procedure DrawTransparentBitmap(
DC : HDC; hBmp : HBITMAP;
xStart : integer; yStart : integer; cTransparentColor : COLORREF);
var
bm : BITMAP;
cColor : COLORREF;
bmAndBack, bmAndObject, bmAndMem, bmSave : HBITMAP;
bmBackOld, bmObjectOld, bmMemOld, bmSaveOld : HBITMAP;
hdcMem, hdcBack, hdcObject, hdcTemp, hdcSave : HDC;
ptSize : TPOINT;
begin
hdcTemp := CreateCompatibleDC(
dc);
SelectObject(hdcTemp, hBmp);
// Select the bitmap
GetObject(hBmp, sizeof(BITMAP), @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(
dc);
hdcObject := CreateCompatibleDC(
dc);
hdcMem := CreateCompatibleDC(
dc);
hdcSave := CreateCompatibleDC(
dc);
// 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,
nil);
// Monochrome DC
bmAndObject := CreateBitmap(ptSize.x, ptSize.y, 1, 1,
nil);
bmAndMem := CreateCompatibleBitmap(
dc, ptSize.x, ptSize.y);
bmSave := CreateCompatibleBitmap(
dc, ptSize.x, ptSize.y);
// Each DC must select a bitmap object to store pixel data.
bmBackOld := SelectObject(hdcBack, bmAndBack);
bmObjectOld := SelectObject(hdcObject, bmAndObject);
bmMemOld := SelectObject(hdcMem, bmAndMem);
bmSaveOld := SelectObject(hdcSave, bmSave);
// Set proper mapping mode.
SetMapMode(hdcTemp, GetMapMode(
dc));
// Save the bitmap sent here, because it will be overwritten.
BitBlt(hdcSave, 0, 0, ptSize.x, ptSize.y, hdcTemp, 0, 0, SRCCOPY);
// Set the background color of the source DC to the color.
// contained in the parts of the bitmap that should be transparent
cColor := SetBkColor(hdcTemp, cTransparentColor);
// 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);
// Set the background color of the source DC back to the original
// color.
SetBkColor(hdcTemp, cColor);
// 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,
dc, xStart, yStart,
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 colored 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(
dc, xStart, yStart, 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);
end;