Tutorial 7 :: A More Flexible BasicEffect

[mikeschuld]

This one is pretty long and drawn out. Let me know if you find any messups

[solidarity]

I ran through it, all seemed to check out just fine.. I could've sworn there was a typo somewhere, but I didn't think much of it so I can't recall where it was anymore. Could have just been my fault too, of course.

Nice tutorial, if there's something I've never been good at, it's shaders.. XP

[Nelson]

Thanks for this. It's an incredibly clear explination of how to get things going.

[Chr0n1x]

Nice tutorial, looking good. Now to get some of the functionality that the XNA BasicEffect has, like Normal Mapping.
Thanks.

[mikeschuld]

That's what the next tut is for

[Chr0n1x]

Excellent, well just so you all know, I will be creating my tutorial to this one, unless Mike releases the Normal Mapping tutorial this weekend. So mine should be up soon enough.

[mikeschuld]

Let me know when you get it done and I'll stick it on in the same format as the rest of them on the main site as well.

[Chr0n1x]

Yeah I will be putting it on my blog in original format and PDF in original format, but first have to find a good way to render the 2d image since SpriteBatch doesn't work with custom pixel shaders.

[EDIT] Okay all done, now to write it up in a tutorial form. Should be up soon enough.
[EDIT x 2] Okay, 99% done on the tutorial, just removing unecessary content like the skybox textures and the hmlogo.dds from the Content directory, to make it smaller. Also removing the bin and obj folders from both projects.
Final filesize is 709kb - Mike, suggest for future tutorials you do similar for those on lower speed internet. Unless you are reenabling the skybox next tutorial.

[sTV]

Hi Mike,
Another great tutorial, thanks for your efforts, I'm really enjoying your XNA series. I have been looking for a good shader primer for a while.

When I follow this tutorial I'm getting different behaviour to you in the shader and I was wondering if you might know why. When I run the app, it seems that the value returned by the BasicShader pixel shader contains transparency information rather than color information. When you include the pixel shader below you get a black model but I get an invisible model.
float4 BasicShader() : COLOR0{
   return (float4)0.0f;
}
If I increase the value returned to 0.5f I get a transparent model, up to 1.0f which is a solid white model.

This seems to run through the rest of the example and I get some pretty exciting shader effects (!), though not what I was expecting or what you get. I'm sure I'm doing something dumb but I can't seem to spot it, I've redone the tutorial twice. Can you think of anything that might cause this behaviour?

[Chr0n1x]

Hi sTV,
When using a float4 to represent color in a Pixel shader, the float4 contains 4 float variables, as seen in its name. Now they are r,g,b, and a.
So if you return a float4 that simply equals 0.0f, then ALL of r,g,b and a will equal 0.0f, meaning you will have a transparent model.

One way around this is to set the alpha to 1 after you set it all to 0, an extra step, but all cards can do it.

Code:

float4 BasicShader() : COLOR0
{
? ? float4 color = (float4)0.0f;
? ? color.a = 1.0f;
? ? return color;
}

That will display a completely black model, but the alpha channel will be set to 1, so it will be fully visible.

[sTV]

Awesome, thanks Chr0n1x, you nailed it, that solved the problem perfectly. I'm a shader n00b.

[Chr0n1x]

Nah thats one part noone really thinks about, the alpha channel, I onyl remembered it because I was working with it in a shader just then. Its good that thats solved.

[mikeschuld]

The alpha channel was only ignored there because a) we are going to be setting it specifically in the next tutorial with an Alpha parameter (like the one BasicEffect has) and b) because alpha blending should be off by default. If your current codebase sets any of the alpha rendering stuff to on somewhere that would cause the phantom mesh

[jadams]

Thanks for another good tutorial mike.

You just answered my question as to why you hardcoded the alpha.

I'm assuming this will go away in the next tut:

Code:

myDiffuseColor = new Vector4(newColor, 1.0f);

I thought that was pretty wierd. Why not just include the alpha in the vector? I guess we'll see down the road.

I have a coule of other questions as well. Why didn't you include SetSpecularPower() in IHMHasMaterial as you did with the diffuse and ambient? It would only make sense. Or am I missing something important?

I just realized my other question isn't valid. I was thinking that the diffuse light wasn't updating correctly. this is because when I rotateted the camera I thought I was rotating the model. Never mind me

Last thing, How do we get textures in? I see three texture coords in the shader. Is it as simple as adding a TextureSampler and another set of coords?

[mikeschuld]

The textures will be using in TEXCOORD0 (which is why i started all the light components are coord1). Also, the SetSpecularPower is an object based thing. Think about having two objects lit in the scene, one being a basketball, and one being a shotput or other metal object. The shotput will have a much higher specular value because it is a lot shinier than the basketball. The way it is implemented now, we can set that component for each object in the Demo code somewhere (or in a custom importer etc.) so everything in the scene shines like it should.