Understanding why some e-Readers fall short of performing as Android tablets (Setting, Hidden Benefits).

There is a fact about modern graphics chips which some people may not be aware of – especially some Linux users – but which I was recently reminded of because I have bought an e-Reader that has the Android O/S, but that features the energy-saving benefits of “e-Ink” – an innovative technology that has a surface somewhat resembling paper, the brightness of which can vary between white and black, but that mainly uses available light, although back-lit and front-lit versions of e-Ink now exist, and that consumes very little current, so that it’s frequently possible to read an entire book on one battery-charge. With an average Android tablet that merely has an LCD, the battery-life can impede enjoying an e-Book.

An LCD still has in common with the old CRTs, being refreshed at a fixed frequency by something called a “raster” – a pattern that scans a region of memory and feeds pixel-values to the display sequentially, but maybe 60 times per second, thus refreshing the display that often. e-Ink pixels are sent a signal once, to change brightness, and then stay at the assigned brightness level until they receive another signal, to change again. What this means is that, at the hardware-level, e-Ink is less powerful than ‘frame-buffer devices’ once were.

But any PC, Mac or Android graphics card or graphics chip manufactured later than in the 1990s has a non-trivial GPU – a ‘Graphics Processing Unit’ – that acts as a co-processor, working in parallel with the computer’s main CPU, to take much of the workload off the CPU, associated with rendering graphics to the screen. Much of what a modern GPU does consists of taking as input, pixels which software running on the CPU wrote either to a region of dedicated graphics memory, or, in the case of an Android device, to a region of memory shared between the GPU and the CPU, but part of the device’s RAM. And the GPU then typically ‘transforms’ the image of these pixels, to the way they will appear on the screen, finally. This ends up modifying a ‘Frame-Buffer’, the contents of which are controlled by the GPU and not the CPU, but which the raster scans, resulting in output to the actual screen.

Transforming an image can take place in a strictly 2D sense, or can take place in a sense that preserves 3D perspective, but that results in 2D screen-output. And it gets applied to desktop graphics as much as to application content. In the case of desktop graphics, the result is called ‘Compositing’, while in the case of application content, the result is either fancier output, or faster execution of the application, on the CPU. And on many Android devices, compositing results in multiple Home-Screens that can be scrolled, and the glitz of which is proven by how smoothly they scroll.

Either way, a modern GPU is much more versatile than a frame-buffer device was. And its benefits can contribute in unexpected places, such as when an application outputs text to the screen, but when the text is merely expected to scroll. Typically, the rasterization of fonts still takes place on the CPU, but results in pixel-values being written to shared memory, that correspond to text to be displayed. But the actual scrolling of the text can be performed by the GPU, where more than one page of text, with a fixed position in the drawing surface the CPU drew it to, is transformed by the GPU to advancing screen-positions, without the CPU having to redraw any pixels. (:1) This effect is often made more convincing, by the fact that at the end of a sequence, a transformed image is sometimes replaced by a fixed image, in a transition of the output, but between two graphics that are completely identical. These two graphics would reside in separate regions of RAM, even though the GPU can render a transition between them.

(Updated 4/19/2019, 15h10 … )

Continue reading Understanding why some e-Readers fall short of performing as Android tablets (Setting, Hidden Benefits).

A New Set Of Headphones

As early as This posting, I had experimented with Bluetooth Headphones, that were specifically designed to handle High-Fidelity sound, for continuous music playback. But the fact is, that in the past 2 years, 3 such headphones failed me. The most-recent, ‘Infinim HBS-910′ set also failed on me, mechanically, only earlier this month, which effectively means that in total, if I continued doing things this way, I’d continue to burn through my money too fast.

So the course which I’ve chosen to go instead, is to use wired headphones, but to buy slightly-higher-quality, wired headphones, that are compatible with an Android device.

There once existed the observation, that the buttons on certain headphones would only work with iOS devices, and the buttons on other headphones would only work on Android-based devices. Interestingly enough, If the packaging doesn’t specify, then today, most headphones will work on either devices. My new Headrush HRB 3012 set has buttons which my Samsung Galaxy S6 recognizes.

(Edit 07/14/2018 : )

About these new ‘Headrush HRB 3012′ headphones:

Their cord consists of a ribbon, instead of the older-type, standard elastic, round-cross-section cords, which I was used to. I think that the current, ribbon design is a clever way to minimize any injuries which a headphone-cord can sustain, let’s say because users often pull the headphones out of their socket, by the cord instead of by the jack. The only way I foresee the ribbon-design getting injured, would be if somebody got a knot into it – and was then foolish enough to try to undo the knot, by just pulling it tight. And, because the ribbon tends to be more stiff, undoing knots correctly, has actually become easier.

There is one little issue with these though. Like the designs that I was used to, this set of headphones has a bump in its ribbon, which splits into two ribbons: One to the left ear, and one to the right ear. And in the segment of ribbon to the right ear, there is a remote-controller-button, inline-mike bump. When all the ribbons are (untwisted) parallel, and at right-angles to the wearer, the ribbon that goes to the right ear, has its mike facing away from the wearer, and has the controller-buttons facing towards the wearer.

As a result, I find myself twisting or rotating the right-hand ear-phone 360⁰ at the end of its ribbon-segment, thereby turning the inline-bump 180⁰, so that the inline-mike is again, facing towards me.



Browsing Android Files using Bluetooth

One of the casual uses of Bluetooth under Android, is just to pair devices with our Android (host) device, so that specific apps can use the paired (slave) device. This includes BT-headphones, and many other devices.

But then a slightly more advanced use for BT under Android could be, that we actually send files to a paired Android device. It’s casually possible to take two Android tablets, or a tablet and a phone, and to pair those with each other. After that, the way to ‘push’ a file to the paired device, from the originating device, is to open whichever app displays files – such as for example, the Gallery app, if users still have that installed, or a suitable file-manager app – and to tap on ‘Share’, and then select ‘Bluetooth’ as what to share the file to. Doing this should open a list of paired devices, one of which should be suitable to receive a pushed file in this way.

But then, some people would like to take Bluetooth file-sharing up another level. We can pair our Android device – such as our phone – with a Bluetooth-equipped, Linux computer, which may be a bit tricky in itself, because the GUI we usually use for that assumes some legacy form of pairing. But eventually, we can set up a pairing as described. What I need to do is select the option in my Linux-BT-pairing GUI, which requires me to enter the pass-code into the Linux-GUI, which my Android device next displays…

And then, a question which many users find asking themselves is, ‘Why can’t I obtain FTP-like browsing capability, from my Linux-computer, over the files on the phone? Am I not giving the correct commands, from my Linux-computer?’

Chances are high, that any user who wishes to do this, is already giving the correct commands from his or her Linux-computer…

(Updated 06/03/2018, 20h45 … )

Continue reading Browsing Android Files using Bluetooth

How to Add a Web-browser to GNURoot + XSDL.

In This earlier posting – out of several – I had explained, that I’ve installed the Android apps “GNURoot Debian” and “XSDL” to my old Samsung Galaxy Tab S (first generation). The purpose is, to install Linux software on that tablet, without requiring that I root it. This uses the Android variant of ‘chroot’, which is actually also called ‘proot’, and is quick and painless.

However, there are certain things which a ch-rooted Linux system cannot do. One of them is to start services to run in the background. Another is, to access hardware, as doing the latter would require access to the host’s ‘/dev’ folder, not the local, ch-root’s ‘/dev’ folder. Finally, because XSDL is acting as my X-server, when GNURoot’s guest-software tries to connect to one, there will be no hardware-acceleration, because this X-server is really just an Android app, and does not really correspond to a display device.

This last detail can be quite challenging, because in today’s world, even many Linux applications require, direct-rendering, and will not function properly, if left just to use X-server protocol, à la legacy-Unix. One such application is any serious Web-browser.

This does not result from any malfunction of either Android app, because it just follows from the logic, of what the apps are being asked to do.

But we’d like to have a Web-browser installed, and will find that “Firefox”, “Arora” etc., all fail over this issue. This initially leaves us in an untenable situation, because even if we were not to use our Linux guest-system for Web-browsing – because there is a ‘real’ Web-browser installed on the (Android) host-system – the happenstance can take place, by which a Web-document needs to be viewed anyway – let’s say, because we want to click on an HTML-file, that constitutes the online documentation for some Linux-application.

What can we do?

Continue reading How to Add a Web-browser to GNURoot + XSDL.