--[[
barGraphValue: the current bargraph value [0..100]
imageHeight: the height of the imageHeight
pixelHeight: the amount of pixels used (e.g. without transparency)
return:
textureRectangle: the textureRectangle for the bargraph
--]]
function roadbookMiniBarGraphTextureRectangle(barGraphValue, imageHeight, pixelHeight)
    u = 0.0
    v = 0.0
    width = 1.0
    height = 1.0

    if barGraphValue >= 0 and barGraphValue <= 100 then
        v = 0.0 - ( barGraphValue / 100.0 ) * ( pixelHeight / imageHeight )
    end

    return { x=u, y=v, z=width, w=height }
end

--[[
alphaMaskOffset: alpha mask offset in the range of [0..1]
rotation: current compass rotation
startValue: start value of fading
endValue: end value of fading
return:
opacity value
--]]
function roadbookMINICardinalOpacityValue( alphaMaskOffset, rotation, startValue, endValue )
    if alphaMaskOffset <= 0.0 then
        return 1.0
    end

    startValue = math.fmod(startValue + rotation + 1.0, 1.0)
    endValue = math.fmod(endValue + rotation + 1.0, 1.0)

    if endValue < startValue then
        -- we animate from -something to + something, so lets clamp to 0.0 as fadeout starts here...
        startValue = 0.0
    end

    delta = endValue - startValue

    if alphaMaskOffset <= startValue then
        return 1.0
    elseif alphaMaskOffset >= endValue then
        return 0.0
    else
        return 1.0 - ( alphaMaskOffset - startValue ) / delta
    end
end

--[[
alphaMaskOffset: alpha mask offset in the range of [0..1]
rotation: current compass rotation
opacity: widget opacity
return:
opacity values for N, E, S, W
--]]
function roadbookMINICardinalOpacity( alphaMaskOffset, rotation, opacity )
    rotation = math.fmod(rotation + 1.0, 1.0)
    alphaMaskOffset = math.max(alphaMaskOffset, 0.0)
    e = roadbookMINICardinalOpacityValue(alphaMaskOffset, rotation, 0.0, 0.25) * opacity
    s = roadbookMINICardinalOpacityValue(alphaMaskOffset, rotation, 0.25, 0.5) * opacity
    w = roadbookMINICardinalOpacityValue(alphaMaskOffset, rotation, 0.5, 0.75) * opacity
    n = roadbookMINICardinalOpacityValue(alphaMaskOffset, rotation, 0.75, 0.99) * opacity

    return n, e, s, w
end

--[[
compassFadeOutValue: current value of a fading out compass
opacity: widget opacity
return:
opacity of the compass
--]]
function roadbookMINICompassOpacity( compassFadeOutValue, targetOpacity )
    compassOpacity = targetOpacity

    if compassFadeOutValue > 0.0 then
        compassOpacity = 1.0
    end

    return compassOpacity
end