void CCPaint8View::OnPaint()
{
    CPaintDC dc(this); // device context for painting
   
    // TODO: Add your message handler code here
    TRIVERTEX vert[4];
    GRADIENT_TRIANGLE gTRi[2];
    vert[0].x=0;
    vert[0].y=0;
    vert[0].Red=0xff00;
    vert[0].Green=0xff00;
    vert[0].Blue=0xff00;
    vert[0].Alpha=0x000;
    vert[1].x=300;
    vert[1].y=0;
    vert[1].Red=0xff00;
    vert[1].Green=0x0000;
    vert[1].Blue=0x0000;
    vert[1].Alpha=0x0000;
    vert[2].x=220;
    vert[2].y=150;
    vert[2].Red=0x0000;
    vert[2].Green=0xff00;
    vert[2].Blue=0x0000;
    vert[2].Alpha=0x0000;
    vert[3].x=0;
    vert[3].y=100;
    vert[3].Red=0x0000;
    vert[3].Green=0x0000;
    vert[3].Blue=0xff00;
    vert[3].Alpha=0x0000;
    gTRi[0].Vertex1=0;
    gTRi[0].Vertex2=1;
    gTRi[0].Vertex3=2;   
    gTRi[1].Vertex1=0;
    gTRi[1].Vertex2=2;
    gTRi[1].Vertex3=3;

Linking...
CPaint8View.obj : error LNK2001: unresolved external symbol __imp__GradientFill@24
Debug/CPaint8.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.

CPaint8.exe - 2 error(s), 0 warning(s)

感谢
    GradientFill(dc.GetSafeHdc(),vert,4,&gTRi,2,GRADIENT_FILL_TRIANGLE);

缺少函数或符号定义，也许是少了包含文件或Lib

#pragma comment(lib,"Msimg32.dll")
加上这句试试

感谢两位
加了#pragma comment(lib,"Msimg32.dll")
显示
--------------------Configuration: CPaint8 - Win32 Debug--------------------
Compiling...
CPaint8View.cpp
Linking...
LINK : fatal error LNK1104: cannot open file "Msimg32.dll"
Error executing link.exe.