Handle SDL_bool like a real boolean

[Matthias]

Actually we should translate SDL_bool by TSDL_Bool. This will generate compiler errors in situations as shown below:

(from sdl2.pas)

function SDL_VERSION_ATLEAST(X,Y,Z: cuint8): Boolean;
begin
  Result := SDL_COMPILEDVERSION >= SDL_VERSIONNUM(X,Y,Z);
end;

How should we handle or fix this?

[Matthias]

C and Pascal handle booleans differently. In C they are basically integer values which are interpreted but in Pascal they form a special, separate type (or are at least treated as such).

So, what follows from this:

• Macros which have a Boolean type result should be written as function with Pascal native Boolean type or cbool type depending on the further use of the macro.
• SDL functions which have a SDL_Bool return value should be converted to return TSDL_Bool
• SDL functions which need SDL_Bool value as argument will treat them correctly obviously
• Pascal functions which rely on a TSDL_Bool value as argument should evaluate the integer values or typecast (see next point)
• Attention: Typecast Boolean(TSDL_Bool) should be safe as TSDL_Bool can be 0 or 1 only, but in general care has to be taken with this cast, see http://www.delphigroups.info/2/10/12833.html
• A logical expression can be returned into a TSDL_Bool value by typecasting, see example code below

program SDLBoolTest;

uses SDL2, ctypes, SysUtils;

var
  a, b: Integer;

function BoolTest(a, b: Integer): TSDL_Bool;
begin
  // works
  Result := TSDL_Bool(a > b);

  // does not work - Error: got "Boolean" expected "TSDL_Bool"
  //Result := (a > b);
end;

begin
  writeln('Bool Test a > b');
  for a:= 0 to 3 do
    for b := 0 to 3 do
      begin
        write('a = ' + IntToStr(a) + '; b = ' + IntToStr(b) +';    Result = ' + IntToStr(BoolTest(a, b)) + ' ');
        writeln(Boolean(BoolTest(a, b)));
      end;

  readln;
end.

So, for the example in the initial post it is correct to use the native Boolean, because a macro without a defined SDL_Bool return value should not adopt a fictional one.

[furious programming]

For me, just change the declaration of TSDL_Bool to this:

type
  TSDL_Bool = System.Boolean;

and adopt all the code to the new type. Casting to native booleans should be avoided — the code should be adopted to the Pascal language, not to the C language. Additionally, some constant values should also be redeclared (eg. SDL_TRUE or SDL_ENABLE), since they also contains value 0 or 1 and they act like a booleans to toggle various options.

What do you think about it?

[suve]

The problem is that we need to maintain binary compatibility with the C library. According to the FPC Language Reference, Boolean has a size of 1 (the same as char), whereas the C definition is typedef int SDL_bool, i.e. the same size as an int (which is usually 2 or 4).

We could consider using LongBool, or ctypes.cbool, though.

[furious programming]

We could consider using LongBool, or ctypes.cbool, though.

Exactly. After all, the same goes for the functions of the Win32 API, wherever the multibyte booleans are required.

[Matthias]

I added a PR (#70) to solve this issue according to you proposal using cbool.

The code below works well, too now.

program SDLBoolTest;

uses SDL2, ctypes, SysUtils;

var
  a, b: Integer;

function BoolTest(a, b: Integer): TSDL_Bool;
begin
  // works
  //Result := TSDL_Bool(a > b);

  // works, too
  Result := (a > b);
end;

begin
  SetHeapTraceOutput('heaptrc.txt');

  writeln('Bool Test a > b');
  for a:= 0 to 3 do
    for b := 0 to 3 do
      begin
        write('a = ' + IntToStr(a) + '; b = ' + IntToStr(b) +';    Result = ');
        writeln(BoolTest(a, b));
      end;

  readln;
end.

[Matthias]

Closed by PR #70