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package draw
import (
"../structs"
"github.com/fogleman/gg"
"math"
)
// initializePlot generates a new plot and returns the plot context
func initializePlot() *gg.Context {
// Define the image size
const imageWidth = 8192
const imageHeight = 8192
// Initialize the new context
dc := gg.NewContext(imageWidth, imageHeight)
// Set the background black
dc.SetRGB(0, 0, 0)
dc.Clear()
// Invert the Y axis (positive values are on the top and right)
dc.InvertY()
// Set the coordinate midpoint to the middle of the image
dc.Translate(imageWidth/2, imageHeight/2)
return dc
}
// saveImages saves the given context to a png at the given path
func saveImage(dc *gg.Context, path string) {
dc.SavePNG(path)
}
// drawStar draws the given stars to the given context
func drawStar(dc *gg.Context, star structs.Star2D) {
// User the value below to controll how big the stars are overall
var StarScalingFactor float64 = 1
// Default Star Size
S := 2.0
// Calculate the Stars Size according to its Mass (Maximal size = 5)
if star.M < 5e4 {
S = float64(math.Ceil(star.M/4e4) * StarScalingFactor)
} else {
S = 5.0
}
// draw the star / point
dc.DrawPoint(star.C.X/50, star.C.Y/50, S)
dc.Fill()
dc.Stroke()
}
func drawVelocity(dc *gg.Context, star structs.Star2D) {
// scaling factor for a better view of the velocity difference
// Use this value to control how long the vectors are drawn
var scalingFactor float64 = 25
// Move the "cursor" to the start position of the vector
dc.MoveTo(star.C.X/50, star.C.Y/50)
// calculate the length of the vector
vecLength := star.V.GetLength()
// Use a sigmoid function to generate useful values for coloring the vectors according to their
// strength
var val = 1.0 / (1.0 + math.Exp(-vecLength*scalingFactor/2))
// Set the color to a blue / red
dc.SetRGB(val, 0, 1-val)
// calculate the direction vector
FUnit := (&star.V).Divide(vecLength)
// set end-position of the vector line
dc.LineTo(star.C.X/50+(FUnit.X*scalingFactor), star.C.Y/50+(FUnit.Y*scalingFactor))
// set line width
dc.SetLineWidth(3)
// And finally: DRAW (stroke) the vector
dc.Stroke()
}
// drawStars draws all the stars in the given slice to the given context
func drawStars(dc *gg.Context, slice []structs.Star2D) {
// draw all the velocity in the given slice
for _, star := range slice {
drawVelocity(dc, star)
}
dc.SetRGB(1, 1, 1)
// draw all the stars in the given slice
for _, star := range slice {
drawStar(dc, star)
}
}
// Slice draws the stars and the forces acting on them and saves the result to the given path
func Slice(slice []structs.Star2D, path string) {
// initialize the plot
dc := initializePlot()
// draw all the stars in the given slice
drawStars(dc, slice)
dc.SetRGB(1, 1, 1)
// drawing the 4 big stars as bigger white dots
//dc.DrawCircle(600, 600, 5)
//dc.DrawCircle(-600, 600, 5)
//dc.DrawCircle(-600, 0, 5)
//dc.DrawCircle(600, -600, 5)
dc.Fill()
// save the plot to the given path
saveImage(dc, path)
}
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