private static void Swap(ref VertexProj v1, ref VertexProj v2)
{
var temp = v2;
v2 = v1;
v1 = temp;
}
// drawing line between 2 points from left to right
// papb -> pcpd
// pa, pb, pc, pd must then be sorted before
private static void ProcessScanLine(
RenderState state,
int currentY,
ref VertexProj va,
ref VertexProj vb,
ref VertexProj vc,
ref VertexProj vd,
Texture texture)
{
Vector3fProj pa = va.Coordinates;
Vector3fProj pb = vb.Coordinates;
Vector3fProj pc = vc.Coordinates;
Vector3fProj 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 = Math.Abs(pa.Y - pb.Y) > 0.0001 ? ((currentY - pa.Y) * 1.0f / (pb.Y - pa.Y)) : 1;
var gradient2 = Math.Abs(pc.Y - pd.Y) > 0.0001 ? ((currentY - pc.Y) * 1.0f / (pd.Y - pc.Y)) : 1;
int sx = (int)Interpolate(pa.X, pb.X, gradient1);
int ex = (int)Interpolate(pc.X, pd.X, gradient2);
if (ex < sx)
{
return;
}
// starting Z & ending Z
float z1 = Interpolate(pa.Z, pb.Z, gradient1);
float z2 = Interpolate(pc.Z, pd.Z, gradient2);
var sqDistA = state.Camera.Position.SqDistBetween(ref va.WorldCoordinates);
var sqDistB = state.Camera.Position.SqDistBetween(ref vb.WorldCoordinates);
var sqDistC = state.Camera.Position.SqDistBetween(ref vc.WorldCoordinates);
var sqDistD = state.Camera.Position.SqDistBetween(ref vd.WorldCoordinates);
var sSqD = Interpolate(sqDistA, sqDistB, gradient1);
var eSqD = Interpolate(sqDistC, sqDistD, gradient2);
// Interpolating normals on Y
var snx = Interpolate(va.Normal.X, vb.Normal.X, gradient1);
var enx = Interpolate(vc.Normal.X, vd.Normal.X, gradient2);
var sny = Interpolate(va.Normal.Y, vb.Normal.Y, gradient1);
var eny = Interpolate(vc.Normal.Y, vd.Normal.Y, gradient2);
var snz = Interpolate(va.Normal.Z, vb.Normal.Z, gradient1);
var enz = Interpolate(vc.Normal.Z, vd.Normal.Z, gradient2);
float su = 0;
float eu = 0;
float sv = 0;
float ev = 0;
// Interpolating texture coordinates on Y
if (texture != null)
{
su = Interpolate(va.TextureCoordinates.X, vb.TextureCoordinates.X, gradient1);
eu = Interpolate(vc.TextureCoordinates.X, vd.TextureCoordinates.X, gradient2);
sv = Interpolate(va.TextureCoordinates.Y, vb.TextureCoordinates.Y, gradient1);
ev = Interpolate(vc.TextureCoordinates.Y, vd.TextureCoordinates.Y, gradient2);
}
// drawing a line from left (sx) to right (ex), but only for what is visible on screen.
for (int x = Math.Max(sx, 0); x < Math.Min(ex, state.Width); x++)
{
float gradient = (x - sx) / (float)(ex - sx);
// Interpolating Z, normal and texture coordinates on X
var z = Interpolate(z1, z2, gradient);
var nx = Interpolate(snx, enx, gradient);
var ny = Interpolate(sny, eny, gradient);
var nz = Interpolate(snz, enz, gradient);
var u = (Interpolate(su, eu, gradient));
var v = (Interpolate(sv, ev, gradient));
var sqD = Interpolate(sSqD, eSqD, gradient);
// changing the native color value using the cosine of the angle
// between the light vector and the normal vector
// and the texture color
MyColor textureColor = new MyColor();
if (texture != null)
{
texture.GetPixel(u, v, ref textureColor);
}
else
{
textureColor = MyColor.White;
}
state.PutPixel(x, currentY, z, textureColor, nx, ny, nz, u, v, sqD);
}
}
private static void DrawTriangle(
RenderState state,
ref VertexProj v1,
ref VertexProj v2,
ref VertexProj v3,
Texture texture,
ref Vector3f buffv)
{
// 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)
{
Swap(ref v1, ref v2);
}
if (v2.Coordinates.Y > v3.Coordinates.Y)
{
Swap(ref v2, ref v3);
}
if (v1.Coordinates.Y > v2.Coordinates.Y)
{
Swap(ref v1, ref v2);
}
// computing lines' directions
// http://en.wikipedia.org/wiki/Slope
// Computing slopes
Vector3fProj p1 = v1.Coordinates;
Vector3fProj p2 = v2.Coordinates;
Vector3fProj p3 = v3.Coordinates;
// When the slope is zero, it doesn't give good
// information. Then have to check manually
//
// P1 P1
// First | \ Second / |
// branch | P2 branch P2 |
// is for | / is for \ |
// P3 P3
// However , when dP1P2 == null
// P1--P2 P2--P1
// First | / Second \ |
// branch | / branch \ |
// is for | / is for \ |
// P3 P3
// And dP1P3 cant be null without DP1P2 null first.
bool useFirst;
if (p1.Y == p2.Y)
{
useFirst = p1.X < p2.X;
}
else
{
float invSlopeP1P2 = (p2.X - p1.X) * 1.0f / (p2.Y - p1.Y);
float invSlopeP1P3 = (p3.X - p1.X) * 1.0f / (p3.Y - p1.Y);
useFirst = invSlopeP1P2 > invSlopeP1P3;
}
for (var y = Math.Max(0, p1.Y); y <= Math.Min(state.Height, p3.Y); y++)
{
if (useFirst)
{
if (y < p2.Y)
{
ProcessScanLine(state, y, ref v1, ref v3, ref v1, ref v2, texture);
}
else
{
ProcessScanLine(state, y, ref v1, ref v3, ref v2, ref v3, texture);
}
}
else
{
if (y < p2.Y)
{
ProcessScanLine(state, y, ref v1, ref v2, ref v1, ref v3, texture);
}
else
{
ProcessScanLine(state, y, ref v2, ref v3, ref v1, ref v3, texture);
}
}
}
}
