Hi I'm trying to find the fastest alternative to solve a GDI problem with DirectX. We have methods that work but I'm trying to find the fastest alternative. So I will start with the method that works for us right now. 1) We're using an OLE object so we are rendering to a Bitmap using OLEDraw 2) We then copy this bitmap to a DirectX Managed surface and render a quad to the D3D screen. 3) The application we're using(Flash) has the following issues though that we need to be aware of to handle transparency. Transparency is done using a color key with this object so when we copy to our DX surface we need to do the color key check. So that is what we're doing which is OK speed what I want to do is this: I want to find a way we can just use OLEDraw to a DX9 Managed Texture and then find a way to Render using a Color Key. I believe this will be the fastest method if I can find a way to use Multipass texture stages to do this. I have been unable to think of a method so far, where I could get the Alpha Channel to handle transparency. The biggest issue I'm running into is the fact that you must use a X8R8G8B8 format if you want to call GetDC on a Dx9 surface. So I'm trying to think of a way I could use a Color Key Texture as 1 texture stage and the OLE Texture as my other texture stage to come up with a way to render transparency correctly. Does anyone have any ideas on a method to do this. Thanks, Keith

So you question basically boils down to, "How do I configure the D3D9 texture stages of the fixed-function pipeline to render a specified color as transparent?"

If that's the case, I think I can help you, but before I spend time testing my theory, I need to know if this is truly what you're trying to do.

Shaders are not an option. And Yes the question boils down to "How do I configure the D3D9 texture stages of the fixed-function pipeline to render a specified color as transparent"

Thanks for any help you can provide. I'm still stumped on this one.

Keith

What I came up with was similar to ET3D's solution. Use DOTPRODUCT3 to set the alpha channel to zero, based on the color values. You'd need to shift each texel by an offset based on the color key prior to performing the dot product operation, so that the dot product of the texel with itself is zero. I used ADDSIGNED for this, but there are probably other ways to do it.

I have code that does all of this and it does work, the problem is a lack of precision which causes colors that are close to the color key to also become transparent. As an example, if I used 0x00f800 (97% green) as the color key, any color from 0x00f100 to 0x00ff00 ended up with an alpha value of zero. This is because the dot product of that range produces values that are less than 1/255, and are assigned a value of zero once the colors have been scaled back to the range [0,255]. Another problem is that there are probably combinations of color components that will result in a dot product (and a resulting alpha value) of zero, even though they are nowhere near the colorkey's color.

BTW, if you use DOTPRODUCT3 as a color op, it will copy the result to all color channels as well as the alpha channel. The alpha op in the stage will be ignored. There's also an offset involved so that negative values can be expressed. I had to look at the source of the reference rasterizer in order to find out how this texture op actually works.

If you're not going to do this with shaders, then you may want to spend your time making that texture load routine as fast as possible and just search for the color key and set the alpha accordingly. There's a D3DX routine that does this, but you might be able to do something using SSE that would be faster. If you have to do this every frame, double-buffering the texture might provide a speed-up since you aren't trying to write to the texture while it's in use by the GPU.

Hi You mentioned using a bitmap to render to using the Alpha. The problem with that is Text. This is what we've been doing but the issue is with Text. For some reason Flash Text always has 0x00 for the Alpha channel in the bitmap. So we currently need to convert that value's Alpha if the color is not the color key when we copy over to our DirectX surface.

Keith