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Contributing to Blend2D

The following is a set of guidelines for contributing to Blend2D and other repositories hosted in the Blend2D Organization on GitHub.

Table of Contents

Asking Questions

We prefer GitHub issues to be used for reporting bugs and similar problems. So please consider using our Gitter Channel to ask questions. It is active and may provide you quick help.

  • Generic questions should be asked on Gitter if possible
  • Feature Suggestions may be discussed on Gitter, we will add features that match our future plans to the roadmap
  • For C/C++ API Questions use either Gitter or open a new issue on GitHub (see pinned issues first, we prefer to write a documentation regarding API functions that are not clear)
  • Read our FAQ as well, we would gladly improve it if you found something missing or can improve the existing content

Reporting Bugs

A good bug report should contain the following information:

  • Brief and detailed bug description
  • Steps to reproduce the bug (isolated test-case is preferred but not required)
  • Build and system information (use <blend2d-debug.h> to obtain it, see below)

To make the reporting bugs as easy as possible Blend2D provides a header file called <blend2d-debug.h>. It contains functions for C and C++ API users that can be used to query useful information from Blend2D runtime and to dump the content of some Blend2D objects.

Use the snippet below in your own code and include its output in your bug report. It will help us to identify the issue quicker. Debug API is provided for both C and C++ users.

#include <blend2d.h>
#include <blend2d-debug.h>

int main(int argc, char* argv[]) {
  // This will query and dump Blend2D build and system information. We
  // need this information to make the initial guess of where the problem
  // could be. Some JIT and SIMD bugs can depend on this information.
  blDebugRuntime();

  // Now dump everything you have by using the following functions.
  blDebugArray(&arr);         // Dumps the content of BLArray
  blDebugContext(&ctx);       // Dumps the state of BLContext
  blDebugMatrix2D(&mat);      // Dumps the content of BLMatrix2D
  blDebugImage(&img);         // Dumps the content of BLImage (without pixels)
  blDebugPath(&path);         // Dumps the content of BLPath
  blDebugStrokeOptions(&opt); // Dumps the content of BLStrokeOptions
}

When reporting bugs related to incorrect renderings it is important to also include the rendered image together with the bug report as it will help us to understand the problem better.

Website Enhancement

If you found a typo or have suggestions about the content on Blend2D website you can either contact us directly via email or discuss it on Gitter. Please don't open GitHub issues that are related to the website.

Coding Style

If you plan to contribute to Blend2D make sure you follow the guidelines described in this section.

Source Files

  • Source files contain a header, which contains a project name [Blend2D], description, and license that refers to LICENSE.md file (when you are creating a new file just copy the header from any other file)
  • Source files that include other Blend2D headers use relative paths starting with ./ or ../
  • Header guard format is BLEND2D_FILE_H for root headers and BLEND2D_PATH_FILE_H for headers in a subdirectory
  • Source files (.cpp) must first include blapi-build_p.h and then other headers
  • Source files that use compiler intrinsics (SSE, AVX, NEON) must have the following suffix:
    • X86/X64
      • *_sse2.cpp - SSE2
      • *_sse3.cpp - SSE3
      • *_ssse3.cpp - SSSE3
      • *_sse4_1.cpp - SSE4.1
      • *_sse4_2.cpp - SSE4.2
      • *_avx.cpp - AVX
      • *_avx2.cpp - AVX2
    • ARM/AArch64
      • *_neon.cpp - NEON

API Design

Namespaces

  • Do not use namespaces in public API if possible

Namespaces are used mostly internally. There are few exceptions like BLRuntime and BLFileSystem though.

C vs C++ API

  • Public headers must place C++ specific functionality between #ifdef __cplusplus and #endif
  • Private headers use C++ by default (no C compatibility)

Since Blend2D exports only C API and can be compiled without linking to standard C++ library it cannot use functions that depend on it. Blend2D at the moment only uses atomics and some other utilities like std::numeric_limits<> that don't require linking to C++ standard library and it must stay like that.

Exception Safety and Error Handling

  • Do not use exceptions or RTTI

Exceptions and RTTI are never used by Blend2D. In general every public function is marked noexcept (or BL_NOEXCEPT_C for C API) that should guarantee that the compiler won't emit unwind tables even when C++ exceptions are enabled at build time. Blend2D users can use exceptions in their code, but Blend2D would never throw them.

  • Use error codes for error handling and propagation
  • Use BLResult as a return value in functions that can fail

Every function that can fail must return BLResult. Use BL_PROPAGATE(expression) to return on failure, but be careful and check how it's used first.

Default Constructed State

  • Always offer a defined default constructed state.

Default constructed state guarantees that no dynamic memory is allocated when creating a default constructed instance. Only initialization like create() or begin() and using setters would turn default initialized instance into an instance that uses dynamically allocated memory. Use .reset() to set the state of any class back to its default constructed state and to release all resources it holds.

Coding Conventions

If you are planning to contribute to Blend2D, please read our coding conventions carefully.

  • Indent by 2 spaces and never use TABs
  • Class and struct names are CamelCased and always start with BL prefix (BLClassName)
  • Global functions and variables are CamelCased and always start with bl prefix (blFunctionName)
  • Structs are used for everything that doesn't have initialization and must be compatible with C API
  • Structs can have utility member functions available in C++ mode like .reset()
  • Classes are only used for implementing C++ API that is based on C API
  • Pointer * or reference & is part of the type, for example void* ptr
  • Namespaces are not indented, use the following:
namespace BLSomeNamespace {
[...]
} // {BLSomeNamespace}
  • No line between a statement and opening bracket {:
class BLSomeClass {
  void someFunction() {
    for (uint32_t i = 0; i < 10; i++) {
      if (i & 0x1) {
        [...]
      }
    }
  }
};
  • No spaces in a conditional expression, function declaration, and call:
// Right:
if (x)
  someFunction(x);

/* WRONG:
if( x )
  someFunction ( x );
*/
  • If obvious, omit == nullptr and != nullptr from conditional expressions, except asserts:
void* ptr;

// Right:
BL_ASSERT(ptr != nullptr);
if (ptr) {
  [...]
}

/* WRONG:
BL_ASSERT(ptr);
if (ptr != nullptr) {
  [...]
}
*/
  • If some branch of a condition (if/else) requires a block {} then all branches of that condition must be surrounded by such block:
// Right:
if (x)
  first();
else
  second();

if (x) {
  first();
}
else {
  second();
}

/* WRONG:
if (x) {
  first();
}
else
  second();
*/
  • There is a space between a switch statement and its expression; case statement and its content are indented:
switch (expression) {
  case 0:
    doSomething();
    break;

  // Case that requires a block.
  case 1: {
    int var = something;
    doSomethingElseWithVar(var);
    break;
  }

  // If the defaul should never be reached, mark it so:
  default:
    BL_NOT_REACHED();
}
  • Sometimes case and its content can be inlined:
switch (condition) {
  case 0: doSomething(); break;
  case 1: doSomethingElse(); break;
}
  • Public enum names are UPPER_CASED and use BL_ prefix
  • Public enums usually end with _COUNT, which should be separated by an empty line
  • Public enums are always uint32_t, use BL_DEFINE_ENUM to make sure they are properly defined in C++ mode:
BL_DEFINE_ENUM(BLSomeEnum) {
  BL_SOME_ENUM_A = 0,
  BL_SOME_ENUM_B = 1,

  BL_SOME_ENUM_COUNT = 2
};
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