All cases covered Bresenham's line-algorithm
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public void line(int x,int y,int x2, int y2, int color) {
int w = x2 - x ;
int h = y2 - y ;
int dx1 = 0, dy1 = 0, dx2 = 0, dy2 = 0 ;
if (w<0) dx1 = -1 ; else if (w>0) dx1 = 1 ;
if (h<0) dy1 = -1 ; else if (h>0) dy1 = 1 ;
if (w<0) dx2 = -1 ; else if (w>0) dx2 = 1 ;
int longest = Math.Abs(w) ;
int shortest = Math.Abs(h) ;
if (!(longest>shortest)) {
longest = Math.Abs(h) ;
shortest = Math.Abs(w) ;
if (h<0) dy2 = -1 ; else if (h>0) dy2 = 1 ;
dx2 = 0 ;
}
int numerator = longest >> 1 ;
for (int i=0;i<=longest;i++) {
putpixel(x,y,color) ;
numerator += shortest ;
if (!(numerator<longest)) {
numerator -= longest ;
x += dx1 ;
y += dy1 ;
} else {
x += dx2 ;
y += dy2 ;
}
}
}
Author by
Frank Lioty
Updated on August 06, 2022Comments
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Frank Lioty over 1 year
I need to check all pixels in a line, so I'm using Bresenham's algorithm to access each pixel in it. In particular I need to check if all pixels are located on valid pixel of a bitmap. This is the code:
private void Bresenham(Point p1, Point p2, ref List<Point> track) { int dx = p2.X - p1.X; int dy = p2.Y - p1.Y; int swaps = 0; if (dy > dx) { Swap(ref dx, ref dy); swaps = 1; } int a = Math.Abs(dy); int b = -Math.Abs(dx); double d = 2*a + b; int x = p1.X; int y = p1.Y; color_track = Color.Blue; Check_Pixel(ref area, new Point(x,y)); track.Clear(); track.Add(new Point(x, y)); int s = 1; int q = 1; if (p1.X > p2.X) q = -1; if (p1.Y > p2.Y) s = -1; for(int k = 0; k < dx; k++) { if (d >= 0) { d = 2*(a+b) + d; y = y + s; x = x + q; } else { if (swaps == 1) y = y + s; else x = x + q; d = 2 * a + d; } Check_Pixel(ref area, new Point(x, y)); track.Add(new Point(x, y)); } } private void Swap(ref int x, ref int y) { int temp = x; x = y; y = temp; }
Check_Pixel is used to check if the line pixel is on a valid bitmap one. I add the pixel founded to a
List<Point>
to render point by point his element and be sureBresenham
checks the correct pixels (it does). The problem is that my algorithm doesn't cover all the cases but about 50% of them.P.S: my coordinates system origin is on the left-upper corner (x grows left to right, y up to down)
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MadLabMatLab over 9 yearsFinally, a working C# version of Bresenham's that actually covers all octets and doesn't invert the point half the time!