Terminal.Gui/UnitTests/Drawing/SixelEncoderTests.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Color = Terminal.Gui.Color;

namespace UnitTests.Drawing;

public class SixelEncoderTests
{

    [Fact]
    public void EncodeSixel_RedSquare12x12_ReturnsExpectedSixel ()
    {

        var expected = "\u001bP" + // Start sixel sequence
                            "0;0;0" + // Defaults for aspect ratio and grid size
                            "q" + // Signals beginning of sixel image data
                            "\"1;1;12;2" + // no scaling factors (1x1) and filling 12px width with 2 'sixel' height = 12 px high

                            /*
                             * Definition of the color palette
                             */
                            "#0;2;100;0;0" + // Red color definition in the format "#<index>;<type>;<R>;<G>;<B>" - 2 means RGB.  The values range 0 to 100

                            /*
                             * Start of the Pixel data
                             *   We draw 6 rows at once, so end up with 2 'lines'
                             *   Both are basically the same and terminate with dollar hyphen (except last row)
                             *   Format is:
                             *       #0 (selects to use color palette index 0 i.e. red)
                             *       !12 (repeat next byte 12 times i.e. the whole length of the row)
                             *       ~ (the byte 111111 i.e. fill completely)
                             *       $ (return to start of line)
                             *       - (move down to next line)
                             */
                            "#0!12~$-" +
                            "#0!12~$" + // Next 6 rows of red pixels

                            "\u001b\\"; // End sixel sequence

        // Arrange: Create a 12x12 bitmap filled with red
        var pixels = new Color [12, 12];
        for (int x = 0; x < 12; x++)
        {
            for (int y = 0; y < 12; y++)
            {
                pixels [x, y] = new Color(255,0,0);
            }
        }

        // Act: Encode the image
        var encoder = new SixelEncoder (); // Assuming SixelEncoder is the class that contains the EncodeSixel method
        string result = encoder.EncodeSixel (pixels);

        // Since image is only red we should only have 1 color definition
        Color c1 = Assert.Single (encoder.Quantizer.Palette);

        Assert.Equal (new Color(255,0,0),c1);

        Assert.Equal (expected, result);
    }

    [Fact]
    public void EncodeSixel_12x12GridPattern3x3_ReturnsExpectedSixel ()
    {
        /*
        *      Each block is a 3x3 square, alternating black and white.
        *      The pattern alternates between rows, creating a checkerboard.
        *      We have 4 blocks per row, and this repeats over 12x12 pixels.
         
            ███...███...
            ███...███...
            ███...███...
            ...███...███
            ...███...███
            ...███...███
            ███...███...
            ███...███...
            ███...███...
            ...███...███
            ...███...███
            ...███...███

                Because we are dealing with sixels (drawing 6 rows at once) we will
                see 2 bands being drawn. We will also see how we have to 'go back over'
                the current line after drawing the black (so we can draw the white).

        */


        var expected = "\u001bP" + // Start sixel sequence
                       "0;0;0" +  // Defaults for aspect ratio and grid size
                       "q" +      // Signals beginning of sixel image data
                       "\"1;1;12;2" + // no scaling factors (1x1) and filling 12px width with 2 'sixel' height = 12 px high

                       /*
                        * Definition of the color palette
                        */
                       "#0;2;0;0;0" +   // Black color definition (index 0: RGB 0,0,0)
                       "#1;2;100;100;100" + // White color definition (index 1: RGB 100,100,100)

                       /*
                        * Start of the Pixel data
                        *
                        * Lets consider only the first 6 pixel (vertically).  We have to fill the top 3 black and bottom 3 white.
                        * So we need to select black and fill 000111.  To convert this into a character we must +63 and convert to ASCII
                        * Later on we will also need to select white and fill the inverse i.e. 111000.
                        *
                        *     111000 (binary) → w (ASCII 119).
                        *     000111 (binary) → F (ASCII 70).
                        *
                        * Therefore the lines become
                        *
                        *   #0 (Select black)
                        *   FFF (fill first 3 pixels horizontally - and top half of band black)
                        *   www (fill next 3 pixels horizontally - bottom half of band black)
                        *   FFFwww (as above to finish the line
                        *
                        * Next we must go back and fill the white (on the same band)
                        *   #1 (Select white)
                        *   
                        */
                       "#0FFFwwwFFFwww$" +   // First pass of top band (Filling black)
                       "#1wwwFFFwwwFFF$-" +     // Second pass of top band (Filling white)

                       // Sequence repeats exactly the same because top band is actually identical pixels to bottom band
                       "#0FFFwwwFFFwww$" +   // First pass of bottom band (Filling white)
                       "#1wwwFFFwwwFFF$" +     // Second pass of bottom band (Filling black)

                       "\u001b\\";                   // End sixel sequence

        // Arrange: Create a 12x12 bitmap with a 3x3 checkerboard pattern
        var pixels = new Color [12, 12];
        for (int y = 0; y < 12; y++)
        {
            for (int x = 0; x < 12; x++)
            {
                // Create a 3x3 checkerboard by alternating the color based on pixel coordinates
                if (((x / 3) + (y / 3)) % 2 == 0)
                {
                    pixels [x, y] = new Color (0, 0, 0); // Black
                }
                else
                {
                    pixels [x, y] = new Color (255, 255, 255); // White
                }
            }
        }

        // Act: Encode the image
        var encoder = new SixelEncoder (); // Assuming SixelEncoder is the class that contains the EncodeSixel method
        string result = encoder.EncodeSixel (pixels);

        // We should have only black and white in the palette
        Assert.Equal (2, encoder.Quantizer.Palette.Count);
        Color black = encoder.Quantizer.Palette.ElementAt (0);
        Color white = encoder.Quantizer.Palette.ElementAt(1);

        Assert.Equal (new Color (0, 0, 0), black);
        Assert.Equal (new Color (255, 255, 255), white);

        // Compare the generated SIXEL string with the expected one
        Assert.Equal (expected, result);
    }
}