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fix "how it works" in docs

I tried loads of ways to fix the rendering of this page, but swapping
the sections headings is the only one that works :(
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jcupitt committed Jul 7, 2019
1 parent 37ef7ad commit bad58598f64e4bbd67fd16f3895026f9cbbe09f9
Showing with 210 additions and 210 deletions.
  1. +11 −11 doc/
  2. +199 −199 doc/How-it-works.xml
@@ -15,15 +15,15 @@ improvement by only keeping the pixels currently being processed in RAM
and by having an efficient, threaded image IO system. This page explains
how these features are implemented.

# Images

VIPS images have three dimensions: width, height and bands. Bands usually
(though not always) represent colour. These three dimensions can be any
size up to 2 ** 31 elements. Every band element in an image has to have the
same format. A format is an 8-, 16- or 32-bit int, signed or unsigned, 32-
or 64-bit float, and 64- or 128-bit complex.

# Regions

An image can be very large, much larger than the available memory, so you
can't just access pixels with a pointer \*.
@@ -65,7 +65,7 @@ for a section of the file to be read in.
(\* there is an image access mode where you can just use a pointer, but
it's rarely used)

# Partial images
**Partial images**

A partial image is one where, instead of storing a value for each pixel, VIPS
stores a function which can make any rectangular area of pixels on demand.
@@ -92,7 +92,7 @@ generate / stop sequence works like a thread.
(\* in fact VIPS keeps a cache of calculated pixel buffers and will return
a pointer to a previously-calculated buffer if it can)

# Operations

VIPS operations read input images and write output images, performing some
transformation on the pixels. When an operation writes to an image the
@@ -109,7 +109,7 @@ set of mechanisms to copy image areas by just adjusting pointers. Most of
the time no actual copying is necessary and you can perform operations on
large images at low cost.

# Run-time code generation
**Run-time code generation**

VIPS uses [Orc](, a run-time compiler, to
generate code for some operations. For example, to compute a convolution
@@ -121,7 +121,7 @@ SSE3 on most x86 processors.
Run-time vector code generation typically speeds operations up by a factor
of three or four.

# Joining operations together
**Joining operations together**

The region create / prepare / prepare / free calls you use to get pixels
from an image are an exact parallel to the start / generate / generate /
@@ -154,7 +154,7 @@ each thread runs a very cheap copy of just the writeable state of the
entire pipeline, threads can run with few locks. VIPS needs just four lock
operations per output tile, regardless of the pipeline length or complexity.

# Data sources
**Data sources**

VIPS has data sources which can supply pixels for processing from a variety
of sources. VIPS can stream images from files in VIPS native format, from
@@ -182,7 +182,7 @@ are demanded by different threads VIPS will move these windows up and down
the file. As a result, VIPS can process images much larger than RAM, even
on 32-bit machines.

# Data sinks
**Data sinks**

In a demand-driven system, something has to do the demanding. VIPS has a
variety of data sinks that you can use to pull image data though a pipeline
@@ -221,7 +221,7 @@ ensure that there are at least two tiles for every thread)
(\*\* tiles can be any shape and size, VIPS has a tile hint system that
operations use to tell sinks what tile geometry they prefer)

# Operation cache
**Operation cache**

Because VIPS operations are free of side-effects\*, you can cache them. Every
time you call an operation, VIPS searches the cache for a previous call to
@@ -236,7 +236,7 @@ the cache size by memory use or by files opened.
"invalidate" signal on the image they are called on and this signal makes
all downstream operations and caches drop their contents.)

# Operation database and APIs
**Operation database and APIs**

VIPS has around 300 image processing operations written in this style. Each
operation is a GObject class. You can use the standard GObject calls to walk
@@ -254,7 +254,7 @@ languages]( on many platforms. Most of
these bindings use the introspection system to generate the binding at

# Snip

The VIPS GUI, nip2, has its own scripting language called Snip. Snip is a
lazy, higher-order, purely functional, object oriented language. Almost all

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