C++: 2D Alpha Blend Q:

[Halsafar]

Alright I wrote a very basic AlphaBlending technique using Dx7 Surfaces and some Win32API: GetPixel/SetPixel.

Check it out:

//-----------------
//Alpha Blend -- DC Basic
//-----------------
void DDSurface7::AlphaBlendDC(LPDIRECTDRAWSURFACE7 &Destination, USINT AlphaValue)
{
    COLORREF SrcRGB, DestRGB;
    BYTE r,g,b;
    HDC hdcDestination=0, hdcAlpha=0;

    while (AlphaValue > 255) AlphaValue -= 255;

    Destination->GetDC(&hdcDestination);
    m_AlphaSurface->GetDC(&hdcAlpha);

    for (USINT y = 0; y < m_Height; y++)
    {
        for (USINT x = 0; x < m_Width; x++)
        {
            SrcRGB = GetDCPixel(x,y);
            DestRGB = GetPixel(hdcDestination, x,y);

            r = (AlphaValue * ( GetRValue(SrcRGB) + 256 - GetRValue(DestRGB) )) / 256 + GetRValue(DestRGB) - AlphaValue;
            g = (AlphaValue * ( GetGValue(SrcRGB) + 256 - GetGValue(DestRGB) )) / 256 + GetGValue(DestRGB) - AlphaValue;
            b = (AlphaValue * ( GetBValue(SrcRGB) + 256 - GetBValue(DestRGB) )) / 256 + GetBValue(DestRGB) - AlphaValue;
            
            SetPixel( hdcAlpha,x,y,RGB(r,g,b) );
        }
    }

    Destination->ReleaseDC(hdcDestination);
    m_AlphaSurface->ReleaseDC(hdcAlpha);
} 

All I did was get that formula for calculating the finalpixel value...from one of ElectroMans posts on the subject.

Now what this does essentially is:
Loops through row by row.
Gets the pixel from the surface in the class and the destination surface passed.
Calculates the proper alpha value.
Sets the pixel in a new surface which is then bltfast to the screen later.


My problem is:
I know 2D Alpha is naturally slow, but jeez, doing it every frame takes at least 10 seconds a frame on my comp for a picture the size of the screen.
This is super slow...
It works...works fine. I get a nice alpha blend for translucency.

All I really need it for is screen fading...Nothing more.

[NoteMe]

If you want it faster why not use D3D. And use TnL vertices to create your light halos?

[Halsafar]

light halo's???

I was pondering using D3D...but it is so much easier to simply modify a surface to have it slowly fade to black.

It is also intensly slow.

I plan on using D3D Alpha for everything else of course...But fading in or out the screen seems easiest with 2D...

[NoteMe]

Pretty easy to do fading in D3D too (with alpha blending), here is even an example.

http://www.gametutorials.com/Tutoria...irectX_Pg2.htm

[Jacob Roman]

He's using DirectX7 and those are DirectX9 examples in www.gametutorials.com . I'm not sure how difficult it would be to convert them.

[NoteMe]

Ohhhhh.......well that might be a problem...wouldn't be to difficult if he used DX8 tho'...but D3D has big changes between DX7 and DX8..

[NoteMe]

Ohhh...but TnL vertices was in DX7 too......so that technique can still be applied...and the best thing is that the coordinates for TnL is in screen coordinates, so that makes them perfect for 2D apps...

[Tec-Nico]

Is this the untitled thread?

[NoteMe]

Is this the untitled thread?

No...the Culling one is...but it got back it's title after I PIIIIIPed the forum...

ØØ

[Halsafar]

The allusive untitled thread.
So where did this thread go???

[Electroman]

The allusive untitled thread.
So where did this thread go???

It was to do with the tooltips that give a preview of the thread. For some reason the begining of your thread interferred with the HTML Coments used for the Tooltip and ended up commenting out most of the page . FF only as well.