element_size, element_size)
  end
  output
end

.extract(view, accessor_offset, count, type, component_size, output_element_size) ⇒ Object

Raises:



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# File 'lib/rgltf/accessor_reader.rb', line 60

def extract(view, accessor_offset, count, type, component_size, output_element_size)
  storage_size = storage_element_size(type, component_size)
  stride = view.byte_stride || storage_size
  start = view.byte_offset + accessor_offset
  required = count.zero? ? 0 : (stride * (count - 1)) + storage_size
  if accessor_offset + required > view.byte_length
    raise FormatError, "accessor data exceeds bufferView #{view.index}"
  end

  bytes = view.buffer.bytes
  raise FormatError, "bufferView #{view.index} exceeds its buffer" if start + required > bytes.bytesize

  if stride == output_element_size && storage_size == output_element_size
    return bytes.byteslice(start, output_element_size * count).dup
  end

  output = String.new(capacity: output_element_size * count, encoding: Encoding::BINARY)
  count.times do |element_index|
    element_start = start + (element_index * stride)
    append_element(output, bytes, element_start, type, component_size, storage_size)
  end
  output
end

.normalize(value, type) ⇒ Object 



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# File 'lib/rgltf/accessor_reader.rb', line 128

def normalize(value, type)
  case type
  when :i8 then [value / 127.0, -1.0].max
  when :u8 then value / 255.0
  when :i16 then [value / 32_767.0, -1.0].max
  when :u16 then value / 65_535.0
  else value
  end
end

.packed(accessor) ⇒ Object 



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# File 'lib/rgltf/accessor_reader.rb', line 22

def packed(accessor)
  info = COMPONENTS_BY_SYMBOL.fetch(accessor.component_type)
  count = ELEMENT_COUNTS.fetch(accessor.type)
  element_size = info[:size] * count
  base = if accessor.buffer_view
           extract(
             accessor.buffer_view,
             accessor.byte_offset,
             accessor.count,
             accessor.type,
             info[:size],
             element_size
           )
         else
           "\0".b * (element_size * accessor.count)
         end

  return base.freeze unless accessor.sparse

  apply_sparse(base, accessor, element_size).freeze
end

.storage_element_size(type, component_size) ⇒ Object 



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# File 'lib/rgltf/accessor_reader.rb', line 52

def storage_element_size(type, component_size)
  dimension = MATRIX_DIMENSIONS[type]
  return ELEMENT_COUNTS.fetch(type) * component_size unless dimension && component_size < 4

  aligned_column_size = align4(dimension * component_size)
  aligned_column_size * dimension
end

.unpack(accessor, bytes) ⇒ Object 



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# File 'lib/rgltf/accessor_reader.rb', line 44

def unpack(accessor, bytes)
  info = COMPONENTS_BY_SYMBOL.fetch(accessor.component_type)
  values = bytes.unpack("#{info[:pack]}*")
  values.map! { |value| normalize(value, accessor.component_type) } if accessor.normalized
  count = ELEMENT_COUNTS.fetch(accessor.type)
  count == 1 ? values : values.each_slice(count).to_a
end