GradientFill API无法正常运行

Question

引言及相关资料：

我想创建一个渐变背景的静态控件。

我想通过以下方式实现：

在主窗口的背景中创建渐变，然后将透明静态控件放在该背景的顶部。

为此，我在RECT处理程序中创建了WM_PAINT变量，将渐变定位在静态控制所在的位置。

另外，我尝试使用双缓冲来避免闪烁（我还处理了WM_ERASEBKGND，从窗口类中删除了标记CS_VREDRAW和CS_HREDRAW。

我还处理了WM_SIZE消息以使窗口无效，并正确地重新定位静态控件。

在我的WM_CTLCOLORSTATIC处理程序中，我已返回NULL_BRUSH。

我已经通过Visual Studio中的应用程序向导制作了一个演示应用程序来说明这一点。

我在Windows XP上工作，使用纯Win32 API和C ++。

Bellow我将提交WM_PAINT的修改代码，以及上面列出的其他处理程序的代码段：

    case WM_CREATE:
         {
             // get rectangle dimensions of the main window

             RECT rec;
             GetClientRect( hWnd, &rec );

             /******* main window's static control ******/

             HWND StaticControl = CreateWindowEx( 0, L"Static", L"", 
                                     WS_VISIBLE | WS_CHILD | SS_NOTIFY,
                                     ( 3 * ( rec.right - rec.left ) / 4 - 340 ) / 3,
                                     120 + ( rec.bottom - rec.top - 450 ) / 3, 
                                     150, 150, hWnd, (HMENU)4000, hInst, 0);
         }
         return (LRESULT)0;

    case WM_SIZE:
        {
             RECT rec; // main window's client rectangle

             GetClientRect( hWnd, &rec ); 

             SetWindowPos( GetDlgItem( hWnd, 4000 ),
                           NULL,
                           ( 3  * ( rec.right - rec.left ) / 4 - 340 ) / 3, 
                           120 + ( rec.bottom - rec.top - 450 ) / 3, 150, 150,
                           SWP_NOZORDER );

            InvalidateRect( hWnd, NULL, FALSE); 
        }
        return (LRESULT)0;

    case WM_ERASEBKGND:
        return (LRESULT)1;

    case WM_CTLCOLORSTATIC:
        return (LRESULT)( (HBRUSH)GetStockObject(NULL_BRUSH) );

    case WM_PAINT:
        {
            hdc = BeginPaint(hWnd, &ps);
            // TODO: Add any drawing code here...

            RECT r; // rectangle for main window's client area

            GetClientRect( hWnd, &r);

            HDC MemDC = CreateCompatibleDC(hdc); // back buffer

            // compatible bitmap for MemDC

            HBITMAP bmp = CreateCompatibleBitmap( hdc,
                                                  r.right - r.left, 
                                                  r.bottom - r.top ),
                    oldBmp = (HBITMAP)SelectObject( MemDC, bmp ); // needed for cleanup

            /***** draw a reference header at the top of the window *******/

            // position it properly at the top

            RECT rect;

            rect.left = r.left;
            rect.top = r.top;
            rect.right = r.right;
            rect.bottom = 120;

            FillRect( MemDC, &rect, (HBRUSH)GetStockObject(LTGRAY_BRUSH) );

            /**** main window's gradient background *******/

            //============ down triangle =========//

            TRIVERTEX vertex[3];

            vertex[0].x     = r.right;
            vertex[0].y     = r.bottom - r.top;
            vertex[0].Red   = 0xDB00;
            vertex[0].Green = 0xE500;
            vertex[0].Blue  = 0xF100;
            vertex[0].Alpha = 0x0000;

            vertex[1].x     = r.left;
            vertex[1].y     = r.bottom - r.top;
            vertex[1].Red   = 0x9500;
            vertex[1].Green = 0xB300;
            vertex[1].Blue  = 0xD700;
            vertex[1].Alpha = 0x0000;

            vertex[2].x     = r.left;
            vertex[2].y     = r.top + 120; 
            vertex[2].Red   = 0xDB00;
            vertex[2].Green = 0xE500;
            vertex[2].Blue  = 0xF100;
            vertex[2].Alpha = 0x0000;

            // Create a GRADIENT_TRIANGLE structure that
            // references the TRIVERTEX vertices.

            GRADIENT_TRIANGLE gTriangle;

            gTriangle.Vertex1 = 0;
            gTriangle.Vertex2 = 1;
            gTriangle.Vertex3 = 2;

            // Draw a shaded triangle.

            GradientFill( MemDC, vertex, 3, &gTriangle, 1, GRADIENT_FILL_TRIANGLE);

            //=============== upper triangle =================//

            TRIVERTEX vertex1[3];

            vertex1[0].x     = r.right;
            vertex1[0].y     = r.bottom - r.top;
            vertex1[0].Red   = 0xDB00;
            vertex1[0].Green = 0xE500;
            vertex1[0].Blue  = 0xF100;
            vertex1[0].Alpha = 0x0000;

            vertex1[1].x     = r.right;
            vertex1[1].y     = r.top + 120;
            vertex1[1].Red   = 0x9500;
            vertex1[1].Green = 0xB300;
            vertex1[1].Blue  = 0xD700;
            vertex1[1].Alpha = 0x0000;

            vertex1[2].x     = r.left;
            vertex1[2].y     = r.top + 120; 
            vertex1[2].Red   = 0xDB00;
            vertex1[2].Green = 0xE500;
            vertex1[2].Blue  = 0xF100;
            vertex1[2].Alpha = 0x0000;

            // Draw a shaded triangle.

            GradientFill( MemDC, vertex1, 3, &gTriangle, 1, GRADIENT_FILL_TRIANGLE);

            //**** draw background of the static control ****//

            //position it properly 

            rect.left = ( 3  * ( r.right - r.left ) / 4 - 340 ) / 3;
            rect.top = 120 + ( r.bottom - r.top - 450 ) / 3;
            rect.right = 150 + ( 3  * ( r.right - r.left ) / 4 - 340 ) / 3;
            rect.bottom = 270 + ( r.bottom - r.top - 450 ) / 3; // this one fails!!!

            //FillRect( MemDC, &rect, (HBRUSH)GetStockObject(WHITE_BRUSH) );

            // vertexes for static's gradient color

            //================= top rectangle =====================//

            TRIVERTEX vertexS[2], vertex1S[2] ;

            vertexS[0].x     = rect.left;
            vertexS[0].y     = rect.top;
            vertexS[0].Red   = 0x9500;
            vertexS[0].Green = 0xB300;
            vertexS[0].Blue  = 0xD700;
            vertexS[0].Alpha = 0x0000;

            vertexS[1].x     = rect.right;
            vertexS[1].y     = ( rect.bottom - rect.top ) / 2; 
            vertexS[1].Red   = 0x4F00;
            vertexS[1].Green = 0x8B00;
            vertexS[1].Blue  = 0xBD00;
            vertexS[1].Alpha = 0x0000;

            //================== bottom rectangle ====================//

            vertex1S[0].x     = rect.left;
            vertex1S[0].y     = ( rect.bottom - rect.top ) / 2; 
            vertex1S[0].Red   = 0x4F00;
            vertex1S[0].Green = 0x8B00;
            vertex1S[0].Blue  = 0xBD00;
            vertex1S[0].Alpha = 0x0000;

            vertex1S[1].x     = rect.right;
            vertex1S[1].y     = rect.bottom;
            vertex1S[1].Red   = 0x9500;
            vertex1S[1].Green = 0xB300;
            vertex1S[1].Blue  = 0xD700;
            vertex1S[1].Alpha = 0x0000;

            // Create a GRADIENT_RECT structure that 
            // references the TRIVERTEX vertices.

            GRADIENT_RECT gRect;

            gRect.UpperLeft  = 0;
            gRect.LowerRight = 1;

            // Draw a shaded rectangle. 

            GradientFill( MemDC, vertexS, 2, &gRect, 1, GRADIENT_FILL_RECT_V );
            GradientFill( MemDC, vertex1S, 2, &gRect, 1, GRADIENT_FILL_RECT_V );

            /****** draw back buffer on the screen DC *****************/

            BitBlt( hdc, 0, 0, r.right - r.left, r.bottom - r.top,
                    MemDC, 0, 0, SRCCOPY );

            /************** cleanup *******************/

            SelectObject( MemDC, oldBmp );

            DeleteObject(bmp); // compatible bitmap for MemDC

            DeleteDC(MemDC);

            EndPaint(hWnd, &ps);
        }
        return (LRESULT)0;

问题：

当我在GradientFill处理程序中使用WM_PAINT API时，屏幕上会出现一个比它应该更大的矩形。

贝娄图片说明了这个结果：

如果我尝试使用实心画笔填充相同的矩形，一切正常。

贝娄图片说明了这个结果：

我解决问题的努力：

我在设置了矩形坐标的地方放置了断点，但没有看到任何问题。

此外，GradientFill会返回TRUE，因此不会失败。

问题：

如何解决这个问题？

提前谢谢。

问候。

Answer 1

我认为只是你对顶点的计算是错误的：

        vertexS[1].y     = ( rect.bottom - rect.top ) / 2; 
        /* .... */
        vertex1S[0].y     = ( rect.bottom - rect.top ) / 2;

它们应该是rect.top + ( rect.bottom - rect.top ) / 2还是类似的？或者甚至只分别是rect.bottom和rect.top？

这取决于你想要实现的目标，但无论哪种方式，我认为它目前不是你想要的。您需要使用rect.bottom和rect.top来获得与已注释掉的FillRect相同的形状。