MFC : Make a bitmap with a transparant color

[FireJocker]

Not as far as I know - though someone might correct me about that.

In fact, yes I modified your code to get the color of a given pixel to make the transparancy

#pragma once
#include "afxext.h"

class CTransparentBitmapButton :
	public CBitmapButton
{
private:
	void DrawTransparentBitmap(HDC hdc, HBITMAP hBitmap);

	// The colour inside this button's bitmap(s) that should be regarded as transparent
	// is selected by the one of the pixel locate by X, Y
	int m_iXPxlTranparent, m_iYPxlTranparent;

public:
	CTransparentBitmapButton(int XPxlT,int YPxlT);
	~CTransparentBitmapButton(void);

	virtual void OnPaint();
	virtual void DrawItem(LPDRAWITEMSTRUCT lpDrawItemStruct);
};







#include "StdAfx.h"
#include ".\transparentbitmapbutton.h"

CTransparentBitmapButton::CTransparentBitmapButton(int XPxlT,int YPxlT)
{
	// Initialise the transparent pixel X,Y
	m_iXPxlTranparent = XPxlT;
	m_iYPxlTranparent = YPxlT;
}

CTransparentBitmapButton::~CTransparentBitmapButton(void)
{
}

// From 'OnPaint()
void CTransparentBitmapButton::OnPaint() 
{
	if ((GetParent()) && (GetParent()->IsIconic()))
	{
		CBitmapButton::OnPaint();
	}
	else
	{
		CPaintDC dc(this); // device context for painting
		
		// At least onw bitmap must be loaded before calling 'Paint()'
		ASSERT(m_bitmap.m_hObject != NULL);

		// and we'll assume until we find otherwise, that
		// the button is being drawn in its normal state.
		CBitmap* pBitmap = &m_bitmap;

		if ((!(IsWindowEnabled())) && (NULL != m_bitmapDisabled.m_hObject))
			pBitmap = &m_bitmapDisabled;

		DrawTransparentBitmap(dc.m_hDC, *pBitmap);
	}
}

void CTransparentBitmapButton::DrawItem(LPDRAWITEMSTRUCT lpDrawItemStruct)
{
	ASSERT(lpDrawItemStruct != NULL);

	// At least onw bitmap must be loaded before calling 'DrawItem()'
	ASSERT(m_bitmap.m_hObject != NULL);

	CBitmap* pBitmap = &m_bitmap;
	UINT state = lpDrawItemStruct->itemState;

	if ((state & ODS_SELECTED) && (NULL != m_bitmapSel.m_hObject))
		pBitmap = &m_bitmapSel;
	else if ((state & ODS_FOCUS) && (NULL != m_bitmapFocus.m_hObject))
		pBitmap = &m_bitmapFocus;
	else if ((state & ODS_DISABLED) && (NULL != m_bitmapDisabled.m_hObject))
		pBitmap = &m_bitmapDisabled;

	DrawTransparentBitmap(lpDrawItemStruct->hDC, *pBitmap);
}

void CTransparentBitmapButton::DrawTransparentBitmap(HDC hdc, HBITMAP hBitmap)
{
BITMAP	bm;
COLORREF cColour;
HBITMAP	bmAndBack, bmAndObject, bmAndMem, bmSave;
HBITMAP	bmBackOld, bmObjectOld, bmMemOld, bmSaveOld;
HDC		hdcMem, hdcBack, hdcObject, hdcTemp, hdcSave;
POINT		ptSize;

	hdcTemp = CreateCompatibleDC(hdc);
	if (HGDIOBJ hOldObj = SelectObject(hdcTemp, hBitmap)) // Select the bitmap
		DeleteObject(hOldObj);

	GetObject(hBitmap, sizeof(BITMAP), (LPSTR)&bm);
	ptSize.x = bm.bmWidth;		  // Get width of bitmap
	ptSize.y = bm.bmHeight;		  // Get height of bitmap
	DPtoLP(hdcTemp, &ptSize, 1); // Convert from device
										  // to logical points

	// Create some DCs to hold temporary data.
	hdcBack	 = CreateCompatibleDC(hdc);
	hdcObject = CreateCompatibleDC(hdc);
	hdcMem	 = CreateCompatibleDC(hdc);
	hdcSave	 = CreateCompatibleDC(hdc);

	// Create a bitmap for each DC. DCs are required for a number of GDI functions.

	// Monochrome DC
	bmAndBack = CreateBitmap(ptSize.x, ptSize.y, 1, 1, NULL);

	// Monochrome DC

	bmAndObject = CreateBitmap(ptSize.x, ptSize.y, 1, 1, NULL);

	bmAndMem = CreateCompatibleBitmap(hdc, ptSize.x, ptSize.y);
	bmSave = CreateCompatibleBitmap(hdc, ptSize.x, ptSize.y);


	// Each DC must select a bitmap object to store pixel data.
	bmBackOld	= (HBITMAP)SelectObject(hdcBack, bmAndBack);
	bmObjectOld = (HBITMAP)SelectObject(hdcObject, bmAndObject);
	bmMemOld		= (HBITMAP)SelectObject(hdcMem, bmAndMem);
	bmSaveOld	= (HBITMAP)SelectObject(hdcSave, bmSave);

	// Set proper mapping mode.
	SetMapMode(hdcTemp, GetMapMode(hdc));

	// Save the bitmap sent here, because it will be overwritten.
	BitBlt(hdcSave, 0, 0, ptSize.x, ptSize.y, hdcTemp, 0, 0, SRCCOPY);

	COLORREF transparentColour = GetPixel(hdcTemp, m_iXPxlTranparent, m_iYPxlTranparent);

	if (transparentColour) cColour = SetBkColor(hdcTemp, transparentColour);

	// Create the object mask for the bitmap by performing a BitBlt
	// from the source bitmap to a monochrome bitmap.
	BitBlt(hdcObject, 0, 0, ptSize.x, ptSize.y, hdcTemp, 0, 0, SRCCOPY);

	SetBkColor(hdcTemp, cColour);

	// Create the inverse of the object mask.
	BitBlt(hdcBack, 0, 0, ptSize.x, ptSize.y, hdcObject, 0, 0, NOTSRCCOPY);

	// Copy the background of the main DC to the destination.
	BitBlt(hdcMem, 0, 0, ptSize.x, ptSize.y, hdc, 0, 0, SRCCOPY);

	// Mask out the places where the bitmap will be placed.
	BitBlt(hdcMem, 0, 0, ptSize.x, ptSize.y, hdcObject, 0, 0, SRCAND);

	// Mask out the transparent coloured pixels on the bitmap.
	BitBlt(hdcTemp, 0, 0, ptSize.x, ptSize.y, hdcBack, 0, 0, SRCAND);

	// XOR the bitmap with the background on the destination DC.
	BitBlt(hdcMem, 0, 0, ptSize.x, ptSize.y, hdcTemp, 0, 0, SRCPAINT);

	// Copy the destination to the screen.
	BitBlt(hdc, 0, 0, ptSize.x, ptSize.y, hdcMem, 0, 0, SRCCOPY);

	// Place the original bitmap back into the bitmap sent here.
	BitBlt(hdcTemp, 0, 0, ptSize.x, ptSize.y, hdcSave, 0, 0, SRCCOPY);

	// Delete the memory bitmaps.
	DeleteObject(SelectObject(hdcBack, bmBackOld));
	DeleteObject(SelectObject(hdcObject, bmObjectOld));
	DeleteObject(SelectObject(hdcMem, bmMemOld));
	DeleteObject(SelectObject(hdcSave, bmSaveOld));

	// Delete the memory DCs.
	DeleteDC(hdcMem);
	DeleteDC(hdcBack);
	DeleteDC(hdcObject);
	DeleteDC(hdcSave);
	DeleteDC(hdcTemp);
}

But as I tell you before this post, I got the grey of the CDialog classic instead of the color of the bitmap I draw on the CDialog with this code :

BOOL CDigiDialog::OnEraseBkgnd(CDC* pDC)
{	

	CBitmap Bitmap;
    CDC MemDC;
  
	Bitmap.LoadBitmap(p_iIDD_Background); // lecture bitmap dans les ressources
    BITMAP InfosBmp;				// structure d'informations.
    Bitmap.GetBitmap(&InfosBmp);
    MemDC.CreateCompatibleDC(pDC);	// creation d'un DC en memoire
    MemDC.SelectObject(&Bitmap);	// selection du bitmap dans le DC en memoire
    // transfert final du bitmap dans le dc de la view.
    pDC->BitBlt( 0,0,InfosBmp.bmWidth, InfosBmp.bmHeight,
                     &MemDC,
                     0,0,
                     SRCCOPY); 

	return TRUE;
}