| Index: site/dev/runtime/index.md
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| -Runtime Configuration
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| -=====================
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| -
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| -Skia supports the configuration of various aspects of its behavior at runtime,
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| -allowing developers to enable\/disable features, or to experiment with numerical
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| -quantities without recompiling.
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| -
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| -## Enabling runtime configuration
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| -
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| -In order to use a runtime-configurable variable in your source, simply:
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| -
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| -<!--?prettify?-->
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| -~~~~
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| -#include "SkRTConf.h"
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| -~~~~
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| -
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| -## Declaring a runtime-configurable variable
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| -
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| -At file scope, declare your variable like so:
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| -
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| -<!--?prettify?-->
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| -~~~~
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| -SK_CONF_DECLARE( confType, varName, confName, defaultValue, description );
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| -~~~~
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| -
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| -For example, to declare a boolean variable called ` c_printShaders ` that can be
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| -changed at runtime, you would do something like
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| -
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| -<!--?prettify?-->
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| -~~~~
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| -SK_CONF_DECLARE( bool, c_printShaders, "gpu.printShaders", false, "print the
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| - source code of any internally generated GPU shaders" );
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| -~~~~
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| -
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| -It is safe to declare variables this way in header files; the variables will be
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| -declared as static, but since they are read\-only\-ish \(they can be changed
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| -through a special mechanism; see below\), this is safe.
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| -
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| -## Using a runtime-configurable variable
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| -
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| -The variables created by `SK_CONF_DECLARE` can be used in normal C\+\+ code as
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| -if they were regular contant variables. For example:
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| -
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| -<!--?prettify?-->
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| -~~~~
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| -if (c_printShaders) {
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| - // actually print out the shaders
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| -}
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| -~~~~
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| -
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| -## Changing a runtime-configurable variable after launch
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| -
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| -If, for some reason, you want to change the value of a runtime-configurable
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| -variable after your program has started, you can do this with the `SK_CONF_SET`
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| -macro:
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| -
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| -<!--?prettify?-->
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| -~~~~
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| -SK_CONF_SET( "gpu.printShaders", false )
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| -~~~~
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| -
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| -Note that we're using the `confName` parameter to the declaration, not
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| -`varName`. This is because this configuration option may appear in multiple
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| -files \(especially if you declared it in a header!\), and we need to make sure
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| -to update all variables' values, not just the one that's locally visible to the
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| -file you are currently in.
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| -
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| -## Changing a runtime-configurable variable before launch
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| -
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| -This is the primary intended use of these variables. There are two ways that you
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| -can control the values of runtime-configurable variables at launch time: a
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| -skia.conf configuration file, or through the use of environment variables.
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| -
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| -### Using skia.conf
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| -
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| -The skia.conf file is a simple line-based configuration file containing
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| -key-value pairs. It supports python-style \# comments. For our example, we might
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| -see a configuration file that looks like:
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| -
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| -<!--?prettify?-->
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| -~~~~
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| -gpu.printShaders true
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| -gpu.somethingElse 3.14159
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| -matrix.invertProperly false # math is hard
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| -...
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| -~~~~
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| -
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| -*Note: boolean values may be set as 1, 0, true, or false. Other values will
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| -result in runtime errors.*
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| -
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| -If the skia library detects a skia.conf file at initialization time, it will
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| -parse it and override the default values of any declared configuration variables
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| -with the values found in the file.
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| -
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| -*Note: although it might appear that the configuration variables have a
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| -hierarchical naming scheme involving periods, that's just a convention I have
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| -adopted so that when all declared configuration variables are sorted
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| -alphabetically, they are roughly grouped by component.*
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| -
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| -## Using environment variables
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| -
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| -You can quickly override the value of one runtime-configurable variable using an
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| -environment variable equal to the variable's key with "skia." prepended. So, for
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| -example, one might run:
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| -
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| -<!--?prettify?-->
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| -~~~~
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| -prompt% skia.gpu.printShaders=true out/Debug/dm
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| -~~~~
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| -
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| -or
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| -
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| -<!--?prettify?-->
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| -~~~~
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| -prompt% export skia.gpu.printShaders=true
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| -prompt% out/Debug/dm
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| -~~~~
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| -
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| -On many shells, it is illegal to have a period in an environment variable name,
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| -so skia also supports underscores in place of the periods:
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| -
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| -<!--?prettify?-->
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| -~~~~
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| -prompt% skia_gpu_printShaders=true out/Debug/dm
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| -~~~~
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| -
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| -or
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| -
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| -<!--?prettify?-->
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| -~~~~
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| -prompt% export skia_gpu_printShaders=true`
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| -prompt% out/Debug/dm
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| -~~~~
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| -
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| -## Discovering all possible configuration variables
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| -
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| -As this system becomes more widely used in skia, there may be hundreds of
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| -configuration variables. What are they all? What are their defaults? What do
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| -they do?
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| -
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| -In order to find out, simply create a zero-length skia.conf file \(on unix,
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| -`touch skia.conf` will do the trick\). If skia detects a zero-length
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| -configuration file, it will overwrite it with a sorted list of all known
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| -configuration variables, their defaults, and their description strings. Each
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| -line will be commented out and have its value already equal to its default, so
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| -you can then edit this file to your liking.
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| -
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| -To trigger this behavior, call the function
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| -`skRTConfRegistry().possiblyDumpFile(); ` or simply use `SkAutoGraphics
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| -ag;`, which also validates your configuration and print out active non-default
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| -options.
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| -
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| -## Are these things enabled all the time?
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| -
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| -No, they are only enabled in builds where SK_DEBUG is defined. This includes both
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| -`Debug` and `Release_Developer` gyp BUILDTYPES. The `Release_Developer` build type
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| -has exactly the same build flags as `Release`, except it re-enables SK_DEBUG, which
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| -in turn enables runtime configuration behavior.
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| -Specifically:
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| -
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| -<!--?prettify?-->
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| -~~~~
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| -prompt% ninja -C BUILDTYPE=Release_Developer
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| -~~~~
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| -
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| -... wait a long time ...
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| -
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| -<!--?prettify?-->
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| -~~~~
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| -prompt % skia_gpu_printShaders=true out/Release_Developer/dm
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| -~~~~
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| -
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| -... enjoy ...
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| -
|
| -## Known issues / limitations
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| -
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| -Lines in 'skia.conf', including comments, are limited to 1024 characters.
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| -Runtime configuration variables of type `char \* ` cannot currently have spaces
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| -in them.
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| -Runtime variables are only fully supported for `int`, `unsigned int`, `float`,
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| -`double`, `bool`, and `char \*`.
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|
|