• How to initial an array with default value of n zero?
    • Init(repeating: #Value, count: #n)
  • How to get bitmap data of UIImage? How to get color of specific pixel?
    • Let width = image.size.width
    • Let height = image.size.height
    • Let provider = image.cgImage!.dataProvider
    • Let providerData = provider!.data
    • Let data = CFDataGetBytePtr(providerData)
    • Let numberOfComponents = 4
    • Let offset = (width * y + x) * numberOfComponents
    • Let a = data![offset]
    • Let r = data![offset + 1]
    • Let g = data![offset + 2]
    • Let b = data![offset + 3]
  • How to change 0xff to 0xff00?
    • First, from 0xff -> 0xff0, value is multiplied by 0x10 or 16
    • So, from 0xff -> 0xff00, value is multiplied by 0x100
  • How to loop from high value down to small value? How to custom loop start value and end value and step?
    • For i in stride(#startValue, through: #endValue, by: #offset)
  • 1s = ?ms
    • 1000
  • How to change a color image to gray image?
    • Use cifilter