绘制8bpp灰度位图（非托管C ++） [英] Drawing on 8bpp grayscale bitmap (unmanaged C++)

问题描述

我一直在尝试绘制一个8bpp的灰度位图没有成功。这里是我的一些尝试。也许有人可以指出我做错了什么。

I've been attempting to draw on an 8bpp grayscale bitmap without success. Here are some of my attempts. Maybe someone can point out what I'm doing wrong.

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尝试1：创建，选择，并绘制：

Attempt 1: Create, select, and draw:

在构造函数中：

CBitmap bm;
bm.CreateBitmap (200, 200, 1, 8, NULL);

在OnDraw中：

CDC *mdc=new CDC ();
HGDIOBJ tmp = mdc->SelectObject(bm);

结果：tmp为NULL，表示失败。

Result: tmp is NULL, indicating failure.

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尝试2：创建DIBSection

Attempt 2: CreateDIBSection

在构造函数中：

HBITMAP hbm;
BITMAPINFOHEADER bih;
BITMAPINFO bi;
HANDLE hb;
CDC* myDc = new CDC ();
HDC hdc = myDc->GetSafeHdc ();
void* bits;
RGBQUAD rq [256];

 initBi ();
 hbm = CreateDIBSection (hdc, &bi, DIB_RGB_COLORS, &bits, NULL, 0);

...

void CEightBitDrawingView::initBi()
{
 bih.biSize = sizeof (BITMAPINFOHEADER);
 bih.biWidth = 200;
 bih.biHeight = -200;
 bih.biPlanes = 1;
 bih.biBitCount = 8;
 bih.biCompression = BI_RGB;
 bih.biSizeImage = 0;
 bih.biXPelsPerMeter = 14173;
 bih.biYPelsPerMeter = 14173;
 bih.biClrUsed = 0;
 bih.biClrImportant = 0;

 memset ((void *) rq, 0, 256 * sizeof (RGBQUAD));

 bi.bmiHeader = bih;
 bi.bmiColors = rq;
}

结果：这甚至不能编译，因为BITMAPINFO bmiColors成员被定义为：
RGBQUAD bmiColors [1];

Result: This doesn't even compile because the BITMAPINFO bmiColors member is defined as: RGBQUAD bmiColors[1];

因此不会接受多于一种RGB颜色。事实上，没有我分配给这个成员编译！ （他们可能会使它更复杂吗？）

so won't accept more than one RGB color. In fact, nothing I assign to this member compiles! (Could they possibly make it any more complex!?)

任何建议将不胜感激！谢谢！

Any suggestions would be appreciated! Thanks!

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推荐答案

这里。代码，演示如何在一个不受管理的世界中 - 在堆栈上分配动态大小的结构，填充并传递给CreateDIBSection。

Here. Code that demonstrates how to - in a not managed world - allocate a dynamically sized structure on the stack, fill it in and pass it to CreateDIBSection.

#include <malloc.h>

HBITMAP CreateGreyscaleBitmap(int cx, int cy)
{
  BITMAPINFO* pbmi = (BITMAPINFO*)alloca( sizeof(BITMAPINFOHEADER) + sizeof(RGBQUAD)*256);
  pbmi->bmiHeader.biSize = sizeof (pbmi->bmiHeader);
  pbmi->bmiHeader.biWidth = cx;
  pbmi->bmiHeader.biHeight = cy;
  pbmi->bmiHeader.biPlanes = 1;
  pbmi->bmiHeader.biBitCount = 8;
  pbmi->bmiHeader.biCompression = BI_RGB;
  pbmi->bmiHeader.biSizeImage = 0;
  pbmi->bmiHeader.biXPelsPerMeter = 14173;
  pbmi->bmiHeader.biYPelsPerMeter = 14173;
  pbmi->bmiHeader.biClrUsed = 0;
  pbmi->bmiHeader.biClrImportant = 0;

  for(int i=0; i<256; i++)
  {
    pbmi->bmiColors[i].rgbRed = i;
    pbmi->bmiColors[i].rgbGreen = i;
    pbmi->bmiColors[i].rgbBlue = i;
    pbmi->bmiColors[i].rgbReserved = 0;
  }

  PVOID pv;
  return CreateDIBSection(NULL,pbmi,DIB_RGB_COLORS,&pv,NULL,0);
}

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