如何用mfc在屏幕上绘制一个三角形，指定三个顶点的颜色分别为红、绿、蓝三色然后用边标志填充算法光滑着色填充该三角形。

可以使用 CDC 类的相关 API 来在屏幕上绘制三角形并进行填充。

以下是示例代码：

CPoint points[3] = { CPoint(100, 100), CPoint(200, 200), CPoint(300, 100) };
COLORREF colors[3] = { RGB(255, 0, 0), RGB(0, 255, 0), RGB(0, 0, 255) };

CBrush brush;
brush.CreateSolidBrush(colors[0]);

CClientDC dc(this);
CBrush* pOldBrush = dc.SelectObject(&brush);
CPen pen(PS_SOLID, 1, RGB(0, 0, 0));
CPen* pOldPen = dc.SelectObject(&pen);

dc.Polygon(points, 3);

dc.SelectObject(pOldBrush);
dc.SelectObject(pOldPen);

COLORREF fillColor = RGB(128, 128, 128);
FillTriangle(&dc, points, colors, fillColor);

其中 `FillTriangle` 是一个自定义函数，使用边标志填充算法进行光滑着色填充。以下是该函数的示例代码：

void FillTriangle(CDC* pDC, CPoint* points, COLORREF* colors, COLORREF fillColor)
{
    int minY = min(min(points[0].y, points[1].y), points[2].y);
    int maxY = max(max(points[0].y, points[1].y), points[2].y);

    for (int y = minY; y <= maxY; y++)
    {
        int x1, x2;
        bool hasIntersection = false;

        for (int i = 0; i < 3; i++)
        {
            int j = (i + 1) % 3;

            if ((points[i].y <= y && points[j].y > y) || (points[i].y > y && points[j].y <= y))
            {
                int dx = points[j].x - points[i].x;
                int dy = points[j].y - points[i].y;

                if (dy == 0) continue;

                double k = (double)dx / dy;
                double x = k * (y - points[i].y) + points[i].x;

                if (!hasIntersection)
                {
                    x1 = x2 = x;
                    hasIntersection = true;
                }
                else
                {
                    if (x < x1) x1 = x;
                    if (x > x2) x2 = x;
                }
            }
        }

        if (hasIntersection)
        {
            COLORREF color = MixColors(points, colors, x1, x2, y);
            CBrush brush;
            brush.CreateSolidBrush(color);
            CBrush* pOldBrush = pDC->SelectObject(&brush);
            pDC->PatBlt(x1, y, x2 - x1 + 1, 1, PATCOPY);
            pDC->SelectObject(pOldBrush);
        }
    }
}

COLORREF MixColors(CPoint* points, COLORREF* colors, int x1, int x2, int y)
{
    double area = GetTriangleArea(points);
    double weight1 = GetTriangleArea(CPoint(x1, y), points[1], points[2]) / area;
    double weight2 = GetTriangleArea(points[0], CPoint(x1, y), points[2]) / area;
    double weight3 = GetTriangleArea(points[0], points[1], CPoint(x1, y)) / area;

    BYTE r = (BYTE)(GetRValue(colors[0]) * weight1 + GetRValue(colors[1]) * weight2 + GetRValue(colors[2]) * weight3);
    BYTE g = (BYTE)(GetGValue(colors[0]) * weight1 + GetGValue(colors[1]) * weight2 + GetGValue(colors[2]) * weight3);
    BYTE b = (BYTE)(GetBValue(colors[0]) * weight1 + GetBValue(colors[1]) * weight2 + GetBValue(colors[2]) * weight3);

    return RGB(r, g, b);
}

double GetTriangleArea(CPoint* points)
{
    return GetTriangleArea(points[0], points[1], points[2]);
}

double GetTriangleArea(CPoint p1, CPoint p2, CPoint p3)
{
    double a = GetDistance(p1, p2);
    double b = GetDistance(p2, p3);
    double c = GetDistance(p3, p1);
    double s = (a + b + c) / 2;
    return sqrt(s * (s - a) * (s - b) * (s - c));
}

double GetDistance(CPoint p1, CPoint p2)
{
    double dx = p1.x - p2.x;
    double dy = p1.y - p2.y;
    return sqrt(dx * dx + dy * dy);
}

这段代码实现了边标志填充算法，并使用三角形重心法计算每个像素点的颜色。