VC++加载透明png图片的两种常用方法——GDI+和CImage_综合

先看看GDI+的方法
方法1：

1.GDI+画透明图层（alpha）的png图片

stdafx加入如下：

#include <comdef.h>//初始化一下com口
#include "GdiPlus.h"
using namespace Gdiplus;
#pragma comment(lib,"gdiplus.lib")

开始初始化：
在app类的声明里（.h）加入：

ULONG_PTR m_gdiplusToken;

InitInstance()里加入：//若没有usingnamespace Gdiplus; 就要在前面加Gdiplus::

GdiplusStartupInput gdiplusStartupInput;
GdiplusStartup(&m_gdiplusToken, &gdiplusStartupInput, NULL);

重载ExitInstance,加入GdiplusShutdown(m_gdiplusToken);

int CxxxApp::ExitInstance()
{// TODO: 在此添加专用代码和/或调用基类GdiplusShutdown(m_gdiplusToken);return CWinApp::ExitInstance();
}

显示图片的过程如下

CClientDC *pDC = new CClientDC(GetDlgItem(IDC_STATIC_PIC));
CRect rect;
GetDlgItem(IDC_STATIC_PIC)->GetWindowRect(&rect);
Graphics graphics(pDC->m_hDC); // Create a GDI+ graphics object
Image image(_T("1.png")); // Construct an image
graphics.DrawImage(&image, 0, 0, image.GetWidth(), image.GetHeight());
delete pDC;

这是用GDI+来显示图片。

2.CImage绘制带alpha透明图层的png图片

用MFC自带的CImage也可以显示，不过要稍微进行转换才能得到正常的带α通道的png图片！

在画图前进行一次转换，其中Image是CImage的对象

if (Image.GetBPP() == 32) //确认该图像包含Alpha通道
{int i;int j;for (i = 0; i < Image.GetWidth(); i++){for (j = 0; j < Image.GetHeight(); j++){byte *pByte = (byte *)Image.GetPixelAddress(i, j);pByte[0] = pByte[0] * pByte[3] / 255;pByte[1] = pByte[1] * pByte[3] / 255;pByte[2] = pByte[2] * pByte[3] / 255;}}
}

具体方法如下：

HWND hwnd = GetSafeHwnd(); //获取窗口的HWND
::InvalidateRect( hwnd, NULL, true ); //或者 ::InvalidateRect( hwnd, NULL, false );
::UpdateWindow(hwnd);
//若使用前不想把原来绘制的图片去掉，可以删去上面那三段
CDC *pDC = GetDC();
CImage Image;
Image.Load(strPath);
if (Image.IsNull())
{MessageBox(_T("没加载成功"));return -1;
}
if (Image.GetBPP() == 32) //确认该图像包含Alpha通道
{int i;int j;for (i = 0; i < Image.GetWidth(); i++){for (j = 0; j < Image.GetHeight(); j++){byte *pByte = (byte *)Image.GetPixelAddress(i, j);pByte[0] = pByte[0] * pByte[3] / 255;pByte[1] = pByte[1] * pByte[3] / 255;pByte[2] = pByte[2] * pByte[3] / 255;}}
}
Image.Draw(pDC->m_hDC, 0, 0);
Image.Destroy();
ReleaseDC(pDC);

代码中内部的框架是对图像的再次处理，对原来进行了修正，这样得到的更加正常，代码实测如下

绘图后效果

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

3.如果图片是在资源里的时候加载方法又不一样

这时需要两个函数，

对于GDI+如下：

BOOL ImageFromIDResource(UINT nID, LPCTSTR sTR,Image *&pImg)
{HINSTANCE hInst = AfxGetResourceHandle();HRSRC hRsrc = ::FindResource (hInst,MAKEINTRESOURCE(nID),sTR); // typeif (!hRsrc)return FALSE;// load resource into memoryDWORD len = SizeofResource(hInst, hRsrc);BYTE* lpRsrc = (BYTE*)LoadResource(hInst, hRsrc);if (!lpRsrc)return FALSE;// Allocate global memory on which to create streamHGLOBAL m_hMem = GlobalAlloc(GMEM_FIXED, len);BYTE* pmem = (BYTE*)GlobalLock(m_hMem);memcpy(pmem,lpRsrc,len);GlobalUnlock(m_hMem);IStream* pstm;CreateStreamOnHGlobal(m_hMem,FALSE,&pstm);// load from streampImg=Gdiplus::Image::FromStream(pstm);// free/release stuffpstm->Release();FreeResource(lpRsrc);GlobalFree(m_hMem);return TRUE;
}

这时加载图片的代码变为：

CClientDC *pDC = new CClientDC(GetDlgItem(IDC_STATIC_PIC));
CRect rect;
GetDlgItem(IDC_STATIC_PIC)->GetWindowRect(&rect);
Graphics graphics(pDC->m_hDC); // Create a GDI+ graphics object
Image *pimage; // Construct an image
ImageFromIDResource(IDB_PNG1,_T("PNG"),pimage);
graphics.DrawImage(pimage, 0, 0,pimage->GetWidth(), pimage->GetHeight());
delete pDC;

用CImage时需要如下函数：

BOOL LoadImageFromResource(CImage *pImage, UINT nResID,LPCTSTR lpTyp)
{if ( pImage == NULL) return false;pImage->Destroy();// 查找资源HRSRC hRsrc = ::FindResource(AfxGetResourceHandle(), MAKEINTRESOURCE(nResID), lpTyp);if (hRsrc == NULL) return false;// 加载资源HGLOBAL hImgData = ::LoadResource(AfxGetResourceHandle(), hRsrc);if (hImgData == NULL){::FreeResource(hImgData);return false;}// 锁定内存中的指定资源LPVOID lpVoid = ::LockResource(hImgData);LPSTREAM pStream = NULL;DWORD dwSize = ::SizeofResource(AfxGetResourceHandle(), hRsrc);HGLOBAL hNew = ::GlobalAlloc(GHND, dwSize);LPBYTE lpByte = (LPBYTE)::GlobalLock(hNew);::memcpy(lpByte, lpVoid, dwSize);// 解除内存中的指定资源::GlobalUnlock(hNew);// 从指定内存创建流对象HRESULT ht = ::CreateStreamOnHGlobal(hNew, TRUE, &pStream);if ( ht != S_OK ){GlobalFree(hNew);}else{// 加载图片pImage->Load(pStream);GlobalFree(hNew);}// 释放资源::FreeResource(hImgData);return true;
}

这时加载图片的代码如下：

HWND hwnd = GetSafeHwnd(); //获取窗口的HWND
::InvalidateRect( hwnd, NULL, true ); //或者 ::InvalidateRect( hwnd, NULL, false );
::UpdateWindow(hwnd); 
CDC *pDC = GetDC();
CImage Image;
LoadImageFromResource(&Image,IDB_PNG1,_T("PNG"));
if (Image.IsNull())
{MessageBox(_T("没加载成功"));return;
}
if (Image.GetBPP() == 32) //确认该图像包含Alpha通道
{ int i;int j;for (i=0; i<Image.GetWidth(); i++){for (j=0; j<Image.GetHeight(); j++){byte *pByte = (byte *)Image.GetPixelAddress(i, j);pByte[0] = pByte[0] * pByte[3] / 255;pByte[1] = pByte[1] * pByte[3] / 255;pByte[2] = pByte[2] * pByte[3] / 255;}}
}
Image.Draw(pDC->m_hDC,0,0);
Image.Destroy();
ReleaseDC(pDC);

另

要注意的是，最好把绘图放在OnPaint消息响应里，否则，OnSize消息触发OnPaint重绘时可能会把之前的绘图全部清除