Uso di rettangoli (Windows GDI)
L'esempio in questa sezione illustra come usare le funzioni rettangole. È costituita dalla procedura principale della finestra da un'applicazione che consente all'utente di spostare e ridimensionare una bitmap.
All'avvio dell'applicazione, disegna una bitmap da 32 pixel a 32 pixel nell'angolo superiore sinistro dello schermo. L'utente può spostare la bitmap trascinandola. Per ridimensionare la bitmap, l'utente crea un rettangolo di destinazione trascinando il mouse, quindi trascina la bitmap e "elimina" nel rettangolo di destinazione. L'applicazione risponde copiando la bitmap nel rettangolo di destinazione.
La procedura della finestra che consente all'utente di spostare e ridimensionare la bitmap viene specificata nell'esempio seguente.
LRESULT CALLBACK MainWndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
HDC hdc; // device context (DC) for window
RECT rcTmp; // temporary rectangle
PAINTSTRUCT ps; // paint data for BeginPaint and EndPaint
POINT ptClientUL; // client area upper left corner
POINT ptClientLR; // client area lower right corner
static HDC hdcCompat; // DC for copying bitmap
static POINT pt; // x and y coordinates of cursor
static RECT rcBmp; // rectangle that encloses bitmap
static RECT rcTarget; // rectangle to receive bitmap
static RECT rcClient; // client-area rectangle
static BOOL fDragRect; // TRUE if bitmap rect. is dragged
static HBITMAP hbmp; // handle of bitmap to display
static HBRUSH hbrBkgnd; // handle of background-color brush
static COLORREF crBkgnd; // color of client-area background
static HPEN hpenDot; // handle of dotted pen
switch (uMsg)
{
case WM_CREATE:
// Load the bitmap resource.
hbmp = LoadBitmap(hinst, MAKEINTRESOURCE(1));
// Create a device context (DC) to hold the bitmap.
// The bitmap is copied from this DC to the window's DC
// whenever it must be drawn.
hdc = GetDC(hwnd);
hdcCompat = CreateCompatibleDC(hdc);
SelectObject(hdcCompat, hbmp);
// Create a brush of the same color as the background
// of the client area. The brush is used later to erase
// the old bitmap before copying the bitmap into the
// target rectangle.
crBkgnd = GetBkColor(hdc);
hbrBkgnd = CreateSolidBrush(crBkgnd);
ReleaseDC(hwnd, hdc);
// Create a dotted pen. The pen is used to draw the
// bitmap rectangle as the user drags it.
hpenDot = CreatePen(PS_DOT, 1, RGB(0, 0, 0));
// Set the initial rectangle for the bitmap. Note that
// this application supports only a 32- by 32-pixel
// bitmap. The rectangle is slightly larger than the
// bitmap.
SetRect(&rcBmp, 1, 1, 34, 34);
return 0;
case WM_PAINT:
// Draw the bitmap rectangle and copy the bitmap into
// it. The 32-pixel by 32-pixel bitmap is centered
// in the rectangle by adding 1 to the left and top
// coordinates of the bitmap rectangle, and subtracting 2
// from the right and bottom coordinates.
BeginPaint(hwnd, &ps);
Rectangle(ps.hdc, rcBmp.left, rcBmp.top,
rcBmp.right, rcBmp.bottom);
StretchBlt(ps.hdc, rcBmp.left + 1, rcBmp.top + 1,
(rcBmp.right - rcBmp.left) - 2,
(rcBmp.bottom - rcBmp.top) - 2, hdcCompat,
0, 0, 32, 32, SRCCOPY);
EndPaint(hwnd, &ps);
break;
case WM_MOVE:
case WM_SIZE:
// Convert the client coordinates of the client-area
// rectangle to screen coordinates and save them in a
// rectangle. The rectangle is passed to the ClipCursor
// function during WM_LBUTTONDOWN processing.
GetClientRect(hwnd, &rcClient);
ptClientUL.x = rcClient.left;
ptClientUL.y = rcClient.top;
ptClientLR.x = rcClient.right;
ptClientLR.y = rcClient.bottom;
ClientToScreen(hwnd, &ptClientUL);
ClientToScreen(hwnd, &ptClientLR);
SetRect(&rcClient, ptClientUL.x, ptClientUL.y,
ptClientLR.x, ptClientLR.y);
return 0;
case WM_LBUTTONDOWN:
// Restrict the mouse cursor to the client area. This
// ensures that the window receives a matching
// WM_LBUTTONUP message.
ClipCursor(&rcClient);
// Save the coordinates of the mouse cursor.
pt.x = (LONG) LOWORD(lParam);
pt.y = (LONG) HIWORD(lParam);
// If the user has clicked the bitmap rectangle, redraw
// it using the dotted pen. Set the fDragRect flag to
// indicate that the user is about to drag the rectangle.
if (PtInRect(&rcBmp, pt))
{
hdc = GetDC(hwnd);
SelectObject(hdc, hpenDot);
Rectangle(hdc, rcBmp.left, rcBmp.top, rcBmp.right,
rcBmp.bottom);
fDragRect = TRUE;
ReleaseDC(hwnd, hdc);
}
return 0;
case WM_MOUSEMOVE:
// Draw a target rectangle or drag the bitmap rectangle,
// depending on the status of the fDragRect flag.
if ((wParam && MK_LBUTTON)
&& !fDragRect)
{
// Set the mix mode so that the pen color is the
// inverse of the background color. The previous
// rectangle can then be erased by drawing
// another rectangle on top of it.
hdc = GetDC(hwnd);
SetROP2(hdc, R2_NOTXORPEN);
// If a previous target rectangle exists, erase
// it by drawing another rectangle on top of it.
if (!IsRectEmpty(&rcTarget))
{
Rectangle(hdc, rcTarget.left, rcTarget.top,
rcTarget.right, rcTarget.bottom);
}
// Save the coordinates of the target rectangle. Avoid
// invalid rectangles by ensuring that the value of
// the left coordinate is lesser than the
// right coordinate, and that the value of the top
// coordinate is lesser than the bottom coordinate.
if ((pt.x < (LONG) LOWORD(lParam)) &&
(pt.y > (LONG) HIWORD(lParam)))
{
SetRect(&rcTarget, pt.x, HIWORD(lParam),
LOWORD(lParam), pt.y);
}
else if ((pt.x > (LONG) LOWORD(lParam)) &&
(pt.y > (LONG) HIWORD(lParam)))
{
SetRect(&rcTarget, LOWORD(lParam),
HIWORD(lParam), pt.x, pt.y);
}
else if ((pt.x > (LONG) LOWORD(lParam)) &&
(pt.y < (LONG) HIWORD(lParam)))
{
SetRect(&rcTarget, LOWORD(lParam), pt.y,
pt.x, HIWORD(lParam));
}
else
{
SetRect(&rcTarget, pt.x, pt.y, LOWORD(lParam),
HIWORD(lParam));
}
// Draw the new target rectangle.
Rectangle(hdc, rcTarget.left, rcTarget.top,
rcTarget.right, rcTarget.bottom);
ReleaseDC(hwnd, hdc);
}
else if ((wParam && MK_LBUTTON)
&& fDragRect)
{
// Set the mix mode so that the pen color is the
// inverse of the background color.
hdc = GetDC(hwnd);
SetROP2(hdc, R2_NOTXORPEN);
// Select the dotted pen into the DC and erase
// the previous bitmap rectangle by drawing
// another rectangle on top of it.
SelectObject(hdc, hpenDot);
Rectangle(hdc, rcBmp.left, rcBmp.top,
rcBmp.right, rcBmp.bottom);
// Set the new coordinates of the bitmap rectangle,
// then redraw it.
OffsetRect(&rcBmp, LOWORD(lParam) - pt.x,
HIWORD(lParam) - pt.y);
Rectangle(hdc, rcBmp.left, rcBmp.top,
rcBmp.right, rcBmp.bottom);
ReleaseDC(hwnd, hdc);
// Save the coordinates of the mouse cursor.
pt.x = (LONG) LOWORD(lParam);
pt.y = (LONG) HIWORD(lParam);
}
return 0;
case WM_LBUTTONUP:
// If the bitmap rectangle and target rectangle
// intersect, copy the bitmap into the target
// rectangle. Otherwise, copy the bitmap into the
// rectangle bitmap at its new location.
if (IntersectRect(&rcTmp, &rcBmp, &rcTarget))
{
// Erase the bitmap rectangle by filling it with
// the background color.
hdc = GetDC(hwnd);
FillRect(hdc, &rcBmp, hbrBkgnd);
// Redraw the target rectangle because the part
// that intersected with the bitmap rectangle was
// erased by the call to FillRect.
Rectangle(hdc, rcTarget.left, rcTarget.top,
rcTarget.right, rcTarget.bottom);
// Copy the bitmap into the target rectangle.
StretchBlt(hdc, rcTarget.left + 1, rcTarget.top + 1,
(rcTarget.right - rcTarget.left) - 2,
(rcTarget.bottom - rcTarget.top) - 2, hdcCompat,
0, 0, 32, 32, SRCCOPY);
// Copy the target rectangle to the bitmap
// rectangle, set the coordinates of the target
// rectangle to 0, then reset the fDragRect flag.
CopyRect(&rcBmp, &rcTarget);
SetRectEmpty(&rcTarget);
ReleaseDC(hwnd, hdc);
fDragRect = FALSE;
}
else if (fDragRect)
{
// Draw the bitmap rectangle, copy the bitmap into
// it, and reset the fDragRect flag.
hdc = GetDC(hwnd);
Rectangle(hdc, rcBmp.left, rcBmp.top,
rcBmp.right, rcBmp.bottom);
StretchBlt(hdc, rcBmp.left + 1, rcBmp.top + 1,
(rcBmp.right - rcBmp.left) - 2,
(rcBmp.bottom - rcBmp.top) - 2, hdcCompat,
0, 0, 32, 32, SRCCOPY);
ReleaseDC(hwnd, hdc);
fDragRect = FALSE;
}
// Release the mouse cursor.
ClipCursor((LPRECT) NULL);
return 0;
case WM_DESTROY:
// Destroy the background brush, compatible bitmap,
// and the bitmap.
DeleteObject(hbrBkgnd);
DeleteDC(hdcCompat);
DeleteObject(hbmp);
PostQuitMessage(0);
break;
default:
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}
return (LRESULT) NULL;
}
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