Step by Step solution about How to resolve the algorithm Pentagram step by step in the Go programming language

1. Introduction

• The provided Go code draws a pentagram, a five-pointed star-like figure, and saves it as a PNG image.

2. Pentagram Function

• This function takes three parameters:
  • x, y: the coordinates of the center of the pentagram.
  • r: the radius of the circle that circumscribes the pentagram.
• It returns a slice of five gg.Points, representing the vertices of the pentagram.
• The function calculates the coordinates of each vertex by using trigonometric functions.

3. main Function

• This function is the entry point of the program.
• It calls the Pentagram function to generate the vertices of the pentagram.
• It creates a new gg.Context (drawing context) and sets its background color to white.
• It iterates through the vertices and draws lines connecting them.
• It sets the fill color to cornflower blue and fills the shape using the winding rule.
• It sets the stroke color to black and draws a thick border around the shape.
• Finally, it saves the drawing as a PNG image with the filename "pentagram.png".

4. gg (GraphicsMagick) Library

• The code uses the gg (GraphicsMagick) library, which provides a simple and efficient API for drawing 2D graphics.
• gg.Context represents a drawing context, and methods like SetRGB, Clear, LineTo, FillPreserve, and Stroke are used to draw the pentagram.

package main

import (
    "github.com/fogleman/gg"
    "math"
)

func Pentagram(x, y, r float64) []gg.Point {
    points := make([]gg.Point, 5)
    for i := 0; i < 5; i++ {
        fi := float64(i)
        angle := 2*math.Pi*fi/5 - math.Pi/2
        points[i] = gg.Point{x + r*math.Cos(angle), y + r*math.Sin(angle)}
    }
    return points
}

func main() {
    points := Pentagram(320, 320, 250)
    dc := gg.NewContext(640, 640)
    dc.SetRGB(1, 1, 1) // White
    dc.Clear()
    for i := 0; i <= 5; i++ {
        index := (i * 2) % 5
        p := points[index]
        dc.LineTo(p.X, p.Y)
    }
    dc.SetHexColor("#6495ED") // Cornflower Blue
    dc.SetFillRule(gg.FillRuleWinding)
    dc.FillPreserve()
    dc.SetRGB(0, 0, 0) // Black
    dc.SetLineWidth(5)
    dc.Stroke()
    dc.SavePNG("pentagram.png")
}