A pixel is commonly misunderstood as solely a unit of area, like a tiny square on a screen. However, it's more accurate to consider a pixel as having both length and area. The length of a pixel refers to the distance between two adjacent pixel centers, influencing measurements like DPI (dots per inch). Pixel area is derived from this length, representing the visible square or rectangular region on the display. While often used interchangeably, distinguishing between pixel length and area is important for calculations involving display resolution, image scaling, and other graphical computations, ensuring accuracy and preventing potential confusion.
The blog post explores optimizing font rendering on SSD1306 OLED displays, common in microcontrollers. It delves into the inner workings of these displays, specifically addressing the limitations of their framebuffer and command structure. The author analyzes various font rendering techniques, highlighting the trade-offs between memory usage, CPU cycles, and visual quality. Ultimately, the post advocates for generating font glyphs directly on the display using horizontal byte-aligned drawing commands, a method that minimizes RAM usage while still providing acceptable performance and rendering quality for embedded systems. This technique exploits the SSD1306's hardware acceleration for horizontal lines, making it more efficient than traditional pixel-by-pixel rendering or storing full font bitmaps.
HN users discuss various aspects of using SSD1306 displays. Several commenters appreciate the deep dive into font rendering and the clear explanations, particularly regarding gamma correction and its impact. Some discuss alternative rendering methods, like using pre-rendered glyphs or leveraging the microcontroller's capabilities for faster performance. Others offer practical advice, suggesting libraries like u8g2 and sharing tips for memory optimization. The challenges of limited RAM and slow I2C communication are also acknowledged, along with potential solutions like using SPI. A few users mention alternative display technologies like e-paper or Sharp Memory LCDs for different use cases.
LVGL is a free and open-source graphics library providing everything you need to create embedded GUIs with easy-to-use graphical elements, beautiful visual effects, and a low memory footprint. It's designed to be platform-agnostic, supporting a wide range of input devices and hardware from microcontrollers to powerful embedded systems like the Raspberry Pi. Key features include scalable vector graphics, animations, anti-aliasing, Unicode support, and a flexible style system for customizing the look and feel of the interface. With its rich set of widgets, themes, and an active community, LVGL simplifies the development process of visually appealing and responsive embedded GUIs.
HN commenters generally praise LVGL's ease of use, beautiful output, and good documentation. Several note its suitability for microcontrollers, especially with limited resources. Some express concern about its memory footprint, even with optimizations, and question its performance compared to other GUI libraries. A few users share their positive experiences integrating LVGL into their projects, highlighting its straightforward integration and active community. Others discuss the licensing (MIT) and its suitability for commercial products. The lack of a GPU dependency is mentioned as both a positive and negative, offering flexibility but potentially impacting performance for complex graphics. Finally, some comments compare LVGL to other embedded GUI libraries, with varying opinions on its relative strengths and weaknesses.
The author experienced system hangs on wake-up with their AMD GPU on Linux. They traced the issue to the AMDGPU driver's handling of the PCIe link and power states during suspend and resume. Specifically, the driver was prematurely powering off the GPU before the system had fully suspended, leading to a deadlock. By patching the driver to ensure the GPU remained powered on until the system was fully asleep, and then properly re-initializing it upon waking, they resolved the hanging issue. This fix has since been incorporated upstream into the official Linux kernel.
Commenters on Hacker News largely praised the author's work in debugging and fixing the AMD GPU sleep/wake hang issue. Several expressed having experienced this frustrating problem themselves, highlighting the real-world impact of the fix. Some discussed the complexities of debugging kernel issues and driver interactions, commending the author's persistence and systematic approach. A few commenters also inquired about specific configurations and potential remaining edge cases, while others offered additional technical insights and potential avenues for further improvement or investigation, such as exploring runtime power management. The overall sentiment reflects appreciation for the author's contribution to improving the Linux AMD GPU experience.
Summary of Comments ( 91 )
https://news.ycombinator.com/item?id=43769478
HN commenters largely agree with the article's premise that "pixel" can refer to both length and area. Some point out the context usually makes the meaning clear, similar to how "foot" can describe length or square footage. Others discuss the distinction between device pixels, CSS pixels, and other pixel variations, highlighting the importance of specifying which type of pixel is being discussed. A few commenters suggest the ambiguity arises from conflating the pixel count (area) with the physical size it represents (length). One commenter humorously likens using pixels for area to ordering a screen by the number of pixels instead of physical dimensions, imagining ordering a 1920x1080 inch screen instead of a standard size. Finally, some users offer alternative ways to express length in web design, like using relative units such as
remandem.The Hacker News post "Pixel is a unit of length and area" generated a moderate amount of discussion, with several commenters exploring nuances and offering differing perspectives on the article's premise.
One of the most compelling threads began with a user pointing out that the article overlooks the context of "device pixels" versus "CSS pixels". They explained that CSS pixels are abstract units designed for layout, while device pixels represent the physical hardware. This distinction is crucial for understanding how browsers handle scaling and resolution differences. Other users built upon this, elaborating on the roles of
devicePixelRatioand the complexities of achieving consistent rendering across diverse devices. This discussion highlighted the practical considerations that web developers face when working with pixels in a real-world environment.Another commenter raised the issue of square versus non-square pixels. They noted that while often assumed to be square, pixels can be rectangular, particularly in older or specialized display technologies. This observation added another layer to the discussion, reminding readers that the simple concept of a "pixel" can have subtle variations.
Several users expressed appreciation for the article's clarity in explaining a commonly misunderstood topic. They found the explanations of pixel density and the relationship between length and area in the context of pixels to be helpful.
Some users mentioned the challenges of working with different coordinate systems, highlighting the differences between screen coordinates and pixel coordinates. This tied back to the earlier discussion on device pixels versus CSS pixels, reinforcing the importance of context when discussing pixel measurements.
Finally, a few comments focused on the historical context of pixels, referencing early computer graphics and the evolution of display technology. This historical perspective provided an interesting backdrop to the more technical points raised in other comments.
Overall, the comments on the Hacker News post enriched the discussion around the concept of pixels, moving beyond the article's core points to explore practical implications, historical context, and the complexities of modern display technologies.