fadeColor

fadeColor is a helper function to make smooth color transitions suitable to fading effects.

function fadeColor(
  time, prologue, attack, sustain, decay, epilogue,
  fade_in_r, fade_in_g, fade_in_b,
  fade_out_r, fade_out_g, fade_out_b
)
  -- [0, prologue)
  if time < prologue then
    return
      fade_in_r,
      fade_in_g,
      fade_in_b,
      255
  end
 
  -- (prologue, prologue + attack]
  time = time - prologue
  if time < attack then
    return
      fade_in_r,
      fade_in_g,
      fade_in_b,
      ( math.cos( time / attack * math.pi ) + 1 ) / 2 * 255
  end
 
  -- (prologue + attack, prologue + attack + sustain]
  time = time - attack
  if time < sustain then
    return
      fade_in_r,
      fade_in_g,
      fade_in_b,
      0
  end
 
  -- (prologue + attack + sustain, prologue + attack + sustain + decay]
  time = time - sustain
  if time < decay then
    return
      fade_out_r,
      fade_out_g,
      fade_out_b,
      255 - ( ( math.cos( time / decay * math.pi ) + 1 ) / 2 * 255 )
  end
 
  -- (prologue + attack + sustain + decay, prologue + attack + sustain + decay + epilogue]
  time = time - decay
  if time < epilogue then
    return
      fade_out_r,
      fade_out_g,
      fade_out_b,
      255
  end
 
  -- End of fading, return all nils.
end

Arguments:

• time is the 0-based time to evaluate the color.
• prologue is how much time the resulting color will be equal to the fully opaque fade_in color.
• attack is how much time it takes to go from fully opaque fade_in to fully transparent fade_in.
• sustain is how much time the color resulting color will be the fully transparent fade_in.
• decay is how much time it takes to go from fully transparent fade_out color to fully opaque fade_out color.
• epilogue is how much time the resulting color will be equal to the fully opaque fade_out color.
• fade_in_[rgb] are the components of the fade_in color.
• fade_out_[rgb] are the components of the fade_out color.

The function returns nil when the transitions are over. The transitions from fully opaque to fully transparent are evaluated with the cosine function to make it smooth. Usage:

-- This is part of your update loop, draw whatever you need here.
 
-- Evaluate a color that makes the screen fade from white and then to black.
local r, g, b, a = fadeColor(
  dt,
  2,   -- Two seconds opaque white.
  2,   -- Two seconds to make it transparent.
  3,   -- Three seconds transparent.
  2,   -- Two seconds to go to opaque black.
  0,   -- Zero seconds opaque black.
  255, 255, 255, -- White.
  0, 0, 0 -- Black.
)
 
-- If the fading is done, better go do something else...
if not r then
  -- Change state to something else...
  return
end
 
-- Fill the entire screen with the resulting color.
love.graphics.setColor( r, g, b, a )
love.graphics.rectangle( 'fill', 0, 0, love.graphics.getWidth(), love.graphics.getHeight() )