在远程桌面上运行的Qt应用程序外观

Question

I work on a desktop application that we sometimes have to run on a virtual machine using Windows Remote Desktop for access. Fonts and gradients are noticeably degraded in appearance when running through Remote Desktop. The fonts are clearly not anti-aliased (and are normally) The gradients degenerate into much larger bands of solid color, losing the smoother look. Initially, I had assumed Windows was doing this to improve performance, but when I compared application fonts in our produce with those in other applications (Visual Studio specifically), I see that Qt is definitely rendered fonts in dialogs and QGraphicsScene differently.

In the application title bar of my app, I see that the font exactly matches the appearance of other application title bars, and that makes sense because Windows draws that. Within my application, all of the top menu items and fonts on dialogs are not anti-aliased and look terrible. We use QGraphicsScene extensively, and those fonts are degraded as well.

I don't have another application that generates gradients to compare those, but I viewed a high resolution image through the Remote Desktop connection using the Windows image viewer, and it looks just as good as on a local desktop.

The degraded appearance means that we can't do screen shots for documentation while using the VM. We are also frequently required to do demos using VMs and Remote Desktop, and the appearance is not appealing to show to customers. In our industry and within our company, there's increasing pressure to use VMs instead of local, physical machines, so this is becoming a bigger problem.

Both symptoms lead me to believe that Qt knows that I'm visualizing through Remote Desktop and that it is choosing to degrade appearance in favor of performance. I don't want that, or at the very least, I need to control it.

I suspect this is buried somewhere in Qt's style/theme system, but I haven't had any luck finding clues that would point me to the correct place to do something about this, or at least an answer that indicates whether or not it's even possible. Any advice is greatly appreciated.

Answer 1

With QGraphicScene we have OpenGL for rendering. And with some of VMs we mostly rely on software simulating OpenGL via MS DirectX, which is for software and not hardware supported rendering. The most popular software OpenGL rendering is based on ANGLE .

To improve the rendering on VM I would try to build a custom Qt for your app using one of proposed Qt build configurations to configure specific Windows Qt build.

With Qt evolving it gets a bit confusing: which configuration is the best. I was told that since Qt 5.5 -opengl dynamic will be an optimal for most of environments. I used to configure -opengl es2 configuration with Qt 5.3 and that worked well without degrading the graphics but mind that VMs used are from VMware and not MS Hyper-V that would not even allow the app to load due to OpenGL failing to initialize and I could not make ANGLE to help here with that specific Qt.

Answer 2

I was able to address the issue with fonts in QGraphicsScene. Because of the nature of our product, the font handling for graphics items was fairly specialized, and very early in development when I was very new to Qt, I had set the style strategy to those fonts to QFont::ForceOutline because I didn't want the font matching to use any bitmapped fonts. Through experimentation, I found that this strategy results in the fonts not being anti-aliased when running through Remote Desktop. Changing to QFont::PreferAntialias addressed the problem for the fonts in the scene, and that's a substantial and welcome improvement.

Unfortunately, I haven't been able to find a solution for the general application fonts, nor for the gradient degradation, but at least with the fonts, I have something more to go on. My next step will be to start inspecting the fonts that Qt is using by default on some of the widgets and seeing what their attributes are.