如何枚举TWAIN支持的分辨率 [英] How do I enumerate resolutions supported via TWAIN

问题描述

我必须通过TWAIN界面枚举扫描仪支持的DPI.

I have to enumerate DPI's supported by scanner via TWAIN interface.

// after Acquire is called... 
TW_CAPABILITY twCap;
GetCapability(twCap, ICAP_XRESOLUTION)

if (twCap.ConType == TWON_ENUMERATION) {
   pTW_ENUMERATION en = (pTW_ENUMERATION) GlobalLock(twCap.hContainer);

   for(int i = 0; i < en->NumItems; i++) {
      if (en->ItemType == TWTY_FIX32)  {
    TW_UINT32 res = (TW_UINT32)(en->ItemList[i*4]); 
    // print res... 
}

那很好，但是输出顺序很奇怪:

That works fine but output sequence is strange:

50 100 150 44 88 176

50 100 150 44 88 176

我确切知道我的扫描仪支持300 DPI，但不会返回此值. 我在这里做错了什么?为什么我可以通过编程设置"300"，但为什么没有按顺序返回?

I know exactly that my scanner supports 300 DPI but this value doesn't returned. What I do wrong here? Why "300" is not returned in sequence though I can set it programmatically?

推荐答案

您显示的代码仅获取分辨率的低字节，然后将其转换为整数(指针指向chars，因此该行仅获取char然后将其转换为整数).

The code you shown takes just the lower byte of the resolutions, and then converts it to integer (the pointer points to chars, so the line fetch just a char and then converts it to integer).

在读取值之前，必须指定指针指向TW_UNIT32值.

You must specify that the pointer points to TW_UNIT32 values BEFORE reading the value.

例如数字44是数字300(300 DPI)的低字节

The number 44 for instance, is the lower byte of the number 300 (300 DPI)

以下代码应执行此操作:

The following code should do it:

TW_UINT32 res = ((TW_UINT32*)(en->ItemList))[i];

或

TW_UINT32 res = *((TW_UINT32*)(en->ItemList + i * 4));

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