Question

尝试在Windows API中使用C和GDI创建基本绘图程序。想法是用户单击并拖动以创建矩形或任何其他选定的形状。大小由用户单击和释放的位置指定（就像任何绘图程序一样）。我遇到了一个问题，即用户绘制的第一个形状将被绘制到屏幕上，但是任何连续的形状都不会。我最初没有在WM_PAINT中绘制形状，但是我在另一个线程上读到了我需要做的事情，因此我创建了一个结构来存储有关已绘制的对象的信息，并且每次收到WM_PAINT消息时都会绘制这些信息。

这是我的WM_PAINT代码

case WM_PAINT:
{
    for (int i = 0; i < drawingcount; i++)
    {

        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hwnd, &ps);
        HPEN hMyPen = CreatePen(mydrawings[i].style, mydrawings[i].thick, RGB(0,255,0));
        HPEN hOldPen = SelectObject(hdc, hMyPen);

        if (mydrawings[i].shape == RECTANGLE)
        {
            Rectangle(hdc, mydrawings[i].start_x, mydrawings[i].start_y, mydrawings[i].end_x, mydrawings[i].end_y);
        }
        else if (mydrawings[i].shape == ELLIPSE)
        {
            Ellipse(hdc, mydrawings[i].start_x, mydrawings[i].start_y, mydrawings[i].end_x, mydrawings[i].end_y);
        }
        else if (mydrawings[i].shape == LINE)
        {
            MoveToEx(hdc, mydrawings[i].start_x, mydrawings[i].start_y, 0);
            LineTo(hdc, mydrawings[i].end_x, mydrawings[i].end_y);
        }
        SelectObject(hdc, hOldPen);
        DeleteObject(hMyPen);
        //DeleteObject(hOldPen);
        EndPaint(hwnd, &ps);
    }
}
break;

这里是WM_LBUTTONUP（一旦用户完成绘制形状）

case WM_LBUTTONUP:
{
    yendclick = GET_Y_LPARAM(lParam);
    xendclick = GET_X_LPARAM(lParam);
    mydrawings[drawingcount].shape = selected_shape;
    mydrawings[drawingcount].start_x = xclick;
    mydrawings[drawingcount].start_y = yclick;
    mydrawings[drawingcount].end_x = xendclick;
    mydrawings[drawingcount].end_y = yendclick;
    mydrawings[drawingcount].thick = thickness;
    mydrawings[drawingcount].style = style;
    drawingcount++;
    SendMessage(hwnd, WM_PAINT, wParam, lParam);
}

结构和枚举声明：

typedef enum myshape
{
    RECTANGLE,
    ELLIPSE,
    LINE,
    MAX_SHAPE
} shape;
typedef struct drawing
{
    int start_x;
    int start_y;
    int end_x;
    int end_y;
    int thick;
    int style;
    shape shape;
} drawings;

非常感谢任何指导！

Answer 1

不要使用PostMessage WM_PAINT，而是使用InvalidateRect和UpdateWindow。另见：why not to send WM_PAINT manually

C中的GDI不绘制连续的对象

1 个答案: