使用CreateCompatibleDC 创建了内存DC之后,要再调用SelectObject选择一张位图放入此DC,然后才可以使用此DC进行绘制,之后绘制的数据会保存在内存中,

详细说明看后文。

在MFC中使用内存DC例子:

          // 创建内存DC
CDC mMemDc;
mMemDc.CreateCompatibleDC( &dc ); // 创建兼容位图
CBitmap bmpMemBmp;
bmpMemBmp.CreateCompatibleBitmap( &mMemDc, , );
CBitmap* pOldBmp = mMemDc.SelectObject( &bmpMemBmp ); // 在内存DC上绘图
BOOL bRet = mMemDc.Ellipse( , , , ); // 从内存DC上拷贝至显示DC
dc.BitBlt( , , , , &mMemDc, , , SRCCOPY ); // 恢复
// When you finish with the CBitmap object created with the
// CreateCompatibleBitmap function, first select the bitmap out of the device context, then delete the CBitmap object.
mMemDc.SelectObject( pOldBmp );

以下内容来自msdn:

CreateCompatibleDC

The CreateCompatibleDC function creates a memory device context (DC) compatible with the specified device.

HDC CreateCompatibleDC(
HDC
hdc // handle to DC
);

Remarks

A memory DC exists only in memory. When the memory DC is created, its display surface is exactly one monochrome pixel wide and one monochrome pixel high. Before an application can use a memory DC for drawing operations, it must select a bitmap of the correct width and height into the DC. To select a bitmap into a DC, use the CreateCompatibleBitmap function, specifying the height, width, and color organization required.

When a memory DC is created, all attributes are set to normal default values. The memory DC can be used as a normal DC. You can set the attributes; obtain the current settings of its attributes; and select pens, brushes, and regions.

Memory Device Contexts

To enable applications to place output in memory rather than sending it to an actual device, use a special device context for bitmap operations called a memory device context. A memory DC enables the system to treat a portion of memory as a virtual device. It is an array of bits in memory that an application can use temporarily to store the color data for bitmaps created on a normal drawing surface. Because the bitmap is compatible with the device, a memory DC is also sometimes referred to as a compatible device context.

The memory DC stores bitmap images for a particular device. An application can create a memory DC by calling the CreateCompatibleDC function.

The original bitmap in a memory DC is simply a placeholder. Its dimensions are one pixel by one pixel. Before an application can begin drawing, it must select a bitmap with the appropriate width and height into the DC by calling the SelectObject function. To create a bitmap of the appropriate dimensions, use the CreateBitmap, CreateBitmapIndirect, or CreateCompatibleBitmap function. After the bitmap is selected into the memory DC, the system replaces the single-bit array with an array large enough to store color information for the specified rectangle of pixels.

When an application passes the handle returned by CreateCompatibleDC to one of the drawing functions, the requested output does not appear on a device's drawing surface. Instead, the system stores the color information for the resultant line, curve, text, or region in the array of bits. The application can copy the image stored in memory back onto a drawing surface by calling the BitBlt function, identifying the memory DC as the source device context and a window or screen DC as the target device context.

When displaying a DIB or a DDB created from a DIB on a palette device, you can improve the speed at which the image is drawn by arranging the logical palette to match the layout of the system palette. To do this, call GetDeviceCaps with the NUMRESERVED value to get the number of reserved colors in the system. Then call GetSystemPaletteEntries and fill in the first and last NUMRESERVED/2 entries of the logical palette with the corresponding system colors. For example, if NUMRESERVED is 20, you would fill in the first and last 10 entries of the logical palette with the system colors. Then fill in the remaining 256-NUMRESERVED colors of the logical palette (in our example, the remaining 236 colors) with colors from the DIB and set the PC_NOCOLLAPSE flag on each of these colors.

For more information about color and palettes, see Colors. For more information about bitmaps and bitmap operations, see Bitmaps.

关于内存DC的更多相关文章

  1. MFC 透明内存DC

    在MFC中绘制比较复杂图形,通常采用双缓冲技术来绘图,的确可以大大加快绘制速度和减少闪烁,但是有些情况也不尽然. 我最近遇到了一个问题,采用的也是双缓冲来加快绘图,但是绘制效果还是不尽人意.A对象里大 ...

  2. 如何将内存中的位图数据绘制在DC上

    假如你定义了一个位图类,里面包含位图头,位图信息头,调色板,位图数据.然后你按照位图的格式将位图文件读入你的类中,现在你知道了位图的全部信息了.主要信息包含在位图信息头里面,数据则在位图数据缓冲里面. ...

  3. 处理.NET中的内存泄露

    Fabrice Marguerie是一位软件架构师和咨询师,他在MSDN发表了如何检测和避免.NET程序内存与资源泄漏的文章.此文章描述了编写.NET程序时可能发生的内存与资源泄漏,以及如何避免这些泄 ...

  4. VC++大数据量绘图时无闪烁刷屏技术实现(我的理解是,在内存上作画,然后手动显示,而不再直接需要经过WM_PAINT来处理了)

    http://hantayi.blog.51cto.com/1100843/383578 引言 当我们需要在用户区显示一些图形时,先把图形在客户区画上,虽然已经画好但此时我们还无法看到,还要通过 程序 ...

  5. 多线程图像处理中对选入DC的位图保护

    我在应用多线程加速图像处理(具体参见图像处理的多线程计算)的过程中,曾遇到过一个线程同步的问题.多线程对图像不同子块进行处理,再合成.结果发现最终不是全部子块都处理成功,有的子块好像没有被处理.而且发 ...

  6. 补充:回答网友的问题,如何不用路径,而直接将CImage画到DC中,之后DC一起显示.

    补充:回答网友的问题,如何不用路径,而直接将CImage画到DC中,之后DC一起显示.注释掉 pDC->BeginPath(); // 打开路径层 pDC->Rectangle(0,0,p ...

  7. (转载)解决GDI闪烁

    一般的windows 复杂的界面需要使用多层窗口而且要用贴图来美化,所以不可避免在窗口移动或者改变大小的时候出现闪烁. 先来谈谈闪烁产生的原因 原因一:如果熟悉显卡原理的话,调用GDI函数向屏幕输出的 ...

  8. MFC双缓存技术代码

    屏蔽背景刷新,在View中添加对WM_ERASEBKGND的响应,直接返回TRUE: BOOL CTEMV1View::OnEraseBkgnd(CDC* pDC) { // TODO: 在此添加消息 ...

  9. CDC的StretchBlt函数载入位图时图片失真问题

    最近遇到加载的bmp图片出现失真问题,查找得知需要用SetStretchBltMode函数设置拉伸模式. 函数原型:int SetSTretchBltMode(HDC hdc, int iStretc ...

随机推荐

  1. iOS开发 ----- 加载动画之牛顿摆的实现

    牛顿摆动画 自己看动画有一段时间了,但是还是不是很能理解其中的一些属性方法之类的东西,琢磨了一下午写了一个牛顿摆的动画,这里记录一下,一遍以后查看先上图 先说下思路 说下牛顿摆的大致运动过程 根据牛顿 ...

  2. Ural 2018The Debut Album(DP)

    题目地址:Ural 2018 简单DP.用滚动数组. 代码例如以下: #include <iostream> #include <cstdio> #include <st ...

  3. sklearn特征选择和分类模型

    sklearn特征选择和分类模型 数据格式: 这里.原始特征的输入文件的格式使用libsvm的格式,即每行是label index1:value1 index2:value2这样的稀疏矩阵的格式. s ...

  4. 通过jstl判断是否给value 赋值

    <input type="text" name="saler.password" id="password"  value=" ...

  5. [ssh新闻公布系统三]存储新闻

    一.存储新闻dao方法 在NewsDao.java中新增存储新闻的saveOrupdate方法 public void saveOrupdate(News news){ getSession().sa ...

  6. codeforces 570 D. Tree Requests 树状数组+dfs搜索序

    链接:http://codeforces.com/problemset/problem/570/D D. Tree Requests time limit per test 2 seconds mem ...

  7. javascript 高级编程系列 - 继承

    1. 原型链继承 (缺点:子类继承父类的引用类型的属性值会在各个实例中共享,创建子类实例时无法向父类构造函数传递参数) // 定义父类构造函数 function SuperClass(father, ...

  8. Vuex demo

    <!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title> ...

  9. ecshop购买记录(近期成交数量)显示历史记录

    默认只显示最近30天内的销售记录, 按照下面方法修改 就可以显示所有的了 打开 /includes/lib_insert.php 文件 找到下面代码,将之删除即可,一共有两处,都要删除. AND ' ...

  10. erlang实现DNS解析域名

    erlang的DNS解析,有个inet模块,可以做这个事情,对应的api如下:(这里用的R16B的版本) inet:getaddr/2解析对应一个ip,而inet:getaddr/2解析有可能对应1个 ...