Using advanced graphics in car dashboards

In recent years, traditional mechanical car dashboards have increasingly been replaced by electronic displays. The first step in this evolution was the introduction of LCDs to display mileage and other simple alphanumeric information.

Graphics-based solutions have become affordable due to the falling prices of TFT displays and the availability of corresponding computing power in the embedded space. Since the instrument cluster is one of the most important HMI components and is placed right in front of the driver for them to see at any time, it is a very important differentiating feature for car manufacturers. For high-end cars, this will lead to large investments in this area by car manufacturers. At present, TFT displays still seem to have added value in this area for drivers because they are considered a high-tech feature. This has led to the use of advanced graphics to simulate mechanical instruments. Trying out new possibilities is only the beginning, but there is still a huge room for improvement in this area. Referring to products in the consumer goods industry, it is clear that well-defined user interfaces have become an important differentiating factor today. The general idea of ​​optimisation in this area is to display more complex information in a simpler way - how to achieve this in the automotive field is still under exploration and development. The advantages of this are not only technical, but also commercial. Graphics technology makes it easy to add branding to the dashboard. New revenue streams may be created by using skins for the HMI or supporting downloads of additional applications.

Car dashboards with graphic displays present new technical challenges for the development of such solutions. The complexity of the dashboard has increased by at least an order of magnitude. Although the graphics technology used in this field itself comes from the PC world, its application in cars is just emerging. This requires new skills for the development team and requires considerable time to complete a steep learning curve.

PC image quality is already common for consumer electronics, but the computing performance in PCs far exceeds that available in the embedded space, which means that rendering realistic images will become more difficult.

Compared to the PC space, the embedded space also has challenges to address, such as power consumption and temperature—some of which are similar to those encountered in handheld devices. A key feature of automotive solutions is functional safety, which is not a requirement in the computer and handheld device markets. At least some of the information presented on the car dashboard is considered safety-related. Here, presenting wrong information is unacceptable.

Application Examples

In the current market, we see that graphical instrument cluster displays are clearly divided into several categories. This division is basically driven by the cost of the solution, as adding a larger display increases the price too much to be affordable for mid-range and low-end cars. One thing that all categories have in common is the need to use an analog needle – which can be implemented as an electromechanical needle or using a complex graphical solution to render a realistic needle.

1.Intermediate plug-in display

The most common example is the plug-in display, which is now becoming popular in low-end cars. The instrument cluster display still uses mechanical needles, but provides an additional display, usually located in the center between the scales. The entry-level uses a 4-inch QVGA or WQVGA display.

The display is used to present current fuel consumption, temperature or similar information. It can also optionally present information from the infotainment system.

Mid-range and high-end cars often use larger scale displays. This allows the display to show camera images such as night view, rear view camera images, or even a bird's eye view for parking assistance systems.

Since the instrument panel partitions of electromechanical instruments are fixed, they are not suitable for this situation.

2. Two display screens with center range

A compromise solution based on the traditional electromechanical pointer but providing extended graphic capabilities is to design a display screen on either side of the central mechanical scale. This solution allows more flexibility in the display of information, but still uses a fixed layout and a fixed electromechanical pointer.

3. Fully configurable dashboard

The fully configurable instrument cluster uses a large display with a resolution of 1600×480 pixels. These displays are still a large cost factor, so their use is currently limited to high-end cars. Since no mechanical needles are used, the current implementation focuses mainly on presenting realistic analog needles. Since the content of the instrument cluster is completely software-defined, it can be flexibly adapted to the specific use case. Context-dependent information such as night view can be effectively integrated into the instrument cluster by enlarging, reducing or moving content that is not relevant to the current situation.

4. Head-up display

Head-up displays project image information onto the windshield. The resolution of such displays is usually low and the image content is very simple. The content of the head-up display must be pre-curved to compensate for the deformation caused by the curved windshield. There are many ways to achieve pre-curving, including software, graphics accelerators or dedicated hardware. Head-up displays are usually combined with TFT displays in instrument clusters.

Technology

The complexity of the application cases varies. There are several reasons.

● Screen size: Various screen sizes result in a large difference in the pixels generated. For the solutions currently available on the market or under development, the pixels that need to be processed for each frame range from 75k pixels to 1.3M pixels.

● Animation frequency: Whenever you want to show fast movement, you must provide a high animation frequency. An important use case is the range needle in a speedometer or tachometer.

● Scene complexity: Various expected optical effects, including typical GUI menus, and rendered 3D scenes with glow, reflection, and shadow effects.

To meet the different levels of complexity of use cases described in the previous section, different techniques need to be applied to generate images.

1. Raster Graphics

In raster graphics, the color value of each pixel is stored. Primitive processing usually refers to processing rectangular areas composed of pixels.

An important characteristic of raster graphics is that they are affected by resolution. Scaling will cause severe light falloff.

Raster graphics is a common natural image (photo) technology. Most graphic formats can represent raster graphics (jpg, bmp, png, gif). Many applications support processing raster graphics, including Adobe Photoshop, GIMP, and Aperture.

1.1 Raster Graphics Processor

To accelerate raster graphics, the standard solution is to use a raster graphics processor, which is a tool that can copy/fill/combine rectangular areas composed of pixels. Raster graphics accelerators usually perform memory-to-memory operations, that is, read metadata from memory and then write the resulting data to memory. There is no universally recognized API standard. Some proprietary APIs provide similar functions. More advanced accelerators provide basic graphics drawing functions such as drawing lines and circles on this basis.

1.2 Direct Bitmap Transfer Engine (Sprite Engine)

Similar to a raster graphics processor, a direct bitmap transfer engine also processes rectangles of pixels. The key difference is that the results of the graphics operations are not written back to memory. The direct bitmap transfer engine is part of the display controller and it reads each frame from different locations in memory to compose the final image. The main advantage of using a direct bitmap transfer engine for embedded systems is that it saves memory and memory bandwidth. It can also generate graphics very efficiently because only metadata, such as the position of certain rectangles, need to be modified, rather than the pixel data itself. The biggest disadvantage of a direct bitmap transfer engine is the limitation after merging. When the device capabilities are exceeded, it becomes difficult to generate more complex graphics. If raster graphics are used, it will only result in longer rendering time. Solutions in this area have a proprietary API and there are significant differences in the engine capabilities.

2. Vector Graphics

Vector graphics are based on mathematical descriptions of shapes in 2D space and are resolution-independent. Therefore, vector graphics can be rendered at any resolution without quality issues. Vector graphics are a common technology that is used in many applications today. The most prominent example is TrueType fonts, but it is also used in the scalable vector graphics format SVG, which is supported by all recent browsers. Formats such as Adobe Flash also make extensive use of vector graphics.

Several applications can generate vector graphics: Adobe Illustrator, Inkscape, Adobe Flash Professional. An industry standard API for vector graphics accelerators is OpenVG[0].

3 3D Graphics

Current real-time rendering is based on a 3D model made up of triangles. To achieve the descent effect, you need to apply textures to the triangles. Dividing the triangles in this way will define the level of detail for the model, which affects the rendering effect. This makes the model somewhat resolution-dependent.

For the embedded world, there are two relevant API definitions for 3D graphics. Both APIs are derived from the standard OpenGL, originally started by Silicon Graphics. For the embedded version, several features not relevant to embedded devices are removed. This reduces the size of the hardware accelerator and simplifies the required drivers.

Many applications can generate 3D models. The most common applications include Autodesk 3ds Max, Blender, and Autodesk Maya.

Development Process

The development process of a car dashboard is still in an evolving stage. In this development process, different development methods will be adopted depending on the underlying graphics technology. This process is divided into several parts.

The art department will first provide sketches of the primitives and complete solutions. In most cases, these will be handed over to the software development department, who will develop the programming logic to actually implement the solution. Since many details are not determined, it usually takes a lot of time to make repeated revisions until the final effect meets the requirements of the design department.

For non-3D graphics, one way to shorten the cycle time of performing repetitive work is to use Adobe® Flash®, a graphic animation tool suitable for defining animation sequences and human-machine interfaces with pixel accuracy. Further processing of animation sequences is usually done manually or semi-automatically and requires hand-written program code.

A major drawback of this development process is the lack of flexibility and difficulty in making changes later in the development process. In addition, a lot of work is required for documentation and maintenance.

There are currently some solutions on the market that can speed up the development process by introducing graphical standard APIs and eliminate the need for hand-written specific code. These products usually make use of the primitives designed using the corresponding graphic design application and provide a graphical user interface to design the HMI of the instrument panel. No programming skills are required to use such HMI building tools. You only need to care about the aesthetics and functionality of the generated HMI. The output of the HMI development tool is a software image running on the embedded target. For convenience, a simulator is usually used to test the HMI directly on the development PC.

Other common extra features include checking the consistency of the generated HMI and generating accurate documentation. By separating the actual representation from the HMI logic, HMI construction tools are also able to eliminate the huge differences between different graphics technologies, which will allow the generation of simplified HMIs on low-end raster graphics platforms and the generation of excellent 3D HMIs using the same HMI description.

discuss

Graphics technology used in car dashboards offers many new possibilities. Most solutions today focus on the look and feel of mechanical dashboards. Generating realistic images in real time is a difficult task from a technical point of view. Especially for 3D graphics, this will overload dedicated 3D acceleration modules and even require borrowing several tricks from the field of 3D games to achieve some general optical effects. Considering that the performance of graphics accelerators will further increase in the future, rendering realistic images will become more feasible. However, the best result of such rendered mechanical dashboards looks similar to the dashboards of cars from ten years ago.

In the future, more efforts will be put into technology development to exploit new functionalities and ultimately improve HMI ergonomics. This is a very broad area that can be actively exploited as a differentiating factor. The general idea for future developments is to present more complex information in a simple way. We already see this kind of evolution in cars today, for example, where the economy of the driving style is graphically indicated by the number of green leaves on the display. There are many potential improvements in this area.

● Skins: Allows users to define the look and feel of the dashboard by providing a variety of skins.

● Use blur effects to focus the driver’s attention.

● Use color to attract the driver's attention, such as changing the color of the rendered speed needle when speeding.

● Dynamically partition the display screen – Display more relevant information about a specific situation based on the degree to which the display screen is flipped.

The consumer electronics market has proven in recent years that HMI is important to customers and a new concept that has had a huge impact on the market. Although it is not possible to foresee what the standard will be in future cars, it is clear that the instrument panel has the potential to create a real differentiating advantage. As the driver's main source of information, it has a huge impact on the overall look and feel of the car.