Ramble Ramble Ramble

So last time on this blog: I had mentioned either talking about mo-cap data or portals and did a lot of ranting on AI! This time: I'm going to talk incoherently about different stuff and doing the Portals for Portal will randomly be explained somewhere in the middle. So if I'm going to ramble then what's the point of this blog post, you ask? Simple! I'm going to take this chance to talk about a lot of small things which I don't think I could use for an entire blog post or which would mean retreading ground I've already covered. So without further adieu...

Reflections!

What do I mean by reflections? I mean making something like a mirror that renders in real time. Doing this is a pretty simple 2-part process so I'll just walk through it with some explanations along the way.

Part 1 - Render the scene from the point of view of the mirror, to do this you want to first get the vector between the camera and the mirror in question, this gives you your viewing angle which you will then reflect along the normal vector of the mirror to give you a reflection viewing angle. The actual equation you would want to use here is: V - 2 * (V dot N) * N. This vector is the direction that your mirror camera is looking at, once you have this you simply calculate the Up vector and you can generate a View Matrix for your mirror. Use this view matrix to render the entire scene once, storing it into a Framebuffer Object. Now that you have the scene the mirror sees, move on to the next step!

Part 2 - Now that we have the scene that the mirror sees, we render the scene like we do normally and apply the FBO texture from the previous pass to the mirror: It will now display the reflection in real time and it will change based on the position of the player's camera.

Now that we have reflections working, we can apply some fun stuff to it. For example, we could make a rippling surface as if it's on a lake, to do this we have multiple options: We could use a tesselation shader and use a ripple texture as a displacement map; We could use an algorithm to change how we sample the image, making it distort in places to simulate a ripple appearance; We could also use surface normals to change how the light reflects off of it to make it appear like there's troughs and crests to fool the player into thinking it's rippling.

Portals!

So the portals that we did in class are pretty similar to how you would do a reflection: You're just rendering the scene from a different point of view. In this case you're taking the direction vector between the viewer's position and the position of the portal they're looking through and rotating it so that it matches the orientation of the portal they're looking out of. Then you render the scene from the position of the out-Portal with the direction you calculated previously to a FBO and apply that FBO's texture to the in-Portal.

For added effects such as the rings they have in Portal, make a texture and it so that you have a pass through colour (i.e. just set the alphas to be 0) and a discard colour (i.e. black, blue, etc.) and when you go to render the portal, send in the FBO texture as well as the portal texture. While sampling, if the sampled UV for the portal texture is the discard value then nothing is drawn while if it's the pass through colour the FBO is rendered and then anything else is blended based on alphas. This results in the fragment shader cropping away any unwanted pieces so that it blends in smoothly with anything behind it such as the walls.

Uniquely Shaped Meters!

So this is something I found interesting, it's a technique for creating functioning meters (i.e. player health) that have unique shapes such as being circular or just a wavy line. Basically what happens is you have two textures which are being sampled from: The actual, rendered texture and a 'cutoff' texture. The cutoff texture matches up with the rendered texture and is just a smooth gradient from 1.0 to 0.0 in the direction you want the meter to go. When you render the meter you would pass in a normalized value to use as your cutoff value.

Cutoff Texture

Render Texture with Base

So say you have a cutoff texture that just goes from black to white in a smooth gradient and it's rendering the player health, the player currently has 750/1250HP. This means that the player is currently at 60% health and so you would pass in a value of 0.6. Now, when it goes to check if it should render the health meter, it will sample from the cutoff texture and if the value is 0.6 or less, it will then proceed to sample from the render texture and output the appropriate colour. If the value is greater, it will simply not render the fragment. I like this technique a lot because it just gives you a lot of versatility in how you might want to render things such as timers or health bars or ammo...It just gives you and your artists a lot of flexibility!

Dual Quaternions!

Yeah...No...Not this time. They warrant a full blog post.

So that's my rambling for the night, I hope you enjoyed me try to blunder my way through how to do simple graphics stuff that I find kind of interesting and fun...

I actually don't have anything witty to say here so I'm just going to put a picture of Phong just to make this blog look longer than it is. Cheers!