了解 GetDiBits.C++ [英] Understanding GetDiBits. C++

问题描述

MSDN 说在调用此函数之前，不应将 GetDiBits 中使用的位图选入 DC.但是根据我的经验(使用 BitBlt)，我知道除非选择位图，否则我无法绘制位图.

1. GetDiBits 如何避免这种情况?我可以只使用一个未选择的、新创建的位图作为这个函数的参数吗?

2. GetDiBits 以及 CreateDibSection 返回一个数组.但是 MSDN 说的是第一个函数:

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   指定兼容位图的位"

   我认为 DI 代表 DeviceIndependent.为什么会有矛盾?这意味着，根据 MSDN，GetDiBits 只能与 CreateCompatibleBitmap(即 DD)一起使用?那么我不能把这个数组发送到另一台机器上显示它，对吗?

3. 这两个函数都使用 hDC.如果 CreateDibSection 是真正的 DIndependent 为什么它需要一个 hDC?所有需要的信息都通过位图信息头提供...

解决方案

1. 除非被选中，否则我无法绘制位图.GetDiBits 如何规避这一点?

GetDIBits 不做任何绘图.它从位图中读取像素数据并将其转换为所需的颜色格式.SetDIBits 也不绘制"，但它会在位图中设置像素数据.

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2. 命名混乱.

GetDIBitmap 中的 DI 指的是像素数据以与设备无关的格式(特别是您要求的格式)返回这一事实.源位图可以是兼容位图或与设备无关的位图.

类似地，SetDIBitmap 获取与设备无关的像素数据并将其转换为目标位图的类型.

这些函数的名称令人困惑.

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3. DC 有什么用?

DC 用于回答有关设备上像素格式的任何问题.例如，如果源格式是基于调色板的设备相关位图，GetDIBits 将假定选择到 DC 中的调色板是正确的.请注意，调色板不在 BITMAPINFOHEADER 中.

CreateDIBSection 创建一个混合位图，以独立于设备的方法存储数据，但也可能保持与设备相关的副本与其同步以提高性能.所以它需要知道目标设备的 DC.

MSDN says that the bitmap used in GetDiBits should not be selected into a DC before calling this function. But from my experience(with BitBlt) I know that I cannot draw an a bitmap unless it is selected.

1. How does GetDiBits circumvents this? Can I just use an unselected, newly created bitmap as argument to this function?

2. GetDiBits as well CreateDibSection returns an array. But MSDN says about the first function:

   "bits of the specified compatible bitmap"

   I thought DI stands for DeviceIndependent. Why is there a contradiction? This means that, according to MSDN, GetDiBits can be used only with CreateCompatibleBitmap (which is DD)? Then I can't send this array to another machine to display it,right?

3. Both functions use a hDC. If CreateDibSection is truly DIndependent why does it need a hDC? All the needed info is provided through the bitmapinfoheader...

解决方案

1. I cannot draw an a bitmap unless it is selected. How does GetDiBits circumvents this?

GetDIBits doesn't do any drawing. It reads pixel data from a bitmap and converts it into the desired color format. SetDIBits doesn't "draw" either, but it will set the pixel data in a bitmap.

2. Naming confusion.

The DI in GetDIBitmap refers to the fact that the pixel data is returned in a device-independent format (specifically, the one you ask for). The source bitmap can be a compatible bitmap or a device-independent bitmap.

Similarly SetDIBitmap takes device-independent pixel data and converts it to the type of the target bitmap.

These functions are confusingly named.

3. What's the DC for?

The DC is used to answer any questions about the pixel format on the device. For example, if the source format is a palette-based device-dependent bitmap, GetDIBits will assume the palette selected into the DC is the correct one. Note that the palette is not in the BITMAPINFOHEADER.

CreateDIBSection creates a hybrid bitmap that stashes data in a device-independent method, but may also keep a device-dependent copy in sync with it for performance. So it needs to know the DC of the intended device.

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