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+*Part II* {align="center"}
+---------
+
+Chapter 23\
+ Bones and Sinew {#Heading1}
+----------------
+
+### At the Very Heart of Standard PC Graphics {#Heading2}
+
+The VGA is unparalleled in the history of computer graphics, for it is
+by far the most widely-used graphics standard ever, the closest we may
+ever come to a *lingua franca* of computer graphics. No other graphics
+standard has even come close to the 50,000,000 or so VGAs in use today,
+and virtually every PC compatible sold today has full VGA compatibility
+built in. There are, of course, a variety of graphics accelerators that
+outperform the standard VGA, and indeed, it is becoming hard to find a
+plain vanilla VGA anymore—but there is no standard for accelerators, and
+every accelerator contains a true-blue VGA at its core.
+
+What that means is that if you write your programs for the VGA, you’ll
+have the largest possible market for your software. In order for
+graphics-based software to succeed, however, it must perform well.
+Wringing the best performance from the VGA is no simple task, and it’s
+*impossible* unless you really understand how the VGA works—unless you
+have the internals down cold. This book is about PC graphics at many
+levels, but high performance is the foundation for all that is to come,
+so it is with the inner workings of the VGA that we will begin our
+exploration of PC graphics.
+
+The first eight chapters of Part II is a guided tour of the heart of the
+VGA; after you’ve absorbed what we’ll cover in this and the next seven
+chapters, you’ll have the foundation for understanding just about
+everything the VGA can do, including the fabled Mode X and more. As you
+read through these first chapters, please keep in mind that the *really*
+exciting stuff—animation, 3-D, blurry-fast lines and circles and
+polygons—has to wait until we have the fundamentals out of the way. So
+hold on and follow along, and before you know it the fireworks will be
+well underway.
+
+We’ll start our exploration with a quick overview of the VGA, and then
+we’ll dive right in and get a taste of what the VGA can do.
+
+### The VGA {#Heading3}
+
+The VGA is the baseline adapter for modern IBM PC compatibles, present
+in virtually every PC sold today or in the last several years. (Note
+that the VGA is often nothing more than a chip on a motherboard, with
+some memory, a DAC, and maybe a couple of glue chips; nonetheless, I’ll
+refer to it as an adapter from now on for simplicity.) It guarantees
+that every PC is capable of documented resolutions up to 640x480 (with
+16 possible colors per pixel) and 320x200 (with 256 colors per pixel),
+as well as undocumented—but nonetheless thoroughly standard—resolutions
+up to 360x480 in 256-color mode, as we’ll see in Chapters 31-34 and
+47-49. In order for a video adapter to claim VGA compatibility, it must
+support all the features and code discussed in this book (with a very
+few minor exceptions that I’ll note)—and my experience is that just
+about 100 percent of the video hardware currently shipping or shipped
+since 1990 is in fact VGA compatible. Therefore, VGA code will run on
+nearly all of the 50,000,000 or so PC compatibles out there, with the
+exceptions being almost entirely obsolete machines from the 1980s. This
+makes good VGA code and VGA programming expertise valuable commodities
+indeed.
+
+Right off the bat, I’d like to make one thing perfectly clear: The VGA
+is hard—sometimes *very* hard—to program for good performance. Hard, but
+not impossible—and that’s why I like this odd board. It’s a throwback to
+an earlier generation of micros, when inventive coding and a solid
+understanding of the hardware were the best tools for improving
+performance. Increasingly, faster processors and powerful coprocessors
+are seen as the solution to the sluggish software produced by high-level
+languages and layers of interface and driver code, and that’s surely a
+valid approach. However, there are tens of millions of VGAs installed
+right now, in machines ranging from 6-MHz 286s to 90-MHz Pentiums.
+What’s more, because the VGAs are generally 8- or at best 16-bit
+devices, and because of display memory wait states, a faster processor
+isn’t as much of a help as you’d expect. The upshot is that only a
+seasoned performance programmer who understands the VGA through and
+through can drive the board to its fullest potential.
+
+Throughout this book, I’ll explore the VGA by selecting a specific
+algorithm or feature and implementing code to support it on the VGA,
+examining aspects of the VGA architecture as they become relevant.
+You’ll get to see VGA features in context, where they are more
+comprehensible than in IBM’s somewhat arcane documentation, and you’ll
+get working code to use or to modify to meet your needs.
+
+The prime directive of VGA programming is that there’s rarely just one
+way to program the VGA for a given purpose. Once you understand the
+tools the VGA provides, you’ll be able to combine them to generate the
+particular synergy your application needs. My VGA routines are not
+intended to be taken as gospel, or to show “best” implementations, but
+rather to start you down the road to understanding the VGA.
+
+Let’s begin.
+
+### An Introduction to VGA Programming {#Heading4}
+
+Most discussions of the VGA start out with a traditional “Here’s a block
+diagram of the VGA” approach, with lists of registers and statistics.
+I’ll get to that eventually, but you can find it in IBM’s VGA
+documentation and several other books. Besides, it’s numbing to read
+specifications and explanations, and the VGA is an exciting adapter, the
+kind that makes you want to get your hands dirty probing under the hood,
+to write some nifty code just to see what the board can do. What’s more,
+the best way to understand the VGA is to see it work, so let’s jump
+right into a sample of the VGA in action, getting a feel for the VGA’s
+architecture in the process.
+
+Listing 23.1 is a sample VGA program that pans around an animated
+16-color medium-resolution (640x350) playfield. There’s a lot packed
+into this code; I’m going to focus on the VGA-specific aspects so we
+don’t get sidetracked. I’m not going to explain how the ball is
+animated, for example; we’ll get to animation starting in Chapter 42.
+What I will do is cover each of the VGA features used in this
+program—the virtual screen, vertical and horizontal panning, color plane
+manipulation, multi-plane block copying, and page flipping—at a
+conceptual level, letting the code itself demonstrate the implementation
+details. We’ll return to many of these concepts in more depth later in
+this book.
+
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+
+* * * * *
+
+Graphics Programming Black Book © 2001 Michael Abrash