XNA DEBUG TERMINAL

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XNA DEBUG TERMINAL

• Created By
• Kevin Cherry

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What is XNA Debug Terminal?

• A library that creates a display to run on top of
  your game allowing you to retrieve/set values and
  invoke methods.

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How Does it Work?

• To understand how this is possible, we need to
  examine some basic and .Net specific concepts

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Compiled Vs. Interpreted

• Interpreted languages evaluate source code at
  runtime
• Code is not compiled but rather parsed and
  evaluated as needed.
• Examples JavaScript, PHP, Python, Ruby
• Compiled languages compile to assembly or
  special/proprietary intermediate language losing
  type information in the process, making arbitrary
  code execution at runtime impossible.
• Examples C, C, Java, VB

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MSIL And Metadata

• Why it is possible to interpret strings
  containing code at runtime with a .Net language
• .Net converts code into Microsoft Intermediate
  Language and a metadata file. The metadata file
  contains all the information obtained from
  parsing the source types and MSIL contains the
  instructions for execution. Querying this
  metadata we can obtain links to type members.

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Source Code -gt MSIL Metadata
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Reflection

• To query this metadata file, we use reflections.
  This part of the .Net framework provides
  information on the specified objects type which
  can be used to retrieve fields/properties or
  invoke methods.

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So, How Does XNA Debug Terminal Work?

• It converts your expression into subexpressions,
  then parses and evaluates them using reflections.

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Sample Expression Parsing
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Sample Arithmetic Parsing
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Basic Layout
Pressing custom set key shows/hides display
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Example
Invoke method for restoring health of player
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Currently Allowed Expressions

• Casting
• Enums
• Identifiers
• Literals
• Methods
• New
• Object chains
• Types

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Not Yet Allowed Expressions

• Anonymous Types/Functions
• Array indexing or initialization
• Arithmetic
• Collection initialization
• Conditional logic
• Generics
• Keywords
• as, base, default (e.g. default(int)), fixed, is,
  out, ref, sizeof, stackalloc, this, throw,
  typeof, unchecked, unsafe
• Lambda Functions
• LINQ
• Logic Operators (, , , , )
• Property indexers

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Version Priorities

• Bugs in expression parsing
• Common/Frequently used C expressions
• Bugs elsewhere
• Common/Frequently used C keywords
• New Terminal commands
• Terminal UI improvements
• Speed optimizations
• Other improvements

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Getting Involved

• Email me at kcherr1_at_tigers.lsu.edu
• with subject XNA Debug Terminal Source Code" to
  obtain the source code
• Look over code and decide on a single task to
  undertake
• Email me details of the task (what it is and
  about how long it will take you)
• Email back the original source code with all of
  your changes when done
• All contributors will get name in Authors file
  and Getting Involved, News, and Download webpages

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Guidelines For Contributing

• Document all types, fields, properties, and
  methods you add using the "///" xml documentation
• Add test cases to the test project that cover
  your newly added functionality and ensure that
  each one passes. All previous test cases must
  pass as well
• Try to follow the coding convention used by the
  existing code
• Only change existing code when it concerns your
  single task

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XNA Debug Terminal Website

• http//www.protohacks.net/xna_debug_terminal