CODEWITHSUNDEEP
c#arrayspolygon
zetar
zetar

Reputation: 1233

Drawing a solid polygon in memory (not on the screen)

I need to draw a solid polygon in memory (into a 2D array) and 'fill' the polygon with numeric values (say '3').

I wish to do this in C#.

I'm getting the solid polygons from Shapefiles using Catfood's Shapefile reader (very good).

Any ideas?

I'm attaching a small portion of this 2D array after I've already 'mapped' 16,000 polylines that represent that road network around San Diego (they appear as the number '9'). I wish to do the same thing by uploading a shapefile of solid polygons and 'drawing' with the number '3'. Small section of the 'Terrain Map' in memory

Upvotes: 0

Views: 1498

Answers (4)

Nikola Davidovic
Nikola Davidovic

Reputation: 8656

Since you are drawing in the 2D array of ints (as far as I can see after you have edited your question) it seems like you should implement your own polygon fill that is storing the numbers in the 2D array. For this purpose you could use this post Good algorithm for drawing solid 2-dimensional polygons?

The other solution is a little workaround. You could use the already implemented PolygonFill that fills polygons in the Bitmap. Check this out. I must warn you that getting bitmap pixel is very slow and for that purposes you can use some FastBitmap implementation. Here I will use regular Bitmap.

Bitmap bmp = new Bitmap(0,0,mostRightPoint.X - mostLeftPoint.X, mostUpperPoint.Y - mostLowerPoint.Y);
//this implies that you are on the northern hemisphere
Graphics g = Graphics.FromImage(bmp);
g.Clear(Color.White); //clear the whole bitmap into white color
int [] points = new points[nmbOfPoints];

for(int i = 0;i<nmbOfPoints;i++)
{
      //put the points in the points array
}
g.FillPolygon(Brushes.Black, points);
g.Dispose();

Now you should iterate through the Bitmap, on those places where the pixel is black, put the number 3 in your 2D array, somethink like this.

for(int i = 0;i<bmp.Width;i++)
for(int j = 0;j<bmp.Height;j++)
if(Bitmap.GetPixel(i,j) == Color.Black)
{
     2DArray[mostLeftPoint.X + i, mostLowerPoint.Y + j] = 3;
}

I think you got the sense of the problem and a possible solution.

Upvotes: 0

Meirion Hughes
Meirion Hughes

Reputation: 26398

Go grab the WriteableBitmapEx Extension. That will allow you to draw just about anything you want into the image memory.

Alternatively, you can make a DrawingVisual, draw whatever you want with it, then render to an image target; See: This example

if you want to go via the System.Drawing route; 

using System.Drawing;

Bitmap bmp = new Bitmap(200, 100);
Graphics g = Graphics.FromImage(bmp);
g.DrawLine(Pens.Black, 10, 10, 180, 80);

REF:(Henk Holterman) Drawing C# graphics without using Windows Forms

But I suspect (based on the wording) this is homework, and you've been told to do it manually;

So; for lines you want Bresenham's Line Algorithm, and then fill them with a fill Algorithm; See This

Upvotes: 1

Timothy Shields
Timothy Shields

Reputation: 79441

Create a Bitmap, get a Graphics from it, call FillPolygon on the Graphics.

Upvotes: 1

Keith Nicholas
Keith Nicholas

Reputation: 44288

in C# you can use the Bitmap class to do offscreen drawing of whatever you wish.

Upvotes: 1

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