LibGGI: Yet Another Graphics API
Now we are set to start drawing. LibGGI uses a GC (graphics context) to represent the current state of the drawing system. We considered a state-free approach, but this would have meant:
Lots of parameters for some functions
A very awkward look for programmers used to the GC concept
Ignoring that actual acceleration hardware normally has a GC
We now draw a few dots in different colors by using ggiSetGCForeground and ggiDrawPixel. As an alternative, we draw the next set of pixels using ggiPutPixel. Higher-level functions are also available, but only to a limited extent. As you can see from the example program, we support various kinds of lines and boxes (and yes, these are accelerated, if the underlying target supports it), but that's about it.
Don't be disappointed here. There is a higher-level library called LibGGI2D providing more complicated functions. LibGGI has been designed to be a basic “foundation” library on top of which specialized libraries can be built for more complex requirements, such as 3-D and animation.
When we are done drawing, we use ggiEventPoll to wait for a key or mouse event. ggiEventPoll determines if an event of the given type(s) is present and will eventually block for it for a specified time or indefinitely, if the pointer to the timeval struct is NULL as in our simple case.
We then use a convenience function to get a keystroke. Note that this will block again, if polling was terminated due to mouse activity. In most cases, you will want to use LibGGI's event system to get input from any device that is attachable to a computer system. For event classification and configuration, a helper library called LibGII is available to give you a flexible and simple way of mapping device input to program actions. After ggiGetc has returned, we close down the visual using ggiClose, and then the whole LibGGI library using ggiExit. Note that you can reopen another visual before ggiExit, which can, for example, be used to transfer the program from one target to another. After ggiExit, every other call to LibGGI functions is undefined. You will need to call ggiInit again first. You have now gained a tiny glimpse at how LibGGI programs look.
Many applications, especially those ported from DOS and other systems where a relatively direct access path to the hardware is present, will want to access graphics RAM directly. While being tied to the layout of the particular card/mode isn't a great idea for portability, it is a good way to get extra speed. LibGGI solves this dilemma by exporting a DirectBuffer structure describing all details of the currently active video buffer. The application can decide whether to use it or fall back to standard LibGGI calls.
LibGGI applications can service multiple visuals at the same time, thus allowing multihead applications like CAD or games screens split over several monitors. For convenience, we have “memory-visuals” that can be used to draw an “invisible” area first and then blit to screen (crossblitting). Simple color-space management, such as gamma setting, is available, as well as support for double/triplebuffering and waiting for vertical retrace, or even for a specific position of the CRT beam (where the hardware allows).
LibGGI ends at about the level of a DrawBox, which is not a desirable environment for many applications, and transparent acceleration is limited. LibGGI was kept small on purpose to work well under constrained conditions such as embedded systems, and not waste space for applications which do not need advanced functionality.
We extended LibGGI so more complex APIs could be implemented “on top” of it. So far we have LibGGI2D, Mesa-GGI and a tiny windowing library, LibGWT, running. A lightweight 3-D library, font and animation support are works in progress. Such libraries are implemented as LibGGI-Extensions. Being an extension has several benefits over just “using” LibGGI; for one thing, you inherit the complete functionality regarding library loading and target support. Thus, extension libraries also bring along their set of API drivers which can be used to allow for transparent acceleration. LibGGI ensures basic services, so all extension libraries will run on all LibGGI targets, but the level of acceleration will vary depending on the availability of driver libraries for the extension.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide