ATI Radeon HD 3870 X2 Review :: MS DirectX 10.1

Microsoft is releasing Windows Vista SP1 in a few short weeks. One of the big updates to their operating system is the inclusion of DirectX 10.1, bringing new features to the gaming API to improve image quality. Features such as FP32 filtering and 4x MSAA are now required instead of optional with DirectX 10. Let’s look at the features. ATI’s 3xxx series is the only shipping video cards with support for DX10.1.

Cube Map Arrays allow the reading and writing of multiple cube maps in a single rendering pass. This allows the graphics card to do efficient global illumination in real-time. Global illumination divides a 3D scene into a 3D array of cubes. A simple version of the scene is rendered from the point of view of someone in the center of the cube looking outward (light probe). When the six faces of each cube are complete they are stored in a cube map texture. After converting each cube mapped into a compressed spherical representation using spherical harmonics, you can determine the amount and color of light falling in any point in the cube from any and all directions with a few math operations.

Ambient Occlusion is a shading technique that determines how much light can reach a given point from all directions and how much is occluded by objects in the way of the light. When a ray of light reaches a surface (wall, floor, sky) it increases the brightness of that surface, while a ray that hits an object in the middle, such as a ball or other object doesn’t increase the brightness of that object. This can result in soft shadows on objects making the objects easier to identify.

DirectX 10.1 offers improvements to the anti-aliasing features of the graphics card. All DirectX 10.1 graphics cards are required to support 4x MSAA, a welcome requirement as virtually every video card on the market supports 4x MSAA. DirectX 10.1 allows custom anti-aliasing filters to be implemented with pixel Shaders. Custom filters can improve AA quality when MSAA may have issues such as HDR+deferred shading techniques. DirectX 10.1 allows all AA buffers to be accessed by Shaders. In the past you could only access multi-sampled color buffers. With DX10.1 you can access information from a depth buffer for each sample individually.