private void DrawTriangle(Vertex v1, Vertex v2, Vertex v3, Color4 colour, Texture texture)
{
// Sorting the points in order to always have this order on screen p1, p2 & p3
// with p1 always up (thus having the Y the lowest possible to be near the top screen)
// then p2 between p1 & p3
if (v1.Coordinates.Y > v2.Coordinates.Y)
{
var temp = v2;
v2 = v1;
v1 = temp;
}
if (v2.Coordinates.Y > v3.Coordinates.Y)
{
var temp = v2;
v2 = v3;
v3 = temp;
}
if (v1.Coordinates.Y > v2.Coordinates.Y)
{
var temp = v2;
v2 = v1;
v1 = temp;
}
Vector3 p1 = v1.Coordinates;
Vector3 p2 = v2.Coordinates;
Vector3 p3 = v3.Coordinates;
// computing the cos of the angle between the light vector and the normal vector
// it will return a value between 0 and 1 that will be used as the intensity of the colour
float nl1 = ComputeNDotL(v1.WorldCoordinates, v1.Normal, _lightPos);
float nl2 = ComputeNDotL(v2.WorldCoordinates, v2.Normal, _lightPos);
float nl3 = ComputeNDotL(v3.WorldCoordinates, v3.Normal, _lightPos);
// computing lines' directions
// http://en.wikipedia.org/wiki/Slope
// Computing slopes
float dP1P2 = p2.Y - p1.Y > 0 ? (p2.X - p1.X) / (p2.Y - p1.Y) : 0;
float dP1P3 = p3.Y - p1.Y > 0 ? (p3.X - p1.X) / (p3.Y - p1.Y) : 0;
if (dP1P2 > dP1P3)
{
// Where triangles are like:
// P1
// - -
// - - P2
// - -
// P3
DrawRightTriangle(
colour, texture,
p1, p2, p3,
v1, v2, v3,
nl1, nl2, nl3);
}
else
{
// Where triangles are like:
// P1
// - -
// P2 - -
// - -
// P3
DrawLeftTriangle(
colour, texture,
p1, p2, p3,
v1, v2, v3,
nl1, nl2, nl3);
}
}
// drawing line between 2 points from left to right
// papb -> pcpd
// pa, pb, pc, pd must then be sorted before
// drawing line between 2 points from left to right
// papb -> pcpd
// pa, pb, pc, pd must then be sorted before
private void ProcessScanLine(ScanLineData data, Vertex va, Vertex vb, Vertex vc, Vertex vd, Color4 colour, Texture texture)
{
Vector3 pa = va.Coordinates;
Vector3 pb = vb.Coordinates;
Vector3 pc = vc.Coordinates;
Vector3 pd = vd.Coordinates;
// Thanks to current Y, we can compute the gradient to compute others values like
// the starting X (sx) and ending X (ex) to draw between
// if pa.Y == pb.Y or pc.Y == pd.Y, gradient is forced to 1
var gradient1 = pa.Y != pb.Y ? (data.currentY - pa.Y) / (pb.Y - pa.Y) : 1;
var gradient2 = pc.Y != pd.Y ? (data.currentY - pc.Y) / (pd.Y - pc.Y) : 1;
int sx = (int)Interpolate(pa.X, pb.X, gradient1);
int ex = (int)Interpolate(pc.X, pd.X, gradient2);
// starting Z & ending Z
float z1 = Interpolate(pa.Z, pb.Z, gradient1);
float z2 = Interpolate(pc.Z, pd.Z, gradient2);
// Interpolating normals on Y
var snl = Interpolate(data.ndotla, data.ndotlb, gradient1);
var enl = Interpolate(data.ndotlc, data.ndotld, gradient2);
// Interpolating texture coordinates on Y
var su = Interpolate(data.ua, data.ub, gradient1);
var eu = Interpolate(data.uc, data.ud, gradient2);
var sv = Interpolate(data.va, data.vb, gradient1);
var ev = Interpolate(data.vc, data.vd, gradient2);
// drawing a line from left (sx) to right (ex)
for (var x = sx; x < ex; x++)
{
float gradient = (x - sx) / (float)(ex - sx);
// Interpolating Z, normal and texture coordinates on X
var z = Interpolate(z1, z2, gradient);
var ndotl = Interpolate(snl, enl, gradient);
var u = Interpolate(su, eu, gradient);
var v = Interpolate(sv, ev, gradient);
Color4 textureColour = texture != null
? textureColour = texture.Map(u, v)
: textureColour = new Color4(1, 1, 1, 1);
// changing the native colour value using the cosine of the angle
// between the light vector and the normal vector
// and the texture colour
DrawPoint(new Vector3(x, data.currentY, z), colour * ndotl * textureColour);
}
}