SilverLite : avHW

HW Acceleration of Layered Windows - Good news!

seemar — Mon, 02 Jul 2007 22:05:00 GMT

Good news! A QFE has been released to enable WPF HW acceleration on layered windows on XP:

http://support.microsoft.com/kb/937106/en-us

enjoy!

Layered windows...SW is sometimes faster than HW

seemar — Thu, 26 Oct 2006 03:43:00 GMT

Previously, I had posted that Avalon’s layered windows on XP will be rendered via the software pipeline. One can create a layered window by setting Window.AllowsTransparency="true". I’ve seen a few forum posts about performance issues, and the key takeaway point is that your mileage will vary depending on your video card.

In order to render layered windows via our hardware pipeline, we need to circumvent the fact that DX Present cannot handle a window with transparency. Instead of using DX present, we render via DX, grab the surface (via GetDC) and present with GDI. GDI is not hardware accelerated on the Vista WDDM video driver model. The above results in a chain of bitblits from video memory to system memory to video memory which creates a performance hit on many video cards. However, with a unified memory model (eg. Intel Lakeport 945g), the rendering of layered windows is faster in hardware than in software, as the bitblit goes from system memory to system memory.

To substantiate the performance hit that could arise from the aforementioned bitblit chain with a few numbers, I did a bit of testing on a card without a unified memory model (nvidia geforce 6800, WDDM video driver). My setup is a recent Vista build, Aero Glass theme, 2.5GHz P4, 1.5 GB RAM, single-monitor, single-video card.

Animating the translation
Scenario: Translating a single 50x50 rectangle around a 300x300 semi-transparent window
Observed: Framerate with hardware acceleration was at ~50 frames/sec. With software, ~ 60frames/sec.

Resizing, forcing an entire redraw
Scenario: With the mouse, resizing an empty 300x300 semi-transparent window with no window style to 300x600
Observed: Framerate was ~8 frames/sec when hardware accelerated. With software, ~60 frames/sec.

Frames with sufficiently complex rendering, particularly 3D, can pass the inflection point and will see a boon to having hardware accelerated layered windows. For layered windows with simple 2D content, our hardware codepath has typically a worse framerate than the software rendering codepath on the video cards without a unified memory model. The enabling of layered windows came late in the game for v1, and we’re looking at developing a more refined codepath for rendering layered windows in vNext, stay tuned.

Key takeaway: a semi-transparent window is a particularly complex feature for WPF's rendering system. Figure out early what type of hardware that you expect your app to run on, the performance that is acceptable for your users, and whether you want to use Window transparency.

HW Acceleration of Layered Windows for RTM

seemar — Tue, 19 Sep 2006 02:20:00 GMT

To obtain GPU-accelerated rendering, Windows Presentation Foundation (WPF) normally renders and presents graphical content through the DirectX pipeline – including the composition of the scene geometry and presentation of the results.

Since before Windows XP, Win32 has supported an alternative window presentation mechanism called “layered windows”. Layered windows allow for top-level window transparency effects when composed with the desktop; on WPF, this feature is available by setting Window.AllowsTransparency="true". For example, to get a dropshadow effect, WPF composes Menus and Popups as layered windows.

There are two aspects to rendering: composing the scene, and presenting the surface. The Windows Vista D3D 9.0 graphics API provides support for rendering to surfaces with an alpha channel, but does not directly support a mechanism to present that surface to the desktop and retain alpha information. On Windows Vista, WPF renders via hardware accelerated DX, acquires the surface via IDirect3DSurface9::GetDC, and presents to the screen via GDI.

DirectX 9.0C, the version of DX available on Windows XP, does not support IDirect3DSurface9::GetDC of a surface with an alpha channel. As such, support for hardware accelerated rendering when using Window.AllowsTransparency="true" will not be available on Windows XP from the RC1 and RTM releases of WPF.

Avalon Hardware Acceleration & Video Driver Compat

seemar — Tue, 06 Jun 2006 03:51:00 GMT

Hello. Seema Ramchandani here, PM of the Avalon 2d & 3D graphics team.

Many people have asked me about what is this celebrated feature called “Hardware Acceleration”. In this post, “hardware acceleration” refers to harnessing the GPU to render, leaving the CPU free for other calculations.

In Beta 2, Avalon attempts to hardware accelerate rendering on machines with video drivers newer than November 2004. Video drivers are implemented and made available by the video card manufacturers.

Our (my team’s and my) foremost goal is to ensure a stable and performant experience for as large portion of our users as possible. I’ve personally uncovered a few driver bugs in testing Avalon, and we want to make sure that the Avalon experience is not just performant but stable as well. Looking at the machines in my parent’s home, I know that a large portion of users have the same drivers that shipped with the computer. Some of our users with 2 year old video cards may not get hardware acceleration, but they will get a stable experience.

In Avalon, we offload the rendering costs of many features to the video driver, but we first check the date of your video driver and what it can handle. We run a basic rating of the driver from 0-2 and store the value as RenderingCapability.Tier. What Avalon hardware accelerates does not change between XPDM and WDDM, it changes based on how we rate the actual video card: does the card support PixelShader 2.0, have X Mb of RAM, etc…

Check out the SDK article: Graphics Rendering Tiers[1]. Due to the memory virtualization features of WDDM, we do not have a VRAM requirement for WDDM drivers.

POR for Hardware Acceleration

For Beta 2, we accelerate the rendering of Avalon graphics on GPUs with:

- WDDM drivers of all dates

- XPDM drivers more recent than November 2004, regardless of the OS.

For RTM, we might change the Hardware acceleration story, and I will update this posting. Changes would be in response to analysis of crash reports from our Beta release.

What are XPDM and WDDM? Their differences?

- XPDM: The Windows XP Display Driver Model.

- WDDM: The Windows Vista Display Driver Model. [Microsoft.com]: WDDM is a significant evolution of the graphics driver infrastructure and will not be backwards compatible with XPDM drivers.

The WDDM video driver model is only available on Vista machines; XPDM video driver model is available for both Vista, XP, and Server 2003 machines.

The DirectX team and the video card manufacturers have worked hard to bring the WDDM model to fruition, which brings a more reliable and stable graphics environment. For example:

- WDDM virtualizes their video memory: with this feature, your Avalon app is less likely to run out of video memory and fallback to software.

- A larger portion of the WDDM driver code is run in user mode rather than kernel mode (as opposed to XPDM); if the driver crashes in the kernel, the machine blue screens.

3D Anti-Aliasing Story
Avalon only offers 3D-Antialiasing on WDDM drivers. WDDM offers a more stable model and video memory management, both of which are more desirable when using 3DAA.

Avalon 3DAA stresses video drivers in a way that, up to the release of the Windows Driver Kit, has not been heavily tested before. When it came between our XP users’ computers bluescreen or seeing aliased 3d, we chose aliased 3d. More to come on this topic later.

Why do we enforce a driver date check on XPDM drivers?

Standard DX GPU usage, before Avalon, was largely graphics-heavy games. In our testing, we uncovered bugs in older, XPDM drivers that were not seen by users. Most video driver bugs are never detected by the user, but interacting with some can result in rendering artifacts and/or crashing of the video driver.

A kernel level crash is bad news. We do not want users to blue screen.

In November 2004, Microsoft released a new version of the driver testing guidelines; the drivers written after this date offer better stability. Avalon will use the hardware acceleration pipeline for these drivers and will fall back to software rendering for drivers that do not meet this date.

- Most machines released after November 2004 will have an acceptable driver out of the box

- Users can also update their drivers by visiting the video card manufacturer’s website.

How do I find the date of my video card driver?

In a cmd shell, run “dxdiag” and go to the Display tab. Some Vista users will find that their video drivers have not been published yet. J

I think my video driver has a bug, how can I tell?

When you see rendering artifacts of an Avalon application, the bug might be in several layers of the Avalon, DirectX, video driver rendering chain. The first debugging step to take is to see if the bug repros without your video driver involved; try turning off Avalon hardware acceleration[2] and compare the rendering with and without hardware acceleration enabled.

If you see a difference, first visit your video card manufacturer’s website and downloading the latest video drivers for your card. If you still see a rendering difference between your Avalon app with and without hardware acceleration, please report the bug via Microsoft’s ladybug tool and attach:

- Your driver information[3]

- Description of expected and actual rendering

- Simple application that repros the behavior (xaml-only is preferred)

- Screenshots of both behaviors, if possible.

Links of Interest

- Greg Schechter on WDDM & DWM
http://blogs.msdn.com/greg_schechter/archive/2006/04/02/566767.aspx

- Windows Driver Kit
http://www.microsoft.com/whdc/DevTools/default.mspx

- Submitting a bug report to Avalon
http://lab.msdn.microsoft.com/productfeedback/default.aspx

- PCI Express FAQ off of Microsoft.com
http://www.microsoft.com/whdc/device/display/PCIe_graphics.mspx

[1] http://windowssdk.msdn.microsoft.com/en-us/library/ms742196.aspx

[2] To disable HW acceleration for Avalon on a machine, add the following to your registry: [HKEY_CURRENT_USER\Software\Microsoft\Avalon.Graphics]

"DisableHWAcceleration"=dword:00000001

To re-set HW acceleration, delete the above registry key or replace the above with a 0 value:

[HKEY_CURRENT_USER\Software\Microsoft\Avalon.Graphics]

"DisableHWAcceleration"=dword:00000000

[3] Run “dxdiag /t” in a cmd window. Save the outputted file “dxdiag.txt” to the bug; this file has the information of your video card manufacturer, the name of your card, the driver date, and the driver version number.