/// <summary>
/// 平底，p1为上顶点,p2，p3
/// </summary>
/// <param name="p1"></param>
/// <param name="p2"></param>
/// <param name="p3"></param>
private void DrawTriangleBottom(Vertex p1, Vertex p2, Vertex p3)
{
for (float y = p1.point.y; y <= p2.point.y; y += 0.5f)
{
int yIndex = (int)(System.Math.Round(y, MidpointRounding.AwayFromZero));
if (yIndex >= 0 && yIndex < this.MaximumSize.Height)
{
float xl = (y - p1.point.y) * (p2.point.x - p1.point.x) / (p2.point.y - p1.point.y) + p1.point.x;
float xr = (y - p1.point.y) * (p3.point.x - p1.point.x) / (p3.point.y - p1.point.y) + p1.point.x;
float dy = y - p1.point.y;
float t = dy / (p2.point.y - p1.point.y);
//插值生成左右顶点
Vertex new1 = new Vertex();
new1.point.x = xl;
new1.point.y = y;
MathUntil.ScreenSpaceLerpVertex(ref new1, p1, p2, t);
//
Vertex new2 = new Vertex();
new2.point.x = xr;
new2.point.y = y;
MathUntil.ScreenSpaceLerpVertex(ref new2, p1, p3, t);
//扫描线填充
if (new1.point.x < new2.point.x)
{
ScanlineFill(new1, new2, yIndex);
}
else
{
ScanlineFill(new2, new1, yIndex);
}
}
}
}
/// <summary>
/// 光栅化三角形
/// </summary>
private void TriangleRasterization(Vertex p1, Vertex p2, Vertex p3)
{
if (p1.point.y == p2.point.y)
{
if (p1.point.y < p3.point.y)
{//平顶
DrawTriangleTop(p1, p2, p3);
}
else
{//平底
DrawTriangleBottom(p3, p1, p2);
}
}
else if (p1.point.y == p3.point.y)
{
if (p1.point.y < p2.point.y)
{//平顶
DrawTriangleTop(p1, p3, p2);
}
else
{//平底
DrawTriangleBottom(p2, p1, p3);
}
}
else if (p2.point.y == p3.point.y)
{
if (p2.point.y < p1.point.y)
{//平顶
DrawTriangleTop(p2, p3, p1);
}
else
{//平底
DrawTriangleBottom(p1, p2, p3);
}
}
else
{//分割三角形
Vertex top;
Vertex bottom;
Vertex middle;
if (p1.point.y > p2.point.y && p2.point.y > p3.point.y)
{
top = p3;
middle = p2;
bottom = p1;
}
else if (p3.point.y > p2.point.y && p2.point.y > p1.point.y)
{
top = p1;
middle = p2;
bottom = p3;
}
else if (p2.point.y > p1.point.y && p1.point.y > p3.point.y)
{
top = p3;
middle = p1;
bottom = p2;
}
else if (p3.point.y > p1.point.y && p1.point.y > p2.point.y)
{
top = p2;
middle = p1;
bottom = p3;
}
else if (p1.point.y > p3.point.y && p3.point.y > p2.point.y)
{
top = p2;
middle = p3;
bottom = p1;
}
else if (p2.point.y > p3.point.y && p3.point.y > p1.point.y)
{
top = p1;
middle = p3;
bottom = p2;
}
else
{
//三点共线
return;
}
//插值求中间点x
float middlex = (middle.point.y - top.point.y) * (bottom.point.x - top.point.x) / (bottom.point.y - top.point.y) + top.point.x;
float dy = middle.point.y - top.point.y;
float t = dy / (bottom.point.y - top.point.y);
//插值生成左右顶点
Vertex newMiddle = new Vertex();
newMiddle.point.x = middlex;
newMiddle.point.y = middle.point.y;
MathUntil.ScreenSpaceLerpVertex(ref newMiddle, top, bottom, t);
//平底
DrawTriangleBottom(top, newMiddle, middle);
//平顶
DrawTriangleTop(newMiddle, middle, bottom);
}
}