StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
text
Body
copied!<p>You're thinking much, much much too complicated. Toolkits like GTK+ or Qt add quite a layer of abstraction over somthing, that's actually rather simple: Your system's graphics device consists of a processor and some memory it can operate on. In the simplemost case the processor is the regular system CPU and the memory is the normal system memory. Modern computers feature a special purpose graphics processor (GPU), though, which has its own, high bandwidth memory.</p> <p>The memory holds framebuffers. Logically a framebuffer is a 2D array of values. The GPU can be programmed to process the values in the framebuffers in a certain way. That can be used to draw into framebuffers. The monitors, displaying a picture are connected to a special piece of circuitry which continuously feeds the data of a certain framebuffer in the memory to the screen (usually called RAMDAC or CRTC). So in the GPU's memory there's a framebuffer that's directly going to the screen. If you draw there, things will appear on the screen.</p> <p>A program, like the X11 server can load drivers that "know" how to program the GPU to draw graphical primitives. X11 itself defines certain graphics primitives, and extension modules can add further ones. X11 itself allows to segregate the framebuffers on the GPU memory into logical areas called Drawables. Drawables on the on-screen framebuffer are called Windows. Since logical Windows can overlap the X server also manages Z stacking, which it uses to sort the Windows for redraw. Everytime a Client wants to draw to some Window that X11 server will tell the GPU, that drawing operations will modify only those pixels of the framebuffer, of which the Window drawn to is visible (this is called "Pixel Ownership Test"). The X11 server will also create Drawables (i.e. framebuffers) that are not part of the on-screen framebuffer memory area. Those are called PBuffers or Pixmaps in X11 terminology (also with a special extension its possible to move a Window off-screen as well).</p> <p>However all those Drawables are just <em>memory</em>. Technically those are Canvas to draw on with something. This something is called "graphics primitives". X11 itself provides a certain set, named X core. Also there's a de-facto standard extension called XRender which provides primitives not found in X core. However neither X11 core nor XRender provide graphics primitives with which the impression of a 3D drawing could be generated. So there's another extension, called GLX which teaches the X11 server another set of graphics primitives, namely in the form of OpenGL.</p> <p>However X core, XRender and GLX/OpenGL are all just different pens, brushes and pencils that all operate on the same kind of Canvas, namely a simply framebuffer manages by X11.</p> <p>And what do toolkits like Qt or GTK+ then? Well, they use X11 and the graphics primitives it provides to actually draw widgets, like Buttons, Menus and stuff like that, which X11 doesn't know about.</p>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload