How to blend two pf24bit images using ScanLine (Views: 28)
Problem/Question/Abstract: Does anyone know how to implement basic alphablending without using Win2000 AlphaBlend function? I am trying to write a simple graphics program that will perform some alphablending on Win95 and Win98, but I don't know the necessary steps. Answer: Here's a method of blending two bitmaps. It uses 24-bit bitmaps and scanlines, so only works with D3 or higher. It assumes that variable b, a TBitmap, has pixelformat pf24bit. type {for scanline access to 24-bit bitmaps} TRGBArray = array[0..32767] of TRGBTriple; pRGBArray = ^TRGBArray; {Gradient is one bitmap, b is the other. Amount is the percentage of the Gradient image to blend with b. tBufr is an existing TBitmap that's used internally for operations, b is the original bitmap. tBufr is sized to match b, and Gradient is stretched into it for this operation. All bitmaps are created and free'd elsewhere!} procedure TForm1.MergeGradient(Amount: integer); var pb, pc: pRGBArray; x, y: integer; GrdPct: Single; ImgPct: Single; begin Screen.Cursor := crHourGlass; GrdPct := Amount / 100; ImgPct := 1 - GrdPct; tBufr.Width := b.Width; tBufr.Height := b.Height; tBufr.PixelFormat := pf24bit; tBufr.Canvas.StretchDraw(Rect(0, 0, tBufr.Width, tBufr.Height), Gradient); for x := 0 to tBufr.Height - 1 do begin pb := tBufr.ScanLine[x]; pc := b.ScanLine[x]; for y := 0 to tBufr.Width - 1 do begin pb[y].rgbtRed := Round(pb[y].rgbtRed * GrdPct + pc[y].rgbtRed * ImgPct); pb[y].rgbtBlue := Round(pb[y].rgbtBlue * GrdPct + pc[y].rgbtBlue * ImgPct); pb[y].rgbtGreen := Round(pb[y].rgbtGreen * GrdPct + pc[y].rgbtGreen * ImgPct); end; end; Image1.Picture.Assign(tBufr); Screen.Cursor := crDefault; end; |