better-tee/Assets/Drawing/Scripts/PencilTool.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PencilTool : DrawTool
{
    public Color selectedColor = Color.black;
    public float size = 1f;
    
    protected Color[] colors;
    
    private Vector2Int? previousPixel;
    private Vector2Int? pixel;

    protected Vector2Int? GetPixelAtScreenPosition(Vector2 screenPosition) {
        Vector2 worldPoint = Camera.main.ScreenToWorldPoint(screenPosition);
        if(frame.Bounds.Contains(worldPoint)) {
            Vector2 normalized = Rect.PointToNormalized(frame.Bounds, worldPoint);
            Vector2Int result = new Vector2Int(Mathf.FloorToInt(normalized.x * frame.resolution.x), Mathf.FloorToInt(normalized.y * frame.resolution.y));
            return result;
        }
        return null;
    }

    protected override void Start() {
        base.Start();
        colors = frame.GetPixels();

        Input.simulateMouseWithTouches = false;
    }

    protected void Update() {
        bool hasChanged = false;

        // Touch
        foreach(Touch t in Input.touches) {
            pixel = GetPixelAtScreenPosition(t.position);
            previousPixel = GetPixelAtScreenPosition(t.position - t.deltaPosition);
            if(pixel.HasValue) {
                if(previousPixel.HasValue) {
                    DrawBresenhamsThickLine(pixel.Value, previousPixel.Value, size, selectedColor);
                }
                else {
                    DrawFilledCircle(pixel.Value, size, selectedColor);
                }
            }
            hasChanged = true;
        }

        // Mouse
        previousPixel = pixel;
        if(Input.GetMouseButton(0)) {
            pixel = GetPixelAtScreenPosition(Input.mousePosition);
            if(pixel.HasValue) {
                if(previousPixel.HasValue) {
                    DrawBresenhamsThickLine(previousPixel.Value, pixel.Value, size, selectedColor);
                }
                else {
                    DrawFilledCircle(pixel.Value, size, selectedColor);
                }
            }
            hasChanged = true;
        }
        else {
            pixel = null;
        }

        if(hasChanged) {
            frame.SetPixels(colors);
        }
    }

    protected void DrawPixel(int x, int y, Color color) {
        if(x < 0 || x >= frame.resolution.x || y < 0 || y >= frame.resolution.y) return;
        colors[x + y*frame.resolution.x] = color;
    }

    protected void DrawCircleEightPoints(Vector2Int center, int x_radius, int y_radius, Color color) {
        DrawPixel(center.x+x_radius, center.y+y_radius, color); 
        DrawPixel(center.x-x_radius, center.y+y_radius, color); 
        DrawPixel(center.x+x_radius, center.y-y_radius, color); 
        DrawPixel(center.x-x_radius, center.y-y_radius, color); 
        DrawPixel(center.x+y_radius, center.y+x_radius, color); 
        DrawPixel(center.x-y_radius, center.y+x_radius, color); 
        DrawPixel(center.x+y_radius, center.y-x_radius, color); 
        DrawPixel(center.x-y_radius, center.y-x_radius, color); 
    }

    // No idea on how does it work
    // https://www.geeksforgeeks.org/bresenhams-circle-drawing-algorithm/
    protected void DrawBresenhamEmptyCircle(Vector2Int center, int radius, Color color) {
        int x = 0;
        int y = radius;
        int d = 3 - 2 * radius;
        DrawCircleEightPoints(center, x, y, color);
        while(y >= x) {
            x++;
            if(d > 0) {
                y--;
                d = d + 4 * (x - y) + 10;
            }
            else {
                d = d + 4 * x + 6;
            }
            DrawCircleEightPoints(center, x, y, color);
        }
    }

    protected void DrawFilledCircle(Vector2Int center, float radius, Color color) {
        int x_start = Mathf.CeilToInt((float)center.x - radius);
        int x_end = Mathf.CeilToInt((float)center.x + radius);
        int y_start = Mathf.CeilToInt((float)center.y - radius);
        int y_end = Mathf.CeilToInt((float)center.y + radius);
        for(int x = x_start; x < x_end; x++) {
            for(int y = y_start; y < y_end; y++) {
                if(Vector2Int.Distance(new Vector2Int(x, y), center) < radius) {
                    DrawPixel(x, y, color);
                }
            }
        }
    }

    // http://www.roguebasin.com/index.php?title=Bresenham%27s_Line_Algorithm
    protected void DrawBresenhamsThickLine(Vector2Int start, Vector2Int end, float radius, Color color) {
        int start_x = start.x, start_y = start.y, end_x = end.x, end_y = end.y;
        bool steep = Mathf.Abs(end_y - start_y) > Mathf.Abs(end_x - start_x);
        if (steep) {
            Utils.Swap<int>(ref start_x, ref start_y);
            Utils.Swap<int>(ref end_x, ref end_y); 
        }
        if (start_x > end_x) {
            Utils.Swap<int>(ref start_x, ref end_x);
            Utils.Swap<int>(ref start_y, ref end_y); 
        }
        int dX = (end_x - start_x), dY = Mathf.Abs(end_y - start_y), err = (dX / 2), ystep = (start_y < end_y ? 1 : -1), y = start_y;

        for (int x = start_x; x <= end_x; ++x)
        {
            if(steep) {
                DrawFilledCircle(new Vector2Int(y, x), radius, color);
            }
            else {
                DrawFilledCircle(new Vector2Int(x, y), radius, color);
            }
            err = err - dY;
            if (err < 0) { y += ystep;  err += dX; }
        }
    }

    protected void Apply() {
    }
}