The DirectWrite and Direct2D APIs in Windows 8, have been optimized to various common usage scenarios. For example, DirectWrite and Direct2D are often used to show short runs of large text on things like headlines and subheadings, so Microsoft has made this scenario faster.Unlike, Windows 7 where Direct2D uses CPU, Direct2D in Windows 8, utilizes Direct3D 11.1, with suitable Direct3D 11.1 hardware, the rasterization and antialiasing step can now be performed by the GPU, avoiding the need to perform this task on the CPU.
A new feature, Target Independent Rasterization (TIR), has been developed for DirectX 11.1 GPUs to render irregularly shaped objects, like geographical borders on a map. The advancements mean fewer CPU cycles are spent on tessellation, allowing it to pump drawing instructions to the GPU faster without influencing visual quality. Direct3D 11.1 also enables support for a feature that's found on some GPU hardware called Tile-Based Deferred-Rendering (TBDR). Traditionally, GPUs have been engineered for game-type graphics, where the whole screen (or at least, almost the whole screen) changes every frame. Imagine running around in a first-person shooter, for example; while your HUD might remain fixed in view, everything else you see will change because you're standing somewhere different in the 3D environment.
TBDR is designed to optimize this kind of scenario. With TBDR, the screen is divided into tiles, and each tile is drawn separately. This allows the GPU to skip redrawing those parts of the screen that haven't changed, such as the YouTube, Vimeo webpage, and only expend resources redrawing the parts of the screen that have changed, such as the video on the webpage itself.
TBDR is implemented in mobile GPUs such as the Mali and PowerVR Series 5 SGX used in the iPhone, iPad, iPod Touch, Apple TV, Samsung Galaxy series, Blackberry Playbook, Motorola Droid series etc. This technique enables the GPU to do less work, it offers both performance advantages, efficiency and power savings.
Moving away from the GPU, but still in the graphics stack, Microsoft has improved the code used to compress and decompress JPEG and PNG images, to make better use of vector instruction sets provided by CPUs. The new JPEG and PNG routines can decompress and display pictures in about 60 percent of the time that they took in Windows 7.
All Metro-style applications will utilize Direct2D and DirectWrite, will definitely get a performance boost from hardware acceleration, which is missing from current Consumer Preview and Release Preview.
Windows 8's graphical stack has plenty of performance to offer, for the right kind of application—but we're going to need to switch to a whole new set of Metro applications if we want to take advantage of it. The inclusion of raw numbers for one test, but a complete omission for everything else makes us makes us suspicious that the raw numbers are not impressive. Microsoft in order to keep up the “show” used the percentages for their marketing blog entry. Still the lack of any reference to the hardware used for this test negates the whole thing since we cannot compare their findings they are little more than unsubstantiated claims.
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