gradient.ps1

[CmdletBinding(DefaultParameterSetName = 'FixedG')]
param(
    [Parameter(ParameterSetName = 'FixedR', Mandatory)]
    [ValidateRange(0, 255)]
    $fixedR,

    [Parameter(ParameterSetName = 'FixedG')]
    [ValidateRange(0, 255)]
    [int]$fixedG = 105,

    [Parameter(ParameterSetName = 'FixedB', Mandatory)]
    [ValidateRange(0, 255)]
    [int]$fixedB,
    
    [char]$Character = [char]" ")

$h = [Console]::WindowHeight - 4 # Use most of the vertical
$w = [Console]::BufferWidth - 2 # and even more of the horizontal

$e = [string][char]0x1b

$sb = [System.Text.StringBuilder]::new()
$null = $sb.AppendLine("$e[mPrinting 24bit gradient with ANSI sequences using powershell")

# Run cycles. Use {ESC [ 48 ; 2 ; R ; G ; B m} to set background
# RGB color of the next printing character (space in this example)
for ($l = 0; $l -lt $h; $l++)
{
    $c1 = [int]($l*255/$h)
    $null = $sb.Append("$e[m ")

    for ($c = 0; $c -lt $w; $c++)
    {
        $c2 = [int]($c*255/$w)
        switch ($PSCmdlet.ParameterSetName)
        {
        'FixedR' { $null = $sb.Append("$e[48;2;$fixedR;$c1;${c2}m$Character"); break; }
        'FixedG' { $null = $sb.Append("$e[48;2;$c1;$fixedG;${c2}m$Character"); break; }
        'FixedB' { $null = $sb.Append("$e[48;2;$c2;$c1;${fixedB}m$Character"); break; }
        }
    }
    $null = $sb.Append("$e[m ")
}

$null = $sb.Append( "Gradient done")
$sb.ToString()