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copied!<p>Something like this should do the trick</p> <pre><code>public class EllipseDrawer { private static PointF GetEllipsePointFromX(float x, float a, float b) { //(x/a)^2 + (y/b)^2 = 1 //(y/b)^2 = 1 - (x/a)^2 //y/b = -sqrt(1 - (x/a)^2) --Neg root for upper portion of the plane //y = b*-sqrt(1 - (x/a)^2) return new PointF(x, b * -(float)Math.Sqrt(1 - (x * x / a / a))); } public static void Ellipse(bool[,] pixels, Rectangle area) { DrawEllipse(pixels, area, false); } public static void FillEllipse(bool[,] pixels, Rectangle area) { DrawEllipse(pixels, area, true); } private static void DrawEllipse(bool[,] pixels, Rectangle area, bool fill) { // Get the size of the matrix var matrixWidth = pixels.GetLength(0); var matrixHeight = pixels.GetLength(1); var offsetY = area.Top; var offsetX = area.Left; // Figure out how big the ellipse is var ellipseWidth = (float)area.Width; var ellipseHeight = (float)area.Height; // Figure out the radiuses of the ellipses var radiusX = ellipseWidth / 2; var radiusY = ellipseHeight / 2; //Keep track of the previous y position var prevY = 0; var firstRun = true; // Loop through the points in the matrix for (var x = 0; x <= radiusX; ++x) { var xPos = x + offsetX; var rxPos = (int)ellipseWidth - x - 1 + offsetX; if (xPos < 0 || rxPos < xPos || xPos >= matrixWidth) { continue; } var pointOnEllipseBoundCorrespondingToXMatrixPosition = GetEllipsePointFromX(x - radiusX, radiusX, radiusY); var y = (int) Math.Floor(pointOnEllipseBoundCorrespondingToXMatrixPosition.Y + (int)radiusY); var yPos = y + offsetY; var ryPos = (int)ellipseHeight - y - 1 + offsetY; if (yPos >= 0) { if (xPos > -1 && xPos < matrixWidth && yPos > -1 && yPos < matrixHeight) { pixels[xPos, yPos] = true; } if(xPos > -1 && xPos < matrixWidth && ryPos > -1 && ryPos < matrixHeight) { pixels[xPos, ryPos] = true; } if (rxPos > -1 && rxPos < matrixWidth) { if (yPos > -1 && yPos < matrixHeight) { pixels[rxPos, yPos] = true; } if (ryPos > -1 && ryPos < matrixHeight) { pixels[rxPos, ryPos] = true; } } } //While there's a >1 jump in y, fill in the gap (assumes that this is not the first time we've tracked y, x != 0) for (var j = prevY - 1; !firstRun && j > y - 1 && y > 0; --j) { var jPos = j + offsetY; var rjPos = (int)ellipseHeight - j - 1 + offsetY; if(jPos == rjPos - 1) { continue; } if(jPos > -1 && jPos < matrixHeight) { pixels[xPos, jPos] = true; } if(rjPos > -1 && rjPos < matrixHeight) { pixels[xPos, rjPos] = true; } if (rxPos > -1 && rxPos < matrixWidth) { if(jPos > -1 && jPos < matrixHeight) { pixels[rxPos, jPos] = true; } if(rjPos > -1 && rjPos < matrixHeight) { pixels[rxPos, rjPos] = true; } } } firstRun = false; prevY = y; var countTarget = radiusY - y; for (var count = 0; fill && count < countTarget; ++count) { ++yPos; --ryPos; // Set all four points in the matrix we just learned about // also, make the indication that for the rest of this row, we need to fill the body of the ellipse if(yPos > -1 && yPos < matrixHeight) { pixels[xPos, yPos] = true; } if(ryPos > -1 && ryPos < matrixHeight) { pixels[xPos, ryPos] = true; } if (rxPos > -1 && rxPos < matrixWidth) { if(yPos > -1 && yPos < matrixHeight) { pixels[rxPos, yPos] = true; } if(ryPos > -1 && ryPos < matrixHeight) { pixels[rxPos, ryPos] = true; } } } } } } </code></pre>

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