# Thread: Triangle - scanline filling

1. ## Triangle - scanline filling

Hi guys
I've come to a halt, i can't seem to figure out an efficient method of implementing a triangle scan line algorithm or even a messy one that works. So far my function can take 3 points and obtain coordinates needed to connect the points, these coordinates are used for my triangle's edges. Now to use these edges in the scan line algorithm i need to figure out which edge coordinates belong on the left and right. I've managed to get a flat base triangle filled but any other triangle cases just have me stumped for logic :-(

One idea i had was to concatenate the edge lists of 2 smaller sides of a triangle and somehow find which side it belongs to.

Code:
```void Core::drawTriangle(Point a, Point b, Point c)
{
vector<Point> AB;
vector<Point> AC;
vector<Point> BC;

vector<Point> lEdge;
vector<Point> rEdge;

makeLine(a, b, &AB);
makeLine(a, c, &AC);
makeLine(b, c, &BC);

//this works for an equilateral triangle
int i = 0;
for (int y = a.y; y < b.y; y++)
{
for (int x = AC[i].x; x < AB[i].x; x++)
{
putpixel(x, y, 0, 200, 0, 0);
}
i++;
}
}```

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