Texture.use_alpha?

[tomasz]

Hi,
Is there way to find out if a texture has alpha channel?
Texture class has no such a method. Material method relates to transparency (opacity).
Will material.materialType help me?

Tomasz

[tbd]

@unknownuser said:

Is there way to find out if a texture has alpha channel?

nope

@unknownuser said:

Will material.materialType help me?

nope again - it returns the same value as for a non-alpha texture

you can look for 'tRNS' chunk inside .png files - if present than it contains transparency

[tbd]

here some quick code to check for PNG transparency

class ReadPNG
  def initialize(file)
    @pngfile = File.open(file,"rb+").read
    read_offset(8) #skip header
  end
  
  def transparent?
    ok = true
    while ok
      chunk_size  = read_offset(4).unpack("N")[0]
      section     = read_offset(4)
      case section
      when 'PLTE'
        read_offset(chunk_size)
      when 'IDAT'
        read_offset(chunk_size)
      when 'tRNS'
        read_offset(chunk_size)
        return true
      else
        @offset += chunk_size
      end
      ok = section != "IEND"
      read_offset(4)  # skip CRC
    end
    return false
  end 
  
  def read_offset(length = 1, offset = nil)
    @offset ||= 0
    @offset = offset if offset
    begin
      ret = @pngfile[@offset, length]
    rescue
      p "error reading at #{@offset}"
    end
    @offset += length
    ret
  end  
end

p ReadPNG.new('texture.png').transparent?

[azuby]

Put the file opening and read to the "transparent?" method. Because this way you 1. can close the file from within the instance when you're ready with analyse and 2. can react on changed png file.

azuby

[tbd]

azuby: true. thanks

[tomasz]

Hi TBD,
I am surprised there is no such a method.
The PNG testing will be helpful for me.
Thank you!
Tomasz