Since I’ve been working on Away3D 4.0 (Broomstick) for the past few months, it was pretty hard to find the energy to keep this blog up to date, and the promised part 2 of Hacking the Lite kept getting delayed. And delayed. And then delayed some more. Having access to the GPU also caused some debate on whether this series would still be relevant enough. However, after looking at my initial goals for it, I decided it is. After all, the idea was to inspire people to start playing around, and to get people to think in terms of using shaders. Most of the concepts outlined here can be used in Molehill as well. And of course, it’s still some time before we can use the GPU in actual commercial projects So on with the show! This part of the series will build heavily upon the previous part, so it’s perhaps a good idea to review that again.

Shadow maps

Casting shadows is often done using shadow maps. In this case, we’d render a “depth map” of the scene from the light’s point of view. This way, we have a texture containing the distances to the objects closest to the light for every projection ray (which is a single pixel in the shadow map). When rendering the scene, we project every point we are rendering to that shadow map. We can then compare the depth value of the point-to-be-rendered with the value in the shadow map. If it is further away from the light, it must be in shadow and should not be lit. This approach works well, but for current versions of Flash, it’s not very feasible. But, since we’re hacking, there’s other options!

Augmenting projective texture mapping

If you take a look at the schematic on the left (click to enlarge), showing where a shadow should fall, you can see it’s much like projection mapping. The sphere is being perspectively projected unto the floor plane with the light as the projection’s origin. This is the exact same projection that projects the light texture onto the objects. As you can see, if we project the sphere onto the light’s texture first, and project that in turn to the floor, the shadow region remains the same. As a result, we could actually simply project and draw the sphere into the light map before it is applied to the floor.

Order and form

To render a scene with multiple objects, we have to take care to render things in correct order. We need to draw the objects closest to the light first, because they will obviously be casting shadows on object further from the light. Starting out with a clean light map (ie.containing no shadows), we project it on the closest object and then draw that object’s shadow into the light map. Move on to the second closest object, light it, and draw the shadow again. And so on until the last object was reached.

That works great for convex objects, as long as they don’t intersect. For concave or intersecting convex objects, it’s possible that object A casts shadows on object B as well as the other way around. Since we’re rendering everything in a strict order, that’s simply not a possibility. However, this error should generally be acceptable. Another problem is self-shadowing for concave objects, which is impossible using this “cheat”.

Demo and source

Fake shadow mapping demo: really just an adapted version of the previous one.

The source is again on Google Code!

Exciting times afoot! In the not too distance future, we’ll finally get what we’ve been nagging about! I’m of course talking about Molehill, the new hardware-accelerated API Adobe is working on. If you’re curious what we’re doing with Away3D, take a peak at the demo we did with the guys from Evoflash for Adobe MAX. Old news, I know. Moving on.

All that and more is still some time in the future, and in the meanwhile we need to make do with what we currently have available. As part of a session at AUG XL and FlashPlatform, I gave some examples of what we currently can do with Away3D Lite if we’re willing to get our hands a bit dirty. As examples I explained some effects I did for the Spiral Out demo. Now, it’s time to clean up the code mess and explain a thing or two to a slightly broader audience

Basically, what I’ll do is show some things that involve making assumptions that prevent the code from being scalable (ahhh… you got me… that’s just a nice way of saying I’m cheating!). The first step isn’t actually cheating at all, and it’s an old and pretty standard shading technique. However, we’ll need this for part 2 in which we’ll do nothing but cheating, and since no one ever seems to do shaders in Lite I thought it’d be a good way to get started.

This it what we’ll end up with. Not the most attractive demo, but it’ll do. Lengthy explanations ahead, for which the source can come in handy (under examples/projectionMapping)

Projective Texture Mapping

Projective texture mapping, as the name clearly suggests, is a texture mapping technique that mimics a light projecting a texture on objects in the scene (think of a projector slide, a lamp shade’s projections on the walls, …). As I said, there’s nothing new or special about this; it’s been done countless times before. The picture on the right pretty much shows all there’s to it (click to enlarge).

Essentially, we place the “light texture” in front of the light. All we need to do, is draw a line from the position we’re currently shading (the “target point”) to the light (the “source point”) and figure out where that line intersects the plane. Grab the light texture’s colour at that position and multiply it with the object’s base texture colour to get the final shaded colour. We can also incorporate additional shading calculations, particularly normal mapping.

Exactly how we calculate the intersection is up to you. You can do a line-plane intersection calculation, or you can – surprise surprise – use a perspective projection matrix to project the target point onto the texture. So rather than projecting the texture onto the object, we’re effectively projecting the object on the texture first. The latter approach is much more flexible and intuitive, since it’s exactly how a camera projection works (in part 2, we’ll see that this will come in handy too).

Shading in Away3DLite

Away3DLite, minimal as it is, has only very limited support for shading. There’s a Dot3BitmapMaterial that no one seems to know about, though, courtesy of Mr. Bateman I recommend taking a look at that code, just to see how you could implement a custom shader. At a minimum, all you’d need to do is extend BitmapMaterial and override the updateMaterial method (don’t forget to include and use the namespace arcane). In there, you can do anything you like as long as you end up passing a valid BitmapData object to the _graphicsBitmapFill.bitmapData property. For shading purposes, it’s best to keep a second BitmapData object to which we’ll be rendering the shaded version of the texture, leaving the original _bitmap object intact for subsequent frames. Of course, for any advanced shading on BitmapData objects, Pixel Bender is king, so we can run a ShaderJob in there.

Taking a look at the source for the ProjectiveTextureMaterial, that’s pretty much exactly what is happening, with one difference. We’re exposing a manual update method rather than overriding updateMaterial. This seems rather odd (and in this particular case it is) but we’ll need that next time (remember, we’re hacking anyway)

There’s of course a final caveat, in that we don’t have any position information since we just have a bunch of BitmapData objects, no actual geometry. And that is of course something essential if we want to do any projecting at all. For that we can take the same approach as the Away3D Pixel Bender shaders do: position maps. Whereas a normal map encodes the normal for every texel, a position map encodes the object position at that point. In Away3D, the pixel shaders generate a position map automatically from the geometry when a material is created, but in Lite, we’ll settle for creating them manually. This actually makes it possible to add details from a height map, providing the shader with much more detailed topological information than what would have been generated from a bunch of triangles. As a result, the projected map can be subtly displaced as it would on a real uneven surface. It’s not very hard to create position maps procedurally (which is part 3) if you keep in mind that xyz maps to rgb and 0×00-0xff for each colour channel maps to the minimum and maximum bounds of the respective coordinate (so where x == minX, r would be 0).

Demo and source

To see the effect in action, check out the demo. Move the mouse to move the projector, click and drag to move the camera, and use the mouse wheel to move the projector closer or farther from the scene. There’s also a small projection avatar floating around that shows to position and orientation of the projector.

Source can be found in my repo at Google Code.

A long post, which I hope is useful for people. If not, let me know and I’ll keep it more concise next time!
And oh yes, happy New Year’s!

A few months ago, Simo Santavirta (aka simppa.fi, aka jac) from EvoFlash invited me to do some effects for a demo they were planning to release at Assembly 2010. I hadn’t actually done anything for the demoscene before, but how could I say no; it’s Assembly, home of Second Reality! (and I do believe there was beer involved at some point). The category was “Real Wild”, which basically means “demos for any platform that can run real-time graphics”, including Flash. And… We ended first! Champagne for all!

Linkage

• Check out the demo: “Spiral Out”
• The video version
• Simo’s original  post
• The other Real Wild submissions

Demo building for the creatively challenged

Before I start yapping too much, first things first: Simo did >90% of the demo, just need to clarify that!

Okay, to continue… I did get confronted with some facts of life in that I am not an artistic person! With code as a starting point, it’s hard for me to come up with something that looks good. Feels like a wall in my brain that’s preventing me to go that way. Typically, I work the other way around and try to turn “looks” into code (like references from real life). With the abstract beauty of many demos, it had me cursing plenty of times. Luckily, Simo was able to adapt my pieces and make them look good, so I’m very proud of the end result!

From the technical side of things, here’s what I did: normal mapping on dynamic models (procedural of course), projection+shadow mapping, and marching cubes (metaballs and, I dunno, some weird tunnely thing). The metaballs are slightly tongue in cheek, and I consider them an homage to the “metaball guy”. I’ll probably get back to some of the effects in future blog posts, so I won’t delve into any detail right now. Most of them were done using Away3D Lite, preferring it over the main engine because it’s so lightweight/fast and darn easy to hack and extend. For me, it makes an excellent playground!

The demo itself was built upon the evoTinyEngine demo framework, which made it very easy to collaborate, sync, and hook effects into the main demo.

In closing

Obviously, many thanks to Simo for giving me the opportunity to join in! Too bad I couldn’t be there in person, but there were some other things I was up to during the weekend. Time to recover

Enjoy the demo!