Sign in to follow this  

Change Alpha Color Without Recreating Polygon

Recommended Posts

I found an awesome method to create a sphere polygon with normals, as well as texture coordinates for tu and tv, but I severely modified it to support changing its color / alpha as well and made it my own thing. That way I don't have to resort to using D3DXCreateSphere() which doesnt support texture coords. Works great, but I wanted to fade from one sphere into another, similar to fading from day sky to night sky. Is there a way to change alpha values of a color without recreating the entire object every frame with the new colors? Note I'm not using HLSL, and just DirectX9 and C++. Thanks.

Share this post

Link to post
Share on other sites

If you wish to change all vertices of your sphere to the same alpha colour, you can do something with SetTextureStageState calls, but it's such a long time since I've done this style of programming that I would need to spend some time working out the correct calls.

However, what it sounds like you really want to do is interpolate between a "day" texture and a "night" texture, so it will be much simpler if you just draw a single sphere with two textures and D3DTOP_LERP - again, use a bunch of SetTextureStageState calls.

Share this post

Link to post
Share on other sites

I'll look into using some SetTextureStageState calls but I think it's messed up that after all these years, I've been setting colors and alphas to polygons upon its creation for years. And all this time if I ever needed to change anything, it involved SetTextureStageState's this whole time. Now alls I gotta do is figure out the right states.



I fixed it after finding a similar post on gamedev:


DWORD AlphaValue;
AlphaValue = D3DCOLOR_ARGB(100,255,255,255);

mpDevice->SetTextureStageState(0, D3DTSS_COLOROP, D3DTOP_MODULATE);
mpDevice->SetTextureStageState(0, D3DTSS_COLORARG1, D3DTA_TEXTURE);
mpDevice->SetTextureStageState(0, D3DTSS_COLORARG2, D3DTA_DIFFUSE);
mpDevice->SetTextureStageState(0, D3DTSS_ALPHAOP, D3DTOP_MODULATE);
mpDevice->SetTextureStageState(0, D3DTSS_ALPHAARG1, D3DTA_TEXTURE);

mpDevice->SetTextureStageState(0, D3DTSS_CONSTANT, AlphaValue);
mpDevice->SetTextureStageState(0, D3DTSS_ALPHAARG2, D3DTA_CONSTANT);
mpDevice->SetTextureStageState(1, D3DTSS_COLOROP, D3DTOP_DISABLE);
mpDevice->SetTextureStageState(1, D3DTSS_ALPHAOP, D3DTOP_DISABLE);


works like a charm and you can dynamically change the alphas WITHOUT recreating the polygons

Edited by Psychopathetica

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this