#ifndef _MEMDC_H_ #define _MEMDC_H_////////////////////////////////////////////////// // CMemDC - memory DC // // Author: Keith Rule // Email: [email protected] // Copyright 1996-1999, Keith Rule // // You may freely use or modify this code provided this // Copyright is included in all derived versions. // // History - 10/3/97 Fixed scrolling bug. // Added print support. - KR // // 11/3/99 Fixed most common complaint. Added // background color fill. - KR // // 11/3/99 Added support for mapping modes other than // MM_TEXT as suggested by Lee Sang Hun. - KR // // Modified by Mark Malburg March 12, 1998 // Email: [email protected] // (added new construction and clipboard handling) // // Construction : // | // | CMemDC pDC (dc, &drawRect, toMemDC) ; // | // | where: // | "dc" - pointer to the CDC that is an argument to OnDraw // | "drawRect" - pointer to the rectangle to draw in // | "boolToMemory" - TRUE: to the client, FALSE: to clipboard or printer // | // // This class implements a memory Device Context which allows // flicker free drawing.class CMemDC : public CDC { private: CBitmap m_bitmap; // Offscreen bitmap CBitmap* m_oldBitmap; // bitmap originally found in CMemDC CDC* m_pDC; // Saves CDC passed in constructor CRect m_rect; // Rectangle of drawing area. BOOL m_bMemDC; // TRUE if CDC really is a Memory DC. public:
CMemDC(CDC* pDC, const CRect* pRect = NULL, bool boolToMemory = TRUE) : CDC() { ASSERT(pDC != NULL); // Some initialization m_pDC = pDC; m_oldBitmap = NULL; if (boolToMemory) m_bMemDC = !pDC->IsPrinting(); else m_bMemDC = FALSE ; // Get the rectangle to draw if (pRect == NULL) { pDC->GetClipBox(&m_rect); } else { m_rect = *pRect; }
if (m_bMemDC) { // Create a Memory DC CreateCompatibleDC(pDC); pDC->LPtoDP(&m_rect); m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height()); m_oldBitmap = SelectObject(&m_bitmap);
SetMapMode(pDC->GetMapMode()); pDC->DPtoLP(&m_rect); SetWindowOrg(m_rect.left, m_rect.top); } else { // Make a copy of the relevent parts of the current DC for printing if (pDC->IsPrinting()) m_bPrinting = pDC->m_bPrinting; m_hDC = pDC->m_hDC; m_hAttribDC = pDC->m_hAttribDC; } // Fill background FillSolidRect(m_rect, pDC->GetBkColor()); } ~CMemDC() { if (m_bMemDC) { // Copy the offscreen bitmap onto the screen. m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(), this, m_rect.left, m_rect.top, SRCCOPY);
//Swap back the original bitmap. SelectObject(m_oldBitmap); } else { // All we need to do is replace the DC with an illegal value, // this keeps us from accidently deleting the handles associated with // the CDC that was passed to the constructor. m_hDC = m_hAttribDC = NULL; } }
// Allow usage as a pointer CMemDC* operator->() { return this; } // Allow usage as a pointer operator CMemDC*() { return this; } };#endif
直接画到这个内存位图上就可以了,要显示再blt到你的当前DC上
CDC MemDC;
CPaintDC dc(this);
CRect rect;
GetClientRect(&rect);MemDC.CreateCompatibleDC(&dc);
...
比喻说我要画一些线段
MemDC.MoveTo(...)
MemDC.LineTo(...)再写上一段文字
MemDC.DrawText(...)还要画一个圆
MemDC.DrawEdge(...)好了,这些工作已经在MemDC(也就是内存DC)中完成了,这里并没有画到设备上来,只是仅仅在内存中画好了.这时我们就可以一次性画到屏上来了
dc.BitBlt(0, 0, rect.Width(), rect.Height(), &MemDC, 0, 0, SRCCOPY);
MemDC.DeleteDC();
CDC memDC;
CBitmap bmp;
memDC.CreateCompatibleDC(pDC);
bmp.CreateCompatibleBitmap(pDC, 100, 100);memDC.SelectObject(&bmp);以下代码为在memDC上绘图操作
#define _MEMDC_H_//////////////////////////////////////////////////
// CMemDC - memory DC
//
// Author: Keith Rule
// Email: [email protected]
// Copyright 1996-1999, Keith Rule
//
// You may freely use or modify this code provided this
// Copyright is included in all derived versions.
//
// History - 10/3/97 Fixed scrolling bug.
// Added print support. - KR
//
// 11/3/99 Fixed most common complaint. Added
// background color fill. - KR
//
// 11/3/99 Added support for mapping modes other than
// MM_TEXT as suggested by Lee Sang Hun. - KR
//
// Modified by Mark Malburg March 12, 1998
// Email: [email protected]
// (added new construction and clipboard handling)
//
// Construction :
// |
// | CMemDC pDC (dc, &drawRect, toMemDC) ;
// |
// | where:
// | "dc" - pointer to the CDC that is an argument to OnDraw
// | "drawRect" - pointer to the rectangle to draw in
// | "boolToMemory" - TRUE: to the client, FALSE: to clipboard or printer
// |
//
// This class implements a memory Device Context which allows
// flicker free drawing.class CMemDC : public CDC
{
private:
CBitmap m_bitmap; // Offscreen bitmap
CBitmap* m_oldBitmap; // bitmap originally found in CMemDC
CDC* m_pDC; // Saves CDC passed in constructor
CRect m_rect; // Rectangle of drawing area.
BOOL m_bMemDC; // TRUE if CDC really is a Memory DC.
public:
CMemDC(CDC* pDC, const CRect* pRect = NULL, bool boolToMemory = TRUE) : CDC()
{
ASSERT(pDC != NULL); // Some initialization
m_pDC = pDC;
m_oldBitmap = NULL;
if (boolToMemory)
m_bMemDC = !pDC->IsPrinting();
else
m_bMemDC = FALSE ; // Get the rectangle to draw
if (pRect == NULL)
{
pDC->GetClipBox(&m_rect);
}
else
{
m_rect = *pRect;
}
if (m_bMemDC)
{
// Create a Memory DC
CreateCompatibleDC(pDC);
pDC->LPtoDP(&m_rect); m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());
m_oldBitmap = SelectObject(&m_bitmap);
SetMapMode(pDC->GetMapMode());
pDC->DPtoLP(&m_rect);
SetWindowOrg(m_rect.left, m_rect.top);
}
else
{
// Make a copy of the relevent parts of the current DC for printing
if (pDC->IsPrinting())
m_bPrinting = pDC->m_bPrinting;
m_hDC = pDC->m_hDC;
m_hAttribDC = pDC->m_hAttribDC;
} // Fill background
FillSolidRect(m_rect, pDC->GetBkColor());
}
~CMemDC()
{
if (m_bMemDC)
{
// Copy the offscreen bitmap onto the screen.
m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
this, m_rect.left, m_rect.top, SRCCOPY);
//Swap back the original bitmap.
SelectObject(m_oldBitmap);
}
else
{
// All we need to do is replace the DC with an illegal value,
// this keeps us from accidently deleting the handles associated with
// the CDC that was passed to the constructor.
m_hDC = m_hAttribDC = NULL;
}
}
// Allow usage as a pointer
CMemDC* operator->()
{
return this;
} // Allow usage as a pointer
operator CMemDC*()
{
return this;
}
};#endif
CDC *pdc=GetWindowDC();
CDC memdc;
memdc.CreateCompatibleDC(pdc);
UINT iRet=memdc.SetPixel(0,0,RGB(0x0,0x1,0x2));为什么iRet的返回值是-1呢?
为何返回值是-1?