HLSL - Part 3.

Bubble

The Bubble effect makes use of several different techniques, bringing them together into one. It features cube mapping, environment mapping, reflection, refraction, colour blending and vertex manipulation.

The effect consists of 2 core passes, one for rendering the environment map and one for rendering the bubble.

The second pass renders the bubble. During this pass, several colours are attained from several sources, and are blended together to produce the final output colour. These sources are a colour from a rainbow texture, the view through the bubble, the reflection off the front of the bubble and the reflection off the inside of the bubble.

The rainbow colour is chosen based on a time variable, added to the distance from the camera to the bubble, and added to the dot product of the view direction and light direction. The combination of these values produces a change in colour when zooming in and out, when rotating around the bubble, and slowly over time.

The next colour to be added is the pass-through colour. This is the colour from the cube map on the other side of the bubble. Refraction would affect the light passing through the bubble, magnifying the view slightly.

The third colour to add is the reflection from the inside of the bubble. The colour is multiplied by the inverse of the rainbow’s alpha value to only draw it where the rainbow colours are not (this reflection should be a weak value, in this case it is visualised as being overpowered by the rainbow colour value).

The final colour value to add to the output colour is the reflection colour from the front of the bubble. The view direction is reflected in the bubble’s normal and the colour is extracted from the cube map. This final colour is multiplied by the sum of the opacity value used for the inverse reflection and an edge value so that the reflection is more intense towards the edge of the bubble. Finally it is added to the output colour which is finally rendered to the screen.

Over Exposure

In real life terms, exposure relates to the length of time a camera lens is open. The longer the lens is opened, the more light is put onto the image. The extra light saturates the image, and eventually the image is overpowered with light and is turned completely white. This shader effect attempts to simulate the feel of over-exposure.

HLSL - Part 2.

More shader effects I have created.

2D Fire Effect

This effect uses a 2D screen aligned quad and applies multiple passes to transform the original texture data into a fire effect. There are many examples of fire shaders available, on the internet; however I decided to create my own. The effect was refined and improved to reduce the number of ALUs needed and thus reaching good performance speeds.

The full effect consists of four passes. The first does most of the work, making the texture look like a fire by applying colours, and distorting the texture co-ordinates. The second, third and fourth down-sample the apply a Gaussian blur to the output of the first pass. Finally the image is upsampled and combined with the first pass' output to provide the final effect.

Render Target Textures

This effect uses render targets to demonstrate techniques seen in games like Super Paper Mario, where 3D visuals are projected onto flat 2D surfaces in a 3D environment. In this effect, a 3D elephant model is drawn to a renderable texture which is mapped onto a 3D cube and a 2D quad plane in 3D space with alpha transparency.

The effect is broken down into three passes. The first renders the rotating elephant to a texture, from the point of view of a second camera. The areas of the texture not populated by elephant pixels are set to be completely transparent.

The second pass renders the outer 3D cube and maps the elephant texture onto the faces of the cube. The transparent areas of the texture are replaced with a golf course image, to provide a background.

The last pass renders a small quad in the centre of the world. The quad is alpha blended so that the only pixels drawn are those depicting the elephant. When the user looks straight at the quad, the elephant appears 3D however it is really just a projection.

HLSL - Part 1.

HLSL (High Level Shader Language) is used to create vertex and pixel shader effects.

In November of 2007 I learnt HLSL and created a some effects using AMD's RenderMonkey 1.71.The following are some of the shader models I created.

Sepia

This sepia shader model is a post-processing effect that could be applied to a colour at any time. Sepia tone effects produce images coloured in tones of brown and can commonly be found as a feature on modern digital cameras.

The implemented effect uses a adjustable percentage value which is used to linearly interpolate from no sepia tone to fully sepia.

I added a 2D sepia effect using thje same function but applied to a screen aligned quad in order to provide good visual examples.

Specular Highlight

Specular highlights are the bright spots of light that are seen when bright lights reflect off shiny objects. In computer games, specular highlights help give the user a clear idea of an object’s shape and position within a scene. There are several specular highlighting models that can be used to give varying visual effects.

The specular highlight is added to the ambient and diffuse colour values to produce a simple model for the output colour of the object at a specific pixel.

There are several basic specular highlight formulae that produce varying visual effects. I have implemented a Gaussian distribution model and a Beckmann distribution model, but will just discuss the Beckmann distribution here.

The Beckmann distribution model offers a more realistic physics model than the Gaussian distribution, however is much more computationally heavy. For this reason, I have calculated the majority of the non-specular processing on the vertex shader to reduce the number of arithmetic logic commands processed by the pixel shader.

The follwing images show the Beckmann distribution with varying surface smoothness values.

Edge Glow

The Edge Glow effect is not based on any realistic lighting model, but on an effect used in the game Super Mario Galaxy. The game is based in space where the backgrounds are primarily dark shades. To help the 3D models rendered against these darker backgrounds stand out, the models all appear to have glowing edges.


From looking at screenshots, I created a formula to generate a similar effect. I also added a scaling value to adjust the amount of glow applied by the process. The following images show the effect in action.